The human serum deprivation response gene (SDPR) maps to 2q32-q33 and codes for a phosphatidylserine-binding protein

The serum deprivation response gene (SDPR, alias sdr) has been previously i solated for its high mRNA expression in serum-starved cells compared to con tact-inhibited NIH3T3 cells; such regulation is not observed in single-onco gene transformed NIH3T3 cells after serum starvation. More recently Sdpr ha s been identified as a substrate of protein kinase C (PKC): this interactio n determines the compartimentalization of PKC to caveolae, a plasma membran e invagination of which Sdpr is a major component. Lack of Sdpr-PKC interac tion in transformed cells has been proposed to be involved in the alteratio n of PKC subcellular localization and substrate specificity, Here we report the cloning of the human SDPR homologue (HGMW-approved symbol SDPR) and it s mapping to 2q32-q33 in the human genome. In analogy with the murine syste m, SDPR mRNA expression is increased when human fibroblasts are serum starv ed, it becomes down-regulated during synchronous cell-cycle reentry, but it is not induced in cells arrested by contact inhibition. Analysis of SDPR e xpression in human tissues reveals a near ubiquitous expression, with highe st levels found in heart and lung. We show that human SDPR encodes PS-p68, a previously characterized phosphatidylserine-binding protein purified from human platelets. Accordingly, recombinant Sdpr is able to specifically bin d phosphatidylserine in the absence of Ca2+. SDPR is homologous to two gene s in the databank. one of which, srbc, is similarly regulated during growth arrest and encodes a phosphatidylserine-binding protein that is a substrat e of PKC. (C) 1999 Academic Press.