Genomic structure and promoter analysis of PKC-δ

Protein kinase C-δ (PKC-δ) is a ubiquitously expressed kinase involved in a variety of cellular signaling pathways including cell growth, differentiation, apoptosis, tumor promotion, and carcinogenesis. While signaling pathways downstream of PKC-δ are well studied, the regulation of the gene has not been extensively analyzed. A mouse genomic DNA fragment containing the PKC-δ gene was sequenced by the primer-walking method, and the subsequent DNA sequence data were used as a query to clone Caenorhabditis elegans and human genomic homologs from the publicly available genomic databases. The genomic structures of C. elegans, mouse, rat, and human PKC-δ were analyzed, and the result revealed that PKC-δ genes comprise 12, 18, 19, and 18 exons for C. elegans, mouse, rat, and human, respectively. The translation start methionine resides in the second exon in mouse and human and in the third exon in rat. The first intron between the first exon and the exon with the translation start methionine in mammalian genes represents a very large gap, as long as 17 kb in human, indicating a complexity involved in gene splicing. Overall exon–intron genomic structure is highly conserved among mammals, while significantly diverged in C. elegans. Putative transcription factor binding sites on the 1.7-kb promoter region of the mouse gene suggest that PKC-δ might be involved in spermatogenesis, embryogenesis, development, brain generation, immune response, oxidative environment, and oncogenesis. Studies on the promoter and subsequent biological testing on mouse keratinocytes indicate that tumor necrosis factor (TNF)-α increases the expression of PKC-δ, and this correlates with the time of NFκB nuclear translocation and activation. This TNF-α-mediated upregulation of PKC-δ is repressed in keratinocytes that are preinfected with IκB superrepressor adenovirus, suggesting that NFκB is involved directly in PKC-δ expression.