Two recurring PKA mutants: two distinct cancers.

Rapid structural and biochemical characterization, by NYSBC researchers, of two recurring PKA mutants found in two distinct cancers will aid in the design of new treatments. Protein kinase A (PKA) is a cAMP-dependent kinase involved in the regulation of a number of important cell processes including metabolism, proliferation, and gene expression. In the past year, genomic studies have discovered two recurring mutations in PKA that are linked to Cushing’s syndrome, a disorder caused by tumors and hyperplasia of the adrenal cortex, and to fibrolamellar hepatocellular carcinoma (FL-HCC), a rare liver cancer. In Cushing’s syndrome, a predominant single L205R point mutation was found in the PKA catalytic subunit. In FL-HCC, a recurring 400-kb deletion was found that resulted in the production of a DnaJ-PKA fusion protein in which exon 1 of the molecular chaperone DnaJ was fused to the start of exon 2 of the PKA catalytic subunit.

The crystal structures of two cancer-related PKA mutants solved at NYSBC are shown in complex with ATP and a peptide inhibitor (yellow ribbons). These mutants contribute to the development of cancer through distinct underlying mechanisms.

NYSBC crystallographers have discovered two distinct underlying disease mechanisms through a combination of rapid structural determination of the aberrant PKA L205R point mutant and the DnaJ-PKA chimera, and subsequent biochemical and biophysical characterization of the proteins. The L205R mutation in the catalytic subunit abolishes binding to regulatory subunits, and thus leads to constitutive cAMP-independent activation of PKA in Cushing’s syndrome. In contrast, the DnaJ-PKA catalytic subunit fusion retains the ability to bind to regulatory subunits and exhibits similar behavior to the wild-type catalytic subunit, but the expression of the fusion is elevated from a more active DnaJ promoter. The resulting overproduction of the enzyme in FL-HCC increases cAMP-dependent PKA signaling in a more acute and sudden manner than in Cushing’s syndrome. This important work performed at NYSBC, with collaboration from NYGC, will aid in the design of new therapeutics for treating these cancers.

Research article:
PNAS, January 2015
doi: 10.1073/pnas.1424206112