The roles of endoplasmic reticulum chaperones in regulating liver homeostasis and tumorigenesis.

摘要

Cancer progression is characterized by the overriding of growth arrest and rapid cell proliferation, which require increased protein synthesis. Additionally, the poor vascularization of cancer tissues leads to glucose deprivation and hypoxia. Therefore, the tumor microenvironment represents physiological endoplasmic reticulum (ER) stress and activates the unfolded protein response (UPR) for survival. ER stress has been linked to a variety of human diseases, including liver steatosis and different cancers, and the conventional function of ER chaperones in protein quality control is updated to promote tumor progression, metastasis, and drug resistance.;Liver cancer is one of the most common solid tumors with poor prognosis and high mortality. 40-50% of liver cancer patients have the tumor suppressor PTEN mutations or deletion, whereas the two major ER chaperones, glucose-regulated protein 94 (GRP94) and glucose-regulated protein 78 (GRP78), have been shown to be overexpressed in liver cancer. Thus, in this dissertation we established multiple mouse models with liver-specific deletion of Grp94 (cGrp94f/f) or Grp78 alone (cGrp78f/f) or in combination with Pten (cPf/f94f/f or cPf/f78f/f) to investigate the roles of GRP94 and GRP78 in liver cancer development. First, we demonstrated that while deletion of GRP94 in the liver led to hyperproliferation of liver progenitor cells (LPCs), deletion of both GRP94 and PTEN accelerated development of liver tumors, including both hepatocellular carcinoma (HCC) and cholangiocarcinoma (CC), suggestive of progenitor cell origin. Moreover, at the premalignant stage, disturbance of cell adhesion proteins and minor liver injury were observed. When GRP94 was deleted in Pten-null livers, ERK was selectively activated.;Next, we further explored the long-term effect of GRP94 deletion on liver tumorigenesis. cGrp94f/f livers showed small nodules at 15 months and spontaneously developed HCC and ductular reactions (DRs) by 21 months, associating with increased liver injury and fibrosis. Interestingly, GRP94-positive hepatocytes progressively repopulated cGrp94f/f livers. At 15 months, we observed expansion of LPCs and mild DRs, as well as increase in cell proliferation. Analysis of signaling pathways revealed TGF-beta1 upregulaion, SMAD2/3, ERK, and JNK activation, and cyclin D1 upregulation in cGrp94 f/f livers. The HCC was found to be GRP94-positive, whereas the expanded LPCs and DRs remained GRP94-negative.;Interestingly, hepatic deletion of Grp78 led to a different story. Ablation of GRP78 was progressive but incomplete. At 3 months, cPf/f78f/f livers showed lipogenic gene activation, exacerbated steatosis, and liver injury. In response to liver injury, increased proliferation of bile duct cells and LPCs was observed in cPf/f78f/f livers, and GRP78 expression was intact in bile ducts and some LPCs. At 6 months, cPf/f78f/f livers exhibited JNK activation, beta-catenin downregulation, along with PDGFRalpha upregulation. HCC and CC development was accelerated and evident in cPf/f78f/f livers at 8-9 months, coinciding with intense GRP78 expression, while adjacent normal areas expressed WT level of GRP78. In summary, this dissertation revealed that ER chaperones GRP94 and GRP78 are novel but distinct regulators for liver homeostasis and cancer progression.