Programmed cell death ligand 1 (PD-L1) is a major immunosuppressive checkpoint protein expressed by tumor cells to subvert anticancer immunity. Recent studies have shown that ionizing radiation (IR) upregulates the expression of PD-L1 in tumor cells. However, whether an IR-induced DNA damage response (DDR) directly regulates PD-L1 expression and the functional significance of its upregulation are not fully understood. Here, we show that IR-induced upregulation of PD-L1 expression proceeds through both transcriptional and post-translational mechanisms. Upregulated PD-L1 was predominantly present on the cell membrane, resulting in T-cell apoptosis in a co-culture system. Using mass spectrometry, we identified PD-L1 interacting proteins and found that BCLAF1 (Bcl2 associated transcription factor 1) is an important regulator of PD-L1 in response to IR. BCLAF1 depletion decreased PD-L1 expression by promoting the ubiquitination of PD-L1. In addition, we show that CMTM6 is upregulated in response to IR and participates in BCLAF1-dependent PD-L1 upregulation. Finally, we demonstrated that the ATM/BCLAF1/PD-L1 axis regulated PD-L1 stabilization in response to IR. Together, our findings reveal a novel regulatory mechanism of PD-L1 expression in the DDR.

Cancer stem cell (CSC)-dictated intratumor heterogeneity accounts for the majority of drug-resistance and distant metastases of breast cancers. Here, we identify a SIRT1-PRRX1-KLF4-ALDH1 circuitry, which couples CSCs, chemo-resistance, metastasis and aging. Pro-longevity protein SIRT1 deacetylates and stabilizes the epithelial-to-mesenchymal-transition (EMT) inducer PRRX1, which inhibits the transcription of core stemness factor KLF4. Loss of SIRT1 destabilizes PRRX1, disinhibits KLF4, and activates the transcription of ALDH1, which induces and functionally marks CSCs, resulting in chemo-resistance and metastatic relapse. Clinically, the level of PRRX1 is positively linked to SIRT1, whereas KLF4 is reversely correlated. Importantly, KLF4 inhibitor Kenpaullone sensitizes breast cancer cells and xenograft tumors to Paclitaxel and improves therapeutic effects. Our findings delineate a SIRT1-centered circuitry that regulates CSC origination, and targeting this pathway might be a promising therapeutic strategy.

Distant metastasis is the main cause of breast cancer-related death; however, effective therapeutic strategies targeting metastasis are still scarce. This is largely attributable to the spatiotemporal intratumor heterogeneity during metastasis. Here we show that protein deacetylase SIRT7 is significantly downregulated in breast cancer lung metastases in human and mice, and predicts metastasis-free survival. SIRT7 deficiency promotes breast cancer cell metastasis, while temporal expression of Sirt7 inhibits metastasis in polyomavirus middle T antigen breast cancer model. Mechanistically, SIRT7 deacetylates and promotes SMAD4 degradation mediated by β-TrCP1, and SIRT7 deficiency activates transforming growth factor-β signaling and enhances epithelial-to-mesenchymal transition. Significantly, resveratrol activates SIRT7 deacetylase activity, inhibits breast cancer lung metastases, and increases survival. Our data highlight SIRT7 as a modulator of transforming growth factor-β signaling and suppressor of breast cancer metastasis, meanwhile providing an effective anti-metastatic therapeutic strategy.Metastatic disease is the major reason for breast cancer-related deaths; therefore, a better understanding of this process and its players is needed. Here the authors report the role of SIRT7 in inhibiting SMAD4-mediated breast cancer metastasis providing a possible therapeutic avenue.

Ubiquitin-specific protease 4 (USP4) represents a potential oncogene involved in various human cancers. Nevertheless, the biological roles and precise mechanism of USP4 in esophageal squamous cell carcinoma (ESCC) progression are not understood. Here, USP4 expression was found to be markedly upregulated in ESCC tumor tissues and cells. Loss- and gain-of-function assays suggested that USP4 silencing inhibited ESCC cell proliferation, migration, and invasion, while USP4 overexpression promoted these behaviors. Consistently, USP4 silencing repressed tumor growth and metastasis in an ESCC nude mouse model in vivo. As a target molecule of USP4, transforming growth factor-β-activated kinase 1 (TAK1) also showed high expression in ESCC. Moreover, we observed that USP4 specifically interacted with TAK1 and stabilized TAK1 protein levels via deubiquitination in ESCC cells. Importantly, USP4 promotes ESCC proliferation, migration, and invasion via the MEK/ERK signaling pathway and can be inhibited by U0126. Neutral red (NR), an inhibitor of USP4 can suppress ESCC progression in vitro and in vivo. Overall, this study revealed that USP4/TAK1 plays crucial roles in ESCC progression by modulating proliferation, migration, and invasion, and USP4 might be a potential therapeutic target in ESCC.

Esophageal squamous cell carcinoma (ESCC), the most prevalent subtype of esophageal cancer, ranks sixth in cancer-related mortality, making it one of the deadliest cancers worldwide. The identification of potential risk factors for ESCC might help in implementing precision therapies. Autophagy-related lncRNAs are a group of non-coding RNAs that perform critical functions in the tumor immune microenvironment and therapeutic response. Therefore, we aimed to establish a risk model composed of autophagy-related lncRNAs that can serve as a potential biomarker for ESCC risk stratification. Using the RNA expression profile from 179 patients in the GSE53622 and GSE53624 datasets, we found 11 lncRNAs (AC004690.2, AC092159.3, AC093627.4, AL078604.2, BDNF-AS, HAND2-AS1, LINC00410, LINC00588, PSMD6-AS2, ZEB1-AS1, and LINC02586) that were co-expressed with autophagy genes and were independent prognostic factors in multivariate Cox regression analysis. The risk model was constructed using these autophagy-related lncRNAs, and the area under the receiver operating characteristic curve (AUC) of the risk model was 0.728. To confirm that the model is reliable, the data of 174 patients from The Cancer Genome Atlas (TCGA) esophageal cancer dataset were analyzed as the testing set. A nomogram for ESCC prognosis was developed using the risk model and clinic-pathological characteristics. Immune function annotation and tumor mutational burden of the two risk groups were analyzed and the high-risk group displayed higher sensitivity in chemotherapy and immunotherapy. Expression of differentially expressed lncRNAs were further validated in human normal esophageal cells and esophageal cancer cells. The constructed lncRNA risk model provides a useful tool for stratifying risk and predicting the prognosis of patients with ESCC, and might provide novel targets for ESCC treatment.

The DNA damage response (DDR) is a highly orchestrated process but how double-strand DNA breaks (DSBs) are initially recognized is unclear. Here, we show that polymerized SIRT6 deacetylase recognizes DSBs and potentiates the DDR in human and mouse cells. First, SIRT1 deacetylates SIRT6 at residue K33, which is important for SIRT6 polymerization and mobilization toward DSBs. Then, K33-deacetylated SIRT6 anchors to γH2AX, allowing its retention on and subsequent remodeling of local chromatin. We show that a K33R mutation that mimics hypoacetylated SIRT6 can rescue defective DNA repair as a result of SIRT1 deficiency in cultured cells. These data highlight the synergistic action between SIRTs in the spatiotemporal regulation of the DDR and DNA repair in humans and mice.

Expression of programmed cell death ligand (PD-L1) is associated with poor prognosis in breast cancer. Understanding the regulation of PD-L1 expression in breast cancer could provide a new strategy for breast cancer treatment. Here, we demonstrate that moesin (MSN) phosphorylation by Rho-associated protein kinase (ROCK) stabilizes PD-L1 protein levels. Our results indicate that phosphorylated MSN may compete with the E3 ubiquitin ligase SPOP for binding PD-L1. ROCK inhibition via the Y-27632 inhibitor or MSN silencing decreased PD-L1 expression, resulting in T-cell activation both in vitro and in vivo. Administration of Y-27632 into immunocompetent Balb/c mice bearing breast tumors suppressed tumor progression and enhanced CD4+ and CD8+ T-cell infiltration. RNA-seq analysis of Y-27632-treated mouse tumors revealed that ROCK inhibition upregulated several immune response genes. However, the combination of Y-27632 and an anti-PD-1 antibody did not show additive or synergistic effects due to reduced PD-L1 in the presence of Y-27632. Our study unravels a previously unappreciated mechanism of PD-L1 regulation through the ROCK-MSN pathway. Moreover, we found that ROCK inhibitors could be combined with breast cancer immunotherapy.

DNA damage accumulates with age (Lombard et al., 2005). However, whether and how robust DNA repair machinery promotes longevity is elusive. Here, we demonstrate that ATM-centered DNA damage response (DDR) progressively declines with senescence and age, while low dose of chloroquine (CQ) activates ATM, promotes DNA damage clearance, rescues age-related metabolic shift, and prolongs replicative lifespan. Molecularly, ATM phosphorylates SIRT6 deacetylase and thus prevents MDM2-mediated ubiquitination and proteasomal degradation. Extra copies of Sirt6 extend lifespan in Atm-/- mice, with restored metabolic homeostasis. Moreover, the treatment with CQ remarkably extends lifespan of Caenorhabditis elegans, but not the ATM-1 mutants. In a progeria mouse model with low DNA repair capacity, long-term administration of CQ ameliorates premature aging features and extends lifespan. Thus, our data highlights a pro-longevity role of ATM, for the first time establishing direct causal links between robust DNA repair machinery and longevity, and providing therapeutic strategy for progeria and age-related metabolic diseases.