The Protease Specificity of Heparin Cofactor 11

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The Protease Specificity of Heparin Cofactor 11 Powered By Docstoc
              OF                                                                                   Val. 260, No. 6, Issue of March 25, pp. 3501-3505, 1985
8 1985 by The American Society of Bioiogical Chemists, Inc.                                                                              Printed in U.S.A.

The Protease Specificity of Heparin Cofactor11

                                                                                              (Received for publication, September 24,1984)

                 Katherine A. Parkerg and Douglas Tollefsen$?
                 From the Division of Hematology-Oncology, Departments of internal Medicine and Biological Chemistry, Washington University
                 School of Medicine, St. Louis, Missouri 63110

   '281-labeledheparincofactor I1 (HCII) was mixed amount of heparin or dermatan sulfate.
with plasma and coagulation initiated by addition Little information is available about the protease specificity
of CaClz, phospholipids, and kaolin or tissue factor. In of HCII. In previous studies, HCII did not inhibit coagulation
the presence of ggfml of dermatan
                67                     sulfate, radioac- factor Xa, plasmin, or trypsin (2, 4,6, 7). In contrast, ATIII
tivity was detected in a band which corresponded to inhibits a broad range of proteolytic enzymes, including the
the thrombin-HCII complex = 96,000)upon sodium coagulation factors thrombin, Xa, IXa, XIa, XIIa, and kalli-
dodecyl sulfate-polyacrylamide electrophoresis.No krein, and the fibrinolytic enzyme plasmin (9, 11).We have
other complexes were observed. The thrombin-HCII now examined all of the proteases known to be involved in
complex was undetectable when 5 units/ml of heparin coagulation and fibrinolysis, as well as several other extracel-
was present or whenprothrombin-deficientplasma           lular proteases, and have discovered that HCII is a relatively
was used. In experiments with purified proteases,  HCII
did not significantly inhibit coagulation factors VIIa,  specific inhibitor of thrombin. Previously we reported that
IXa,Xa,XIa,XIIa,                                                           in
                      kallikrein, activated protein C, ' " ~ - t ~ r o ~ badded to plasma containing dermatan sulfate
plasmin, urokinase,tissue plasminogen activator, leu- becomes bound to HCII (5).We have now shown that throm-
kocyte elastase, the r-subunit of nerve growth factor, bin generated in plasma during coagulation is inhibited by
and the epidermal  growth factor-binding protein.  HCII HCII when dennatan sulfate is present, thus explaining the
inhibited leukocyte cathepsin G slowly, with a rate anticoagu~ant         effect of dermatan sulfate that has been ob-
constant of 8 X lo4 I"1 min" in the presence of der- served i vitro (10, 12).
matan sulfate. These results indicate that the protease
specificity of HCIIis more restricted than that of other                    EXPERIMENTALPROCEDURES
plasma protease inhibitors and suggest that the anti-       Materiok-Benzoyl-11-Glu-Gly-Arg-pnitroanilide  (S-22221,pyro-
coagulant effect of dermatan sulfate is due solely to Glu-Gly-Arg-p-nitroanilide(5-24441, Val-Leu-Lys-p-nitroanilide (S-
inhibition of thrombin HCII.                             2251), Pro-Phe-Arg-p-nitroanilide(8-23023, and Phe-Pip-Arg-p-ni-
                                                                     troanilide (5-2238) were purchased from Helena Laboratories; succi-
                                                                     nyl-Ala-Ala-Pro-Phe-p-nitroanilide Vega Biochemicals; succi-
                                                                     nyl-A~a-Ala-Ala-p-nitroanilide from Sigma; and tosyl-Gly-Pro-Arg-
   Heparin cofactor I1 (HCII') is a65,600-dalton glycoprotein p-nitroanilide (Chromozyme TH) from Boehringer Mannheim. Hep-
in human plasma which inhibits thrombinby forming a stable, arin from porcine intestinal mucosa was obtained from Abbott Lab-
equimolar complex with the protease (1-7). Heparinand                oratories. Porcine skin dermatan sulfate was obtained from Sigma
                                                                     and was treated with nitrous acid prior to use to remove contaminat-
dermatan sulfate bindto HCII and thereby increase the rate ing heparin (5, 1 ) S ~ i ~ m [ ~ * ~ I ~ (16.8iCi/mg) was purchased
                                                                                      0.                      iod de
of inhibition of thrombin -1000-fold (4,5, 8). Heparin also from Amersham. Iodogen was purchased from Pierce. Prothrombin-
catalyzes the inhibition of thrombin and other proteases by deficient plasma containing -2% of the normal concentration of
antithrombin I11 (ATIII) (9). In contrast, dermatan sulfate prothrombin was purchased from George King Biologicals. Normal
specifically catalyzes the thrombin-HCII reaction but has no plasma was obtained from blood (4.5 ml)drawn into evacuated tubes
appreciable effect on the activity of ATIII (5, 10). HCII is containing 0.5 mi of0.129 M buffered sodium citrate (Vacutainer
                                                                     #6418, Bectin-Dickinson). Activated partial thromboplastin reagent
present in plasma at a concentration of -1.2 P M . ~A t this was obtained from Hyland Laboratories. Rabbit brain t h r o m ~ p l a s t i n
concentration, thrombincould theoretically be inhibited with was obtained from Ortho Diagnostics and was reconstituted with
a t I j 2approaching 50-100 ms in the presence of an optimal water according to the manufacturer. Human brain thromboplastin
                                                                     (13) was obtained from Dr. George Broze, Washington University.
   * This research was supported by grants from the National Insti- Rabbit brain cephalin was purchased from Sigma. Polybrene (1,5-
tutes of Health (HL-27589) and the Monsanto Co. The costs of dimethyl-l,5-~azaundecamethyIenepolymethobromidef was ob-
publication of this article were defrayed in part by the payment of tained from Aldrich.
page charges. This article must therefore be hereby marked "adver-      Proteins-Human HCII and thrombin were purified as previously
tisement" in accordance with 18U.S.C. Section 1734 solely indicate described (4). Human factor XIIa (14) was prepared by Dr. Allen
this fact.                                                           Kaplan, State University of New York, Stony Brook. Human factor
   4 Present address: Department of Internal Medicine, University of XIa (15) was obtained from Dr. Paul Bajaj, University of California,
Texas Southwestern Medical School, Dallas, TX.                       San Diego. Human coagulation factors VIIa (13), IX, X, Xa (16), and
   8 Recipient of National Institutes of Health Career Development activated protein C (17) were obtained from Drs. Hatem Salem,
Award HL-01079.                                                                                                          on
                                                                     George Broze, and Joseph Miletich, ~ a s h i n ~ University. Factor
   'The abbreviations used are: HCII, heparin cofactor 11; ATIII, IX (69 FM)was converted to IXa by incubation with 40 nM factor
antithrombin 111; TPA, tissue plasminogen activator; yNGF, the       XIa for 2 h at 37 "cin buffer containing 5 mMCaC12, 0.05 M NaCl,
pept,idase subunit of nerve growth factor; EGF-BP, epidermal growth 0.02 M Tris-HC1, pH 7. Tissue plasminogen activator derived from
factor-binding protein, the peptidase subunit of epidermal growth cultured human melanoma cells (18) was obtained from Dr. DesirB
factor; and SDS-PAGE, sodium dodecyl sulfate-polyacrylamide gel Collen, University of Leuven. Human urokinase was the product of
electrophoresis.                                                     Winthrop Laboratories. Glu-plasminogen I1 waspurified from human
   * D. M. Tollefsen and C. A. Pestka, manuscript submitted.         plasma by the method of Deutsch and Mertz (19) and the zymogen

3502                                of               Protease
                                           Specificity                              HCII
(1 p ~ was converted to plasminby incubation with 50 nM urokinase
          )                                                                 Assay for factor VIIa-Factor VIIa was incubated with HCII and
for 30 min at 37 "c in buffer containing 8 mM lysine, 20% glycerol,      heparin or dermatan sulfate in the presence of 5 mM CaClz and 1mg/
0.8 M Tris-HC1, pH 9.6. Human leukocyte elastase (20) and cathepsin      ml human brain thromboplastin in 0.15 M NaC1,0.02 M Tris-HC1,
G (21, 22) were prepared by Dr. Robert Senior, Washington Univer-        pH 7.4, for 15 min at 37 "C. Tritiated human factor X (4.8 X lo6
sity. The proteolytic subunits of murine nerve growth factor (-y-NGF)    cpm/nmol) prepared by the method of Silverberg et al. (27) was then
(23) and epidermal growth factor (EGF-BP) (24) were provided by          added at a final concentration of 0.4 p ~ After 1 min, proteolysis of
Dr. Thomas Maciag, Meloy Laboratories. Human plasma kallikrein,          3H-factor X was terminated by addition of 50 mM EDTA, and the
human fibrinogen, Bothrops atrox venom, and bovine serum albumin         protein was precipitated with 5% trichloroacetic acid at 4 "C. The
were purchased from Sigma.                                               radioactivity of the supernatant solution containing thelabeled acti-
   Iodination of HCII-200 pl of HCII (-8 p~ in 0.15 M NaC1, 0.02         vation peptide of factor Xa was then determined. In control incuba-
M Tris-HC1, pH 7.4) were incubated with 2 mCi of carrier-free NaIZ5I     tions without HCII, the amount of 3H-peptide released was propor-
for 10 min at 4 " C in a polypropylene tube coated with 100 pg of                                     of
                                                                         tional to the concentration factor VII..
Iodogen according to themethod of Fraker and Speck (25). Unbound            Assay for Factor IXa-Factor IXa, HCII, and heparin or dermatan
Iz5Iwas removed by gel filtration on a 1 X 10-cm column of Sephadex      sulfate were incubated for 15 min at 37 "C in 55pl of buffer containing
(2-25. The final specific radioactivity was 1.2 X lo9 cpm/nmol of        0.15 M NaCI, 0.02 M Tris-HC1, pH 7.4, and 1 mg/ml bovine serum
HCII.                                                                    albumin. At the end of the incubation period, 45 pl of0.1 mg/ml
   Electrophoresis-SDS-PAGE was performed with 7.5% gels and             Polybrene in the above buffer, 100 pl of citrate-anticoagulated normal
the Laemmli buffer system (26) under nonreducing conditions. Au-         plasma, 50 pl of rabbit brain cephalin, and 100 pl of 25 mM CaClZ
toradiography was performed as described previously (3). Molecular       were added sequentially at 15-5 intervals. The clotting time following
weight standards obtained from BioRad included ovalbumin (M,         =
                                                                         the addition of CaC& was determined with a Fibrometer (Bectin-
45,000), bovine serum albumin (M, 66,000), phosphorylase b (M,
                                    =                               =
                                                                         Dickinson). Samples (55 p l ) of factor IXa at concentrations of 15-
92,000), @-galactosidase(M, 116,000), and myosin (M, 200,000).
                              =                            =
                                                                         245 nM yielded clotting timeswhich decreased from 72 to 36 s. A plot
   Assays for Thrombin, Factors  Xa, XIa,Kallikrein, Actiuated Protein
                                                                         of log clotting time versus log [factor IXa] was linear in this range.
C, Plasmin, Urokinase, Cathepsin G, Elastase, y-NGF, and EGF-BP-
                                                                            Assay for Factor XIIa-Factor XIIa was assayed in the laboratory
Reactions were carried out in 1.5-ml polypropylene microcentrifuge
tubes at 37 "C. The enzyme, HCII, heparin, and dermatan sulfate          of Dr. Allen Kaplan as previously described (14).
were mixed at the final concentrations specified in Table I in buffer       Assay for Tissue Plasminogen Actiuator-TPA, HCII, and heparin
containing0.15 M NaCl, 0.02 M Tris-HC1, pH 7.4, and 1 mg/ml bovine       or dermatan sulfatewere mixed with 0.9 mg/ml fibrinogen in 0.15 M
serum albumin. Reactions were initiated by addition of the protease.     NaC1,0.02 M Tris-HC1, pH 7.4. B. atrox venom (1 unit/ml final
At specified times, protease activity was determined by addition of      concentration) was added immediately to clot the fibrinogen. After a
an equal volume of the appropriate chromogenic substrate in water.       60-min incubation at 37 "c,an equal volume of 0.6 mM $3-2444was
Therate of hydrolysis of thesubstrate was determined froma               added. Hydrolysis of the substrate was terminated after 3 min by
continuous recording of the absorbance at 405 nm.Alternatively,          addition of aceticacid (5% final concentration), the mixture was
hydrolysis of the substratewas terminated after 3 min by addition of     centrifugedfor 10 min in an Eppendorfmicrocentrifuge, and the
1/10 volume of 50% (v/v) acetic acid, the precipitated glycosamino-      absorbance at 405 nm of the supernatant solution was determined.
glycan was removed by centrifugation if necessary, and the absor-                                                        M
                                                                         Control experiments demonstrated (a) thatA 5 was proportional to
bance of the supernatant solution was determined at 405 nm. In the       the amount of TPA present in the absence of HCII; (b) that the
absence of HCII, a standard curve of A A 4 0 5 versus protease concen-   venom did not hydrolyze the substrate S-2444; and (c) that HCII did
tration was linear for each proteaseintheconcentration           range                    was
                                                                         not inhibit nor it degraded by the venom protease. In preliminary
employed in the experiment. The    following substrates were used 0.1    experiments, fibrinogen and B. atrox venom were omitted from con-
mM Chromozym T H for thrombin, r-NGF, and EGF-BP mM S-      0.3          trol incubations without HCII; as previously reported (18), the rate
2222 for factor Xa; 3 mM S-2222 for factor XIa; 0.4 mM S-2302 for        of substrate hydrolysis by TPA in the absence of fibrin was -30% of
kallikrein; 0.2 mM S-2238 for activated protein C; 0.5 m M S-2251 for    the rate obtainedin the presence of fibrin.
plasmin; 0.6 mM $2444 for urokinase; 0.2 mM succinyl-Ala-Ala-Pro-           Kinetic Analysis-The second-order rate constantfor inhibition of
Phe-p-nitroanilide for cathepsin G; and 0.2 mM succinyl-Ala-Ala-         a protease by HCII was estimated according to the equation: k =
Ala-p-nitroanilide for elastase.                                         ln([P]o/[P],)/t/[[HCII], in which [PIo= initial protease activity, [PIl

                                                 Inhibition of purified proteases by HCII
                Reactants were incubated at 37 "C at thefinal concentrations indicated in 0.15 M NaCl, 0.02 M Tris-HC1, and 1
              mg/ml bovine serum albumin, pH 7.4. At the end of the incubation period, the remaining protease activity was
              determined as described under "Experimental Procedures."
                                                                                               Activity remaining after incubation with

       Protease          [Protease]
                              [HCII]            Incubation
                                                    time     [Heparin]   'Dermatan
                                                                           sulfate]    HCII     Heparin     HCII +      Dermatan          HC1l   +

                                                                                       alone     alone      heparin
                                                                                                                            alone         sulfate
                                    nM              min      unitlrnl      ccglml                           % of control'
   Thrombin                  2.2    0.5 150         20                       100         22      101          <2            100            <2
   Factor Xa                11.6         200        30         1             100        109      NDb           94           ND             108
   Factor VIIa               0.83        760        15         1              80        108      ND           110           ND             115
   Factor IXa               69          1220        20         1             100         95      ND           106           ND             116
   Factor XIa                2.8         100        15         1             100        105      103          106            79             83
   Factor XIIa               4.3          50        15         1             100        100      101           92            98             95
   Kallikrein                2.9         100        10         1             100        102       98           99           100            101
   Protein Ca               83           760        10         1             100         98       98           99            47             50
   Plasmin                 290           750        30         1             100        100      101           84            87             98
   Urokinase               540           830        30         1             100        107      108          104           109            106
   TPA                      55           760        60         0.5           400        102       51           56            95             95
   Cathepsin G             730          1250        40         0.5           400         30       43           36            76             <2
   Elastase                670          1780        60         0.5           400         56       45           50            95             57
   y-NGF                   100           760        10         1             100        106      105          103            91             91
   EGF-BP                  100           760        10         1             100         95       95           96            76             69
                  a Averages of duplicate determinations.
                    ND, not determined.
                                                       Protease Specificity of HCII                                                3503
= protease activity at time = t, and [HCII] = initial HCII concentra-   ted did not contain labeled complexes regardless of whether
tion, assuming pseudo-first orderconditions.                            heparin or dermatan sulfate was present (lanes B-D).        These
                                                                        experiments indicate that thrombin generated in plasma by
                                                                        activation of the intrinsic coagulation pathway is inhibited by
   Inhibition of Thrombin by HCII in Recalcified Plasma-We              HCII in the presence of dermatan sulfate.
have previously shown that thrombin combines with HCII to                  Inhibition of Thrombin by HCII in Plasma Activated by
form a 96,000-dalton complex that is stable during SDS-                 Tissue Factor or Kaolin-In an attempt to detect complexes
PAGE (3, 4 .To determine whether HCII inhibits thrombin
             )                                                          of HCII with proteases other than thrombin, prothrombin-
or other proteases as they are generated during coagulation,            deficient plasma containing '251-HCII was incubated for 1 h
tracer '251-HCII wasadded to citrate-anticoagulated plasma,             at 37 "C with CaC12, phospholipids, and a source of tissue
the mixture was warmed to 37 "C in a glass tube, and coagu-                                                      to
                                                                        factor (human brain thromboplastin) activate factor VI1 or
lation was initiated by addition of CaC12.After 1h, the plasma          kaolin (activated partial thromboplastin reagent) to activate
was analyzed by SDS-PAGE and autoradiography (Fig. 1,                   factor XI1 and kallikrein. In neither case was any of the lZ5I-
lanes E-G). Coagulation occurred in the absence of heparin              HCII detected in complexes (Fig. 1, lanes Hand K). Identical
or dermatan sulfate, and none of the lZ5I-HCII   was detected           results were obtained in the presence of 5 units/ml of heparin
in higher molecular weight complexes (lune E). However,                 (lanes I and L). When incubations were repeated in the
coagulation did not occur in the presence of67 pg/ml of                 presence of 67 pg/ml of dermatan sulfate, a trace amount of
dermatan sulfate, and densitometry revealed that -13% of                the label was present in a band corresponding to the throm-
the label was present in a 96,000-dalton band (lane G) which            bin-HCII complex (lanes J and M). No other complexes were
co-migrated with the complex formed by incubation of an                 observed. When the exposure times of the autoradiographs in
excess of purified thrombin with '251-HCII(luneA ) . Less than          Fig. 1were extended from 1to 20 h to increase the sensitivity
1% the label was present inthe complex when prothrombin-
     of                                                                 of the experiments, we observed numerous additional bands
deficient plasma was substituted for normal plasma in the                                               of
                                                                        representing as a whole 0.1% the total radioactivity present.
incubation (not shown). Coagulation also did not occur in the           Because there were no significant differences between the
presence of 5 units/ml of heparin. In this case, none of the                                                of
                                                                        additional bands and the pattern a gel containing '251-HCII
'251-HCII wasdetected in the 96,000-dalton complex (lane F).            alone (not shown), the bands were considered to represent
                                                                        trace contaminants inthe HCII preparation.
This result is consistent with previous experiments which
                                                                           Inhibition of Purified Proteases by HCII-We assayed four-
demonstrated that '251-thrombinis preferentially inhibited by
                                                                        teen purified proteases for activity after incubation with a
ATIII in undiluted plasma at similar concentrations of hep-             molar excess of HCII (Table I). The concentrations of pro-
arin (3). Control incubations  from which the CaC12 wasomit-            tease and HCII were determined primarily according to the
                                                                        sensitivity of the assay for the protease. Incubation times
                                                                        were long in comparison to thet112for inhibition of thrombin
200 -                                                                   by HCII (e.g. tl,2 = 8 s in the presence of 50 nM HCII and 0.5
                                                                        unit/ml of heparin; Ref. 4). Under the conditions of each
                                                                        experiment, 20% inhibition of the protease would indicate a
 116   -                                                                second-order rate constant 3 X lo5 M" min" (ie. 2000 times
                                                                        less than the rate constant inhibition of thrombin by HCII
                                                                        in the presence of dermatan sulfate; see "Discussion"). Hep-
                                                                        arin or dermatan sulfate were present at concentrations pre-
  66 -                                                                  viously determined to accelerate the inhibition of thrombin
                                                                        by HCII (4,5). In addition, controls were performed to deter-
                                                                         mine the effects of heparin and dermatan sulfate alone on
                                                                        protease activity. As shown in Table I, 22% of thrombin
  45   -                                                                 activity remained after a 20-min incubation with 150 m
                                                                         HCII, while <2% activity remained in incubations that also

  MW       A   B   C    D   E    F   G    H    I   J    K   L   M        included heparin or dermatan sulfate. The second-order rate
  Stds.                                                                  constant calculated for inhibition of thrombin by HCII alone
   FIG. 1. IncorDorationof 12'I-HCII into comdexes in Dlasma             inthis experiment was 5 X lo5 M" min", as previously
during coagulation. Reagents were brought t o a final voiume of          reported (4). Rate constants for inhibition of thrombin by
150 pl with 0.15 M NaC1, 0.02 M Tris-HC1, 1 mg/ml bovine serum           HCII in the presence of heparin or dermatan sulfate could
albumin, pH 7.4, and incubated for 1 h at 37 "C in glass (lunes B-G)     not be determined accurately from the datain Table I, but in
or polypropylene (lunes A and H-M) tubes. Each incubation con-           both cases were >1.3 x lo6 M" min" (see "Discussion"). In
tained 7.5 nM lZ5I-HCIIalong with the following additional reagents:                     did
                                                                         contrast, HCII not inhibit      significantly coagulation factors
lune A , 13 p~ thrombin; lane B, 25 p1 of normal plasma; lune C, same
as I3 plus 5 units/ml heparin; lune D, same as B plus 67 pg/ml           VIIa, IXa, Xa, XIa,XIIa, kallikrein, activated protein C,
dermatan sulfate; lune E,25 pl of normal plasma and 6 mM CaCl2;          plasmin, urokinase, TPA? or 7-NGF. Activated protein C
lune F,same as E plus 5 units/ml heparin; lune G, same as E plus 67      and TPAwere moderately inhibited by dermatan sulfate and
pg/ml dermatan sulfate; lune H , 25 pl of prothrombin-deficient          heparin, respectively, but there was no further inhibition in
plasma, 13 mM CaClZ, and 100 pl of human brain thromboplastin;           either case when HCII was also present. Leukocyte elastase
lune I, same as H plus 5 units/ml heparin; lane J , same as H plus 67    was partially inhibited during a 60-min incubation with 1.78
pg/ml dermatan sulfate; lune K, 25 p1 prothrombin-deficient plasma,
8 mM CaClZ,and 50 p1 of activated partial thromboplastin reagent;        p~ HCII alone or with dermatan sulfate; in both cases the
lune L,same asK plus 5 units/ml heparin; lune M , same as K plus 67      rate constants were 5 x lo3 M" min". Although elastase was
pg/ml dermatan sulfate. At the end of the incubation period, 5-10 p1     moderately inhibited by heparin alone, heparin appeared to
of each reaction mixture were subjected to SDS-PAGE. An autora-
diograph of the gel exposed for 1 h at -70 "C is shown. The positions       HCII was incubated with TPA alone (data not shown) or in the
of molecular weight standards and of the 96,000-dalton thrombin-        presence of fibrin as described under"Experimental Procedures"
HCII complex (+) are indicated.                                         (data in Table I).
3504                                                                    f i e1
                                                    Protease ~ ~ e ~ ~ of Hc1i t ~
protect the protease from further inhibition by HCII. EGF-            other than thrombin, only leukocyte cathepsin G was inhib-
B P was inhibitedpartially by dermatan sulfate and to a               ited at a significant rate. However, the calculated second-
slightly greater extent when both dermatan sulfate and HCII           order rate constant for inhibition of cathepsin G by HCII in
were present; in the latter case the calculated rate constant         the presence of dermatan sulfate was -40,000-fold less than
was 1 X io4 M" min-'.                                                 the rate constant reported for inhibition of cathepsin G by
   Inhibition of Cathepsin G by HCZZ-Because HCII appeared            a1-antichymotrypsin (29). Therfore, inhibition of cathepsin
to inhibit cathepsin G at a significant rate in the presence of       G by HCII is unlikely to occur i n uiuo. In contrast, HCII
dermatan sulfate (Table I), the time course of inhibition was         inhibits thrombin with rate constants of 6.4 X lo8 M" min"
studied in more detail (Fig. 2). In the absence of heparin or         in the presence of 250 pg/ml of dermatan sulfate and 4.0 X
dermatan sulfate, inhibition by 1.25 PM HCII occurred with            10' M" min" in the presence of 10 units/ml of heparin (5).
a tllz= 24 min ( k = 1.4 X lo4M ' min-I). Although dermatan
                                 -                                    Rate constants of this magnitude are characteristic of inhi-
sulfate alone decreased cathepsin G activity 20-30% (Table            bition reactions that arelikely to be "physiological" (30).
I), it increased the rate of inhibition by HCII &fold (tIl2 4
                                                           =             Our data indicate that the protease specificity of HCII is
min; k = 8.4 x IO5 M" min"). In contrast, heparin decreased           more restricted than thatof other plasma protease inhibitors,
the activity of cathepsin G 50-60%, and it appeared to prevent        including ATIII (9),al-proteinase inhibitor (30), a2-antiplas-
                                                                      min (31), and a2-macroglobulin (32), each of which can inhibit
further inhibition of the protease by HCII.
                                                                      several of the proteases that we have tested. In addition, the
                           DISCUSSION                                 lack of inhibition of y-NGF, EGF-BP,   plasmin, and urokinase
                                                                      distinguishes HCII from the cellular protease inhibitors
  The purpose of this investigation was to identify enzymes           termed "protease nexins" (33). We have also found that, in
that HCII can inhibit, and thereby to arrive at a hypothesis          the presence of dermatan sulfate, HCII binds thrombin as it
concerning the physiological function of HCII. We have tested         is being generated in plasma during coagulation. Thus, inhi-
various serine proteases, including all of thosecurrently             bition of thrombin by HCII appears to explain the anticoag-
known to be involved in coagulation and fibrinolysis (28),            ulant activity of dermatan sulfate that has been observed in
leukocyte cathepsin G (21) and elastase (ZO), and the pepti-          vitro (lo, 12) and may also explain the antithrombotic effect
dase subunits of nerve growth factor (23) (y-NGF) and epi-            observed in uiuo after the administration of exogenous der-
dermal growth factor (24) (EGF-BP).Of the enzymes tested              matan sulfate (34). In addition, HCIImay inhibit other effects
                                                                      of thrombin, including platelet aggregation and secretion (35),
                                                                      chemotaxis (36), and mitogenesis (37), underappropriate
    0.50   r                                                          circumstances.
                                                                         Rapid inhibition of thrombin by HCII i n vivo probably
                                                                      occurs only in the immediate vicinity of proteoglycans which
                                                                      contain oligosaccharide sequences that bind HCII (4,8). Sim-
    0.3oJi          \                                                 ilarly, ATIII requires specific oligosaccharide sequences for
                                                                      maximum activity (9). HCII and ATIII may becomeactivated
                                                                      in different environments,since there is evidence that differ-
                                                                      ent heparin molecules activate HCII and ATIII (38) and that
                                                                      dermatan sulfate only activates HCII (5). Dermatan sulfate
                                                                      comprises 60-70% of the glycosaminoglycans in the intima
                                                                      and media of large arteries (39), in addition to being present
                                                                      in skin, heart valves, and tendons (40). A small amount of
                                                                      dermatan sulfate is also synthesized by cultured endothelial
                                                                      cells (41). Whether the glycosaminoglycans present in these
                                                                      locations contain the proper sequences to active HCII remains
0                                                                     to be determined.
m 0.10 -                                                                 Acknowledgments-We thank Dr. Allen Kaplan for performing the
w      ..                                                              factor XIIa assays and Drs. Paul Bajaj, George Broze, DBsirB Collen,
2 0.08 -                                                               Thomas Maciag, Joseph Miletich, Hatem Salem, and Robert Senior
                                                                       for providing proteases and otherreagents.
U        -
    0.06 -                                                              1. Briginshaw, G. F., and Shanberge, J. N. (1974) Arch. Biochem.
                                                                            Biophys. 161,683-690
          r                                                             2. Briginshaw, G . F., and Shanberge, J. X. (1974) Thromb. Res. 4,
                        10             20             30            40  3. Tollefsen, D.M., and Blank, M. K. (1981) J. Clin. Invest. 68,
                                 TIME (Min)                                 589-596
   FIG. 2. Inhibition of leukocyte cathepsin G by HCII. Cathep-         4. Tollefsen, D. M., Majerus, D.W., and Blank, M. K. (1982) J.
sin G (0.73 p ~ and HCII (1.25 p ~ were incubated for 1-40 min a t
                  )                      )                                  Rid. Chem. 257,2162-2169
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