Pten null prostate tumorigenesis and AKT activation are blocked by targeted knockout of ER chaperone GRP78/BiP in prostate epithelium

Abstract

GRP78/BiP has recently emerged as a novel biomarker for aggressive prostate cancer. Here, we report that homozygous deletion of Grp78 specifically in mouse prostate epithelium suppresses prostate tumorigenesis without affecting postnatal prostate development and growth. Mouse prostates with double conditional knockout of Grp78 and Pten exhibit normal histology and cytology, in contrast to the invasive adenocarcinoma in mouse prostates with Pten inactivation. AKT activation in Pten null prostate epithelium is inhibited by Grp78 homozygous deletion, corresponding with suppression of AKT phosphorylation by GRP78 knockdown in prostate cancer cell line. Thus, inactivation of GRP78 may represent a previously undescribed approach to stop prostate cancer and potentially other cancers resulting from the loss of PTEN tumor suppression and/or activation of the oncogenic AKT.cancer suppressor ͉ chaperone gene ͉ inactivation P rostate cancer is the most common cancer in men and develops through successive stages including prostatic intraepithelial neoplasia (PIN), carcinoma in situ, invasive adenocarcinoma, and metastatic disease. Although local surgery, radiation, or hormonal ablation provide initial response at early stages of the disease, tumor cells often develop resistance and relapse. Thus, the identification of new therapeutic targets for prostate cancer is of critical importance. The 78-kDa glucose regulated protein (GRP78) was initially linked to prostate cancer progression and metastasis through epitope mapping of humoral immune response from cancer patients, and identified as a functional molecular target for circulating ligands (1). Recent studies further revealed that Ϸ2/3 of human prostate cancers expressed high level of GRP78, associating with recurrence, development of castration-resistance, and poor survival (2, 3). These studies provide the first hints that GRP78 may have a critical role in prostate cancer development and therapeutic resistance.GRP78, also referred to as BiP or HSPA5, is a member of the HSP70 protein family. As a major endoplasmic reticulum (ER) chaperone, GRP78 facilitates protein folding and assembly, protein quality control, ER-associated protein degradation, Ca 2ϩ binding, and regulation of transmembrane ER stress inducers (4, 5). GRP78 is encoded by a single copy gene in rodents and humans. It is expressed as early as at the 2-cell stage of embryonic development, and is essential for proliferation and survival of embryonic cells (6). GRP78 is highly induced in a wide range of tumors through intrinsic factors such as altered glucose metabolism of cancer cells, compounded by extrinsic factors such as glucose deprivation, hypoxia, and acidosis in the microenvironment of poorly-perfused solid tumor (7). In a wide variety of cancer cell lines and xenograft models, GRP78 has emerged as having a critical role in cancer cell survival, tumor progression, and resistance to therapy (7-10). Despite these advances, it remains unknown whether GRP78 could also be essential for the genesis of tumor. I...

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

“…Chemical inhibition of AKT suppressed both human and murine ADM (44). Previous studies of GRP78 and Pten-null-induced prostate cancer and leukemia revealed that GRP78 haploinsufficiency potently suppressed AKT activation mediated by loss of PTEN in these cancers (21,22). Subsequently, it was demonstrated that the cell-surface form of GRP78 (scGRP78) complexes with PI3K to promote phosphatidylinositol (3-5)-trisphosphate formation (18).…”

“…Genotyping of DNA from the mouse tail or pancreas was performed by PCR. Primers for detection of the Pdx1-Cre and floxed or knockout alleles for Grp78 and p53 were described previously (21,57). To determine if recombination of the Kras G12D lox-stop-lox cassette occurred, DNA was extracted from pancreas and PCR was performed following the protocol described from the Jacks Lab (https://jacks-lab.mit.edu/protocols/genotyping/ kras_cond).…”

“…Although homozygous knockout of Grp78 results in embryonic lethality, heterozygous Grp78 mice expressing an ∼50% level of GRP78 are viable and phenotypically normal (20). The creation of targeted heterozygous knockout of Grp78 in various organs revealed that although it has a minimal effect on organ development and function, it exerts a profound suppressive effect in both solid and blood tumors notably driven by loss of the Pten tumor suppressor gene (14,21,22). Despite these advances, the mechanistic involvement of GRP78 in oncogenic mutant KRASdriven cancers is just emerging.…”

Modelling the effect of GRP78 on anti-oestrogen sensitivity and resistance in breast cancer

“…In addition, EnR stress-induced signalling to apoptosis via CASPASE-4/12 [94,95] or the IRE1 -JNK pathway may be important. GRP78 knockdown is also known to induce apoptosis by blocking AKT activation in colon, PTEN-null leukaemia and prostate cancer cell lines [88,96,97]. Hence, it will be important to measure the effect of knocking down GRP78 on AKT signalling in LCC9 cells.…”

ER stress transcription factor Xbp1 suppresses intestinal tumorigenesis and directs intestinal stem cells

“…Human tumor cells indeed exhibit evidence of ER stress, and reduced capacity to elicit an UPR within malignant cells results in decreased tumorigenesis in model systems (Ma and Hendershot, 2004;Bi et al, 2005;Fu et al, 2008;Luo and Lee, 2013). Xbp1 has been considered protumorigenic sustained, augments tumor formation in both an inflammatory (i.e., CAC after DSS/AOM) and noninflammatory (i.e., CRC in Apc min mice) context.…”