Requirement of γ-carboxyglutamic acid residues for the biological activity of Gas6: contribution of endogenous Gas6 to the proliferation of vascular smooth muscle cells

Abstract

Gas6 (encoded by growth-arrest-specific gene 6) is a gamma-carboxyglutamic acid (Gla)-containing protein which is released from growth-arrested vascular smooth muscle cells (VSMCs) and potentiates VSMC proliferation induced by Ca2+-mobilizing growth factors, but not that induced by receptor tyrosine kinases. In this study we examined the importance of Gla residues for the biological activities of Gas6 and tried to assess the importance of endogenous Gas6 in VSMC proliferation. We demonstrated that Gla-deficient Gas6 lacked receptor-binding and growth-potentiating activities. Therefore the vitamin K-dependent modification of Gas6 appeared to be essential for its biological activities. Next we used warfarin, an inhibitor of vitamin K-dependent gamma-carboxylation, to estimate the contribution of endogenous Gas6 to VSMC proliferation. Warfarin markedly inhibited the thrombin-induced proliferation of VSMC without affecting the mRNA or protein expression of Gas6. Therefore the inhibition seems to be due to prevention of the vitamin K-dependent modification of Gas6. However, warfarin did not affect epidermal growth factor-induced proliferation. A neutralizing antibody against Gas6 gave a similar result, i.e. it inhibited thrombin-induced VSMC proliferation but not that induced by epidermal growth factor. These results indicate that endogenously produced Gas6 is very important for VSMC proliferation induced by Ca2+-mobilizing growth factors.

Low vitamin K status is associated with osteoarthritis in the hand and knee

“…First, inadequate ␥-carboxylation of Gas-6, as may occur with insufficient vitamin K, impairs the function of Gas-6 (2,18,19) and, as such, may impair chondrocyte viability in articular cartilage. Second, both mice and humans deficient in MGP express phenotypes that are similar to that seen with warfarin embryopathy, with growth plate calcification abnormalities that in theory might be mimicked by the process of osteophyte formation (11,13).…”

“…Insufficient vitamin K leading to undercarboxylation of MGP and Gas-6 can reduce the functioning of these proteins and affect chondrocyte differentiation and endochondral bone formation (2,(16)(17)(18)(19). Given the extent of vitamin K's skeletal effects, we hypothesized that low vitamin K status as determined by a biochemical measure, the plasma phylloquinone level, would be related to radiographic features of OA in the hand and knee.…”

Immunobiology of the TAM receptors

“…(Gla-domaincontaining proteins are prominent components of the blood coagulation cascade.) These Gla domains bind the phospholipid phosphatidylserine 13 , and this is an important feature of the in vivo function of GAS6 and protein S [14][15][16][17] . The Gla domain is followed by four epidermal growth factor (EGF)-like modules, and then by two tandem laminin G domains that are related to those of the sex hormone binding globulin (SHBG) (FIG.…”

Vitamin K-dependent proteins in Ciona intestinalis , a basal chordate lacking a blood coagulation cascade

“…In addition, both protein S and its homolog Gas6 activate certain members of the Axl subfamily of receptor tyrosine kinases to transduce antiapoptotic and proliferative signals (10). In the case of Gas6, many of the functions ascribed to the molecule are abrogated when it is produced in the presence of warfarin, underscoring the essential nature of ␥-glutamyl carboxylation (11)(12)(13).…”