Background:Radio- and chemotherapy (RT/CT) resistance hampers success in combating small and non-small cell lung cancers (SCLC/NSCLC). The underlying molecular mechanisms of RT/CT resistance of LCs are multifactorial and have been understood in part hitherto. miRNAs, key regulators of mRNAs, are well-recognised oncomirs; however, their role in regulating RT response remains poorly understood.Methods:Six human NSCLC and five SCLC cell lines with different SF2 values were investigated. Using microarray we examined whether expression of miRNAs is linked to the RT resistance of NSCLCs or SCLCs. Obtained data were validated by quantitative real-time PCR. Apoptosis and senescence were analysed using siRNA transfection, western blot and flow cytometry.Results:miRNA-21, miRNA-1827, miRNA-214, miRNA-339-5p, miRNA-625, miRNA-768-3p, miRNA-523-3p, miRNA-1227, miRNA-324-5p, miRNA-423-3p, miRNA-1301 and miRNA-1249 are differentially expressed in LC cells. miRNA-214 is upregulated in RT-resistant NSCLC cells relative to radiosensitive counterparts. Considering miRNA-214 as a putative regulator of RT resistance, we demonstrate that knockdown of miRNA-214 in radioresistant NSCLCs sensitised them to RT by stimulation of senescence. Consistently, overexpression of miRNA-214 in radiosensitive NSCLCs protected against RT-induced apoptosis. Protection was mediated by p38MAPK, as downregulation of this kinase could reverse the miRNA-214 overexpression-induced resistance of NSCLC cells.Conclusion:miRNA profiling of LC revealed putative RT resistance signalling circuits, which might help in sensitisation of LC to RT.

Recent studies underline the important role of microRNAs (miRNA) in the development of lung cancer. The main regulators of miRNA biogenesis are the ribonucleases Drosha, Dicer and Ago2. Here the role of core proteins of miRNA biogenesis machinery in the response of human non-small and small cell lung carcinoma cell lines to treatment with ionizing radiation was assessed. We found that Drosha and Dicer were expressed at higher levels in radioresistant but not in sensitive cell lines. However, down-regulation of either Dicer or Drosha had no effect on the sensitivity of cells to irradiation. Elimination of components of the RNA-induced silencing complex Ago2 and Tudor staphylococcal nuclease also did not sensitize cells to the same treatment. Thus, modulation of miRNA biogenesis machinery is not sufficient to increase the radiosensitivity of lung tumors and other strategies are required to combat lung cancer.

Lung cancer is the leading cause of cancer-related deaths worldwide. Non-small cell lung cancer (NSCLC), the major lung cancer subtype, is characterized by high resistance to chemotherapy. Here we demonstrate that Tudor staphylococcal nuclease (SND1 or TSN) is overexpressed in NSCLC cell lines and tissues, and is important for maintaining NSCLC chemoresistance. Downregulation of TSN by RNAi in NSCLC cells led to strong potentiation of cell death in response to cisplatin. Silencing of TSN was accompanied by a significant decrease in S100A11 expression at both mRNA and protein level. Downregulation of S100A11 by RNAi resulted in enhanced sensitivity of NSCLC cells to cisplatin, oxaliplatin and 5-fluouracil. AACOCF3, a phospholipase A2 (PLA2) inhibitor, strongly abrogated chemosensitization upon silencing of S100A11 suggesting that PLA2 inhibition by S100A11 governs the chemoresistance of NSCLC. Moreover, silencing of S100A11 stimulated mitochondrial superoxide production, which was decreased by AACOCF3, as well as N-acetyl-L-cysteine, which also mimicked the effect of PLA2 inhibitor on NSCLC chemosensitization upon S100A11 silencing. Thus, we present the novel TSN-S100A11-PLA2 axis regulating superoxide-dependent apoptosis, triggered by platinum-based chemotherapeutic agents in NSCLC that may be targeted by innovative cancer therapies.

Due to a technical error during image processing, an incorrect high resolution version of Figure 7 was included with the manuscript.

Lung cancer (LC) is among the most common tumors liable for worldwide highest mortality rate. It has a poor prognosis and symptoms related to disease occur at an advanced stage where therapy response becomes less effective. Resistance to radio- and chemotherapy of all tumors in general and LC, in particular, is a complex phenomenon. Evasion of cell death is one of the key hallmarks of both tumorigenesis and resistance to treatment. Differential expression of microRNAs (miRNAs or miRs), a class of small non-coding RNAs, 19-25 nucleotides in length, and proteins involved in miRNAs maturation (Drosha, Exportin-5, Dicer1, PACT, Tudor-SN, Argonaute-2, and FXR1) have been linked to carcinogenesis and therapy resistance. Nevertheless, comprehensive information is needed to better understand their function in tumor formation and resistance/sensitization to therapy. Therefore, the aim of this study was to investigate the role of miRNA machinery in chemoresistance of a selected panel of non-small cell lung carcinoma (NSCLC) cell lines (U1810, H661 and A549) resistant to treatment. It was revealed that knockdown of Drosha, Dicer-1 and Ago-2 was not sufficient to sensitize them to subsequent treatment with either cisplatin, 5-FU, etoposide or camptothecin (CPT), while silencing of Staphylococcal nuclease domain containing 1(SND1/p100/TSN), a key component of RISC complex, led to increased sensitivity of NSCLC cells to the DNA-damaging agents. Besides its function as a component of the multiprotein complex involved in miRNA functioning, TSN is known to act as a transcriptional activator and oncogene in many cancers. Additionally, it is cleaved during apoptosis, losing its pro-carcinogenic function. Our results show that these NSCLC cells with TSN-knocked down exhibited much stronger response to treatment with CPT and cisplatin compared to wild-type cells, as monitored by enhanced cleavage of PARP, increase in percentage of subG1 cells and potentiation of caspase-3-like activity. Overall, obtained data suggest that this nuclease can play an important role in the resistance of NSCLC cells to chemotherapy and can be used as a potential target to increase sensitivity of lung tumors to this type of treatment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4882. doi:1538-7445.AM2012-4882