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Proc Natl Acad Sci U S A. 2015 Feb 3;112(5):1374-9. doi: 10.1073/pnas.1424206112. Epub 2015 Jan 20.

Structural insights into mis-regulation of protein kinase A in human tumors.

Author information

1
New York Structural Biology Center, New York, NY 10027; jcheung@nysbc.org wayne@xtl.cumc.columbia.edu.
2
New York Structural Biology Center, New York, NY 10027;
3
New York Genome Center, New York, NY 10013;
4
New York Genome Center, New York, NY 10013; Howard Hughes Medical Institute and Laboratory of Molecular Neuro-Oncology, The Rockefeller University, New York, NY 10021; and.
5
New York Structural Biology Center, New York, NY 10027; Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032 jcheung@nysbc.org wayne@xtl.cumc.columbia.edu.

Abstract

The extensively studied cAMP-dependent protein kinase A (PKA) is involved in the regulation of critical cell processes, including metabolism, gene expression, and cell proliferation; consequentially, mis-regulation of PKA signaling is implicated in tumorigenesis. Recent genomic studies have identified recurrent mutations in the catalytic subunit of PKA in tumors associated with Cushing's syndrome, a kidney disorder leading to excessive cortisol production, and also in tumors associated with fibrolamellar hepatocellular carcinoma (FL-HCC), a rare liver cancer. Expression of a L205R point mutant and a DnaJ-PKA fusion protein were found to be linked to Cushing's syndrome and FL-HCC, respectively. Here we reveal contrasting mechanisms for increased PKA signaling at the molecular level through structural determination and biochemical characterization of the aberrant enzymes. In the Cushing's syndrome disorder, we find that the L205R mutation abolishes regulatory-subunit binding, leading to constitutive, cAMP-independent signaling. In FL-HCC, the DnaJ-PKA chimera remains under regulatory subunit control; however, its overexpression from the DnaJ promoter leads to enhanced cAMP-dependent signaling. Our findings provide a structural understanding of the two distinct disease mechanisms and they offer a basis for designing effective drugs for their treatment.

KEYWORDS:

Cushing’s syndrome; cancer mutations; chimeric protein; fibrolamelllar hepatocellular carcinoma

PMID:
25605907
PMCID:
PMC4321305
DOI:
10.1073/pnas.1424206112
[Indexed for MEDLINE]
Free PMC Article

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