DIVERSITY OF THE PYRUVATE-DEHYDROGENASE KINASE GENE FAMILY IN HUMANS

Recent evidence from this laboratory indicates that at least two isoen zymic forms of pyruvate dehydrogenase kinase (PDK1 and PDK2) may be in volved in the regulation of enzymatic activity of mammalian pyruvate d ehydrogenase complex by phosphorylation (Popov, K. M., Kedishvili, N, Y,, Zhao, Y,, Gudi, R,, and Harris, R. A. (1994) J. Biol. Chem, 269, 2 9720-29724), The present study was undertaken to further explore the d iversity of the pyruvate dehydrogenase kinase gene family, Here we rep ort the deduced amino acid sequences of three isoenzymic forms of PDK found in humans, In terms of their primary structures, two isoenzymes identified in humans correspond to rat PDK1 and PDK2, whereas a third gene (PDK3) encodes for a new isoenzyme that shares 68% and 67% of ami no acid identities with PDK1 and PDK2, respectively, PDK3 cDNA express ed in Escherichia coli directs the synthesis of a polypeptide with a m olecular mass of approximately 45,000 Da that possesses catalytic acti vity toward kinase-depleted pyruvate dehydrogenase. PDK3 appears to ha ve the highest specific activity among the three isoenzymes tested as recombinant proteins, Tissue distribution of all three isoenzymes of h uman PDK was characterized by Northern blot analysis. The highest amou nt of PDK2 mRNA was found in heart and skeletal muscle, the lowest amo unt in placenta and lung, Brain, kidney, pancreas, and liver expressed an intermediate amount of PDK2 (brain > kidney = pancreas > liver), T he tissue distribution of PDK1 mRNA differs markedly from PDK2, The me ssage for PDK1 was ex pressed predominantly in heart with only modest levels of expression in other tissues (skeletal muscle > liver > pancr eas > brain > placenta = lung > kidney), In contrast to PDK1 and PDK2, which are expressed in all tissues tested, the message for PDK3 was f ound almost exclusively in heart and skeletal muscle, indicating that PDK3 may serve specialized functions characteristic of muscle tissues, In all tissues tested thus far, the level of expression of PDK2 mRNA was essentially higher than that of PDK1 and PDK3, consistent with the idea that PDK2 is a major isoenzyme responsible for regulation of pyr uvate dehydrogenase in human tissues.