Despite accumulating evidence for the pro-apoptotic role for X-linked inhibitor of apoptosis-associated factor 1 (XAF1), its involvement in endoplasmic reticulum (ER) stress response remains undefined. Here, we report that XAF1 enhances cell sensitivity to ER stress and acts as a switch in unfolded protein response (UPR)-mediated cell-fate decisions favoring apoptosis over adaptive autophagy. XAF1 interacts with and destabilizes ER stress sensor GRP78 through the assembly of zinc finger protein 313-mediated destruction complex. Moreover, XAF1 gene transcription is activated by ER stress through PERK-Nrf2 signaling to direct an adaptive to apoptotic switch of stress response by blocking C-terminus of Hsc70-interacting protein (CHIP)-mediated K63-linked ubiquitination and subsequent phosphorylation of inositol-required enzyme-1α (IRE1α). In tumor xenograft assays, XAF1-/- tumors display substantially lower regression compared to XAF1+/+ tumors in response to cytotoxic dose of ER stress inducer. XAF1 and GRP78 expression show an inverse correlation in human cancer cell lines and primary breast carcinomas. Collectively this study uncovers an important role for XAF1 as a linchpin to govern the sensitivity to ER stress and the outcomes of UPR signaling, illuminating the mechanistic consequence of XAF1 inactivation in tumorigenesis.

Hepatitis C Virus (HCV) is the main causative factor for liver cirrhosis and the development of liver cancer, with a confirmed ~ 180 million infections worldwide. E2 is an HCV structural protein responsible for virus entry to the host cell. Heat Shock Protein A5 (HSPA5), also termed BiP and GRP78, is the master regulator of the unfolded protein response mechanism, where it mainly localizes in the lumen of the Endoplasmic Reticulum (ER) in normal conditions. Under the stress of HCV infection or carcinogenesis, HSPA5 is upregulated. Consequently, HSPA5 escapes the ER retention localization and translocates to the cytoplasm and plasma membrane. Pep42, a cyclic peptide that was reported to target explicitly cell-surface HSPA5 in vivo. Owing to the high sequence and structural conservation between the C554-C566 region of HCV E2 and the Pep42, then we propose that the HCV E2 C554-C566 region could be the recognition site. The motivation of this work is to predict the possible binding mode between HCV E2 and HSPA5 by implementing molecular docking to test such proposed binding. Docking results reveal the high potent binding of the HCV E2 C554-C566 region to HSPA5 substrate-binding domain β (SBDβ). Moreover, the full-length HCV E2 also exhibits high binding potency to HSPA5 SBDβ. Defining the binding mode between HCV E2 and HSPA5 is of significance, so one can interfere with such binding and reducing the viral infection.

Aggressive mature T-cell lymphoma (TCL) is a disease that carries a poor prognosis. The mechanism, at the functional protein level, of the resistance to therapy of TCL has not yet been well clarified. To comprehensively clarify the mechanism, we first reviewed the literature, as mentioned in the Introduction section, on 22 types of representative functional proteins reported as being potentially associated with treatment resistance, mainly in hematologic tumors. Next, we retrospectively analyzed the tumor cell expressions of these 22 functional proteins in 16 randomly selected patients with TCL who had received CHOP (cyclophosphamide, hydroxyl doxorubicin, oncovin, and prednisolone) therapy as first-line treatment. As a result, we propose a new three-group prognostic classification of TCL (the TCL Urayasu Classification) based on the mechanism of resistance to treatment of these tumors. The study subjects included 7 patients (44%) with peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS), 6 patients (38%) with angioimmunoblastic T-cell lymphoma (AITL), and 3 patients (19%) with anaplastic large T-cell lymphoma (ALCL). Immunohistochemistry was performed in paraffin-embedded tumor tissue sections prepared from these patients as antigens using antibodies against the 22 previously reported treatment-resistance-related proteins to determine the tumor cell expression statuses of these proteins. Log-rank test was performed to compare the overall survival (OS) after CHOP therapy of the patients showing positive and negative immunostaining for these proteins, as well as among patients grouped based on other factors. Overall, the median OS of the TCL patients was about 33.5 months. When compared by the disease type, the prognosis was found to be worse in the order of ALCL, AITL, and PTCL. A multivariate analysis showed that expression of glucose-regulated protein 94 (GRP94), a protein that serves as a pro-survival component under endoplasmic reticulum (ER) stress in the tumor microenvironment, was significantly associated with shortened survival. No significant difference was observed for the conventional poor prognostic factors: high-risk International Prognostic Index (IPI) and high-risk Prognostic Index for peripheral T-cell lymphoma, unspecified (PTCL-U) (PIT). However, when GRP94 was combined with six other factors, listed below, as survival-shortening factors, significant differences were observed. The 6 factors were 1) programmed cell death-ligand 1 (PD-L1) and 2) programmed cell death 1 (PD-1), which are involved in immune surveillance; 3) aldo-keto reductase family 1 member C3 (AKR1C3), which is an enzyme that inactivates HO (hydroxyl doxorubicin [H] and oncovin [O]) of CHOP; 4) P53, a tumor suppressor; 5) Glucose-regulated protein 78 (GRP78), an ER stress protein; 6) thymidine phosphorylase (TP), which is an enzyme involved in thymidine catabolism. Based on the combination of GRP94 and the six other factors expressed in the tumors, we propose a new prognostic classification system for TCL (TCL Urayasu classification). Group 1 (group with a relatively good prognosis): GRP94-negative (n = 6; median OS, 88 months; p < 0.01); Group 2 (group with a poor prognosis): GRP94-positive, plus expression of 2 of the 6 aforementioned factors (n = 5; median OS, 25 months; p > 0.05); and Group 3 (group with a very poor prognosis): GRP94-positive, plus expression of at least 3 of the 6 aforementioned factors (n = 5; median OS, 10 months; p < 0.01). Thus, the TCL Urayasu prognostic classification is a simple, useful, and innovative classification that also explains the mechanism of resistance to treatment for each functional protein. Accumulation of more cases and further analyses are expected in the future to enable clinical application, such as use of a stratified treatment approach and treatment using inhibitors.