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Apoptosis

Gary E. Gallick, Ph.D.

Professor of Cancer Biology

Research in my laboratory focuses on of the role of protein tyrosine kinases in promoting cellular survival and angiogenesis, and the result of aberrant activation of these enzymes on tumor progression and metastasis of colon, prostate and pancreatic cancers. Using a combination of in vitro techniques and animal models, we have demonstrated that increases in activity of Src family kinases are common in solid tumors and causative of increased metastatic potential. We are dissecting the signal transduction pathways responsible for these critical events in tumor progression with an emphasis on regulation of Src regulation of pro-angiogenic factors and migration and invasion. In pancreatic cancer, we are focusing on Src-regulated signal transduction pathways leading to constitutive and hypoxia-inducible expression of vascular endothelial growth factor (VEGF). Specifically, Src regulates VEGF transcription through HIF-1α, STAT3 and ID2. We have demonstrated that ID2 is a HIF-regulated gene at the transcriptional level and then regulates HIF-1α stability in an autocrine "feed-forward" loop. Decreased ID2 decreases VEGF expression in vitro, and tumor growth and angiogenesis in orthotopic mouse models of pancreatic cancer in vivo. Roles of ID2 in angiogenesis and its potential as a novel target for cancer therapeutic agents are under investigation.

In prostate cancer, we are determining roles of Src activation in both tumor cells and host endothelial cells in the development of lymph node metastases. These studies use a combination on in vitro and in vivo work to test the hypothesis that Src activation in the tumor cell leads to Src activation in the endothelial cell. We have demonstrated that increased Src activity in the tumor is sufficient to promote lymph node metastases. To examine the role of Src in the host in this process, we have developed src-/- nude mice to compare tumor growth and metastatic potential with "conventional" nude mice.

With respect to migration, we have developed and characterized novel models in which cells selected for increased migration in vitro are greatly increased in metastatic potential in nude mouse models. These biologically selected cells are altered in expression of regulators of the Rac pathway, a "G" protein known to be important in migration. In addition, we are examining mediators of focal adhesion structure and their role in migration and tumor progression. We are the first to demonstrate that actin filament associated protein 110 (AFAP-110), a known Src substrate) is increased in progressive stages of prostate cancer, and by siRNA technology, that this protein is important in tumorigenicity of prostate cancer cells. AFAP-110 regulates integrin stability and Src/Focal Adhesion Kinase (FAK)-mediated signaling, a process we are investigating.

In the last two years, Src inhibitors have reached clinical trial for solid tumors. As a result, we work closely with clinicians conducting these trials to identify both predictive markers for efficacy of Src family inhibitors and markers for success of these inhibitors. We are also involved in testing novel inhibitors in pre-clinical studies. These clinically related studies are highly integrated into our fundamental laboratory work. All the projects in my laboratory involve trainees, including graduate students, postdoctoral fellows, residents and clinical fellows.

David J. McConkey, Ph.D.

Associate Professor of Cancer Biology

Research in my laboratory is concerned with identifying the biochemical mechanisms that regulate apoptosis in tumor cells. Our first project focuses on defining the roles of BCL-2 family proteins in release of Ca2+ from the endoplasmic reticulum (ER) and consequent increase in mitochondrial Ca2+ that is required for cytochrome c release in cells exposed to some (but not all) proapoptotic stimuli. In a second project we are defining the mechanisms underlying resistance to death receptor-mediated apoptosis in human bladder cancer. A third project deals with identifying molecular mechanisms that regulate apoptosis induced by endoplasmic reticular (ER) stress. We are interested in determining how the oncogenes that drive the progression of human pancreatic cancer (particularly K-ras) affect ER stress, focusing on the role that translation-associated processes play in the response. We are also interested in determining how ER stress activates particular ER-localized caspases (including caspase-4). Finally, we are using what we know about the effects of clinically relevant agents, including proteasome inhibitors, histone deacetylase inhibitors, and other agents on ER stress can used to design better combination therapy regimens. Our collaborators in the MD Anderson Pancreatic Cancer SPORE have opened one such trial (to study the effects of the proteasome inhibitor bortezomib plus carboplatin) and plan to open a second (to study the effects of bortezomib plus the histone deacetylase inhibitor SAHA) within the coming year.

The last major project in my laboratory is aimed at defining the biological properties of tumor cells that make subsets of them dependent upon the epidermal growth factor receptor (EGFR) for their proliferation. Using panels of human pancreatic cancer, bladder cancer, colon cancer and head and neck squamous cell carcinoma cell lines, we have identified cells within each panel that undergo p27-dependent G1 arrest when they are exposed to either small molecule or antibody-based inhibitors of the EGFR. In all of the models there appears to be a correlation between expression of “epidermal” markers (i.e., E-cadherin) and drug sensitivity, whereas expression of “mesenchymal” markers (vimentin, etc.) correlates with resistance. We have also found that combining EGFR inhibitors with conventional chemotherapeutic agents does not result in increased apoptosis in the EGFR-dependent cells, but combining EGFR inhibitors plus TRAIL results in synergistic induction of cell death. Characterization of the molecular mechanisms involved indicates that the effects are mediated by inhibition of AKT and subsequent downregulation of X-linked inhibitor of apoptosis protein (XIAP), and in ongoing studies we are investigating the therapeutic activity of AKT and XIAP inhibitors on TRAIL sensitization in vitro and in vivo. Our collaborative studies have prompted our clinical colleagues on the Bladder SPORE to design and submit a proposal to perform a neoadjuvant clinical trial of erlotinib (Tarceva) in patients with bladder cancer, where we will directly test the hypothesis that the markers we have identified in the preclinical studies will allow us to identify the tumors that are most likely to respond to therapy.

Alan J. Schroit, Ph.D.

John Q. Gaines Professor for Cancer Biology
Professor of Cancer Biology

Ongoing research in my laboratory focuses on the chemistry, biology and pathology of phosphatidylserine (PS) exposure in the outer leaflet of cells. The major goal of our research has been to understand the mechanism by which cells control the transbilayer distribution of phospholipids between the bilayer leaflet and the machinery responsible for the pathologic redistribution of phospholipids in different cell types. These studies are divided into several distinct projects.

In the first, we are investigating the role lipid peroxidation products play in the initiation, regulation and progression of apoptosis. Our studies have determined that defined intracellular redox pathways are critical to the generation of the apoptotic phenotype and in the regulation of lipid asymmetry in the apoptotic cell membrane. These studies suggest that cytochrome c is not only required for formation of the apoptosome, important in the activation of death-inducing caspases, but also functions as a regulator of the distribution of PS within the cell membrane. Our experiments are designed to test the hypothesis that the presence of both catalytic cytochrome c and hydrogen peroxide or lipid hydroperoxides as sources of oxidizing equivalents, result in the formation of a highly active prooxidant form of cytochrome c that oxidizes membrane phospholipids in a self-propelled autocatalytic manner that culminates in PS exposure and cell death.

Another project focuses on identifying the molecular targets of beta-2-glycoprotein 1 (ß2GP1), a 50-kDa plasma protein that mediates the binding of apoptotic and tumor cells to phagocytes. We are investigating the mechanism by which target cells are recognized by ß2GP1 and the ß2GP1-specific receptor on reticuloendothelial cells. Our results indicate that ß2GP1 binds negatively charged lipids present on the surface of apoptotic and tumor cells that function as a primary target moiety. Recent studies suggest that ß2GP1is also a negative regulator of angiogenesis that can inhibit the growth of primary tumors and metastasis. Recent results raise the possibility that ß2GP1regulates tumor vascularity through a direct effect on a vascular endothelial growth factor (VEGF)-dependent mechanism. Ongoing experiments are designed to determine the mechanism by which this regulation occurs and develop ß2GP1as an antiangiogenic agent.

Keping Xie, M.D., Ph.D.

Associate Professor

Metastatic pancreatic adenocarcinoma is a lethal disease. Using molecular and cell biology techniques coupled with human specimens and animal models, we have continued to investigate the molecular mechanisms governing pancreatic cancer metastasis, with a focus on the regulation and interplay of multiple transcription factors such as AP-1, NF-kB, Sp1 and Stat3. Abnormal activation of these factors leads to aberrant expression of multiple metastasis-related proteins such as inducible nitric oxide synthase (iNOS), interkeukin-8 (IL-8) and vascular endothelial growth factor (VEGF), which confer a tremendous growth advantage to metastatic pancreatic cancer cells. There are two major pathways leading to overactivation of these transcription factors. One mechanism relates to the genetic mutations of oncogenes and/or suppressor genes, such as Ras and p53, resulting in constitutive activation of the transcription factors. This may be especially true in the early stage of pancreatic cancer growth. In the latter stage of pancreatic cancer development, however, notable "stress factors" such as hypoxia, acidosis and free radicals that are often seen in the tumor microenvironment further upregulates those metastasis-related proteins through overactivating the transcription factors. Therefore, at advanced stages, uncontrolled tumor growth and the consequent development of a stress environment may enhance tumor angiogenesis, growth and metastasis. Understanding the expression and regulation of these molecules may shed more light on the biology of pancreatic cancer metastasis, as well as suggest new preventive and therapeutic approaches.

Tutorials in my laboratory include work on cell lines, animal model and as surgical specimens from human gastrointestinal cancer. A tutorial in my laboratory would provide experience with cell culture, animal models and various basic and advanced molecular biology in gene expression and regulation of tumor angiogenesis and metastasis.


© 2014 The University of Texas MD Anderson Cancer Center