Cloning and mapping of human PKIB and PKIG, and comparison of tissue expression patterns of three members of the protein kinase inhibitor family, including PKIA

Two novel members of the human cAMP-dependent protein kinase inhibitor (PKI ) gene family, PKIB and PKIG, were cloned. The deduced proteins showed 70%, and 90% identity with mouse PKI beta and PKI gamma respectively. Both the already identified pseudosubstrate site and leucine-rich nuclear export sig nal motifs were defined from the 11 PKIs of different species. The PKIB and PKIG genes were mapped respectively to chromosome 6q21-22.1, using a radia tion hybrid GB4 panel, and to chromosome 20q13.12-13.13, using a Stanford G 3 panel. Northern-blot analysis of three PKI isoforms, including the PKIA i dentified previously, revealed significant differences in their expression patterns. PKIB had two transcripts of 1.9 kb and 1.4 kb. The former transcr ipt was abundant in both placenta and brain and the latter was expressed mo st abundantly in placenta, highly in brain, heart, liver, pancreas, moderat ely in kidney, skeletal muscle and colon, and very little in the other eigh t tissues tested. PKIG was widely expressed as a 1.5-kb transcript with the highest level in heart, hardly detectable in thymus and peripheral blood l eucocytes and was moderately expressed in the other tissues, with slightly different levels. However, PKIA was specifically expressed as two transcrip ts of 3.3 kb and 1.5 kb in heart and skeletal muscle. The distinct expressi on patterns of the three PKIs suggest that their roles in various tissues a re probably different.