GRP78 haploinsufficiency suppresses acinar-to-ductal metaplasia, signaling, and mutant Kras -driven pancreatic tumorigenesis in mice

Abstract

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;Kras G12D/+ ;p53 f/+ (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 Grp78 f/+ allele (PKC78 f/+ 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 PKC78 f/+ 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 (c78 f/+ ) and subjected to 3D culture in collagen. We further discovered that GRP78 haploinsufficiency in both the PKC78 f/+ and c78 f/+ 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.glucose-regulated protein 78 | GRP78 | pancreatic ductal adenocarcinoma | acinar-to-ductal metaplasia | Kras P ancreatic ductal adenocarcinoma (PDAC) remains one of the deadliest diseases with limited therapeutic options and an overall 5-y survival rate of <10%; therefore, identification of targetable key players in tumor initiation as well as tumor maintenance is urgently needed (1). PDAC is believed to arise from a range of preneoplastic mucinous lesions with ductal morphology, pancreatic intraepithelial neoplasia (PanIN) being the most common in humans (2). About 90% of PDAC contains activating mutations of KRAS whereas 50-75% contain mutations in Tp53 (1). Mutationally activated oncogenic KRAS signals through the PI3K-PDK1-AKT pathway and the canonical mitogen-activated protein kinase pathway via RAF-MEK1/2-ERK1/2, as well as via positive feedback activation of receptor tyrosine kinases engaged by autocrine and paracrine stimuli (3). Although the histological appearance of PDAC suggests a ductal cell of origin, accumulating evidence reveals that PDAC originates primarily through transdifferentiation of acinar cells into ductal cells in a process referred to as acinar-to-ductal metaplasia (ADM), although centroacinar cells and pancreas precursor cells could also give rise to PDAC (2, 4, 5). To study PDAC, a pancreatic cancer mouse model mimicking human PDAC has been established using the pancreatic...

Heterozygosity of Chaperone Grp78 Reduces Intestinal Stem Cell Regeneration Potential and Protects against Adenoma Formation

“…Furthermore, targeted heterozygous knockout of Grp78 in bone marrow suppressed blast numbers without affecting normal hematopoiesis (46). Recently, using the Pdx1 Cre -Ras G12D/þ -P53 fl/þ model for pancreatic ductal carcinoma, it was shown that epithelium-specific heterozygosity of Grp78 resulted in reduced tumorigenesis and increased survival of mice (47). Pancreatic ductal cells are known for their large translational capacity and dependence on the ER and thus on Grp78 levels.…”

New role of endoplasmic reticulum chaperones in regulating metaplasia during tumorigenesis

“…PKC mice showed detectable PDAC by 3 months and rapid subsequent tumor growth, associating with upregulation of Grp78 and the phosphorylated form of eukaryotic translation initiation factor 2 a (eIF2a) in the ductal cells, indicative of ER stress. 5 While homozygous knockout of Grp78 in the pancreas led to extensive fat infiltration and poorly developed acinar cells, heterozygous Grp78 knockout with 50% reduction in Grp78 level had no effect on pancreas development and function; thus, it is well suited for studying the role of Grp78 in PDAC and it also more closely mimics what can be achieved in the clinic with therapeutic agents.…”

“…Through creation of the PKC78 C/¡ (Pdx-Cre;Kras G12D/C ; p53 C/¡ ;Grp78 C/¡ ) model, we established that Grp78 haploinsufficiency in the pancreas is sufficient to reduce proliferation, suppress activation of Akt, ribosomal protein S6 (S6), extracellular regulated MAP kinase (Erk), and signal transducer and activator of transcription 3 (Stat3), delay tumor growth and significantly prolong survival. 5 Previous studies have shown that acinar cells expressing mutant Kras G12D are induced to transdifferentiate through the process of ADM recently recognized as a key tumor initiation event of PDAC. 1 Importantly, we discovered that PKC78 C/¡ pancreata exhibited reduced ADM, as well as deficient ADM in acinar cells isolated from the heterozygous Grp78 pancreas in response to transforming growth factor a (TGFa) stimulation.…”

“…7,8 Our mouse models revealed that Grp78 haploinsufficiency in acinar cells reduced Egfr expression and hampered the activation of Erk, Akt, Stat3 and b-catenin signaling in the PKC model. 5 It is possible that GRP78 is needed for processing or stabilizing of EGFR and various client proteins required for kinase signaling facilitating ADM. As an essential chaperone, GRP78 may also be needed for the reprogramming of the repertoire of proteins from the acinar into ductal cell signature.…”

GRP78‐mediated antioxidant response and ABC transporter activity confers chemoresistance to pancreatic cancer cells

“…To survive the pressure created by the tumor microenvironment, including hypoxia and nutrient deprivation, tumor cells utilize the UPR pathways (Avril et al ., 2017; Chevet et al ., 2015; Lee, 2007; Ma and Hendershot, 2004). Multiple components of the UPR have been linked to advanced tumor stage and chemoresistance in cancer (Lee, 2014; Roller and Maddalo, 2013; Shen et al ., 2017; Wang and Kaufman, 2014). For example, overexpression of PDIA5 in chronic myeloid leukemia shows increased resistance to imatinib (Chevet et al ., 2015).…”