Predominant expression of nPKC eta, a Ca(2+)-independent isoform of protein kinase C in epithelial tissues, in association with epithelial differentiation.

Of the nine known members of the protein kinase C (PKC) family, we found that novel (n-) PKC eta, a newly isolated Ca(2+)-independent isoform, was expressed at the highest level in the epidermis of mouse skin and epithelia of the digestive and respiratory tracts including the tongue, esophagus, forestomach, glandular stomach, intestine, colon, trachea, and bronchus. Expression of nPKC eta mRNA in these epithelial tissues was 3-10 times that in the brain and was especially high in squamous epithelium. Two other PKC isoforms, conventional (c-) PKC alpha and nPKC delta, were also expressed in these epithelial tissues, but no cPKC gamma was detected. In situ hybridization and immunohistochemical analyses demonstrated the localization of nPKC eta in suprabasal layers of the skin, tongue, esophagus, and forestomach. In the intestine, it was expressed in the epithelial cells of villi, but not of crypts. In the lung, only bronchial epithelium expressed nPKC eta. The localization of nPKC eta in differentiating or differentiated epithelial cells, rather than in proliferating basal cells, suggests the involvement of nPKC eta in epithelial differentiation.