The presence of h2-calponin in human keratinocyte

Calponin (h1 isoform) was characterized as a smooth muscle specific, actin-, tropomyosin-, calmodulin-binding protein and described as a factor which inhibits contraction. H2-calponin, encoded by a different gene from h1-calponin, was identified from the smooth muscles of mouse and pig. However, non-muscle calponin analogues have recently been reported in rat and pig brains. Here we show the presence of calponin expressed in human skin tissue and in cultured human keratinocytes using polyclonal antibodies to bovine aortic smooth muscle calponin. Western blot analysis demonstrated that calponin with a molecular weight around 36,000 existed in extracts of keratinocytes. Immunofluorescence microscopy displayed the localization of calponin in the cytoplasm of the basal cells in situ, and along the cell-to-cell borders in cultured human keratinocytes maintained in standard calcium medium. Furthermore, according to RT-PCR analysis using human h1- and h2-calponin-specific primers, calponin expressed by cultured human keratinocytes was identified as the h2 isoform. We demonstrated the presence of h2-calponin in human keratinocytes, and it might play a role in the structural organization of actin cytoskeleton at the cytoplasmic region of cell-to-cell junctions of keratinocytes.