Basic Science Tower, Stony Brook University, Stony Brook, NY 11794-8651 / 631-444-3219
Medical Scientist (M.D./Ph.D.) Training Program

Eileen T. Carpenter
B.E. Cooper Union for the Advancement of Science, 2007

3rd Year Graduate Student

Advisors: Howard Crawford, Ph.D. / Richard Lin, M.D.

Departments: Pharmacological Sciences / Medicine

Graduate Program: Molecular & Cellular Pharmacology


Title:
 The PI3K p110a-Rac1 signaling pathway is essential for Kras-induced pancreatic tumorigenesis.

Abstract:

ES Carpenter, CY Wu, LM Ballou, HC Crawford, RZ Lin.

         New drug targets are urgently needed to develop primary and adjuvant therapies for pancreatic ductal adenocarcinoma (PDA). Almost all PDAs are caused by mutations in the Kras gene. Pharmacological inhibition of Kras has so far proven unsuccessful. Fortunately, mutant Kras activates several molecules more easily targeted with pharmacological inhibitors, including the focus of our studies, phosphatidylinositol 3-kinase (PI3K). Our studies utilize the pancreas-specific Ptf1a-Cre;LSL-KrasG12D (abbreviated as KC) mouse model that faithfully reproduces human pancreatic tumorigenesis. Using the cre-lox system, we generated conditional knockout mice for PI3K catalytic isoforms p110a and p110ß. We found that genetic ablation of p110a, but not p110ß, in the mouse pancreas completely abrogated the development of pancreatic tumors in KC mice without causing detectable harmful effects. Furthermore, we generated a mouse strain expressing a constitutively active p110a mutant in the pancreas and found that activation of PI3K alone is sufficient to induce pancreatic tumor formation. Previous reports indicate that Kras can activate PI3K through direct binding to the Ras-binding domain of p110a. Surprisingly, replacement of pancreatic p110a with mutant p110a incapable of binding to Kras did not protect KC mice against tumorigenesis, indicating an indirect mechanism by which oncogenic Kras signals to p110a to induce pancreatic tumor formation. Interestingly, KC pancreata exhibited markedly elevated p110a expression, suggesting an alternative mechanism by which Kras activates PI3K in our model. We also investigated signaling pathways downstream of PI3K in KC mice. Unexpectedly, Akt, a known downstream effector of PI3K, did not show increased activation in the KC pancreas, and loss of p110a did not decrease its activation level. Upon exploring alternate PI3K effectors, we found that the KC pancreas exhibited a marked increase in activation of Rac1, a small G protein involved in actin cytoskeleton rearrangement. More importantly, ablation of p110a, but not p110ß, completely blocked this Rac1 activation, a finding consistent with a previous study showing that ablation of Rac1 blocks oncogenic Kras-induced pancreatic tumorigenesis. In summary, we found that Kras requires and activates the p110a-Rac1 pathway to induce pancreatic tumorigenesis through an indirect mechanism and not through direct binding to p110a. Further studies are needed to determine if pancreatic tumor maintenance requires the continual presence of p110a signaling in order to assess the viability of targeting this enzyme in treating PDA.

Publications:
(pre-MSTP publications indicated with an *)

Ardito CA, Grüner BM; Takeuchi KK, Lubeseder-Martellato C, Teichmann N, Mazur PK, DelGiorno KE, Halbrook CJ, Carpenter ES, Hall JC, Pal D, Briel T, Herner A, Trajkovic-Arsic M, Sipos B, Liou G-Y, Storz P, Murray NR, Threadgill DW, Sibilia M, Washington MK, Wilson CL, Schmid RM, Raines EW, Crawford HC and Siveke JT. (2012). EGF Receptor is Required for KRAS-induced Pancreatic Tumorigenesis. Cancer Cell. In press.

Bombardelli L, Carpenter ES, Wu AP, Alston N, DelGiorno KE, Crawford HC. (2010). Pancreas-specific ablation of beta1 integrin induces tissue degeneration by disrupting acinar cell polarity. Gastroenterology. 138(7):2531-40, 2540.e1-4. Epub 2010 Feb 23. PMID:20188101.

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