Doctor of Philosophy (PhD)
Dr. Michael G. Brattain
Cyclic adenosine monophosphate (cAMP) is a second messenger responsive to many external stimuli, playing an important role in cellular gene expression, metabolism, migration, differentiation, hypertrophy, apoptosis and secretion. All of these cellular functions are important in many diseases including cancer. Most of its effects were initially attributed to the classical protein kinase A (PKA) protein, but cellular functions such as proliferation and migration were found to be PKA independent and dependent on the newly discovered exchange proteins directly activated by cAMP (EPACs). EPACs are single polypeptides that primarily function as guanine exchange factors (GEFs) for Rap proteins that allow the replacement of guanine diphosphate (GDP) with the more abundant guanosine triphosphate (GTP), under cAMP stimulation.
EPAC has been reported to promote cancer cell growth and activate phosphhatidylinositol 3-kinase (PI3K) in direct opposition to the effects of PKA. This was confirmed in the Brattain Laboratory, treating colorectal cancer (CRC) cell lines with the EPAC specific activator 8CPT (8-pCPT-2-O-Me-cAMP) induced AKT expression along with increased expression of inhibitor of apoptosis protein (IAP) survivin and X-linked IAP (XIAP); which are implicated with poor prognosis in cancer. However, there are 2 isoforms of EPAC – EPAC1 and 2 and to dissect which EPAC is pro-tumorigenic we used EPAC specific inhibitors (ESI) – ESI09 (inhibits EPAC1 and 2), ESI05 (inhibits EPAC2) and CE3F4 (inhibits EPAC1) and confirmed that EPAC1 is associated with cell survival in CRC cell line as well as in pancreatic cancer (PaCa) cell lines.
Inhibition of EPACs decreased histone deacetylase (HDAC) 4 and 5 that are overexpressed in many cancers. Inhibition of HDAC4 and 5 with LMK235 decreased survivin and XIAP allowing us to hypothesize that the cell survival effects observed on EPAC inhibition must be due to the repression of HDACs 4 and 5 making EPACs epigenetic regulators.
Murari, Catherine, "EPACs: epigenetic regulators that affect cell survival in cancer." (2015). Theses & Dissertations. 60.