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The Role of Shp2 in the Alpha 6 Beta 4 Integrin-dependent Metastasis
The concept of making targeted chemotherapy a clinical reality for breast cancer treatment began over a century ago when studies began concentrating on identifying proteins that are associated with breast cancer progression and the mechanism by which they promote the survival, invasion, and metastasis of breast carcinoma cells. The a6b4 integrin is one such protein that has been shown to play a role in breast cancer invasion and survival and tumor metastasis by signaling through the large cytoplasmic domain of the b4 subunit. The mechanism by which the a6b4 integrin transmits signals that influence breast carcinoma progression is not fully understood. However, it is known that phosphorylation of tyrosine 1494 (Y1494) in the b4 cytoplasmic domain is required for carcinoma invasion. In this proposal, we hypothesize that Y1494 is phosphorylated by a src family kinase, which recruits the tyrosine phosphatase SHP-2 to the b4 subunit, and the interaction of SHP-2 with b4 is essential for a6b4 -dependent invasion and metastasis. To investigate this hypothesis, we will perform three Specific Aims. In the first Aim, we will investigate the role of src family kinases in the binding of b4 to SHP-2 by using in vitro src kinase assays and src inhibitors. In Aim 2, we will use various SHP-2 and b4 dominant-negative mutants to determine the role of SHP-2 in a6b4 integrin-dependent breast carcinoma invasion and survival. Finally, in Aim 3, we will stably transfect MDA-MBA-435 and 231 breast cancer cells with expression constructs of SHP-2 and b4 mutants to determine the importance of Y1494 and the role of SHP-2 in a6b4 integrin-dependent metastasis when these cells are grown as tumors in mice. Taken together, our results will establish a mechanism for a6b4-dependent signaling to promote breast cancer progression and identify potential novel diagnostic and therapeutic targets for new drug development for the prevention of breast carcinoma metastasis.
In recent years, progress has been made in the treatment of breast cancer through targeting of specific proteins with selective drugs. The key issue in these discoveries was to understand the mechanism by which a normal cell becomes a cancer cell, and a cancer cell becomes invasive and metastatic. Another important factor was to identify cellular proteins that participate in the mechanism of cancer progression. One such protein is the a6b4-integrin. This protein is expressed in normal cells and is important for the stability of cell structure and function. In cancer cells, the a6b4-integrin transfers signals from outside of the cell to proteins inside the cell, which makes the tumor cells more invasive so they are more likely to metastasize. In this study, we propose a mechanism by which the a6b4 integrin promotes the progression of breast cancer through this transfer of signals. We hypothesize that amino acid 1494, which is a tyrosine, in the b4 intracellular domain is modified by src family kinases. This modification allows SHP-2, another intracellular protein, to bind to the b4 subunit, and we predict that this binding is essential for a6b4 to make breast cancer cells more metastatic. In our experiments, we will determine how the b4-protein is modified to transmit signals from outside of the cell. Next, we will determine if the interaction of SHP-2 with b4 is important for making the breast cancer cells more invasive. Finally, we will perform experiments to determine if the modification of tyrosine 1494 in the a6b4 integrin and the binding of SHP-2 to this site makes breast cancer cells more metastatic when grown as tumors in mice. Taken together our studies will contribute to understanding the pathways that promote breast cancer progression. These new findings will be beneficial for developing new therapeutic drugs for prevention of breast cancer metastasis.