Rat vascular smooth muscle cells (SMC) in culture synthesize and secrete a approximately 38,000-Mr protein doublet or triplet that, as previously described (Majack and Bornstein. 1984. J. Cell Biol. 99:1688-1695), rapidly and reversibly accumulates in the SMC culture medium upon addition of heparin. In the present study, we show that this approximately 38,000-Mr heparin-regulated protein is electrophoretically and immunologically identical to apolipoprotein E (apo-E), a major plasma apolipoprotein involved in cholesterol transport. In addition, we show that expression of apo-E by cultured SMC varies according to growth state: while proliferating SMC produced little apo-E and expressed low levels of apo-E mRNA, quiescent SMC produced significantly more apo-E (relative to other proteins) and expressed markedly increased levels of apo-E mRNA. Northern analysis of RNA extracted from aortic tissue revealed that fully differentiated, quiescent SMC contain significant quantities of apo-E mRNA. These data establish aortic SMC as a vascular source for apo-E and suggest new functional roles for this apolipoprotein, possibly unrelated to traditional concepts of lipid metabolism.
Expression of apolipoprotein E by cultured vascular smooth muscle cells is controlled by growth state.
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R A Majack, C K Castle, L V Goodman, K H Weisgraber, R W Mahley, E M Shooter, P J Gebicke-Haerter; Expression of apolipoprotein E by cultured vascular smooth muscle cells is controlled by growth state.. J Cell Biol 1 September 1988; 107 (3): 1207–1213. doi: https://doi.org/10.1083/jcb.107.3.1207
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