Level of Expression of Phospholipid Scramblase Regulates Induced Movement of Phosphatidylserine to the Cell Surface

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We recently identified a 35-kDa erythrocyte , scramblase, that promotes +-dependent transbilayer movement of phosphatidylserine (PS) and other (PL) in reconstituted proteoliposomes (Zhou, Q., Zhao, J., Stout, J. G., Luhm, R. A., Wiedmer, T., and Sims, P. J. (1997) J. Biol. Chem. 272, 18240-18244). To determine whether this same protein is responsible for the rapid movement of PS from inner-to-outer leaflets in other cells exposed to elevated cytosolic calcium concentration ([+]c), we analyzed how induced movement of PS to the related to expression of PL scramblase. Exposure to + A23187 resulted in rapid PS exposure in those cell lines constitutively high in PL scramblase (, -transformed B-lymphocytes, and Jurkat), whereas this response was markedly attenuated in cells expressing low amounts of this protein (Raji, HL60, and Dami). To confirm this apparent correlation between PL scramblase expression and PS egress at elevated [+]c, Raji cells were transfected with PL scramblase cDNA in pEGFP-C2, and stable transformants expressing various amounts of -PL scramblase fusion protein were obtained. Clones expressing -PL scramblase showed distinctly -localized fluorescence. When compared either with untransfected Raji cells or with transformants expressing alone, clones expressing -PL scramblase fusion protein showed increased exposure of PS at the in response to elevated [+]c, accompanied by increased expression of catalytic function for the enzyme complex. These data indicate that transfection with PL scramblase cDNA promotes movement of PS to and suggest that this protein normally mediates redistribution of in activated, injured, or apoptotic cells.

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Humans Tumor Cells, Cultured Cell Membrane Calcimycin Membrane Proteins Phospholipid Transfer Proteins Biological Transport Carrier Proteins Phosphatidylserines