Energy status dictates PD-L1 protein abundance and anti-tumor immunity to enable checkpoint blockade.

Aberrant energy status contributes to multiple metabolic diseases, including obesity, diabetes, and cancer, but the underlying mechanism remains elusive. Here, we report that ketogenic-diet-induced changes in energy status enhance the efficacy of anti-CTLA-4 immunotherapy by decreasing PD-L1 protein levels and increasing expression of type-I interferon (IFN) and antigen presentation genes. Mechanistically, energy deprivation activates AMP-activated protein kinase (AMPK), which in turn, phosphorylates PD-L1 on Ser283, thereby disrupting its interaction with CMTM4 and subsequently triggering PD-L1 degradation. In addition, AMPK phosphorylates EZH2, which disrupts PRC2 function, leading to enhanced IFNs and antigen presentation gene expression. Through these mechanisms, AMPK agonists or ketogenic diets enhance the efficacy of anti-CTLA-4 immunotherapy and improve the overall survival rate in syngeneic mouse tumor models. Our findings reveal a pivotal role for AMPK in regulating the immune response to immune-checkpoint blockade and advocate for combining ketogenic diets or AMPK agonists with anti-CTLA4 immunotherapy to combat cancer.

Construction of stable membranal CMTM6-PD-L1 full-length complex to evaluate the PD-1/PD-L1-CMTM6 interaction and develop anti-tumor anti-CMTM6 nanobody.

CKLF (chemokine-like factor)-MARVEL transmembrane domain containing protein 6 (CMTM6) is a novel regulator to maintain the stability of PD-L1. CMTM6 can colocalize and interact with PD-L1 on the recycling endosomes and cell membrane, preventing PD-L1 from lysosome-mediated degradation and proteasome-mediated degradation thus increasing the half-life of PD-L1 on the cell membrane. The difficulties in obtaining stable full-length PD-L1 and CMTM6 proteins hinder the research on their structures, function as well as related drug development. Using lauryl maltose neopentyl glycol (LMNG) as the optimized detergent and a cell membrane mimetic strategy, we assembled a stable membrane-bound full-length CMTM6-PD-L1 complex with amphipol A8-35. When the PD-1/PD-L1-CMTM6 interactions were analyzed, we found that CMTM6 greatly enhanced the binding and delayed the dissociation of PD-1/PD-L1, thus affecting immunosuppressive signaling and anti-apoptotic signaling. We then used the CMTM6-PD-L1 complex as immunogens to generate immune repertoires in camels, and identified a functional anti-CMTM6 nanobody, called 1A5. We demonstrated that the anti-CMTM6 nanobody greatly decreased T-cell immunosuppression and promoted apoptotic susceptibility of tumor cells in vitro, and mainly relied on the cytotoxic effect of CD8+ T-cells to exert tumor growth inhibitory effects in CT26 tumor-bearing mice. In conclusion, the stable membrane-bound full-length CMTM6-PD-L1 complex has been successfully used in studying PD-1/PD-L1-CMTM6 interactions and CMTM6-targeting drug development, suggesting CMTM6 as a novel tumor immunotherapy target.

Identification and validation of EMT-immune-related prognostic biomarkers CDKN2A, CMTM8 and ILK in colon cancer.

Colon cancer (CC) is a disease with high incidence and mortality rate. The interaction between epithelial-mesenchymal transition (EMT) and immune status has important clinical significance. We aim to identify EMT-immune-related prognostic biomarkers in colon cancer. The GEO2R and GEPIA 2.0 were utilized to calculate the differential expression genes between CC and normal mucosa. Immport, InnateDB and EMTome databases were used to define EMT-immune-related genes. We conducted batch prognostic analysis by TCGA data. The expression patterns were verified by multiple datasets and lab experiments. GEPIA 2.0 and TIMER 2.0 were utilized to analyze the correlation of the hub genes with EMT markers and immune infiltration. GeneMANIA, STRING, and Metascape were used for co-expression and pathway enrichment analysis. Finally, we established a signature by the method of multivariate Cox regression analysis. CDKN2A, CMTM8 and ILK were filtered out as prognostic genes. CDKN2A and CMTM8 were up-regulated, while ILK was down-regulated in CC. CDKN2A was positively correlated with infiltration of macrophages, Th2 cells, Treg cells, and negatively correlated with NK cells. CMTM8 was negatively correlated with CD8+ T cells, dendritic cells, and NK cells. ILK was positively correlated with CD8+ T cells and dendritic cells. Moreover, CDKN2A, CMTM8 and ILK were significantly correlated with EMT markers. The three genes could participate in the TGF-ß pathway. The prognosis model established by the three hub genes was an independent prognosis factor, which can better predict the prognosis. CDKN2A, CMTM8 and ILK are promising prognostic biomarkers and may be potential therapeutic targets in colon cancer.

CMTM7 plays key roles in TLR-induced plasma cell differentiation and p38 activation in murine B-1 B cells.

Terminal differentiation of B cells into antibody-secreting cells is the foundation of humoral immune response. B-1 cells, which are different from B-2 cells, preferentially differentiate into plasma cells. CMTM7 is a MARVEL-domain-containing membrane protein predominantly expressed in B cells that plays an important role in B-1a cell development. The present study assessed CMTM7 function in response to antigen stimulation. Following immunization with T cell-dependent and T cell-independent antigens, Cmtm7-deficient mice exhibited decreased IgM but normal IgG responses in vivo. In vitro stimulation with LPSs induced Cmtm7-/- B-1 cell activation, whereas proliferation was marginally reduced. Notably, Cmtm7 deficiency markedly suppressed plasma cell differentiation in response to TLR agonists, accompanied by a decrease in IgM and IL-10 production. At the molecular level, loss of Cmtm7 repressed the downregulation of Pax5 and the upregulation of Xbp1, Irf4, and Prdm1. Furthermore, p38 phosphorylation was inhibited in Cmtm7-/- B-1 cells. Experiments using a p38 inhibitor revealed that p38 activation was essential for the terminal differentiation of B-1 cells, suggesting that Cmtm7 contributes to B-1 cell differentiation by maintaining p38 activation. Overall, the data reveal the crucial functions of CMTM7 in TLR-induced terminal differentiation and p38 activation in B-1 cells.

Coexpression of CMTM6 and PD-L1 as a predictor of poor prognosis in macrotrabecular-massive hepatocellular carcinoma.

The "macrotrabecular-massive" (MTM) pattern of hepatocellular carcinoma (HCC) has been suggested to represent a distinct HCC subtype and is associated with specific molecular features. Since the immune microenvironment is heterogenous in HCC, it is important to evaluate the immune microenvironment of this novel variant. CMTM6, a key regulator of PD-L1, is an important immunocheckpoint inhibitor. This study aimed to evaluate the prognostic effect of CMTM6/PD-L1 coexpression and its relationship with inflammatory cells in HCC. We analyzed 619 HCC patients and tumors were classified into MTM and non-MTM HCC subtypes. The expression levels of CMTM6 and PD-L1 in tumor and inflammatory cells were evaluated by immunohistochemistry. The density of inflammatory cells in the cancer cell nest was calculated. Tumoral PD-L1 expression and inflammatory cell density were higher in the MTM type than in the non-MTM type. CMTM6-high expression was significantly associated with shorter OS and DFS than CMTM6-low expression in the whole HCC patient population and the MTM HCC patient population. Moreover, MTM HCC patients with CMTM6/PD-L1 coexpression experienced a higher risk of HCC progression and death. In addition, CMTM6/PD-L1 coexpression was shown to be related to a high density of inflammatory cells. Notably, a new immune classification, based on CMTM6/PD-L1 coexpression and inflammatory cells, successfully stratified OS and DFS in MTM HCC. CMTM6/PD-L1 coexpression has an adverse effect on the prognosis of HCC patients, especially MTM HCC patients. Our study provides evidence for the combination of immune status assessment with anti-CMTM6 and anti-PD-L1 therapy in MTM HCC patients.

Inhibition of CKLF1 ameliorates hepatic ischemia-reperfusion injury via MAPK pathway.

BACKGROUND: Hepatic ischemia/reperfusion (I/R) injury is a major complication of liver resection or transplantation. However, the mechanism underlying hepatic I/R injury remains obscure. The aim of the present study was to investigate the role of Chemokine-like factor 1 (CKLF1) in hepatic I/R injury. METHODS: Rats were subjected to 70% hepatic ischemia for 90 min, followed by 6, 12, 24, 48 and 96 h of reperfusion. The expression of CKLF1 was measured by real-time PCR and western blot. The effect of C19, an antagonism peptide of CKLF1, on hepatic I/R injury was investigated. RESULTS: After subjected to 70% hepatic ischemia and reperfusion, the ALT and AST were increased. H&E results showed serious liver damage. The mRNA and protein levels of CKLF1 expression were upregulated during hepatic I/R. Immunohistochemistry staining results showed that neutrophil infiltration was increased in the ischemia lobe. MPO activity was significantly higher post reperfusion. TNF-α and IL-1ß were upregulated during hepatic I/R. C19 administration significantly reduced the level of ALT and AST, decreased the necrosis area of liver tissue. Furthermore, C19 treatment inhibited neutrophil infiltration and reduced MPO activity. Meanwhile, C19 decreased the expression of TNF-α and IL-1ß. The phosphorylation of P38, JNK were inhibited by C19 treatment. CONCLUSION: CKLF1 was upregulated during hepatic I/R. Inhibiting CKLF1 by C19, an antagonism peptide of CKLF1, could alleviate hepatic I/R injury, reduce neutrophil infiltration, decrease inflammatory response. The protective effect of C19 may related to MAPK signaling pathway.

PD-L1 is induced on the hepatocyte surface via CKLF-like MARVEL transmembrane domain-containing protein 6 up-regulation by the anti-HBV drug Entecavir.

Chronic hepatitis B is now controllable when treated with nucleoside reverse transcriptase inhibitors (NRTIs), which inhibit hepatitis B virus (HBV) replication. However, once the NRTIs are discontinued, most patients relapse, necessitating lifelong NRTIs treatment. HBV infection relapse is assumed to be caused by the persistent existence of covalently closed circular DNA (cccDNA) in the nuclei of infected hepatocytes. The mechanism by which cccDNA-positive hepatocytes escape immune surveillance during NRTIs treatment remains elusive. Entecavir (ETV), a commonly used NRTI, post-transcriptionally up-regulates programmed cell death-ligand 1 (PD-L1), an immune checkpoint molecule, on the cell surface of hepatocytes regardless of HBV infection. Up-regulation by ETV depends on up-regulation of CKLF-like MARVEL transmembrane domain-containing 6, a newly identified potent regulator of PD-L1 expression on the cell surface. ETV-treated hepatic cells suppressed the activity of primary CD3 T cells and programmed cell death protein-1 (PD-1)-over-expressed Jurkat cells. Finally, ETV induces PD-L1 in primary hepatocytes infected by HBV. These results provide evidence that ETV considerably up-regulates PD-L1 on the cell surface of infected hepatocytes, which may be one of the mechanisms by which infected hepatocytes subvert immune surveillance.

Essential role for Cmtm7 in cell-surface phenotype, BCR signaling, survival and Igµ repertoire of splenic B-1a cells.

B-1a cells represent a distinct B cell population with unique phenotype, self-renewing capacity and restricted Igµ repertoire. They primarily locate in body cavity and also exist in spleen. The different subpopulations of B-1a cells are heavily affected by local environment. Our previous studies revealed that MARVEL-domain-containing membrane protein, CMTM7, was involved in B-1a cell development. Here, we focused its influence on peritoneal and splenic B-1a cells. Unlike peritoneal B-1a cells, we found that splenic Cmtm7-/- B-1a cells expressed higher level of CD5, CD80 and CD86 compared with WT counterparts. They also exhibited an enhanced tonic BCR signals in steady state. Though the cell viability was unaffected in vitro, Cmtm7 knockout markedly promoted splenic B-1a cell apoptosis in situ, which was likely associated with down-regulation of Il-5rα. With regard to Igµ repertoire, peritoneal and splenic Cmtm7-/- B-1a cells exhibit similar changes exemplified by the loss of VH11 and gain of VH12, whereas an increase in VH1 usage and skewed J segments from JH1 to JH2 and JH4 families could only be detected within splenic Cmtm7-/- B-1a cells. Overall, these data indicate that Cmtm7 functions differently in peritoneal and splenic B-1a cells and plays a more important role in splenic cells.

Cmtm7 knockout inhibits B-1a cell development at the transitional (TrB-1a) stage.

Innate-like B-1a cells are an important cell population for production of natural IgM and interleukin-10 (IL-10), and act as the first line against pathogens. We determined that CMTM7 is essential for B-1a cell development. Following Cmtm7 (CKLF-like MARVEL transmembrane domain-containing 7) knockout, B-1a cell numbers decreased markedly in all investigated tissues. Using a bone marrow and fetal liver adoptive transfer model and conditional knockout mice, we showed that the reduction of B-1a cells resulted from B-cell-intrinsic defects. Because of B-1a cell loss, Cmtm7-deficient mice produced less IgM and IL-10, and were more susceptible to microbial sepsis. Self-renewal and homeostasis of mature B-1a cells in Cmtm7-/- mice were not impaired, suggesting the effect of Cmtm7 on B-1a cell development. Further investigations demonstrated that the function of Cmtm7 in B-1a cell development occurred at the specific transitional B-1a (TrB-1a) stage. Cmtm7 deficiency resulted in a slow proliferation and high cell death rate of TrB-1a cells. Thus, Cmtm7 controls B-1a cell development at the transitional stage.

Progress in pharmacological research of chemokine like factor 1 (CKLF1).

Currently, the research of chemokines has penetrated into many fields of life science. A new kind of chemokines, chemokine like factor 1 (CKLF1), which is cloned through suppression subtractive hybridisation (SSH) technology is expressed widely in human body, especially in the lung and peripheral blood leukocytes. CKLF1 has a broad spectrum of chemotaxic activity for many cells, such as lymphocytes, macrophages, bone marrow cells, nerve cells and so on. In addition, CKLF1 also stimulates the regeneration of skeletal muscle cells in vivo. Collecting data derived from our and other laboratories show that CKLF1 has an important relationship with allergic diseases, autoimmune diseases, tumors, cardio-cerebrovascular diseases and so on. Therefore, there be an important theoretical purport and applied value to make a summary of pharmacological progress of CKLF1.

Haploid genetic screens identify an essential role for PLP2 in the downregulation of novel plasma membrane targets by viral E3 ubiquitin ligases.

The Kaposi's sarcoma-associated herpesvirus gene products K3 and K5 are viral ubiquitin E3 ligases which downregulate MHC-I and additional cell surface immunoreceptors. To identify novel cellular genes required for K5 function we performed a forward genetic screen in near-haploid human KBM7 cells. The screen identified proteolipid protein 2 (PLP2), a MARVEL domain protein of unknown function, as essential for K5 activity. Genetic loss of PLP2 traps the viral ligase in the endoplasmic reticulum, where it is unable to ubiquitinate and degrade its substrates. Subsequent analysis of the plasma membrane proteome of K5-expressing KBM7 cells in the presence and absence of PLP2 revealed a wide range of novel K5 targets, all of which required PLP2 for their K5-mediated downregulation. This work ascribes a critical function to PLP2 for viral ligase activity and underlines the power of non-lethal haploid genetic screens in human cells to identify the genes involved in pathogen manipulation of the host immune system.

Neutralization of chemokine-like factor 1, a novel C-C chemokine, protects against focal cerebral ischemia by inhibiting neutrophil infiltration via MAPK pathways in rats.

BACKGROUND: Inflammation plays a key role in the pathophysiology of ischemic stroke. Some proinflammatory mediators, such as cytokines and chemokines, are produced in stroke. Chemokine-like factor 1 (CKLF1), as a novel C-C chemokine, displays chemotactic activities in a wide spectrum of leukocytes and plays an important role in brain development. In previous studies, we have found that the expression of CKLF1 increased in rats after focal cerebral ischemia and treatment with the CKLF1 antagonist C19 peptide decreased the infarct size and water content. However, the role of CKLF1 in stroke is still unclear. The objective of the present study was to ascertain the possible roles and mechanism of CKLF1 in ischemic brain injury by applying anti-CKLF1 antibody. METHODS: Male Sprague-Dawley rats were subjected to one-hour middle cerebral artery occlusion. Antibody to CKLF1 was applied to the right cerebral ventricle immediately after reperfusion; infarct volume and neurological score were measured at 24 and 72 hours after cerebral ischemia. RT-PCR, Western blotting and ELISA were utilized to characterize the expression of adhesion molecules, inflammatory factors and MAPK signal pathways. Immunohistochemical staining and myeloperoxidase activity was used to determine the extent of neutrophil infiltration. RESULTS: Treatment with anti-CKLF1 antibody significantly decreased neurological score and infarct volume in a dose-dependent manner at 24 and 72 hours after cerebral ischemia. Administration with anti-CKLF1 antibody lowered the level of inflammatory factors TNF-α, IL-1ß, MIP-2 and IL-8, the expression of adhesion molecules ICAM-1 and VCAM-1 in a dose-dependent manner. The results of immunohistochemical staining and detection of MPO activity indicated that anti-CKLF1 antibody inhibited neutrophil infiltration. Further studies suggested MAPK pathways associated with neutrophil infiltration in cerebral ischemia. CONCLUSIONS: Selective inhibition of CKLF1 activity significantly protects against ischemia/reperfusion injury by decreasing production of inflammatory mediators and expression of adhesion molecules, thereby reducing neutrophils recruitment to the ischemic area, possibly via inhibiting MAPK pathways. Therefore, CKLF1 may be a novel target for the treatment of stroke.

CKLF1/CCR5 axis is involved in neutrophils migration of rats with transient cerebral ischemia.

BACKGROUND: Chemokine-like factor 1 (CKLF1) is a chemokine increased significantly in ischemic brain poststroke. It shows chemotaxis effects on various immune cells, but the mechanisms of CKLF1 migrating neutrophils are poorly understood. Recent studies have provided evidence that CC chemokine receptor 5 (CCR5), a receptor of CKLF1, is involved in ischemic stroke. PURPOSES: To investigate the effects of HIF-1α guided AAV in ischemic brain, investigating the outcome of stroke, and examining the involvement of CKLF1/CCR5 axis in recruitment of neutrophils. RESULTS: HIF-1α guided AAV knocked down CKLF1 in ischemic area and alleviated brain damage of rats. CKLF1 migrated neutrophils through CCR5, worsening inflammatory responses. Akt/GSK-3ß pathway may involve in CKLF1/CCR5 axis guided neutrophils chemotaxis. CONCLUSIONS: CKLF1/CCR5 axis is involved in neutrophils migration of rats with transient cerebral ischemia. CKLF1/CCR5 axis may be a useful target for stroke therapy.

CMTM6 is positively correlated with PD-L1 expression and immune cells infiltration in lung squamous carcinoma.

BACKGROUND: The aim of this study was to clarify the association between CMTM6 and PD-L1 expression as well as microenvironment in lung squamous carcinoma (LUSC). MATERIAL AND METHODS: Using Spearman's correlation and Tumor Immune Estimation Resource (TIMER), we analyzed the relationship between CMTM6 and PD-L1 mRNA in LUSC. Immunohistochemistry (IHC) assay was applied to validate the correlation between CMTM6 and PD-L1 protein level in 80 LUSC samples originated from Shandong Provincial Hospital. Then, using The Cancer Genome Atlas (TCGA) database and fisher test, we analyzed the differential mutation genes in high and low CMTM6 expression group. TISIDB was used to explore the distribution of CMTM6 across immune- and molecular-subtypes. TCGA database and Gene Set variation analysis (GSVA) were used to analyze the relationship between CMTM6 and immune genes, immune related pathways. RESULT: Positive correlation between CMTM6 and PD-L1 in mRNA and protein level was found in LUSC patients. More gene mutations were found in CMTM6 high expression group compared with low expression group. Meanwhile, we also found the correlation between CMTM6 expression and molecular subtypes, immune genes, immune related pathways. Furthermore, our result revealed that B cells memory, T cells memory testing, T cells folicular helper, macrophages M0, macrophages M1 and neutrophils varied significantly between patients with CMTM6 high and low expression group. Finally, we found that CMTM6 expression was positively related to CD8 + T cell, macrophage, neutrophil and dendtritic cell (all, P < 0.05) and negatively related to CD4 + T cell (P = 0.018). CONCLUSION: CMTM6 is positively associated with PD-L1 expression and correlates with infiltration of immune cells in microenvironment of lung squamous carcinoma.

Inhibition of chemokine-like factor 1 improves blood-brain barrier dysfunction in rats following focal cerebral ischemia.

Disruption of blood-brain barrier (BBB) and subsequent edema are major contributors to the pathogenesis of ischemic stroke, and the current clinical therapy remains unsatisfied. Chemokine-like factor 1 (CKLF1), as a novel C-C chemokine, plays important roles in immune response. The expression of CKLF1 increased after focal cerebral ischemia and inhibition of CKLF1 activity showed neuroprotective effect by alleviating infiltration of neutrophil and neuron apoptosis in cerebral ischemia. However, few studies have focused on the role of CKLF1 on BBB integrity. The objective of present study was to investigate the role of CKLF1 on BBB integrity by applying anti-CKLF1 antibodies in rat focal cerebral ischemia and reperfusion model. Brain water content, Evans blue leakage and the expression of aquaporin-4 (AQP-4), matrix metalloproteinase-9 (MMP-9), Zonula Occludens-1 (ZO-1) and Occludin were measured. After treatment with anti-CKLF1 antibody, brain water content and Evans blue leakage in ipsilateral hemisphere were decreased in a dose-dependent manner at 24h after reperfusion, but not changed in contralateral hemisphere. Anti-CKLF1 antibody reduced the expression of AQP-4 and MMP-9, and upregulated the expression of ZO-1 and Occludin. These results suggest that CKLF1 is involved in BBB disruption after reperfusion. Inhibition of CKLF1 protects against cerebral ischemia by maintaining BBB integrity, possibly via inhibiting the expression of AQP-4 and MMP-9, and increasing the expression of tight junction protein.

The chemokine-like factor 1 induces asthmatic pathological change by activating nuclear factor-κB signaling pathway.

CKLF1, which exhibits chemotactic activities on a wide spectrum of leukocytes, is up-regulated during the progress of asthma. It plays a vital role in the pathogenesis of pulmonary disease. Here, we report that CKLF1 has the capability to activate the NF-κB signaling pathway leading to the pathological change in the lung. The HEK293-CCR4 cell line, which expressed CCR4 stably, was established and screened. Western blot analysis was performed to determine the expression of NF-κB in HEK293-CCR4 and A549 cells following the C27 (10µg/ml) added in each well at different times. These results showed that C27 (10µg/ml) time-dependently induced the accumulation of NF-κB in the nucleus of HEK293-CCR4 and A549 cells. In addition, CKLF1 plasmid (100µg) injection and electroporation led to the asthmatic change in the lung in mice as shown by HE and PAS staining. Furthermore, it was confirmed that CKLF1 significantly up-regulated the p-IκB expression, decreased the IκB expression, and suppressed the NF-κB expression in the cytoplasm of pulmonary tissue in vivo study. Intriguingly, an enhanced nuclear accumulation of NF-κB was observed in the lung of pCDI-CKLF1 electroporated mice, compared to that in the sham group. Therefore, the NF-κB signaling pathway was involved in the asthmatic change induced by CKLF1, among which CCR4 might play a crucial role.