The clinical success of immunotherapy that inhibits the negative immune regulatory pathway programmed cell death protein 1/PD-1 ligand (PD-1/PD-L1) has initiated a new era in the treatment of metastatic cancer. PD-L1 expression is upregulated in many solid tumors including lung cancer and functions predominantly in lactate-enriched tumor microenvironments. Here, we provided evidence for PD-L1 induction in response to lactate stimulation in lung cancer cells. Lactate-induced PD-L1 induction was mediated by its receptor GPR81. The silencing of GPR81 signaling in lung cancer cells resulted in a decrease in PD-L1 protein levels and functional inactivation of PD-L1 promoter activity. In addition, GPR81-mediated upregulation of PD-L1 in glucose-stimulated lung cancer cells that recapitulates the enhanced glycolysis in vivo was dependent on lactate dehydrogenase A (LDHA). We also demonstrated that activation of GPR81 decreases intracellular cAMP levels and inhibits protein kinase A (PKA) activity, leading to activation of the transcriptional coactivator TAZ. Interaction of TAZ with the transcription factor TEAD was essential for TAZ activation of PD-L1 and induction of its expression. Furthermore, we found that lactate-induced activation of PD-L1 in tumor cells led to reduced production of interferon-γ and induction of apoptosis of cocultured Jurkat T-cell leukemia cells. Our findings reveal an unexpected role of lactate in contributing to tumor cell protection from cytotoxic T-cell targeting and establishes a direct connection between tumor cell metabolic reprograming and tumor evasion from the immune response.

Worldwide, breast cancer is the most frequently diagnosed life-threatening cancer in women and is the leading cause of cancer-related mortality among women. It is extremely rare but highly lethal in men. The deubiquitinating enzyme USP39 plays important roles in mRNA processing, and our previous data showed that high levels of USP39 are selectively present in different types of human breast tumor cells. The potential of USP39 as a therapeutic target for breast cancer was investigated. The expression levels of USP39 protein in 23 breast cancer specimens were quantified using an immunohistochemical assay and were found to have high levels in human breast cancer tissues when compared to these levels in normal breast tissues. In the breast cancer cell line MCF-7, USP39 expression was knocked down by a lentiviral short hairpin RNA (shRNA) delivery system. The RNA interference (RNAi)-mediated downregulation of USP39 expression markedly reduced the proliferative and colony forming ability of MCF-7 cells. In addition, the inhibition of USP39 induced G0/G1-phase arrest and apoptosis of the cells. These results suggest that USP39 may act as an oncogenic factor in breast cancer and could be a potential molecular target for breast cancer gene therapy.

Metastasis is unequivocally the most lethal aspect of breast cancer and the most prominent feature associated with disease recurrence, the molecular mechanisms whereby epithelial-to-mesenchymal transition (EMT) mediates the initiation and resolution of breast cancer metastasis remains poorly understood. Transforming growth factor-β1 (TGF-β1) is a multifunctional cytokine that is intimately involved in regulating numerous physiological processes, including cellular differentiation, homeostasis and EMT. Recent findings have implicated high levels of TGF-β1 were associated with poor outcome, whereas inhibition of TGF-β signaling reduces metastasis in breast cancer, suggesting that the chemo-therapeutic targeting of TGF-β1 or TGF-β signaling may offer new inroads in ameliorating metastatic disease in breast cancer patients. In this study, we showed immunohistochemical evidence for EMT, which is associated with TGF-β1 expression, at the invasion front of breast cancer in vivo. The data also indicated that human breast cancer cell lines, MCF-7 and MDA-MB-435S, of epithelial cell characteristics were induced to undergo EMT by TGF-β1 and dependent on the Smad2 signaling pathway. Following TGF-β1 treatment, cells showed dramatic morphological changes assessed by phase contrast microscopy, accompanied by decreased epithelial marker and increased mesenchymal markers. Importantly, cell invasion was also enhanced in the EMT process, while knockdown of the Smad2 gene by silencing siRNA partially inhibited these effects in MDA-MB435S (P<0.05). These data suggested that EMT of breast cancer induced by TGF-β1 is dependent on Smad2 signaling and promotes breast cancer cell metastasis.

Background Interleukin-6 (IL-6) has been demonstrated to be a critical factor for breast cancer malignancy. However, the molecular mechanisms by which IL-6 induce breast cancer cells epithelial–mesenchymal-transition (EMT) and stemness remain elusive. Methods Breast cancer cell lines T47D and MCF7 were exposed to IL-6, the expression of PIM1 was examined by quantitative real-time PCR (qRT-PCR) and western blot. Luciferase reporter assay was used to determine the transcriptional modulation of PIM1 by IL-6 and STAT3 inhibitor. Transwell assay was used to detect the invading ability of breast cancer cells induced by IL-6 or PIM1. The expressions of EMT and stemness markers were determined by qRT-PCR. Results IL-6 promoted PIM1 expression in a dose- and time-dependent manner, and this induction could be abrogated by inhibiting STAT3 activation, subsequently suppressing the transcriptional level of PIM1. Moreover, we noticed that knocking down of PIM1 in cells which was exposed to IL-6 significantly impaired the invasion ability and the expression of EMT and stemness markers. On the contrary, overexpression of PIM1 promoted cell invasion and upregulated the expression of EMT and stemness markers. In addition, we demonstrated that c-myc, the cofactor of PIM1, involved in the pro-oncogenic roles of PIM1. Knocking down of c-myc attenuated the PIM1-induced cell EMT and stemness. Conclusion This study proposed the upregulation of PIM1 by IL-6 contributed to breast cancer cell aggressiveness and targeting PIM1 or c-myc could be novel approaches for breast cancer treatment.

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