The protein encoded by a growth arrest-specific gene (gas6) is a new member of the vitamin K-dependent proteins related to protein S, a negative coregulator in the blood coagulation cascade.

Abstract

A set of growth arrest-specific genes (gas) whose expression is negatively regulated after serum induction has previously been described (C. Schneider, R. M. King, and L. Philipson, Cell 54:787-793, 1988). The detailed analysis of one of them, gas6, is reported here. gas6 mRNA (2.6 kb) is abundantly expressed in serum-starved (48 h in 0.5% fetal calf serum) NIH 3T3 cells but decreases dramatically after fetal calf serum or basic fibroblast growth factor stimulation. The human homolog ofgas6 was also cloned and sequenced, revealing a high degree of homology and a similar pattern of expression in IMR90 human fibroblasts. Computer analysis of the protein encoded by murine and human gas6 cDNAs showed significant homology (43 and 44% amino acid identity, respectively) to human protein S, a negative coregulator in the blood coagulation pathway. By using an anti-human Gas6 monospecific affinity-purified antibody, we show that the biosynthetic level of human Gas6 fully reflects mRNA expression in IMR9O human fibroblasts. This finding thus defines a new member of vitamin K-dependent proteins that is expressed in many human and mouse tissues and may be involved in the regulation of a protease cascade relevant in growth regulation.Interactions between serine proteases, their substrates, and their inhibitors have largely been exploited during evolution. Protease cascades are not confined to the classical blood coagulation or complement cascade. A network of proteases that control the synthesis or activity of a ligand appears an ideal and finely regulatable mechanism to trigger a rapid response to an extracellular event, with the inherent advantage of powerful amplification. Thrombin, in addition to catalyzing fibrin polymerization, can act as a novel ligand for the recently identified thrombin receptor (61), a member of the seven-transmembrane domain receptor family, possibly mediating other known effects of thrombin, including its role as a mitogen for lymphocytes and fibroblasts (8, 9). Hepatocyte growth factor (scatter factor), which promotes cell division (53) and epithelial morphogenesis (47), is similar in structure to serine proteases (38% amino acid sequence identity with plasminogen), although it lacks proteolytic activity as a result of mutation of two residues in the catalytic triad (31,48). Hepatocyte growth factor is the ligand for the c-met proto-oncogene product (5, 49), a transmembrane 190-kDa heterodimer with tyrosine kinase activity that is widely expressed in normal epithelial tissues (20).Recently, a protease pathway has been shown to play a crucial role in the dorsoventral patterning of Drosophila embryos (36). At least three genes (snake, gastrulation defective, and easter) appear to encode extracellular proteases (7,36). Easter appears to be the ultimate protease that processes spatzle that binds and activates its receptor Toll

Gas6-mediated survival in NIH3T3 cells activates stress signalling cascade and is independent of Ras

“…In addition to a weak mitogenic signal, the most prominent Gas6 feature is its ability to protect the cells from apoptosis induced by growth factor withdrawal (Goruppi et al, 1996;Nakano et al, 1996), TNFa (Bellosta et al, 1997) and several other genotoxic stress (SG unpublished results). Since Gas6 expression is enhanced at growth arrest (Man®oletti et al, 1993), it is likely that its survival-enhancing activity should be most relevant for quiescent cells, possibly indicating that signals departing from Axl act by interfering with speci®c elements involved in the apoptotic process. Here we have analysed the Gas6-activated signalling activities linked to its function as an inhibitor of cell death.…”

“…Polypeptide growth factors are known to suppress cell death after interaction with the respective receptors and subsequent activation of speci®c transduction pathways (Segal and Greenberg, 1996;Stewart and Rotwein, 1996). The product of the growth arrest speci®c gene gas6 (Gas6) (Man®oletti et al, 1993) is a growth factor identi®ed as the ligand for Axl/Ufo tyrosine kinase receptors (RTK) (referred thereafter as Axl) (Janssen et al, 1991;O'Bryan et al, 1991;Varnum et al, 1995). Axl is a RTK de®ning a subfamily of RTK with Rse/Sky, c-Mer/Nyk and Rek (Biscardi et al, 1996;Graham et al, 1994;Ling and Kung, 1995;Mark et al, 1994).…”

Genes related to growth and invasiveness are repressed by sodium butyrate in ovarian carcinoma cells

“…Figure 2b (panel 3) shows that FN transcript levels were dramatically increased after 8 h of exposure to the differentiation inducer. NaB exposure and the gene growth arrest-specific 6 (gas6) NIH 3T3 cells that are growth arrested by serum deprivation start to synthesise gas6 (Schneider et al, 1988), which is a vitamin K-dependent gene suspected to participate in growth control (Manfioletti et al, 1993). N. 1 cells constitutively express gas6 and the mRNA accumulates when N.1 cells become confluent and retard growth (unpublished observation).…”

Plasma concentrations of growth arrest specific protein 6 and the soluble form of its tyrosine kinase receptor Axl as markers of large abdominal aortic aneurysms

“…The expression of Axl is upregulated in response to vascular injury being primarily located in the cells of the neointima, suggesting that Axl may be a mediator of vascular smooth muscle migration and proliferation 10 . Axl is stimulated by Gas6 (product of the growth arrest specific gene 6) that was originally found as a protein expressed by growth arrested fibroblasts 9,11,12 . Axl is phosphorylated in response to Gas6 binding and the activation of Axl results in anti-apoptotic and prosurvival effects, mainly due to involvement of the PI3 kinase and Akt pathways 9,12 .…”

“…The Axl ligand Gas6 is a member of the vitamin K-dependent protein family, Gas6 being homologous to the anticoagulant protein S 11,12,18 . Gas6 is expressed in many cell types, including endothelial cells, vascular smooth muscle cells and fibroblasts 11 .…”