Our lab research Interests include signal transduction initiated by tyrosyl phosphorylation, which plays an important role in regulating the growth and behaviors of normal and malignant cells. The level of cellular protein tyrosyl phosphorylation is determined by the balanced activities of protein tyrosine kinases and protein tyrosine phosphatases (PTPs). Currently, we are trying to understand the mechanism by which PTPs (i.e. Shp-1) and scaffolding adapter or signal relay proteins (i.e. Gab1 and Gab2) regulate mammary gland development and tumorigenesis. Ultimately, we hope that results from our study would provide valuable information for designing new breast cancer therapies. Below are brief descriptions of the on-going projects in the lab.
1) Scaffolding adapter Gab2 acts in stromal cells to promote mammary tumor development and progression.
The progression of breast cancer to its malignant state involves the close interaction between the hyper-proliferative mammary epithelial cells and its surrounding stromal cells. The Gab family of scaffolding adapters mainly plays positive roles in transmitting extracellular stimuli from cell surface receptors including ErbB family of receptor protein tyrosine kinases to downstream cell signaling cascades including the PI3K/Akt and Ras/Erk pathways important for the growth, survival, migration, and functions of various cell types. Our previous studies indicate that Gab2, a Gab family member, plays a causative role in breast carcinogenesis in tumor cells via activation of the Erk pathway. Our unpublished data from mammary fatpad transplanting experiment indicate that Gab2 expression in stromal cells is required for efficient mammary tumor growth. Interestingly, we find that tumor stroma of Gab2 knockout mice contains only ~15% mast cells compared to tumor stroma of Gab2 wild type mice, strongly suggesting that loss of mast cells whose development requires Gab2 results in impaired mammary tumor growth. Mast cells are the major effector cells involved in allergic responses as well as in other inflammatory diseases. Although mast cells are important in the progression of various types of cancers, its role in breast cancer is still not clear.
Currently, we are testing the hypothesis that mast cells are involved in promoting breast tumor growth and development by crossing MMTV-PyMT mice with the Kit w-sh/w-sh mouse strain that is deficient in mast cells in tissues. MMTV-PyMT mouse is a well-known mammary tumor transgenic model that follows a progression path including hyperplasia, adenoma, early carcinoma, late carcinoma, and metastases, which is similar as those seen in human breast cancers. Furthermore, we want to examine whether drugs that can inhibit mast cells growth and function can be used to treat mammary tumor in mouse model as a proof of principal for targeting mast cells in treating breast cancer.
2) Characterization of the potential oncogenic properties of the breast cancer associated mutants of Gab1.
While Gab2 is overexpressed in a subset of breast cancer cells, another member of the Gab family protein, Gab1 does not show overexpression in breast cancer cells, which suggests against a role of Gab1 in breast carcinogenesis. A recent study involving genome-wide sequencing of all coding genes uncovers two somatic mutations in the coding region of the Gab1 gene only, which are specifically associated with breast cancer cells. This result strongly suggests that these two Gab1 mutants play a role in breast carcinogenesis. Our preliminary study by expressing these two Gab1 mutants in MCF10A cells indicate that these Gab1 mutants enhance EGF-evoked Akt activation, further suggesting that these mutations are gain-of-function oncogenic events. To further test the role of these Gab1 mutants in breast carcinogenesis, we plan to examine 1) whether expression the Gab1 mutants induce breast carcinogenesis in MCF10A-3D culture or in mice by itself or cooperating with ErbB2/Her2. 2) the molecular mechanism by which these Gab1 mutants enhance Akt activation and activate specific cell signaling pathways required for their oncogenic properties. 3) The incidence of these Gab1 mutations in a large cohort of breast tumor samples and its correlation with prognosis.
3) The role of SH2 domain containing tyrosine phosphatase Shp-1 in mammary gland development and tumorigenesis.
Shp-1 is mainly expressed in hematopoietic and epithelial cells. It plays a negative role in most types of the hematopoietic cells by attenuating the signaling from cell surface receptors including cytokine receptors. Although Shp-1 is also expressed in mammary epithelial cells and a subset of breast cancer cells, the function of Shp-1 in mammary gland development and tumorigenesis is largely unknown. To address this question, we are investigating the effects of loss of Shp-1 expression specifically in the mammary epithelial cells of mice using the Cre-Loxp mediated deletion technology.
1. Gu H, Oliver N. Transcriptional repression of fibronectin gene expression in v-src transformation. Exp Cell Res. 1995;217(2):428-39.
2. Gu H, Griffin JD, Neel BG. Characterization of two SHP-2-associated binding proteins and potential substrates in hematopoietic cells. J Biol Chem. 1997;272(26):16421-30.
3. Timms JF, Carlberg K, Gu H, Chen H, Kamatkar S, Nadler MJ, Rohrschneider LR, Neel BG. Identification of major binding proteins and substrates for the SH2-containing protein tyrosine phosphatase SHP-1 in macrophages. Mol Cell Biol. 1998;18(7):3838-50.
4. Gu H, Pratt JC, Burakoff SJ, Neel BG. Cloning of p97/Gab2, the major SHP2-binding protein in hematopoietic cells, reveals a novel pathway for cytokine-induced gene activation. Mol Cell. 1998;2(6):729-40.
5. Gu H, Maeda H, Moon JJ, Lord JD, Yoakim M, Nelson BH, Neel BG. New role for Shc in activation of the phosphatidylinositol 3-kinase/Akt pathway. Mol Cell Biol. 2000;20(19):7109-20.
6. Pratt JC, Igras VE, Maeda H, Baksh S, Gelfand EW, Burakoff SJ, Neel BG, Gu H. Cutting edge: Gab2 mediates an inhibitory phosphatidylinositol 3'-kinase pathway in T cell antigen receptor signaling. J Immunol. 2000;165(8):4158-63.
7. Gu H, Saito K, Klaman LD, Shen J, Fleming T, Wang Y, Pratt JC, Lin G, Lim B, Kinet JP, Neel BG. Essential role for Gab2 in the allergic response. Nature. 2001;412(6843):186-90.
8. Sattler M, Mohi MG, Pride YB, Quinnan LR, Malouf NA, Podar K, Gesbert F, Iwasaki H, Li S, Van Etten RA, Gu H*, Griffin JD, Neel BG. Critical role for Gab2 in transformation by BCR/ABL. Cancer Cell. 2002;1(5):479-92. (*Co-corresponding author.)
9. Daly RJ, Gu H, Parmar J, Malaney S, Lyons RJ, Kairouz R, Head DR, Henshall SM, Neel BG, Sutherland RL. The docking protein Gab2 is overexpressed and estrogen regulated in human breast cancer. Oncogene. 2002;21(33):5175-81.
10. Ischenko I, Petrenko O, Gu H, Hayman MJ. Scaffolding protein Gab2 mediates fibroblast transformation by the SEA tyrosine kinase. Oncogene. 2003;22(41):6311-8.
11. Gu H, Neel BG. The "Gab" in signal transduction. Trends Cell Biol. 2003;13(3):122-30.
12. Neel BG, Gu H, Pao L. The 'Shp'ing news: SH2 domain-containing tyrosine phosphatases in cell signaling. Trends Biochem Sci. 2003;28(6):284-93.
13. Yu M, Cliff A. Lowell CA, Benjamin G. Neel BG, Gu H . Scaffolding adapter Gab2 requires Syk to transmit signals from FcRI. J Immunol. 2006; 176(4):2421-9.
14. Bentires-Alj M, Gil SG, Chan R, Wang ZC, Wang Y, Imanaka N, Harris LN, Richardson A, Neel BG, Gu H . A role for the scaffolding adapter GAB2 in breast cancer. Nat Med. 2006;12:114-121.
15. Yu M, Luo J, Yang W, Wang Y, Mizuki M, Kanakura Y, Besmer P, Neel BG, Gu H. The scaffolding adapter Gab2, via SHP-2, regulates kit-evoked mast cell proliferation by activating the Rac/JNK pathway. J Biol Chem. 2006; 281(39):28615-26.
16. Yuan T, Wang Y, Zhao Z J, and Gu H. Protein Tyrosine Phosphatase PTPN9 Negatively Regulates ErbB2 and EGFR Signaling in Breast Cancer Cells. 2010. Submitted.