HGNC Approved Gene Symbol: PDK2
Cytogenetic location: 17q21.33 Genomic coordinates (GRCh38): 17:50,094,737-50,112,152 (from NCBI)
PDK2 belongs to the family of pyruvate dehydrogenase (PDH) kinases (EC 2.7.11.2), which reversibly inactivate the mitochondrial PDH complex by ATP-dependent serine phosphorylation of the alpha subunit of the complex's E1 component (see 300502) (summary by Korotchkina and Patel, 2001).
By screening a human liver cDNA library with rat Pdk2, Gudi et al. (1995) cloned PDK2. The deduced 407-amino acid protein, with a calculated molecular mass of 46.2 kD, has a putative mitochondrial protein kinase catalytic domain with 5 characteristic subdomains. The human and rat proteins share 96% identity. Northern blot analysis detected variable expression of a 2.4-kb PDK2 transcript in all 8 human tissues examined, with highest expression in heart, followed by skeletal muscle.
Gudi et al. (1995) noted that the products of the PDH reaction stimulate the kinase activity of PDKs, whereas the substrates are inhibitory. ADP also acts synergistically with pyruvate to inhibit PDK kinase activity. Using kinase-depleted PDH complexes isolated from rat heart as substrate, Gudi et al. (1995) found that recombinant human PDK1 (602524), PDK2, and PDK3 (300906) inactivated PDH in an ATP-dependent manner. PDK3 showed the highest kinase activity, and PDK2 the lowest. However, the products of the PDH reaction, NADH and acetyl-CoA, increased the ability of PDK2 to inhibit PDH.
Baker et al. (2000) found that the E2 subunit of PDH (DLAT; 608770), and the isolated second N-terminal lipoyl (L2) domain of E2, differentially enhanced the rates at which recombinant human PDK2 and PDK3 phosphorylated E1. There was little direct activation of PDK2 by the free L2 domain, but the E2 60mer, which forms the core structure of the PDH complex, enhanced PDK2 activity by 10-fold. PDK3 was activated 17-fold by E2; the majority of this activation was facilitated by the free L2 domain. PDK2 and PDK3 also differed in their inhibition by pyruvate, ADP, dichloroacetic acid, and acetylated lipoyl groups, activation by NADH and acetyl-CoA, and combined effect of mixed inhibitors and activators.
Each of the 2 E1 alpha subunits of PDH contains 3 serines that are phosphorylated by PDKs. Using recombinant enzymes expressed in E. coli and double site mutants of human E1, Korotchkina and Patel (2001) found that rat Pdk1, Pdk2, and Pdk4 (602527), and human PDK3, showed unique specificity and activity toward each of these serines. Only Pdk1 had detectable activity with site 3, which the authors called ser203. Each kinase also showed unique activity in the presence or absence of E2 in complex with its binding partner E3BP (PDHX; 608769), and unique sensitivity to the redox and/or acetylation state of the lipoyl moieties of E2, and the buffer system employed.
Boulatnikov and Popov (2003) found that rat Pdk1 and Pdk2 could form homodimers when expressed singly, or heterodimers when expressed together, in E. coli. The heterodimeric kinase was catalytically active, with kinetic parameters, site specificity, and regulation clearly distinct from those of homodimeric Pdk1 or Pdk2. The Pdk1-Pdk2 heterodimers catalyzed phosphorylation of E1 site 3 serine, in addition to sites 1 and 2 serines. Homodimers of Pdk1 or Pdk2 and the Pdk1-Pdk2 heterodimer also readily bound the isolated E2 component of PDH as well as the E2-E3BP subcomplex. Interactions were strengthened by the presence of the lipoate prosthetic groups in E2.
The nuclear peroxisome proliferator-activator receptors (PPARs; see PPARA, 170990) are critical regulators of fatty acid oxidation. Using quantitative real-time PCR, Degenhardt et al. (2007) found that expression of PDK2, PDK3, and PDK4, but not PDK1, was induced by PPAR-beta/delta (PPARD; 600409) agonists. In mice, induction of PPAR-beta/delta increased renal expression of Pdk2 and Pdk4, but not Pdk1 or Pdk3. In both human and mouse cells, PDK4 showed strongest induction by PPAR-beta/delta ligands. Ligands for other PPAR subtypes showed weaker regulation of PDK gene expression. In silico analysis, chromatin immunoprecipitation, and Western blot analysis revealed that PPAR-beta/delta bound regulatory elements in the PDK2, PDK3, and PDK4 genes, but not the PDK1 gene, and activated transcription in association with its regulatory partners RXR-alpha (RXRA; 180245), PGC1-alpha (PPARGC1A; 604517), and TRAP220 (MED1; 604311), and phosphorylated RNA polymerase II (see POLR2A, 180660). Degenhardt et al. (2007) also found that fibroblasts from Ppard-null mice showed reduced expression of Pdk2, Pdk3, and Pdk4 compared with wildtype fibroblasts. Expression of Pdk4 was reduced 1200-fold. Degenhardt et al. (2007) concluded that PDK2, PDK3, and PDK4 genes are primary PPAR targets and that PPAR-beta/delta is a major regulator of PDK4 expression.
Deuse et al. (2014) showed that during the development of myointimal hyperplasia in human arteries, smooth muscle cells (SMCs) show hyperpolarization of their mitochondrial membrane potential and acquire a temporary state with a high proliferative rate and resistance to apoptosis. PDK2 was identified as a key regulatory protein, and its activation proved necessary for relevant myointima formation. Pharmacologic PDK2 blockade with dichloroacetate or lentiviral PDK2 knockdown prevented hyperpolarization of the mitochondrial membrane potential, facilitated apoptosis, and reduced myointima formation in injured human mammary and coronary arteries, rat aortas, rabbit iliac arteries, and swine coronary arteries. In contrast to several commonly used antiproliferative drugs, dichloroacetate did not prevent vessel reendothelialization. Deuse et al. (2014) concluded that targeting myointimal mitochondrial membrane potential and alleviating apoptosis resistance is a novel strategy for the prevention of proliferative vascular disease.
Hartz (2013) mapped the PDK2 gene to chromosome 17q21.33 based on an alignment of the PDK2 sequence (GenBank AK055119) with the genomic sequence (GRCh37).
Baker, J. C., Yan, X., Peng, T., Kasten, S., Roche, T. E. Marked differences between two isoforms of human pyruvate dehydrogenase kinase. J. Biol. Chem. 275: 15773-15781, 2000. [PubMed: 10748134] [Full Text: https://doi.org/10.1074/jbc.M909488199]
Boulatnikov, I., Popov, K. M. Formation of functional heterodimers by isozymes 1 and 2 of pyruvate dehydrogenase kinase. Biochim. Biophys. Acta 1645: 183-192, 2003. [PubMed: 12573248] [Full Text: https://doi.org/10.1016/s1570-9639(02)00542-3]
Degenhardt, T., Saramaki, A., Malinen, M., Rieck, M., Vaisanen, S., Huotari, A., Herzig, K.-H., Muller, R., Carlberg, C. Three members of the human pyruvate dehydrogenase kinase gene family are direct targets of the peroxisome proliferator-activated receptor beta/delta. J. Molec. Biol. 372: 341-355, 2007. [PubMed: 17669420] [Full Text: https://doi.org/10.1016/j.jmb.2007.06.091]
Deuse, T., Hua, X., Wang, D., Maegdefessel, L., Heeren, J., Scheja, L., Bolanos, J. P., Rakovic, A., Spin, J. M., Stubbendorff, M., Ikeno, F., Langer, F., and 15 others. Dichloroacetate prevents restenosis in preclinical animal models of vessel injury. Nature 509: 641-644, 2014. [PubMed: 24747400] [Full Text: https://doi.org/10.1038/nature13232]
Gudi, R., Bowker-Kinley, M. M., Kedishvili, N. Y., Zhao, Y., Popov, K. M. Diversity of the pyruvate dehydrogenase kinase gene family in humans. J. Biol. Chem. 270: 28989-28994, 1995. Note: Erratum: J. Biol. Chem. 271: 1250 only, 1996. [PubMed: 7499431] [Full Text: https://doi.org/10.1074/jbc.270.48.28989]
Hartz, P. A. Personal Communication. Baltimore, Md. 8/9/2013.
Korotchkina, L. G., Patel, M. S. Site specificity of four pyruvate dehydrogenase kinase isoenzymes toward the three phosphorylation sites of human pyruvate dehydrogenase. J. Biol. Chem. 276: 37223-37229, 2001. [PubMed: 11486000] [Full Text: https://doi.org/10.1074/jbc.M103069200]