The recent discovery that GRP78, traditionally regarded as a major endoplasmic reticulum (ER) chaperone and regulator of ER stress signaling, can also localize to the cell surface under pathophysiologic conditions such as cancer, changes the paradigm on how this protein may exert its pro-proliferative and anti- apoptotic function in cancer. In the past grant period, we established that GRP78 haploinsufficiency suppresses breast tumorigenesis through inhibition of tumor proliferation, angiogenesis and increased apoptosis. Through creation of a novel mutant mouse model with conditional biallelic deletion of both Grp78 and the tumor suppressor gene Pten, we discovered that not only is GRP78 critically required for prostate tumorigenesis and hematologic cancers, but is also required for PI3K/AKT activation in both types of cancer, both in vivo and in vitro. Cel surface GRP78 (sGRP78) is emerging as a co-receptor controlling cell signaling. In understanding how GRP78 regulates oncogenic signaling, we established that ER stress not only upregulates GRP78 but also actively promotes relocalization of GRP78 from the ER to the cell surface, and this process is regulated by the KDEL retrieval machinery. Taking advantage of cell surface localization of GRP78 in cancer cells but not in normal organs, we screened and identified a lead monoclonal antibody (MAb159) which specifically binds to cell surface GRP78, induces cancer cell apoptosis and suppresses tumor growth. Here we hypothesize that sGRP78 is a major effector of tumor growth and therapeutic resistance through its ability to regulate the PI3K/AKT signaling pathway and that targeting sGRP78 represents a novel and powerful approach for anti-PI3K therapy that will suppress tumor growth and alleviate drug resistance.
In Aim 1, we seek to understand the underlying molecular mechanisms that allow GRP78 to escape from the ER to the cell surface, through analysis of the functional domains of GRP78 required for surface localization and the integrity of the ER retrieval machinery, coupled with liv cell imaging of GRP78 mobilization.
In Aim 2, we will determine how sGRP78 regulates PI3K/AKT signaling by investigating the functional and physical interactions of sGRP78 with components of the PI3K pathway and the effect of targeting sGRP78 on other oncogenic pathways.
In Aim 3, we will directly test the role of sGRP78 in tumorigenesis and therapeutic resistance in spontaneous mouse cancer models and xenograft models using human cancer cell lines resistant to therapy. As a logical extension of our work on prostate cancer, we will utilize a novel Pten-null prostate cancer model which allows bioluminescence monitoring of cancer development, progression and recurrence after castration. Castration sensitive and resistant cells derived from this model will also be studied. The efficacy and safety of MAb159 will be tested in other cancer models, either alone or in combination therapy. Thus, this work not only addresses fundamental mechanisms but also has wide clinical implications.
This proposal represents a first comprehensive study on the molecular mechanisms for cell surface localization of GRP78 and how the cell surface form of GRP78 serves as an upstream regulator of PI3K/AKT pathway, which is critical for cancer survival and resistance. This study will also address the efficacy and safety of a novel anti-cancer therapeutic antibody against cell surface GRP78 in the treatment of resistant cancers while sparing normal organs, which will have wide clinical implications.
|Poirier, Steve; Mamarbachi, Maya; Chen, Wan-Ting et al. (2015) GRP94 Regulates Circulating Cholesterol Levels through Blockade of PCSK9-Induced LDLR Degradation. Cell Rep 13:2064-71|
|Zhu, Genyuan; Lee, Amy S (2015) Role of the unfolded protein response, GRP78 and GRP94 in organ homeostasis. J Cell Physiol 230:1413-20|
|Lin, Y G; Shen, J; Yoo, E et al. (2015) Targeting the glucose-regulated protein-78 abrogates Pten-null driven AKT activation and endometrioid tumorigenesis. Oncogene 34:5418-26|
|Hussien, Yassir; Podojil, Joseph R; Robinson, Andrew P et al. (2015) ER Chaperone BiP/GRP78 Is Required for Myelinating Cell Survival and Provides Protection during Experimental Autoimmune Encephalomyelitis. J Neurosci 35:15921-33|
|Tsai, Yuan-Li; Zhang, Yi; Tseng, Chun-Chih et al. (2015) Characterization and mechanism of stress-induced translocation of 78-kilodalton glucose-regulated protein (GRP78) to the cell surface. J Biol Chem 290:8049-64|
|Lee, Amy S; Chen, Wan-Ting (2015) Reply: To PMID 24027047. Hepatology 61:1767-8|
|Chen, Wan-Ting; Tseng, Chun-Chih; Pfaffenbach, Kyle et al. (2014) Liver-specific knockout of GRP94 in mice disrupts cell adhesion, activates liver progenitor cells, and accelerates liver tumorigenesis. Hepatology 59:947-57|
|Zhu, Genyuan; Wang, Miao; Spike, Benjamin et al. (2014) Differential requirement of GRP94 and GRP78 in mammary gland development. Sci Rep 4:5390|
|Chen, Wan-Ting; Ha, Dat; Kanel, Gary et al. (2014) Targeted deletion of ER chaperone GRP94 in the liver results in injury, repopulation of GRP94-positive hepatocytes, and spontaneous hepatocellular carcinoma development in aged mice. Neoplasia 16:617-26|
|Lee, Amy S (2014) Glucose-regulated proteins in cancer: molecular mechanisms and therapeutic potential. Nat Rev Cancer 14:263-76|
Showing the most recent 10 out of 105 publications