Identification and characterization of PKN beta, a novel isoform of protein kinase PKN: Expression and arachidonic acid dependency are different fromthose of PKN alpha

The cDNA clone encoding a novel isoform of protein kinase PKN, termed PKN b eta, was isolated from a HeLa cDNA library. PKN beta had high sequence homo logy with PKN alpha, originally isolated PKN, especially in the repeats of charged amino acid-rich region with leucine-zipper like sequences (CZ regio n/HR1), in the carboxyl-terminal catalytic domain, and in similar to 130 am ino acid stretch (D region/HR2), located between CZ region/HR1 and the cata lytic domain. However, the amino acid sequence of PKN beta differed from th at of PKN alpha in the region immediately amino-terminal to the catalytic d omain, which contained two distinct proline-rich sequences consistent with the class II consensus sequence, PXXPXR, for binding to SH3 domain. Distrib ution of PKN beta differed from that of PKN alpha in the following two resp ects: (1) Northern blotting indicated that PKN beta mRNA could not be detec ted in human adult tissues, but was expressed abundantly in human cancer ce ll lines; (2) immunochemical analysis indicated that PKN beta localized in nucleus and perinuclear Gels apparatus, and was almost absent in cytoplasmi c region in NIH3T3 cells. Recombinant PKN beta expressed in COS7 cells disp layed autophosphorylation and peptide kinase activity, but was found to be significantly less responsive to arachidonic acid than PKN alpha. The ident ification of this novel isoform underscores the diversity of PKN signaling pathway. (C) 1999 Academic Press.