Scavenger receptor, Class B, Type I provides an alternative means for β-VLDL uptake independent of the LDL receptor in tissue culture

Recent evidence suggests that scavenger receptor, class B, type I (SR-BI) plays a physiological role in VLDL metabolism. SR-BI was reported to mediate beta-VLDL uptake; however cellular details of this process, are not well characterized. In the present study we show that SR-BI delivers cholesterol derived from beta-VLDL to LDL receptor negative SR-BI over-expressing Chinese Hamster Ovarian cells (IdlA7-SRBI). Cell association of beta-VLDL was similar to 3 times higher after SR-BI over-expression, which was competed by beta-VLDL but only to a lesser extent by HDL and LDL Almost all of the associated beta-VLDL was located intracellularly, and therefore could not be released by a 50-fold excess of unlabeled beta-VLDL beta-VLDL was degraded at a rate of 6 ng beta-VLDL/mg cell protein and hour. In contrast to IdlA7 cells, beta-VLDL association was competed by LDL in cells with a functional LDL receptor like CHO and HepG2 cells, indicating a strong impact of the LDL receptor in beta-VLDL uptake. beta-VLDL degradation was similar to IdlA7-SRBI cells. When beta-VLDL uptake was followed using fluorescence microscopy beta-VLDL showed a, different uptake pattern in SR-BI over-expressing cells, IdlA7-SRBI, compared to LDL receptor containing cells, CHO and HepG2. (C) 2009 Elsevier B.V. All rights reserved.