Structural characterization of promoter sequences of the gene coding human PKI55 protein, a protein kinase C inhibitor

The PKI55 protein was identified in our laboratory as specific protein kinase C inhibitor. We previously demonstrated that PKI55 is poorly translated in vivo and acts promoting PKC degradation and establishing a feedback loop of inhibition. However, our understanding of mechanisms by which the expression of PKI55 is regulated, is limited. In the present work we investigated the mRNA expression of PKI55 in human tissues by Northern blotting and RT-PCR, demonstrating that it is highly expressed in brain tissue. Moreover, since the computational analysis of the gene promoter region showed two sites (Box 1 and Box 2) similar to consensus sequences for AP1 and GAGA factors, we investigated their ability to bind to these proteins. Electrophoretic mobility shift assays showed that GAGA factors preferentially interacted with Box 2, while AP1 elements linked preferentially Box 1 sequence. We suggest that the interaction of these transcription factors with Box 1 and Box 2 could regulate the transcription of the PKI55 gene and, consequently, the expression of PKC.