A human homologue of Drosophila kelch associates with myosin‐VIIa in specialized adhesion junctions

Abstract

Mutations in myosin-VIIa are responsible for the deaf-blindness, Usher disease. Myosin-VIIa is also highly expressed in testis, where it is associated with specialized adhesion plaques termed ectoplasmic specializations (ES) that form between Sertoli cells and germ cells. To identify new roles for myosin-VIIa, we undertook a yeast two-hybrid screen to identify proteins associated with myosin-VIIa in the ES. We identified Keap1, a human homologue of the Drosophila ring canal protein, kelch. The kelch-repeats in the C-terminus of human Keap1 associate with the SH3 domain of myosin-VIIa. Immunolocalization studies revealed that Keap1 is present with myosin-VIIa in the actin bundles of the ES. Myosin-VIIa and Keap1 copurify with ES and colocate with each other and with F-actin at the electron microscopy level. Interestingly, in many epithelial cell types including cells derived from retina and inner ear, Keap1 is a component of focal adhesions and zipper junctions. Keap1 can target to the ES in the absence of myosin-VIIa, suggesting that Keap1 associates with other molecules in the adhesion plaque. Keap1 and myosin-VIIa overlapped in expression in the inner hair cells of the cochlea, suggesting that Keap1 may be a part of a family of actin-binding proteins that could be important for myosin-VIIa function in testis and inner ear.

KBTBD7, a novel human BTB-kelch protein, activates transcriptional activities of SRE and AP-1

“…A series of domain function analyses of Keap1 showed that the BTB domains are crucial for Transcription factor Nrf2 degradation (9). A recent study, however, indicates that Keap1 might also have a function in cell morphology and organization by binding to the SH3 domain of myosin-VIIa and associates with it in specialized adhesion junctions through the kelch-repeat domain (15). BTB/kelch protein Mayven was predominantly expressed in the human brain and was predicted to be important in the organization of the actin cytoskeleton by binding directly with actin through their kelch repeats (16).…”

Cytoskeletal dynamics and spermatogenesis

“…This lack of contractility was illustrated by the failure to produce contractions in actin at the ES (Vogl & Soucy 1985). Interestingly, an actin-based motor protein myosin VIIa has been found to localize to actin bundles at the apical ES by electron microscopy, and it was also detected at the BTB by immunofluorescence microscopy (Velichkova et al 2002). Studies in other epithelia suggest the participation of myosin VIIa during AJ formation.…”

Anchoring Junctions As Drug Targets: Role in Contraceptive Development

“…So far, a growing list of proteins has been shown to underlie ectoplasmic specialization function including ␣6␤1 integrin (Palombi et al, 1992;Salanova et al, 1995;Mulholland et al, 2001), laminin , actin (Vogl et al, 1993), ␣-actinin (Russell and Goh, 1988), myosin VIIA (Hasson et al, 1997), fimbrin (Grove and Vogl, 1989), espin (Bartles et al, 1996), vinculin (Grove et al, 1990;Pfeiffer and Vogl, 1991), phosphorylated c-Src , paxillin (Mulholland et al, 2001), gelsolin , cadherin , ILK (Mulholland et al, 2001), phosphorylated FAK (Siu et al, 2003), testin (Grima et al, 1998), and Keap1 Velichkova et al, 2002) (Fig. 1).…”