We have identified a panel of colon cancer cell lines with PIK3CA gain of function mutations and have shown they are closely associated with cell survival and metastases from orthotopic primary colon tumors to the liver and lung. These mutations have recently been shown to predict for poor survival in both colorectal and breast cancer. The objectives of this competing renewal application are to characterize the basis for the mutant PI3K contribution to survival and malignant progression and to identify signaling effects both upstream and downstream of the mutants that contribute to survival and metastatic colonization. This line of investigation is expected to lead to the identification of strategies for matching appropriate targeting agents to the subgroup of colorectal cancer patients bearing these mutations and to allow for further refinement of patient subgroups from among the patients with p1101 mutations. We have noted in that knockdown of the cell surface receptor RONK (Met family receptor) results in loss of signaling by the H1407R mutant under stress conditions and inhibition of metastasis from an orthotopic colon cancer model. Thus, in Aim 1 the hypothesis that activation of PI3K mutants is linked to RONK autocrine activity will be tested. The understanding of this issue is potentially important to the development of novel strategies of intervention independent of, or complementary to, direct attack upon mutant PI3K p1101 catalytic subunits.
Specific Aim II will test the hypothesis that cell survival signaling through Bax and pBad is a critical element for imparting the metastatic phenotype to cells bearing these mutations. This hypothesis will be tested by utilizing siRNA and dominant negative approaches to determine critical survival targets for metastasis from among the several AKT substrate-related mechanisms that co-exist during stress conditions in these cells.
Specific Aim III will determine whether ectopic expression of the mutant enzymes in cells bearing only the wild type gene will generate similar mechanisms of survival and metastasis. We will also characterize the relationship between the PLC3 mediated mechanisms of cell survival with that of the mutant PI3K/AKT pathway. The hypothesis that both are invoked by exposure to stress and act simultaneously on the modification of Bad to enable metastasis will be tested. PLC3 and AKT are linked by competition for the same substrate and are often inhibitory to each other. Despite this they are simultaneously effective for cell survival signaling in the presence of the mutant PIK3CA's, but not in wild type cells. We will test the hypothesis that mutant PI3K allows for greater catalytic efficiency at low ATP concentrations that in turn provides sufficient product to satisfy the needs of both pathways.
Specific Aims are: I. Determine if autocrine growth factor activity is required for mutant PIK3CA mediated metastasis. II. Determine whether Bax degradation and Bad phosphorylation by mutant PIK3CA's are necessary for metastasis. III. Determine the effects of different PIK3CA mutations on cell survival signaling and metastatic capability.
Mutation in a key cell survival mediator called PI3K augments this enzyme's activity when cells bearing the mutations are subjected to stresses that normally cause apoptosis. We have shown that these mutations promote metastatic capabilities as well as cell survival. The objective of this project is to understand the upstream mechanisms that activate the mutant enzymes and the downstream consequences of the enzymes that result in resistance to apoptosis and metastasis. This information will be used to develop new strategies for treating patients with metastatic colon cancer bearing this mutation (~30% of colon cancer patients).
