Gas 6 promotes Axl-mediated survival in pulmonary endothelial cells

We examined Gas 6-Ax1 interactions in human pulmonary artery endothelial ce lls (HPAEC) and in Ax1-transduced HPAEC to test Gas 6 function during endot helial cell survival. We identified the 5.0-kb Ax1, 4.2-kb Rse, and 2.6-kb Gas 6 mRNAs in HPAEC. Immunoprecipitation and Western blotting confirmed th e presence of these proteins. Gas 6 is present in cell-associated and secre ted fractions of growth-arrested HPAEC, independent of cell density. In add ition, the Ax1 receptor is constitutively phosphorylated in growth-arrested cultures, and exogenous Gas 6 enhanced Ax1 phosphorylation threefold. Gas 6 added to growth-arrested HPAEC resulted in a significant increase in cell number (1.5 nM Gas 6 increased cell number 35%). Flow cytometry revealed t hat Gas 6 treatment resulted in 28% fewer apoptosing cells. Transduction of a full-length Ax1 cDNA into HPAEC resulted in 54% fewer apoptosing cells a fter Gas 6 treatment. Collectively, the data demonstrate antiapoptotic acti vities for Gas 6 in HPAEC and suggest that Gas 6 signaling may be relevant to endothelial cell survival in the quiescent environment of the vessel wal l.