Unfolded Protein Response: Cause or Consequence of Lipid and Lipoprotein Metabolism Disturbances?

Study on the Antitumor Mechanism of Tanshinone IIA In Vivo and In Vitro through the Regulation of PERK-ATF4-HSPA5 Pathway-Mediated Ferroptosis

As a traditional Chinese medicine, Salvia miltiorrhiza Bunge was first recorded in the Shennong Materia Medica Classic and is widely used to treat "the accumulation of symptoms and masses". The main active ingredient of Salvia miltiorrhiza Bunge, Tanshinone IIA (TIIA), has shown anti-inflammatory, antitumor, antifibrosis, antibacterial, and antioxidative activities, etc. In this study, the results showed that TIIA could inhibit the proliferation and migration of HepG2 cells and downregulate glutathione (GSH) and Glutathione Peroxidase 4 (GPX4) levels; besides, TIIA induced the production of Reactive Oxygen Species (ROS), and upregulated the total iron content. Based on network pharmacology analysis, the antitumor effect of TIIA was found to be focused on the endoplasmic reticulum (ER)-mediated ferroptosis signaling pathway, with protein kinase R (PKR)-like ER kinase (PERK)-activating transcription factor 4 (ATF4)-heat shock 70 kDa protein 5 (HSPA5) as the main pathway. Herein, TIIA showed typical ferroptosis characteristics, and a ferroptosis inhibitor (ferrostatin-1) was used to verify the effect. The antitumor effects of TIIA, occurring through the inhibition of the PERK-ATF4-HSPA5 pathway, were further observed in vivo as significantly inhibited tumor growth and the improved pathological morphology of tumor tissue in H22-bearing mice. In summary, the antitumor mechanism of TIIA might be related to the downregulation of the activation of PERK-ATF4-HSPA5 pathway-mediated ferroptosis.

Novel MicroRNA-Regulated Transcript Networks Are Associated with Chemotherapy Response in Ovarian Cancer

High-grade serous ovarian cancer (HGSOC) is a highly lethal gynecologic cancer, in part due to resistance to platinum-based chemotherapy reported among 20% of patients. This study aims to generate novel hypotheses of the biological mechanisms underlying chemotherapy resistance, which remain poorly understood. Differential expression analyses of mRNA- and microRNA-sequencing data from HGSOC patients of The Cancer Genome Atlas identified 21 microRNAs associated with angiogenesis and 196 mRNAs enriched for adaptive immunity and translation. Coexpression network analysis identified three microRNA networks associated with chemotherapy response enriched for lipoprotein transport and oncogenic pathways, as well as two mRNA networks enriched for ubiquitination and lipid metabolism. These network modules were replicated in two independent ovarian cancer cohorts. Moreover, integrative analyses of the mRNA/microRNA sequencing and single-nucleotide polymorphisms (SNPs) revealed potential regulation of significant mRNA transcripts by microRNAs and SNPs (expression quantitative trait loci). Thus, we report novel transcriptional networks and biological pathways associated with resistance to platinum-based chemotherapy in HGSOC patients. These results expand our understanding of the effector networks and regulators of chemotherapy response, which will help to improve the management of ovarian cancer.

Molecular mechanisms of lipotoxicity-induced pancreatic β-cell dysfunction

Type 2 diabetes (T2D), a heterogeneous disorder derived from metabolic dysfunctions, leads to a glucose overflow in the circulation due to both defective insulin secretion and peripheral insulin resistance. One of the critical risk factor for T2D is obesity, which represents a global epidemic that has nearly tripled since 1975. Obesity is characterized by chronically elevated free fatty acid (FFA) levels, which cause deleterious effects on glucose homeostasis referred to as lipotoxicity. Here, we review the physiological FFA roles onto glucose-stimulated insulin secretion (GSIS) and the pathological ones affecting many steps of the mechanisms and modulation of GSIS. We also describe in vitro and in vivo experimental evidences addressing lipotoxicity in β-cells and the role of saturation and chain length of FFA on the potency of GSIS stimulation. The molecular mechanisms underpinning lipotoxic-β-cell dysfunction are also reviewed. Among them, endoplasmic reticulum stress, oxidative stress and mitochondrial dysfunction, inflammation, impaired autophagy and β-cell dedifferentiation. Finally therapeutic strategies for the β-cells dysfunctions such as the use of metformin, glucagon-like peptide 1, thiazolidinediones, anti-inflammatory drugs, chemical chaperones and weight are discussed.

Phosphorylation of eIF2α signaling pathway attenuates obesity-induced non-alcoholic fatty liver disease in an ER stress and autophagy-dependent manner

Non-alcoholic fatty liver disease (NAFLD) is the most common liver disorder and frequently exacerbates in postmenopausal women. In NAFLD, the endoplasmic reticulum (ER) plays an important role in lipid metabolism, in which salubrinal is a selective inhibitor of eIF2α de-phosphorylation in response to ER stress. To determine the potential mechanism of obesity-induced NAFLD, we employed salubrinal and evaluated the effect of ER stress and autophagy on lipid metabolism. Ninety-five female C57BL/6 mice were randomly divided into five groups: standard chow diet, high-fat (HF) diet, HF with salubrinal, HF with ovariectomy, and HF with ovariectomy and salubrinal. All mice except for SC were given HF diet. After the 8-week obesity induction, salubrinal was subcutaneously injected for the next 8 weeks. The expression of ER stress and autophagy markers was evaluated in vivo and in vitro. Compared to the normal mice, the serum lipid level and adipose tissue were increased in obese mice, while salubrinal attenuated obesity by blocking lipid disorder. Also, the histological severity of hepatic steatosis and fibrosis in the liver and lipidosis was suppressed in response to salubrinal. Furthermore, salubrinal inhibited ER stress by increasing the expression of p-eIF2α and ATF4 with a decrease in the level of CHOP. It promoted autophagy by increasing LC3II/I and inhibiting p62. Correlation analysis indicated that lipogenesis in the development of NAFLD was associated with ER stress. Collectively, we demonstrated that eIF2α played a key role in obesity-induced NAFLD, and salubrinal alleviated hepatic steatosis and lipid metabolism by altering ER stress and autophagy through eIF2α signaling.

The Unfolded Protein Response: A Novel Therapeutic Target in Acute Leukemias

The unfolded protein response (UPR) is an evolutionarily conserved adaptive response triggered by the stress of the endoplasmic reticulum (ER) due, among other causes, to altered cell protein homeostasis (proteostasis). UPR is mediated by three main sensors, protein kinase RNA-like endoplasmic reticulum kinase (PERK), activating transcription factor 6α (ATF6α), and inositol-requiring enzyme-1α (IRE1α). Given that proteostasis is frequently disregulated in cancer, UPR is emerging as a critical signaling network in controlling the survival, selection, and adaptation of a variety of neoplasias, including breast cancer, prostate cancer, colorectal cancer, and glioblastoma. Indeed, cancer cells can escape from the apoptotic pathways elicited by ER stress by switching UPR into a prosurvival mechanism instead of cell death. Although most of the studies on UPR focused on solid tumors, this intricate network plays a critical role in hematological malignancies, and especially in multiple myeloma (MM), where treatment with proteasome inhibitors induce the accumulation of unfolded proteins that severely perturb proteostasis, thereby leading to ER stress, and, eventually, to apoptosis. However, UPR is emerging as a key player also in acute leukemias, where recent evidence points to the likelihood that targeting UPR-driven prosurvival pathways could represent a novel therapeutic strategy. In this review, we focus on the oncogene-specific regulation of individual UPR signaling arms, and we provide an updated outline of the genetic, biochemical, and preclinical therapeutic findings that support UPR as a relevant, novel target in acute leukemias.