CLONING AND CHARACTERIZATION OF PDK4 ON 7Q21.3 ENCODING A 4TH PYRUVATE-DEHYDROGENASE KINASE ISOENZYME IN HUMAN

Different isoenzymes of pyruvate dehydrogenase kinase (PDK) inhibit th e mitochondrial pyruvate dehydrogenase complex by phosphorylation of t he E1 alpha subunit, thus contributing to the regulation of glucose me tabolism. By positional cloning in the 7q21.3-q22.1 region linked with insulin resistance and non-insulin-dependent diabetes mellitus in the Pima Indians, Fee identified a gene encoding an additional human PDR isoform, as evidenced by its amino acid sequence identity (>65%) with other mammalian PDKs, and confirmed by biochemical analyses of the rec ombinant protein. We performed detailed comparative analyses of the ge ne, termed PDK4, in insulin-resistant and insulin-sensitive Pima India ns, and detected five DNA variants with comparable frequencies in both subject groups. Using quantitative reverse transcription polymerase c hain reaction, we found that the variants identified in the promoter a nd 5'-untranslated region did not correlate with differences in mRNA l evel in skeletal muscle and adipose tissue. We conclude that alteratio ns in PDK4 are unlikely to be the molecular basis underlying the obser ved linkage at 7q21.3-q22.1 in the Pima Indians. Information about the genomic organization and promoter sequences of PDK4 will be useful in studies of other members of this family of mitochondrial protein kina ses that are important for the regulation of glucose metabolism.