Ki-Ras Signaling in Pancreatic Cancer: Role of a Novel Akt Regulator

University Of Texas Hlth Sci Ctr Houston, Houston TX

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Abstract

PROJECT SUMMARY The 5-year survival rate for Pancreatic ductal adenocarcinoma (PDAC) patients is about 5% and has remained largely unchanged over the past 25 years. It is imperative that the mechanisms that underlie this cancer be rapidly identified and investigated so that novel molecular therapies can be developed. For the most part, the signaling mechanisms deregulated in response to genetic alterations in the Ki-Ras gene, and by other well- established hallmarks of pancreatic carcinogenesis, are still incompletely understood. The long-term goal is to elucidate the role and regulation of the phosphoinositide 3-kinase (PI3K) signaling pathway and its protein ki- nase mediator Akt in PDAC and develop more effective antagonists against them for cancer prevention and therapy than are currently available. In pursuit of this goal, a modified yeast two-hybrid screen with Akt as bait helped identify BSTA as a previously unknown mediator of PI3K/Akt signaling. The objective of this proposal is to further understand BSTA regulation and function and the effects of blocking its activity on PDAC. The central hypothesis is that BSTA is a key regulator of oncogenic Ki-Ras-induced Akt signaling and promotes pancreatic tumorigenesis. Based on strong preliminary data, this hypothesis will be tested by pursuing the fol- lowing two specific aims: 1) Identify the mechanism by which Ki-Ras activates Akt and delineate the amino acid sequence of BSTA that is essential for BSTA-Akt interaction; and 2) Identify BSTA function in pancreatic tumorigenesis. An RNAi-based approach, and site-directed mutagenesis coupled to GST pull-down assays, will be used to test the working hypothesis (Aim 1) that oncogenic Ki-Ras and one of its effectors activate Akt by increasing BSTA expression. A cell-permeable peptide patterned after the minimal Akt-binding sequence of BSTA sequence will also be synthesized to evaluate its effects on Akt activity and function. To test if oncogenic Ki-Ras promotes pancreatic tumorigenesis through BSTA overexpression and the Akt signaling pathway (Aim 2), BSTA will be downregulated in orthotopic PDAC and liver colonization (metastatic) nude mice animal mod- els with BSTA-siRNA-DOPC conjugate. The rationale for the proposed project is that understanding the role and regulation of BSTA may help identify novel ways to target the PI3K pathway and oncogenic Ki-Ras signal- ing for the effective treatment of PDAC. This contribution is significant because it is expected to help reveal details of a novel mechanism by which K-RasG12D additionally controls Akt and lead to the development of alternative pharmacologic strategies for targeting the PI3K/Akt pathway in pancreatic ductal cancer. The re- search proposal is innovative because it describes a novel mechanistic link between oncogenic Ki-Ras and Akt that will, once properly delineated, offer a new and substantially different approach for targeting the PI3K/Akt pathway than currently available. Together, these studies are expected to have a positive impact by fundamentally advancing the understanding of Ki-Ras and PI3K/Akt signaling and uncover new molecular tar- gets for the treatment of pancreatic ductal cancer.