Immunotherapy of PD-L1/PD-1 blockage elicited impressive clinical benefits for cancer treatment. However, the relative low response and therapy resistance highlight the need to better understand the molecular regulation of PD-L1 in tumors. Here, we report that PD-L1 is a target of UFMylation. UFMylation of PD-L1 destabilizes PD-L1 by synergizing its ubiquitination. Inhibition of PD-L1 UFMylation via silencing of UFL1 or Ubiquitin-fold modifier 1 (UFM1), or the defective UFMylation of PD-L1, stabilizes the PD-L1 in multiple human and murine cancer cells, and undermines antitumor immunity in vitro and mice, respectively. Clinically, UFL1 expression was decreased in multiple cancers and lower expression of UFL1 negatively correlated with the response of anti-PD1 therapy in melanoma patients. Moreover, we identified a covalent inhibitor of UFSP2 that promoted the UFMylation activity and contributed to the combination therapy with PD-1 blockade. Our findings identified a previously unrecognized regulator of PD-L1 and highlighted UFMylation as a potential therapeutic target.

Intestinal exocrine secretory cells, including Paneth and goblet cells, have a pivotal role in intestinal barrier function and mucosal immunity. Dysfunction of these cells may lead to the pathogenesis of human diseases such as inflammatory bowel disease (IBD). Therefore, identification and elucidation of key molecular mechanisms that regulate the development and function of these exocrine cells would be crucial for understanding of disease pathogenesis and discovery of new therapeutic targets. The Ufm1 conjugation system is a novel ubiquitin-like modification system that consists of Ufm1 (Ubiquitin modifier 1), Uba5 (Ufm1-activating enzyme, E1), Ufc1 (Ufm1-conjugating enzyme, E2) and poorly characterized Ufm1 E3 ligase(s). Recent mouse genetic studies have demonstrated its indispensable role in embryonic development and hematopoiesis. Yet its role in other tissues and organs remains poorly defined. In this study, we found that both Ufl1 and Ufbp1, two key components of the Ufm1 E3 ligase, were highly expressed in the intestinal exocrine cells. Ablation of either Ufl1 and Ufbp1 led to significant loss of both Paneth and goblet cells, which in turn resulted in dysbiotic microbiota and increased susceptibility to experimentally induced colitis. At the cellular and molecular levels, Ufbp1 deficiency caused elevation of endoplasmic reticulum stress and activation of the Unfolded Protein Response (UPR) and cell death program. Administration of small molecular chaperone partially prevented loss of Paneth cells caused by acute Ufbp1 deletion. Taken together, our results have provided unambiguous evidence for the crucial role of the Ufm1 E3 ligase in maintenance of intestinal homeostasis and protection from inflammatory diseases.

Background: Ufm1-specific ligase 1 (Ufl1) and Ufm1-binding protein 1 (Ufbp1), as putative targets of ubiquitin-fold modifier 1 (Ufm1), have been implicated in several pathogenesis-related signaling pathways. However, little is known about their functional roles in liver disease. Methods: Hepatocyte-specific Ufl1^Δ/Δhep and Ufbp1^Δ/Δhep mice were used to study their role in liver injury. Fatty liver disease and liver cancer were induced by high-fat diet (HFD) and diethylnitrosamine (DEN) administration, respectively. iTRAQ analysis was employed to screen for downstream targets affected by Ufbp1 deletion. Co-immunoprecipitation was used to determine the interactions between the Ufl1/Ufbp1 complex and the mTOR/GβL complex. Results: Ufl1^Δ/Δhep or Ufbp1^Δ/Δhep mice exhibited hepatocyte apoptosis and mild steatosis at 2 months of age and hepatocellular ballooning, extensive fibrosis, and steatohepatitis at 6–8 months of age. More than 50% of Ufl1^Δ/Δhep and Ufbp1^Δ/Δhep mice developed spontaneous hepatocellular carcinoma (HCC) by 14 months of age. Moreover, Ufl1^Δ/Δhep and Ufbp1^Δ/Δhep mice were more susceptible to HFD-induced fatty liver and DEN-induced HCC. Mechanistically, the Ufl1/Ufbp1 complex directly interacts with the mTOR/GβL complex and attenuates mTORC1 activity. Ablation of Ufl1 or Ufbp1 in hepatocytes dissociates them from the mTOR/GβL complex and activates oncogenic mTOR signaling to drive HCC development. Conclusions: These findings reveal the potential role of Ufl1 and Ufbp1 as gatekeepers to prevent liver fibrosis and subsequent steatohepatitis and HCC development by inhibiting the mTOR pathway.

Spinal cord injury (SCI) is generally divided into primary and secondary injuries, and apoptosis is an important event of the secondary injury. As an endogenous bile acid and recognized endoplasmic reticulum (ER) stress inhibitor, tauroursodeoxycholic acid (TUDCA) administration has been reported to have a potentially therapeutic effect on neurodegenerative diseases, but its real mechanism is still unclear. In this study, we evaluated whether TUDCA could alleviate traumatic damage of the spinal cord and improve locomotion function in a mouse model of SCI. Traumatic SCI mice were intraperitoneally injected with TUDCA, and the effects were evaluated based on motor function assessment, histopathology, apoptosis detection, qRT-PCR, and western blot at different time periods. TUDCA administration can improve motor function and reduce secondary injury and lesion area after SCI. Furthermore, the apoptotic ratios were significantly reduced; Grp78, Erdj4, and CHOP were attenuated by the treatment. Unexpectedly, the levels of CIBZ, a novel therapeutic target for SCI, were specifically up-regulated. Taken together, it is suggested that TUDCA effectively suppressed ER stress through targeted up-regulation of CIBZ. This study also provides a new strategy for relieving secondary damage by inhibiting apoptosis in the early treatment of spinal cord injury.

Zbtb38 is a novel target for spinal cord injury Zbtb38 is a novel target for spinal cord injury

DDRGK domain-containing protein 1 (DDRGK1) is an important component of the newly discovered ufmylation system and its absence has been reported to induce extensive endoplasmic reticulum (ER) stress. Recently, emerging evidence indicates that the ufmylation system is correlated with autophagy, although the exact mechanism remains largely unknown. To explore the regulation mechanism of DDRGK1 on autophagy, in this study, we established an immortalized mouse embryonic fibroblast (MEF) cell lines harvested from the DDRGK1^F/F:ROSA26-CreERT2 mice, in which DDRGK1 depletion can be induced by 4-hydroxytamoxifen (4-OHT) treatment. Here, we show that DDRGK1 deficiency in MEFs has a dual effect on autophagy, which leads to a significant accumulation of autophagosomes. On one hand, it promotes autophagy induction by impairing mTOR signaling; on the other hand, it blocks autophagy degradation by inhibiting autophagosome–lysosome fusion. This dual effect of DDRGK1 depletion on autophagy ultimately aggravates apoptosis in MEFs. Further studies reveal that DDRGK1 loss is correlated with suppressed lysosomal function, including impaired Cathepsin D (CTSD) expression, aberrant lysosomal pH, and v-ATPase accumulation, which might be a potential trigger for impairment in autophagy process. Hence, this study confirms a crucial role of DDRGK1 as an autophagy regulator by controlling lysosomal function. It may provide a theoretical basis for the treatment strategies of various physiological diseases caused by DDRGK1 deficiency.