Scavenger receptor, Class B, Type I provides an alternative means for beta-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 (ldlA7-SRBI). Cell association of beta-VLDL was approximately 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 ldlA7 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 ldlA7-SRBI cells. When beta-VLDL uptake was followed using fluorescence microscopy, beta-VLDL showed a different uptake pattern in SR-BI over-expressing cells, ldlA7-SRBI, compared to LDL receptor containing cells, CHO and HepG2.
Röhrl
Clemens
C
Center for Physiology and Pathophysiology, Department of Medical Chemistry, Medical University of Vienna, Währingerstrabetae 10, 1090 Vienna, Austria.
Fruhwürth
Stefanie
S
Schreier
Sabine Maria
SM
Lohninger
Alfred
A
Dolischka
Andrea
A
Hüttinger
Manfred
M
Zemann
Nina
N
Hermann
Marcela
M
Strobl
Witta
W
Stangl
Herbert
H
D000818:Animals; D018955:CD36 Antigens / Q000378:metabolism*; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D056945:Hep G2 Cells; D006801:Humans; D008055:Lipids / Q000032:analysis; D053419:Lipoproteins, IDL / Q000378:metabolism*; D011973:Receptors, LDL / Q000502:physiology*
D018955:CD36 Antigens; D008055:Lipids; D053419:Lipoproteins, IDL; D011973:Receptors, LDL