Genomic organization and chromosomal localization of the mouse protein kinase C alpha gene

Deficiency of Protein Kinase Cα in Mice Results in Impairment of Epidermal Hyperplasia and Enhancement of Tumor Formation in Two-Stage Skin Carcinogenesis

We generated a mouse strain lacking protein kinase Calpha (PKCalpha) and evaluated the significance of the enzyme in epithelial hyperplasia and tumor formation. PKCalpha-deficient mice exhibited increased susceptibility to tumor formation in two-stage skin carcinogenesis by single application of 7,12-dimethylbenz(a)anthracene (DMBA) for tumor initiation and repeated applications of 12-O-tetradecanoylphorbol-13-acetate (TPA) for tumor promotion. Tumor formation was not enhanced by DMBA or TPA treatment alone, suggesting that PKCalpha suppresses tumor promotion. However, the severity of epidermal hyperplasia induced by topical TPA treatment was markedly reduced. In mutant mice, the number of 5-bromo-2'-deoxyuridine-labeled epidermal basal keratinocytes increased 16 to 24 hours after topical TPA treatment as in the case of wild-type mice, but significantly decreased at 36 and 48 hours. Furthermore, the regenerating epithelium induced by skin wound significantly decreased in thickness but was not structurally impaired. The enhanced tumor formation may not be associated with epidermal hyperplasia. The induction levels of epidermal growth factor (EGF) receptor ligands, tumor growth factor alpha (TGF-alpha), and heparin-binding EGF-like growth factor, in the skin of mutant mice by TPA treatment were significantly lower than those in the skin of wild-type mice. PKCalpha may regulate the supply of these EGF receptor ligands in basal keratinocytes, resulting in a reduced epidermal hyperplasia severity in the mutant mice. We propose that PKCalpha positively regulates epidermal hyperplasia but negatively regulates tumor formation in two-stage skin carcinogenesis.

Genomic organization of human myotonic dystrophy kinase-related Cdc42-binding kinase alpha reveals multiple alternative splicing and functional diversity

Myotonic dystrophy kinase-related Cdc42-binding kinase alpha (MRCKalpha) is a Cdc42/Rac interactive binding-containing serine/threonine kinase with multiple functional domains. Its roles in the regulation of peripheral actin reorganization in HeLa cells and NGF-induced neurite outgrowth in PC12 cells have been documented. Here we report the characterization of the genomic structure and alternative splicing of the human counterpart. Human MRCKalpha gene is located on chromosome 1q42.1, spanning a genomic region of 250-300 kb and is composed of 41 exons. Four exons in the internal variable region and six in the 3' end were found to undergo extensive alternative splicing, giving rise to 96 possible transcripts of different combinations. The region of the internal splice site that defines a variable region in between two functional domains of opposite regulatory effects on MRCKalpha catalytic activity, and the 3' end splice site that generates variants with differential GTPase binding activity suggest a role for these alternative splicing events in MRCKalpha regulation.