Translocation of calcium-permeable TRPV2 channel to the podosome: Its role in the regulation of podosome assembly

Abstract

The present study was conducted to investigate localization and function of TRPV2 channel in a mouse macrophage cell line, TtT/M87. We infected an adenovirus vector encoding TRPV2 tagged with c-Myc in the extracellular domain. Immunoreactivity of c-Myc epitope exposed to the cell surface formed a ring structure, which was colocalized with markers of the podosome, namely β-integrin, paxillin and Pyk2. The ring structure was also observed in TRPV2-GFP-expressing cells using total internal reflection fluorescent microscopy. Addition of formyl-Met-Leu-Phe (fMLP) increased the number of podosome and increased the intensity of the TRPV2 signal associated with the podosome. Measurement of subplasmalenmal free calcium concentration ([Ca(2+)](pm)) revealed that [Ca(2+)](pm) was elevated around the podosome. fMLP further increased [Ca(2+)](pm) in this region, which was abolished by a TRPV2 inhibitor ruthenium red. Phosphorylated Pyk2 was detected in fMLP-treated cells, and knockdown of TRPV2 reduced the expression of phospho-Pyk2. Introduction of dominant-negative Pyk2 or knockdown of TRPV2 increased the number of podosome. Conversely, elevation of [Ca(2+)](pm) by the addition of ionomycin reduced the number of podosome. These results indicate that TRPV2 is localized abundantly in the podosome and increases [Ca(2+)](pm) by the podosome. The elevation of [Ca(2+)](pm) is critical to regulate assembly of the podosome.