ALTERNATIVE FORMS OF THE SCAVENGER RECEPTOR BI (SR-BI)

The class B, type I scavenger receptor has been implicated as a recept or for high density lipoprotein (HDL). We have isolated a murine cDNA clone encoding an alternative form of SR-BI that differs in the putati ve cytoplasmic domain of the receptor. This variant form, likely the r esult of alternative mRNA splicing, is designated SR-BI.2. SR-BI.2 mRN A was detected in mouse tissues known to express SR-BI and tissue-spec ific differences in the relative abundance of SR-BI.2 were apparent. I n mouse adrenal glands, SR-BI.2 represented approximately one-third of total SR-BI mRNA, whereas in mouse testes, SR-BI.2 represented the ma jor mRNA species (79% of total). SR-BI.2 was also detected in the huma n cell lines examined, namely HeLa, HepG2, and THP-1 cells. CHO cells transfected with the mouse SR-BI.2 cDNA expressed significant levels o f SR-BI.2 protein and acquired the ability to take up fluorescent lipi d (DiI) from DiI-HDL. Alternative splicing of SR-BI represents a poten tially important process for the regulation of SR-BI expression and fu nction.