Interaction of Alpha-Actinin-4 with Class I PxxP Motif-Containing OK/SW-CL.16 Protein

Abstract

Background: The aim of this study was to identify novel binding partners for α-actinin-4 (actinin-4), an essential component of the glomerular filtration barrier. Methods: We performed bacterial two-hybrid screenings of a human kidney cDNA library using as a bait human actinin-4 containing the spectrin-like repeat R1. The identified interactions were further verified by in vitro affinity assays. To investigate the expression of the identified molecules in the kidney and other tissues, a human tissue cDNA panel screening and in situ hybridization were performed. Results: One isolated cDNA from the library encoded OK/SW-CL.16 protein with a segment similar to known actinin-interacting regions. OK/SW-CL.16 protein also contained the class I PxxP motif, which can participate in binding to Src homology 3 (SH3) domain-containing signaling proteins. In vitro affinity assays showed interactions of recombinant actinin-4 R1 and full-length renal actinin-4 with recombinant OK/SW-CL.16 protein. A tissue cDNA panel screening revealed a ubiquitous expression of OK/SW-CL.16 mRNA.In situ hybridization showed glomerular expression of OK/SW-CL.16 mRNA, mainly in podocytes and mesangial cells. Conclusion: Our results suggest that OK/SW-CL.16 protein is a novel binding partner for actinin-4. OK/SW-CL16 protein might act as a linker between actinin-4 and some SH3 domain-containing signaling proteins in podocytes.