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Research Grants Awarded
Differential Regulation of Breast Cancer Cell Invasive Migration by Akt Isoforms.
The PI 3-K and Akt pathway is frequently deregulated in cancer, and the current paradigm is that Akt promotes cancer cell transformation, survival and growth. Recent studies from our laboratory have added a new layer to the pleiotropic effects of Akt by showing that the Akt1 isoform inhibits breast cancer cell migration and invasion. Conversely, Akt2 has been shown to promote breast cancer cell migration. These contrasting effects on invasive migration have far reaching implications for the use of Akt inhibitors as anti-cancer therapeutic agents. My proposal will therefore seek to test the hypothesis that Akt isoforms regulate breast cancer cell invasive migration in a distinct manner and will investigate the mechanistic basis for this selectivity. Aim 1. To determine the function of Akt1, Akt2 and Akt3 in modulating breast cancer cell motility, I will use 1) Akt1/2/3 siRNA; 2) gain-of-function approaches with activated Akt isoform alleles; and 3) Akt isoform-specific chemical inhibitors. I will also investigate the potential synergy between ERK and NFAT acting downstream of Akt. Aim 2. To test if subcellular localization of Akt isoforms determines their function in breast cancer invasive migration. Akt1 is predominantly localized in the nucleus of breast cancer cells, whereas Akt2 is excluded from the nucleus and localized proximal to the extracellular matrix. Since Akt1 and Akt2 inhibit and enhance breast cancer cell migration, respectively, I propose that the nuclear localization of Akt1 is critical for its inhibition of breast cancer cell invasive migration, whereas the cell-matrix localization of Akt2 is important for its enhancement of motility. Two complementary approaches will be used: 1) Targeting Akt isoforms using localization-specific signals; and 2) Inhibiting Akt kinase activity at specific subcellular compartments. Aim 3. To determine if PHLPP regulates Akt function in breast cancer cell migration. By dephosphorylating Akt, the Ser/Thr phosphatase PHLPP induces apoptosis and suppresses tumor growth. However, the role of PHLPP in cancer cell migration and the contribution of specific PHLPP isoforms in Akt signaling has yet to be determined. Here I propose that by regulating the activation state of Akt, PHLPP plays a critical role in breast cancer cell migration in an isoform-specific manner. I will first determine the role of PHLPP in cancer cell motility using both gain-of-function and siRNA approaches. Secondly, I will test if PHLPP1 and PHLPP2 dephosphorylate specific Akt isoforms. Finally, I will test if the localization of PHLPP determines its regulation of Akt and therefore cell motility. The results of these studies will lead to a better understanding of the mechanisms by which Akt isoforms control breast cancer cell invasive migration. There is also the potential that the outcome of these studies will provide for the future development of more effective and novel therapeutic interventions for tumor progression.
Akt is a cellular protein which plays a key role in mediating the growth and survival of cancer cells in response to agents which induce premature cell death. Therefore, considerable efforts have been made to develop pharmacological inhibitors of Akt as therapeutic intervention for cancer. However, little information is known regarding the role of Akt in regulating the ability of breast cancer cells to migrate and become invasive, two features which are critical for the metastasis of breast tumors in humans. As with many proteins in cancerous cells, Akt exists as a family of closely related species, and these are known as Akt1, Akt2 and Akt3. Whereas Akt2 is known to promote breast cancer cell migration, recent studies from my laboratory have revealed an unexpected finding that Akt1 decreases breast cancer cell migration. Therefore, the studies outlined in this proposal are designed to test the hypothesis that the three Akt proteins exert distinct effects on the ability of breast cancer cells to become invasive. I will begin the project by testing the effect of Akt3 on breast cancer cell migration, as it has not been addressed yet. Akt proteins are enzymes, or biological catalysts, and as such they exert their effects inside a cell by altering important biochemical reactions. Such reactions dictate the efficiency by which cancer cells divide and then metastasize. Therefore, another aim of the study is to elucidate the mechanisms by which Akt proteins alter biochemical reactions which are essential for breast cancer cell invasion. Since Akt proteins reside in different parts of the cell, I propose experiments to test if the location of Akt proteins determines their function in breast cancer cell migration. I will also test the effect of PHLPP, a cellular protein which reduces the activity of Akt, on breast cancer cell migration. Therefore, the overall goal of the application is to dissect the function of the three Akt proteins in the ability of breast cancer cells to migrate and invade inappropriate locations during cancer progression, leading to metastasis. This proposal qualifies for the Susan G. Komen Breast Cancer Foundation Postdoctoral Fellowship Award because the studies will provide insight into the mechanisms which account for the different effects of the three Akt proteins on breast cancer cell migration. It is expected that a greater understanding of breast cancer cell invasion can contribute to the design of more effective anti-cancer drugs.