Physical and functional interactions between TMC1 and LHFPL4/5 in cochlear hair cells

Abstract

The channel that governs mechanotransduction (MT) by hair cells in the inner ear has been investigated intensively for 4 decades, but its precise molecular composition remains enigmatic. Transmembrane channel–like protein 1 (TMC1) was recently identified as a component of the MT channel, and lipoma HMGIC fusion partner–like 5 (LHFPL5) is considered to be a part of the MT complex and may functionally couple the tip link to the MT channel. LHFPL4, a tetranspan membrane protein sharing extremely high similarity with LHFPL5, is reported to be expressed in hair cells but its function is still unknown. As components of the MT complex, TMC1 and LHFPL5 are expected to interact with each other and both locate at the lower end of the tip link in hair cells. In addition, an early study suggested functional interaction of TMC1 and LHFPL5. However, the evidence of physical interaction between these 2 proteins is still missing and the localization of LHFPL5 is unclear in adult hair cells. To better dissect their function and regulation, we used several approaches to examine the interaction and regulation among TMC1, LHFPL5 and LHFPL4 in both mammalian cell lines and cochlear hair cells. Here, we report several notable findings: 1) TMC1 and LHFPL5 interact physically and functionally in both cell lines and hair cells; 2) Deafness-causing dominant mutations, D572N/H, in TMC1 decrease its physical and functional interactions with LHFPL5, indicating the potential pathogenesis in D572N/H patients; 3) LHFPL4 interacts with both LHFPL5 and TMC1 and downregulates their protein levels in heterologous systems and cochlear hair cells, suggesting the possibility of LHFPL4 as a component of the MT complex; 4) LHFPL5 persists in the hair bundle of hair cells after postnatal day (P) 7, which clarifies the previously reported unexpected absence of LHFPL5 after P7 and supports the view that LHFPL5 is a permanent component in the MT complex. Our work revealed the function and regulation of TMC1, LHFPL5 and LHFPL4 in cochlear hair cells.

Date of Award	2019
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology