Deciphering the Role of RIalpha as a Tumor Suppressor

Michele Day

Appointment Period: 2004-2007, Grant Years: [20,21,22]

My project focuses on the RIalpha subunit of cAMP-dependent protein kinase (PKA), which is associated with many diseases. RIalpha is up-regulated in breast cancer and in many other cancers and is also associated with RIalpha cardiac disorders such as myxomas and Carney complex disease. These cardiac disorders are nonmalignant tumors and have led to the prediction that RIalpha may be a tumor suppressor. RIalpha is also subject to nonsense-mediated mRNA decay (NMD) so that the message is destroyed rather than expressing mutant or deletion RIalpha mutants that are non-functional.

We believe that the oxidation state of RIalpha may serve as a redox sensor. To confirm this, I developed a 2-D gel system that discriminates disulfide-bonded proteins and have worked to confirm the disulfide bonding by mass spectrometry. This is a significant part of our effort to map the PKA proteome, and we can now analyze cultured cells as well as tissues. This also may be significant for cancer cells where RIbeta expression is even higher than RIalpha. I will use my newly developed assay system to determine whether this is true in cells and whether this provides a mechanism for abolishing homodimers of RIalpha. I will also be characterizing the R73C mutant of RIalpha to see if it forms aberrant complexes with other proteins that might account for its effect in causing cardiac myxomas.

Day ME, Gaietta GM, Sastri M, Koller A, Mackey MR, Scott JD, Perkins GA, Ellisman MH, Taylor SS. Isoform-specific targeting of PKA to multivesicular bodies. J Cell Biol. (2011) 193:347-63. PMID: 21502359; PMCID: PMC3080257.