Clustering of CaV1.3 L-type calcium channels by Shank3
Clustering of neuronal L-type voltage-gated Ca2+ channels (LTCC) in the plasma membrane is increasingly implicated in creating highly localized Ca2+ signaling nanodomains. For example, LTCC activation can increase phosphorylation of the nuclear CREB transcription factor by increasing Ca2+ concentrations within a nanodomain close to the channel, without requiring bulk Ca2+ increases in the cytosol or nucleus. However, the molecular basis for LTCC clustering is poorly understood. The postsynaptic scaffolding protein Shank3 specifically associates with one of the major neuronal LTCCs, the CaV1.3 calcium channel, and is required for optimal LTCC-dependent excitation-transcription coupling. Here, we co-expressed CaV1.3 1 subunits with two distinct epitope-tags with or without Shank3 in HEK cells. Co-immunoprecipitation studies using the cell lysates revealed that Shank3 can assemble multiple CaV1.3 1 subunits in a complex under basal conditions. Moreover, CaV1.3 LTCC complex formation was facilitated by CaV{beta} subunits ({beta}3 and {beta}2a), which also interact with Shank3. Shank3 interactions with CaV1.3 LTCCs and multimeric CaV1.3 LTCC complex assembly were disrupted following addition of Ca2+ and calmodulin (Ca2+/CaM) to cell lysates, perhaps simulating conditions within an activated CaV1.3 LTCC nanodomain. In intact HEK293T cells, co-expression of Shank3 enhanced the intensity of membrane-localized CaV1.3 LTCC clusters under basal conditions, but not after Ca2+channel activation. Live cell imaging studies also revealed that Ca2+ influx through LTCCs disassociated Shank3 from CaV1.3 LTCCs clusters and reduced the CaV1.3 cluster intensity. Deletion of the PDZ domain from Shank3 prevented both binding to CaV1.3 and the changes in multimeric CaV1.3 LTCC complex assembly in vitro and in HEK293 cells. Finally, we found that shRNA knock-down of Shank3 expression in cultured rat primary hippocampal neurons reduced the intensity of surface-localized CaV1.3 LTCC clusters in dendrites. Taken together, our findings reveal a novel molecular mechanism contributing to neuronal LTCC clustering under basal conditions.