Molecular characterization of mesoderm-restricted basic helix-loop-helix protein, POD-1/Capsulin.

Members of the basic helix-loop-helix (bHLH) family of transcription factors have been implicated in the regulation of cell proliferation and differentiation. Here we describe molecular characterization of mesoderm-specific bHLH protein, POD-1/Capsulin. Northern blot analysis showed that POD-1/Capsulin are preferentially expressed in human vascular smooth muscle cells, and are enriched in mouse heart, kidney, testis, spleen, and lung. Ectopic expression of the HA-tagged POD-1/Capsulin in 293T cells revealed that this protein has an apparent molecular mass of 26 kDa and localized in the nucleus. Furthermore, in order to identify possible interactants of the bHLH protein, we performed yeast two-hybrid screen in a human kidney cDNA library, and identified alternative-splicing form of HEB, as potential heterodimeric partner of POD-1/Capsulin. Our results provide the molecular basis for cell type-specific transcriptional regulation by POD-1/Capsulin.