CaVβ1a Nuclear Translocation: Potential Mechanisms and Functions

CaVβ1a Nuclear Translocation: Potential Mechanisms and FunctionsCaVβ subunits are traditionally considered constituents of CaV complexes (CaV1or2, CaVβ, CaV α2/δ), where they localize at the plasma membrane and serve to regulate channel expression and gating properties. Several recent publications also show CaVβ subunit localization in the nucleus. This phenomenon has been observed under a variety of conditions (different cell types, β subunit isoforms, co-expressed proteins, etc). However, the exact mechanisms responsible for CaVβ subunit nuclear shuttling, as well as a physiological role for this nuclear localization, remain major questions. In the present work, we use primary mouse myoblasts as a model to study CaVβ subunit nuclear localization. These mitotic cells express CaVβ1a protein, despite the absence of any CaV1 subunits, and thus provide an ideal model to study non-CaV- related function (i.e. nuclear) of CaVβ subunits. Using both immunofluorescence and subcellular fractionation, we show that endogenous and exogenous CaVβ1a proteins are rapidly translocated into the nucleus of myoblasts. We also use shRNA knockdown and transgenic CaVβ1-null myoblasts to examine the importance of CaVβ1 in gene expression and cell proliferation. A mouse model of partial CaVβ1 knockdown is used to determine the role of CaVβ1a in skeletal muscle regeneration following injury in vivo. Finally, we attempt to identify nuclear binding partners of CaVβ1a-YFP using affinity purification from nuclear fractions coupled with mass spectrometry. Our results support the idea of CaVβ subunits having alternate functions separate from CaV's, within the nucleus, and suggest these functions may be specific to progenitor cells.