IDENTIFICATION AND CHARACTERIZATION OF DBK, A NOVEL PUTATIVE SERINE/THREONINE PROTEIN-KINASE FROM HUMAN ENDOTHELIAL-CELLS

Protein kinases are involved in signal transduction pathways and play important roles in the regulation of cell functions. cDNA clones encoding a novel serine/threonine protein kinase sequence, designated as DBK, were isolated from cDNA libraries made from human endothelial cells. The compiled nucleotide sequence is 1636 base pairs long, consisting of an open reading frame encoding a 479-amino-acid protein with a calculated molecular mass of 53 kDa. The deduced amino acid sequence contains a protein kinase catalytic domain of 263 residues which includes all the characteristic features of a serine/threonine protein kinase. The invariant amino acid residues scattered throughout the catalytic domain of almost all known protein kinases are also found in DBK. Sequence comparison of DBK catalytic domain shows approximately 51% sequence identities to that of human protein kinase C family members. DBK shares the highest sequence identity, 53%, to that of Drosophila PKC. Northern blot analysis of various human tissues and cultured cell Lines with a DBK gene-specific cDNA probe demonstrated a single band of 2.0 kb that is expressed in all tissues and cell Lines examined. Although the expression of DBK kinase was detected in all human tissues analyzed, the levels of expression varied significantly, with the highest expression detected in lung and heart, and the lowest expression found in brain and liver. Anti-DBK peptide-specific rabbit antisera were prepared, and were capable of immunoprecipitating DBK protein from COS cells transfected with DBK cDNA. The DBK gene is a single-copy gene, and is highly conserved across species from human to yeast. Using somatic cell hybrids, the DBK gene has been localized to human chromosome 14. The ubiquitous expression and high degree of conservation of DBK across species suggest that DBK may play an important role in cell functions.