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General Comment |
Ishii J, et al 2002 reported that SREC-II, a new member of the scavenger receptor type F family, trans-interacts with SREC-I through its extracellular domain.
The scavenger receptor expressed by endothelial cells (SREC) with an extremely large cytoplasmic domain, was originally identified in a human endothelial cell line. The authors cloned a second isoform named SREC-II and showed that there is a heterophilic interaction between SREC-I and SREC-II at their extracellular domains. The cDNA for murine SREC-II encodes an 834-amino acid protein with 35% homology to SREC-I. Like SREC-I, SREC-II contains multiple EGF-like repeats in its extracellular domain. However, in contrast to SREC-I, SREC-II had little activity to internalize modified low density lipoproteins (LDL). A Northern blot analysis revealed a tissue expression pattern of SREC-II similar to that of SREC-I with predominant expression in human heart, lung, ovary and placenta. Mouse fibroblast L cells with no tendency to associate show noticeable aggregation when SREC-I is overexpressed in these cells, while overexpression of SREC-II causes only slight aggregation. Remarkably, intense aggregation was observed when SREC-I-expressing cells were mixed with those expressing SREC-II. Deletion of almost all of the cytoplasmic receptor domain had no effect on the receptor expression and cell aggregation, indicating that solely the extracellular domain is involved in cell aggregation. The association of SREC-I and SREC-II was effectively suppressed by the presence of scavenger receptor ligands such as acetylated LDL and oxidized LDL. These findings suggest that SREC-I and SREC-II show weak cell-cell interaction by their extracellular domains (termed homophilic trans-interaction), while SREC-I and SREC-II show a strong heterophilic trans-interaction through their extracellular EGF-like repeat domains.
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