GAS6, THE LIGAND OF AXL AND RSE RECEPTORS, IS EXPRESSED IN HEMATOPOIETIC-TISSUE BUT LACKS MITOGENIC ACTIVITY

GAS6, a gene previously identified as growth arrest specific, has been demonstrated to be the ligand of Ax1, a novel tyrosine kinase recepto r widely expressed in both normal and neoplastic hematopoietic tissue. We have observed previously that GAS6 mRNA was present in whole bone marrow. This preliminary finding prompted us to investigate the presen ce of GAS6 in hematopoietic tissue and the possible role of this molec ule in controlling the proliferation of hematopoietic precursors. We r eport here that the protein GAS6 is diffusely present in hematopoietic tissue, both in stromal and in hematopoietic cells, and that, among t hese cells, positivity is observed in megakaryocytes and myelomonocyti c precursors. Furthermore, our data suggest that GAS6 is not a growth factor for hematopoietic progenitors or stromal fibroblasts. Despite t he fact that both the Ax1 receptor and its ligand, GAS6, are expressed in hematopoietic tissue, the biological role of their interactions re mains to be determined.