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Pancreatic ductal adenocarcinoma (PDAC) remains a highly lethal disease in critical need of new therapeutic strategies. Here, we report that the stress-inducible 78-kDa glucose-regulated protein (GRP78/HSPA5), a key regulator of endoplasmic reticulum homeostasis and PI3K/AKT signaling, is overexpressed in the acini and PDAC of Pdx1-Cre;KrasG12D/+;p53f/+ (PKC) mice as early as 2 mo, suggesting that GRP78 could exert a protective effect on acinar cells under stress, as during PDAC development. The PKC pancreata bearing wild-type Grp78 showed detectable PDAC by 3 mo and rapid subsequent tumor growth. In contrast, the PKC pancreata bearing a Grp78f/+ allele (PKC78f/+ mice) expressing about 50% of GRP78 maintained normal sizes during the early months, with reduced proliferation and suppression of AKT, S6, ERK, and STAT3 activation. Acinar-to-ductal metaplasia (ADM) has been identified as a key tumor initiation mechanism of PDAC. Compared with PKC, the PKC78f/+ pancreata showed substantial reduction of ADM as well as pancreatic intraepithelial neoplasia-1 (PanIN-1), PanIN-2, and PanIN-3 and delayed onset of PDAC. ADM in response to transforming growth factor α was also suppressed in ex vivo cultures of acinar cell clusters isolated from mouse pancreas bearing targeted heterozygous knockout of Grp78 (c78f/+ ) and subjected to 3D culture in collagen. We further discovered that GRP78 haploinsufficiency in both the PKC78f/+ and c78f/+ pancreata leads to reduction of epidermal growth factor receptor, which is critical for ADM initiation. Collectively, our studies establish a role for GRP78 in ADM and PDAC development.

GRP78, a multifunctional protein with potent cytoprotective properties, is an emerging therapeutic target to combat cancer development, progression and drug resistance. The biological consequences of prolonged reduction in expression of this essential chaperone which so far has been studied primarily in young mice, was investigated in older mice, as older individuals are likely to be important recipients of anti-GRP78 therapy. We followed cohorts of Grp78+/+ and Grp78+/− male and female mice up to 2 years of age in three different genetic backgrounds and characterized them with respect to body weight, organ integrity, behavioral and memory performance, cancer, inflammation and chemotoxic response. Our results reveal that body weight, organ development and integrity were not impaired in aged Grp78+/− mice. No significant effect on cancer incidence and inflammation was observed in aging mice. Interestingly, our studies detected some subtle differential trends between the WT and Grp78+/− mice in some test parameters dependent on gender and genetic background. Our studies provide the first evidence that GRP78 haploinsufficiency for up to 2 years of age has no major deleterious effect in rodents of different genetic background, supporting the merit of anti-GRP78 drugs in treatment of cancer and other diseases affecting the elderly.

Metaplasia is emerging as a key process in tumorigenesis. We discovered that 2 essential endoplasmic reticulum (ER) chaperones, 78-kilodalton glucose-regulated protein (GRP78) and 94-kilodalton glucose-regulated protein (GRP94) have a role in metaplasia. Grp78 haploinsufficiency in the mouse pancreas impairs acinar-to-ductal metaplasia, whereas in the uterus, Grp94 loss induces squamous cell metaplasia; both resulting in tumor suppression.

The 78 kDa glucose-regulated protein (GRP78), also referred to as BiP/HSPA5, is a major endoplasmic reticulum (ER) chaperone with antiapoptotic properties and also serves as a regulator of ER stress signaling (1). Tumor cells are subjected to ER stress due to intrinsic factors such as genetic mutations, altered metabolism and hyperproliferation, as well as extrinsic factors in the tumor microenvironment including oxygen and nutrient deprivation (2). As an adaptive measure, cancer cells turn on the unfolded protein response (UPR), and ER stress induction of GRP78 in cancer cells represents a major prosurvival response, suppressing apoptosis while promoting proliferation and invasiveness. Thus, GRP78 is an emerging target for therapy to blunt cancer development, progression, and drug resistance. GRP78 conditional knockout mouse models further established the requirement of GRP78 in solid and blood tumorigenesis driven by mutation of the tumor suppressor gene PTEN and that GRP78 is an upstream regulator of the PI3K/AKT/S6 pathway (3,4). KRAS is commonly mutated in various cancers, including pancreatic adenocarcinoma (PDAC) and lung cancer, and thus far is deemed “undruggable”. We discovered that haploinsufficiency of a single moiety, GRP78, while having no effect on the normal pancreas, is sufficient to impede acinar-to-ductal metaplasia, block oncogenic signaling, curb PDAC progression, and prolong survival. Similarly, Grp78 haploinsufficiency is able to suppress mutant KRAS-driven lung cancer development. Further, we recently established that ER stress can actively promote cell surface localization of GRP78, where it assumes novel co-receptor functions with cell surface protein partners in regulating signal transduction pathways (5). Our studies uncover that csGRP78 interacts with specific cell surface signaling partner proteins and through those interactions impacts cancer cell adhesion, polarity, migration, and survival. References 1. Lee AS. Glucose-regulated proteins in cancer: molecular mechanisms and therapeutic potential. Nat Rev Cancer 2014;14:263-76. 2. Luo B, Lee AS. The critical roles of endoplasmic reticulum chaperones and unfolded protein response in tumorigenesis and anticancer therapies. Oncogene 2013;32:805-18. 3. Fu Y, Wey S, Wang M, Ye R, Liao CP, Roy-Burman P, et al. Pten null prostate tumorigenesis and AKT activation are blocked by targeted knockout of ER chaperone GRP78/BiP in prostate epithelium. Proc Natl Acad Sci USA 2008;105:19444-9. 4. Wey S, Luo B, Tseng CC, Ni M, Zhou H, Fu Y, et al. Inducible knockout of GRP78/BiP in the hematopoietic system suppresses Pten-null leukemogenesis and AKT oncogenic signaling. Blood 2012;119:817-25. 5. Tsai YL, Zhang Y, Tseng CC, Stanciauskas R, Pinaud F, Lee AS. Characterization and mechanism of stress-induced translocation of 78-kilodalton glucose-regulated protein (GRP78) to the cell surface. J Biol Chem 2015;290:8049-64. Citation Format: Amy S. Lee, Jieli Shen, Daisy Rangel, Chun-Chih Tseng, Yuan Li Tsai, Dat P. Ha, He Zhao, Louis Dubeau. GRP78/BiP: Cancer's comrade in crime [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr SY13-03. doi:10.1158/1538-7445.AM2017-SY13-03