2013 Scientific Report

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VARI | <strong>2013</strong> Based on our observations that differentiation begins prior to complete loss of integrin a6b1 and that Myc controls integrin a6b1 transcription in epithelial cells, we hypothesize that prostate oncogenesis occurs within a subpopulation of transiently differentiating cells in which AR is partially stabilized but the cells still retain a6b1. Using normal cells engineered to overexpress two known prostate oncogenes, Myc and TMPRSS2/Erg, and an shRNA to Pten, we generated tumorigenic cells that coexpress integrin a6b1 and AR. Surprisingly, these oncogene-modified cells were unable to differentiate. Thus, we developed an in vitro model for studying prostate tumorigenesis that recapitulates many of its in vivo aspects and links prostate cancer to defects in differentiation. CD82/KAI1 CD82/KAI1 is encoded by a metastasis suppressor gene whose loss in primary prostate tumors correlates with poor patient prognosis. CD82 is one of 33 tetraspanins whose functions remain enigmatic but are linked to cell adhesion. Our hypothesis is that CD82 suppresses metastasis by limiting signal transduction pathways that promote integrin-based migration and invasion while simultaneously increasing cell-cell adhesion. CD82 suppresses both integrin- and ligand-based activation of the tyrosine kinases Met and Src; it also suppresses their ability to stimulate prostate tumor cell migration and invasion in vitro, as well as metastasis in vivo. Other tetraspanins, CD9 and CD151, are required for CD82-dependent suppression of Met. CD82 expression also increases E-cadherin-based cell-cell adhesion. Several CD82 mutants were generated to decipher how CD82 suppresses Met-dependent metastasis and promotes cell-cell adhesion. The reexpression of CD82 in metastatic tumor cells is sufficient to suppress metastasis. However, using a conditional null CD82 mutant mouse, we found that loss of CD82 alone in a mouse primary prostate tumor model was not sufficient to induce metastasis. To address the possibility that loss of other genes is also needed, we are crossing floxed CD82 mice with mice that are null for another metastasis suppressor gene, RKIP. RKIP regulates miRNAs that are involved in controlling Myc and MAPK signaling, pathways that are not influenced by CD82. We generated CD82-null mice to better understand the normal function of CD82. The most striking phenotype is enhanced platelet clotting and reduced bleeding, as well as a twofold increase in total platelets. The increase in platelets is due to changes in megakaryocyte differentiation, which is controlled by tyrosine kinase and cytokine signaling and is tightly linked to the cytoskeleton. CD82-null mice also have increased bone density, defects in toll receptor signaling, and reduced capacity to stimulate T-cell signaling. Thus, the in vivo data support our in vitro work, suggesting the major function of CD82 is to regulate cell signaling, and further suggesting CD82 regulates cell differentiation. Recent Publications Nollet, Eric A., and Cindy K. Miranti. In press. Integrin and matrix regulation of autophagy and mitophagy. In Autophagy, Yannick Bailly, ed. New York: InTech. Klionsky, Daniel J., Fabio C. Abdalla, Hagai Abeliovich, Robert T. Abraham, Abraham Acevedo-Arozena, Khosrow Adeli, Lotta Agholme, Maria Aganello, et al. 2012. Guidelines for the use and interpretation of assays for monitoring autophagy. Autophagy 8(4): 445–544. Lamb, Laura E., Jelani C. Zarif, and Cindy K. Miranti. 2011. The androgen receptor induces integrin a6b1 to promote prostate tumor cell survival via NF-kB and Bcl-xL independently of PI3K signaling. Cancer Research 71(7): 2739–2749. 43
Mark W. Neff, Ph.D. Laboratory of Canine Genetics and Genomics Dr. Neff received his Ph.D. in biological sciences from the University of Virginia and completed a postdoctoral fellowship in canine genetics and genomics at the University of California, Berkeley. Most recently, he served as associate director of the Veterinary Genetics Laboratory at the University of California, Davis. Dr. Neff joined VARI in 2009 as an Associate Professor and Director of the Program for Canine Health and Performance. From left: Minard, Neff, Hodges, Kefene, Borgman, Roemer Staff Lisa Kefene, B.S. Michelle Minard Students Andrew Borgman, B.S. Jenea Chesnic Daniel Hodges, M.A. Alex Roemer 44
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2013 Scientific Report

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