Pulmonary fibrosis is characterized by fibroblast proliferation and extracellular matrix remodelling, leading to respiratory insufficiency. The mechanisms underlying this progressive and devastating disease remain unclear. Conditions that can impair the function of the endoplasmic reticulum (ER) cause accumulation of unfolded or misfolded proteins, resulting in ER stress and activation of the unfolded protein response (UPR). ER stress has been implicated in many conditions including cancer, diabetes, obesity, and inflammation. It is also involved in lung fibrosis, through myofibroblastic differentiation of fibroblasts; however, the precise role of ER stress in lung fibrosis is unknown. The current study aimed to investigate the underlying mechanisms of ER stress inhibitors in the treatment of bleomycin-induced lung fibrosis. We demonstrated that bleomycin can activate ER stress associated proteins, including GRP78, CHOP, and ATF-4, both in vitro and in vivo. PI3K/AKT acts upstream of ER stress to affect lung fibroblast proliferation, resulting in bleomycin-induced pulmonary fibrosis. Treatment with ER stress inhibitors or a PI3K inhibitor caused a reduction in fibroblast proliferation and improved pulmonary function. The relationship between PI3K/AKT/mTOR and ER stress in pulmonary fibrosis, and the application of PI3K inhibitors and ER stress inhibitors in the treatment of pulmonary fibrosis require further investigation.

Tumors are influenced by a microenvironment rich in inflammatory cytokines, growth factors and chemokines, which may promote tumor growth. Interleukin‐6 (IL‐6) is a multifunctional cytokine and known as a regulator of immune and inflammation responses. IL‐6 has also been reported to be associated with tumor progression and chemoresistance in different types of cancers. In our study, we demonstrated that IL‐6 enriches the properties of lung cancer stem‐like cells in A549 lung cancer cells cultured in spheroid medium. IL‐6 also promotes sphere formation and stem‐like properties of A549 cells by enhancing cell proliferation. Methylation‐specific polymerase chain reaction (PCR) was performed and revealed that IL‐6 increased methylation of p53 and p21 in A549 cancer cells. Western blot analysis and quantitative real‐time PCR demonstrated that IL‐6 increased the expression of DNA methyltransferase 1 (DNMT1) in A549 cells cultured in spheroid medium, but not the expression of DNMT3a or DNMT3b. Knockdown of DNMT1 eliminated IL‐6‐mediated hypermethylation of cell cycle regulators and enrichment of lung cancer stem‐like properties. In conclusion, our study, for the first time, shows that the IL‐6/JAK2/STAT3 pathway upregulates DNMT1 and enhances cancer initiation and lung cancer stem cell (CSC) proliferation by downregulation of p53 and p21 resulting from DNA hypermethylation. Upon blockage of the IL‐6/JAK2/STAT3 pathway and inhibition of DNMT1, the proliferation of lung CSCs was reduced and their formation of spheres and ability to initiate tumor growth were decreased. These data suggest that targeting of the IL‐6/JAK2/STAT3 signaling pathway and DNMT1 may become important strategies for treating lung cancer.

BACKGROUND: In the current study, the authors sought to identify the molecular mechanisms underlying the chemoresistance of lung cancer stem or initiation cells (cancer stem cells).METHODS: A549 lung cancer cells before and after selective enrichment of a subpopulation of cancer stem cells were treated with superoxide and traditional chemotherapeutics to determine their sensitivity or resistance to these cytotoxic agents. Apoptotic activity was measured using a variety of fluorescence‐based and biochemical techniques. Specific pathways involved in the chemoresistance of cancer stem cell‐enriched lung cancer cells were analyzed with Western blotting and pharmacologic targeting therapy in a xenograft model.RESULTS: Lung cancer stem cells exhibited significantly decreased apoptotic response to treatment with superoxide, cisplatin, gemcitabine, or a combination of cisplatin and gemcitabine compared with control A549 cells. Apoptotic resistance was mediated through the inactivation of caspase‐9 and caspase‐3. Increased activation of p38MAPK, MAPKAPK2, and Hsp27 was observed in lung cancer stem cells compared with control A549 cells both before and after exposure to superoxide and chemotoxic agents. In a mouse model of lung cancer, chemotherapy‐induced cells increased in the antiapoptosis pathway, and quercetin, an inhibitor of Hsp27, combined with traditional chemotherapy was effective in blocking the pathway and in the treatment of lung tumors in vivo.CONCLUSIONS: The authors' data demonstrate that lung cancer stem cells have elevated levels of activated Hsp27 upon treatment with superoxide and traditional chemotherapy. When combined with chemotoxic agents, blockage of Hsp27 decreased the survival of lung cancer stem cells, which otherwise were resistant to traditional chemotherapy. Cancer 2011. © 2010 American Cancer Society.

BACKGROUND: Signal transducer and activator of transcription 3 (STAT3) signaling reportedly promotes tumor malignancy and recurrence in nonsmall cell lung cancer (NSCLC). It was demonstrated previously that the STAT3 pathway maintains the tumorigenicity and therapeutic resistance of malignant tumors as well as cancer stem cells (CSCs). The objective of the current study was to investigate the effect of the strong STAT3 inhibitor, cucurbitacin I, in prominin-1 (CD133)-positive lung cancer cells. METHODS: CD133-positive and CD133-negative NSCLC-derived cells were isolated from 7 patients with NSCLC. CD133-positive NSCLC cells that were treated with or without cucurbitacin I were evaluated for their expression of phosphorylated STAT3 (p-STAT3), tumorigenicity, stemness properties, and resistance to chemotherapeutic drugs and ionizing radiation. RESULTS: Compared with parental or CD133-negative NSCLC cells, CD133-positive NSCLC cells had greater tumorigenicity, greater radioresistance, and higher expression of octamer-binding transcription factor 4 (Oct-4), Nanog homeobox, and sex-determining region Y, box 2 (Sox2) at high p-STAT3 levels. Cucurbitacin I treatment at 100 nM effectively abrogated STAT3 activation, tumorigenic capacity, sphere formation ability, radioresistance, and chemoresistance in CD133-positive NSCLC cells. Microarray data suggested that cucurbitacin I inhibited the stemness gene signature of CD133-positive NSCLC cells and facilitated the differentiation of CD133-positive NSCLC cells into CD133-negative NSCLC cells. It is noteworthy that 150 nM cucurbitacin I effectively blocked STAT3 signaling and downstream survival targets, such as B-cell chronic lymphocytic leukemia/lymphoma 2 (Bcl-2) and Bcl-2-like 1 (Bcl-xL) expression and induced apoptosis in CD133-positive NSCLC cells. Finally, xenotransplantation experiments revealed that cucurbitacin I plus radiotherapy or chemotherapeutic drugs significantly suppressed tumorigenesis and improved survival in NSCLC-CD133-positive-transplanted, immunocompromised mice. CONCLUSIONS: Targeting STAT3 signaling in CD133-positive NSCLC cells with cucurbitacin I suppressed CSC-like properties and enhanced chemoradiotherapy response. The potential of cucurbitacin I should be verified further in future anti-CSC therapy. Cancer 2011. © 2011 American Cancer Society.

Collagen XVII/laminin-5 activates epithelial-to-mesenchymal transition and is associated with poor prognosis in lung cancer