CLONING, EXPRESSION AND CHROMOSOMAL LOCALIZATION OF HUMAN CA2+ CALMODULIN-DEPENDENT PROTEIN-KINASE KINASE/

A human cDNA clone encoding the calcium/calmodulin-dependent protein k inase kinase (CaMKK) was isolated by RT-PCR amplification of the fragm ent corresponding to the conserved kinase catalytic domain followed by rapid amplification of cDNA ends and cDNA library screening. Compilat ion of nucleotide sequencing data yielded a consensus cDNA sequence of 1.9 kb with an open reading frame of 1,251 nucleotides in length whic h translates to a polypeptide of 417 amino acids (47 kd). It showed si gnificant homology to the rat brain CaMKK isozymes. The human CaMKK, w hich was expressed as a Flag-tagged protein in human non-small cell lu ng cancer H-1299 cells followed by immunoprecipitation with anti-mag a ntibody, was shown to phosphorylate recombinant human CaMK I in a calc ium/CaM-dependent fashion. Northern blot analysis revealed that human CaMKK is ubiquitously expressed, with brain showing the highest level of expression. The CaMKK gene is localized to human chromosome 12. The presence of cDNA clones with divergent 3' terminal sequences suggests a family of CaMKK variants which may arise from alternative splicing.