Functional Human IL-22 Autocrine Loop In Lung Carcinoma: A Key Role In Mechanism Of Anti-apoptosis

IL-22 is one of IL-10-related cytokines. The functional IL-22 receptor complex consists two chains: IL-22R1 and IL-10R2, which ubiquitously expressed on a variety of organs and cell types including immune cells, lung, liver and colon. In response to IL-22, rapid STAT phosphorylation or (and) activation Akt were observed and contributed to the improving hepatocyte survival and proliferation. IL-22 expression had been found in alveolar macrophages and alveolar epithelial (AE) cells isolated from bronchoalveolar lavage fluid (BALF) and normal lung sections. Lower levels of IL-22 were detected in the BALF from patients with pulmonary sarcoidosis and acute respiratory distress syndrome (ARDS) than normal control groups. Although these observations suggest involvement of IL-22 in the regulation of pulmonary inflammation, the potential role of IL-22 in cell survival of lung cancer has not been explained so far.Lung cancer is the third most common malignant disease and about 75% of all diagnosed lung cancers are the non-small cell lung carcinoma (NSCLC), which is associated with very dismal prognoses. Chemotherapy in addition to surgical resection and radiotherapy remains a basic strategy for treatment of malignant tumor. Unfortunately, it has been showed that NSCLC only has a limited sensitivity to chemotherapeutic drugs. A major obstacle in the treatment of patients is the inherent resistance to chemotherapeutic agents. Inhibition of cell apoptosis pathway was reported as one important cellular mechanism responsible for the resistance of NSCLC cells to treatment.In order to explore the anti-apoptotic mechanisms by which NSCLC progresses and resists, we examined the expression of IL-22 in NSCLC and evaluated anti-apoptotic effect of IL-22 in human lung cancer. First, NSCLC specimens and normal lung samples were analyzed by immunohistochemistry. The expression of IL-22 in peripheral blood and pleural effusion was measured by ELISA. We found that IL-22 was highly expressed in primary tumor tissue, malignant pleural effusion and serum of human NSCLC. IL-22R1 mRNA was also detected in lung cancer tissues as well as lung cancer cell lines. Next, to further investigate the effects of IL-22 in NSCLC, we generated two NSCLC cell lines stably expressed IL-22, by transfecting with pcDNA3/IL-22 recombinant plasmids. Several methods including Annexin V/PI staining assay, Caspase activity test and DNA fragment analysis, were used to evaluate the apoptosis when IL-22 transfected cells and their parent cells were exposed to serum free medium or antitumor agents, respectively. Data showed that over expression of IL-22 protected lung cancer cell lines from serum starvation- or chemotherapeutic drugs-induced apoptosis via activation of STAT3 and its downstream anti-apoptotic proteins such as Bcl-2, Bcl-xL. Exposure to blocking antibody against IL-22R1 resulted in apoptosis of these lung cancer cells. Finally, interference sequences targeting at IL-22 mRNA were ligated into the shRNA expression vector pU6+27, and used to examine changes in NSCLC cell apoptosis and human lung cancer exnografts. Inhibition of IL-22 expression by RNAi caused a significant increase in apoptosis induced by chemotherapeutic-drug in comparaion with the control cells. Furthermore, in vivo xenograft study showed that administration of IL-22-RNAi plasmid significantly inhibited the tumor growth in BALB/c nude mice.Taken together, high expression level of IL-22 was detected in primary tumor tissue, malignant pleural effusion and serum in patients with NSCLC, and both IL-22R1 and IL-22 were highly expressed in primary lung cancer, which suggested that there might be an autocrine loop of IL-22 in NSCLC. Over expression of IL-22 by gene transfer protects lung cancer cells from apoptosis via activation of STAT3 and anti-apoptotic proteins. IL-22R1 Ab or IL-22-RNAi in vitro resulted in apoptosis of these lung cancer cells. Administration of IL-22-RNAi plasmid significantly inhibited growth of human lung cancer in BALB/c nude mice. Our data suggests that autocrine production of IL-22 promotes lung cancer cell survival and resistance to chemotherapy through the up-regulation of anti-apoptotic proteins. Although the role of autocrine production of IL-22 need to further study, but our in vitro and in vivo observation suggest that this cytokines may possibly be a novel target for diagnosis, treatment and prognosis of NSCLC.