PubMed (a service of the National Library of Medicine) provides a comprehensive list of Dr. Ruvolo's recent publications.

This section, in operation since January 2007, is committed to understanding the cell signaling mechanisms that regulate cell death and ultimately influence tumor development and drug resistance in cancer and tissue destruction in diseases such as emphysema. A major focus of our research is the characterization of signal transduction pathways that are regulated by the sphingolipid ceramide. The Hormel Institute has a long history as a leader in lipid biology, so it is fitting that ceramide is at the center of many of the Section’s projects. Ceramide is a potent second signal molecule and its production in most cells results in the induction of programmed cell death (also known as apoptosis). The production of ceramide is so common during cell death induced by diverse stress stimuli (including chemotherapy) that it is considered a near universal feature of apoptosis. Our major project, funded by the National Cancer Institute, involves the regulation of the Bcl2 oncogene by phosphorylation, particularly those pathways involving ceramide activated protein phosphatase 2A (PP2A).

Bcl2 is the founding member of a family of proteins that regulate apoptosis. Bcl2 was discovered as the cellular oncogene product associated with the t(14,18) translocation commonly seen in B-cell lymphomas. While other oncogenes known at the time of Bcl2’s discovery were found to affect cell proliferation, Bcl2’s function to prolong cell survival represented a novel mechanism for tumorigenesis. In recent years it has become apparent that post-translational modification of Bcl2 affects its anti-apoptotic function. Recently, we have examined Bcl2 phosphorylation patterns in blast cells from patients with acute myeloid leukemia (AML) in collaboration with Michael Andreeff’s group at MD Anderson Cancer Center in Houston, Texas (published in Leukemia in 2006). We were the first group to determine that Bcl2 is phosphorylated in blast cells from AML patients (nearly half of patients exhibited phosphorylated Bcl2). Furthermore, we determined that AML patients with blast cells expressing phosphorylated Bcl2 exhibit shorter overall survival (~ 79 days on average) compared to patients with blast cells expressing unphosphorylated Bcl2 (~ 198 days on average). In other studies with the Andreeff group, we discovered further evidence that phosphorylated Bcl2 might render cells more resistant to chemotherapy when we found that phosphorylation of Bcl2 promoted resistance to ABT-737. This finding is important since ABT-737 is a novel compound that targets the Bcl2 BH3 domain and is currently being developed for clinical trials for AML and other cancers.

Bcl2 phosphorylation is a dynamic process that involves both kinases and protein phosphatases. Our laboratory previously determined that the Bcl2 phosphatase was activated by ceramide and involved a mitochondrial PP2A isoform. The finding that Bcl2 function is inhibited by a ceramide-activated mitochondrial PP2A has important potential for our understanding of chemoresistance in leukemia considering the effect of phosphorylation on Bcl2’s anti-apoptotic function. Indeed, our laboratory has found that inhibition of PP2A with low dose okadaic acid prevented Bcl2 dephosphorylation while protecting cells from apoptosis by ceramide or chemotherapeutic drug treatment (such as araC which is commonly used for the treatment of AML). Current efforts in the laboratory are focused on characterizing how ceramide activates the Bcl2 phosphatase. The identification of which PP2A isoform acts as the Bcl2 phosphatase was critical since PP2A is not really a single enzyme but rather a family of enzymes. PP2A is a hetero-trimer containing a catalytic subunit (subunit C), a scaffold subunit (subunit A) and regulatory subunit (subunit B). Because PP2A function is controlled by the B subunit (of which there are at least 21 proteins from 3 major families), it was necessary to determine which B subunit was responsible for Bcl2 phosphatase function. Our laboratory determined that the B56 · subunit is the regulatory subunit comprising the physiologic Bcl2 phosphatase. Recent studies in our laboratory have shown that ceramide appears to promote up-regulation of the B56 · PP2A subunit by a post-translational mechanism involving double stranded dependent protein kinase (PKR). These findings represent a novel role for this kinase in stress signaling and may be a new target for chemotherapy.

In the next year, we will pursue our studies to characterize the Bcl2 phosphatase and to determine its role in chemoresistance in leukemia. We will continue our studies on how the ABT-737 compound kills leukemia cells and the role Bcl2 phosphorylation plays in ABT-737-induced cell death. We also plan to begin investigations into how a novel PKC inhibitor promotes apoptosis in acute leukemia cells and which PKC isoforms are involved.