Characterization and expression of calpain 10 - A novel ubiquitous calpainwith nuclear localization

Calpains are calcium-dependent intracellular nonlysosomal proteases that ar e believed to hydrolyze specific substrates important in calcium-regulated signaling pathways. Recently, an atypical member of the calpain family, cal pain 10, was described, and genetic variation in this gene was associated w ith an increased risk of type II diabetes mellitus in humans. In the presen t report, a polyclonal antibody directed against rat calpain 10 was develop ed. This antibody was used to monitor the expression of calpain 10 protein in tissues from rats, mice, and humans. Calpain 10 protein was found to be present in all tissues examined by Western blotting including the lens, ret ina, brain, heart, and skeletal muscle. Although some calpain 10 was detect able in the water-soluble protein fraction of these tissues, it was prefere ntially found in the water-insoluble fraction. In the lens, immunohistochem istry revealed that calpain 10 was predominately located in the cytoplasm o f epithelial and newly differentiating lens fibers at the transition zone. However, calpain 10 was found to be associated with the plasma membrane of differentiated lens fiber cells and the sarcolemma of skeletal muscle. In t he lens epithelium-derived cell line, alpha TN4-1, the calpain 10 protein w as found in a punctate distribution in the cell nucleus as well as the cyto plasm. After the elevation of intracellular calcium levels with ionomycin, calpain 10 protein levels in the nucleus of alpha TN4-1 cells increased mar kedly, whereas those in the cytoplasm decreased. In the lens, the elevation of intracellular calcium levels after selenite administration resulted in increased levels of calpain 10 RNA within I day and a loss of calpain 10 pr otein from the lens nucleus coincident with the onset of selenite cataract. In conclusion, calpain 10 seems to be a ubiquitous calpain, the expression level and subcellular distribution of which are dynamically influenced by calcium.