Reprogramming Of Global Histone Methylation During The Variation Of Internal And External Environment Induced By Ionizing Radiation In Lung Cancer

Lung cancer is now the most common malignant that threatens human health worldwide.Radiotherapy is the mainstay of curative lung cancer treatments,but radio-resistance and tumor relapse after radiotherapy seriously restricts the therapeutic effect.A large number of evidence show that the mechanism of radio-resistance to lung cancer cells can be attributed to genetic alteration.However,the gene network is intricate,and the effective target molecules and regulatory channels are still not clearly understood.In addition,the tumor microenvironment is also a significant factor that affects the radiation-resistance.The pathological changes occur both inside and outside the tumor at the same time eventually lead to tumor malignancy and radiation resistance.Therefore,it is necessary to investigate the synergistic mechanism of the environment inside and outside the tumor,and epigenetic alteration is a new direction to elucidate the mechanism.Histone modification is one of the epigenetic modifications,which can mediate the reprograming of chromatin structure and regulation of gene transcription,but its mechanism of radio-resistance in lung cancer and the pathological change in extracellular environment of lung cancer remains to be further explored.In this study,we established radio-resistant model of non-small cell lung cancer(NSCLC)by fractionated irradiation of X-rays(induced).ChIP-Seq genomics analysis showed that the reprogramming of genomic H3K4 covalent modification exists in NSCLC with acquired radio-resistance,but the methylation status varies in different lung cancer cells.The genotype H3K4me3 was inhibited in A549 cells with radio-resistance,but no obvious change was observed in H1299 cells.The detection of H3K4me3-specific methyltransferase revealed that the binding of methyltransferase to chromatin in A549 cells decreased with the emergence of radio-resistance,that is,the decrease of histone methyltransferase mediated the decrease of H3K4me3.Significant changes were not detected in H1299 cells.Analysis of the target genes selected by ChIP-Seq showed that SMARCA5 and FANCI,which are important genes in DNA damage repair,were differentially regulated in two different lung cancer cells.However,treatment of with H3K4me3 inhibitor in A549 and H1299 cells also down-regulated the expression of these two genes.This result indicated that H3K4me3 promote radio-resistance of lung cancer cell by regulating the gene expression involved in DNA damage repair.Treatment of inhibitors can increase the radiosensitivity of lung cancer cells through reducing the level of H3K4me3.In the external environment of the tumor,the MEN1 gene inhibits the differentiation and activation of fibroblasts by inhibiting the expression of extracellular matrix,the expression of fibrosis factor and the chemotaxis of fibroblasts in fibroblasts.Moreover,MEN1 promotes epithelial-mesenchymal transition in epithelial cells.Little is known about how H3K4 reprogramming regulates the activation and differentiation of fibroblast.This study found that fractionated radiation down-regulated the combination of histone methyltransferase complex with chromatin,which resulted in the chromatin remodeling in NSCLC.Furthermore,this reprogramming regulates the key gene expression involved in DNA damage repair and results in the radio-resistance in lung cancer cell.In addition,MEN1 in the tumor external environment inhibits the differentiation from fibroblasts to myofibroblas ts and its activation,and promotes epithelial-mesenchymal transition.Menin encoded by MEN1 gene mediates H3K4me3 remodeling,which is also involved in the differentiation and activation of fibroblasts.This study investigated the epigenetic mechanism of radio-resistance of lung cancer and the function of MEN1 in the tumor external environment,which provided a new way to overcome the problem of raio-resistence.