Type F Scavenger Receptor SREC-I Interacts with Advillin, a Member of the Gelsolin/Villin Family, and Induces Neurite-like Outgrowth

Abstract

The scavenger receptor expressed by endothelial cells (SREC) was isolated from a human endothelial cell line and consists of two isoforms named SREC-I and -II. Both isoforms have no significant homology to other types of scavenger receptors. They contain 10 repeats of epidermal growth factor-like cysteine-rich motifs in the extracellular domains and have unusually long C-terminal cytoplasmic domains with Ser/Pro-rich regions. The extracellular domain of SREC-I binds modified low density lipoprotein and mediates a homophilic SREC-I/SREC-I or heterophilic SREC-I/SREC-II trans-interaction. However, the significance of large Ser/Pro-rich cytoplasmic domains of SRECs is not clear. Here, we found that when SREC-I was overexpressed in murine fibroblastic L cells, neurite-like outgrowth was induced, indicating that the receptor can lead to changes in cell morphology. The SREC-I-mediated morphological change required the cytoplasmic domain of the protein, and we identified advillin, a member of the gelsolin/villin family of actin regulatory proteins, as a protein binding to this domain. Reduction of advillin expression in L cells by RNAi led to the absence of the described SREC-I-induced morphological changes, indicating that advillin is a prerequisite for the change. Finally, we demonstrated that SREC-I and advillin were co-expressed and interacted with each other in dorsal root ganglion neurons during embryonic development and that overexpression of both SREC-I and advillin in cultured Neuro-2a cells induced long process formation. These results suggest that the interaction of SREC-I and advillin are involved in the development of dorsal root ganglion neurons by inducing the described morphological changes.