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Molecular Biology, Pathobiology and Genetics |
1 Human Cancer Genetics Program and 2 Division of Endocrinology, Diabetes and Metabolism, Department of Internal Medicine, The Ohio State University, Columbus, Ohio
Requests for reprints: Lawrence S. Kirschner, Human Cancer Genetics Program, Ohio State University, 544 TMRF, 420 West 12th Avenue, Columbus, OH 43210. Phone: 614-292-1190; Fax: 614-688-4006; E-mail: Lawrence.Kirschner{at}osumc.edu.
Phosphorylation is a key event in cell cycle control, and dysregulation of this process is observed in many tumors, including those associated with specific inherited neoplasia syndromes. We have shown previously that patients with the autosomal dominant tumor predisposition Carney complex carry inactivating mutations in the PRKAR1A gene, which encodes the type 1A regulatory subunit of protein kinase A (PKA), the cyclic AMP–dependent protein kinase. This defect was associated with dysregulation of PKA signaling, and genetic analysis has suggested that complete loss of the gene may be required for tumorigenesis. To determine the mechanism by which dysregulation of PKA causes tumor formation, we generated in vitro primary mouse cells lacking the Prkar1a protein. We report that this genetic disruption of PKA regulation causes constitutive PKA activation and immortalization of primary mouse embryonic fibroblasts (MEFs). At the molecular level, knockout of Prkar1a leads to up-regulation of D-type cyclins, and this increase occurs independently of other pathways known to increase cyclin D levels. Despite the immortalized phenotype, known mediators of cellular senescence (e.g., p53 and p19ARF) seem to remain intact in Prkar1a–/– MEFs. Mechanistically, cyclin D1 mRNA levels are not altered in the knockout cells, but protein half-life is markedly increased. Using this model, we provide the first direct genetic evidence that dysregulation of PKA promotes important steps in tumorigenesis, and that cyclin D1 is an essential target of PKA.
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J. T. Samuelsen, P. E. Schwarze, H. S. Huitfeldt, E. V. Thrane, M. Lag, M. Refsnes, E. Skarpen, and R. Becher Regulation of rat alveolar type 2 cell proliferation in vitro involves type II cAMP-dependent protein kinase Am J Physiol Lung Cell Mol Physiol, January 1, 2007; 292(1): L232 - L239. [Abstract] [Full Text] [PDF]
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M. Mavrakis, J. Lippincott-Schwartz, C. A. Stratakis, and I. Bossis Depletion of type IA regulatory subunit (RI{alpha}) of protein kinase A (PKA) in mammalian cells and tissues activates mTOR and causes autophagic deficiency Hum. Mol. Genet., October 1, 2006; 15(19): 2962 - 2971. [Abstract] [Full Text] [PDF]
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