Abnormal Expression Of PLZF And DACH1 Affects The Molecular Mechanism Of The Development And Progression Of Non - Small Cell Lung Cancer

Lung cancer is the leading cause of mortality in men and women worldwide, with an overall 5-year survival rate of less than 15%. Although tobacco smoking has been established as the predominant risk factor for lung cancer, genetic variation is also important to tumorigenesis of bronchial epithelial cells. The variation mainly involves the activation of oncogenes and the reduction of tumor suppressor genes, both of which are closely related to carcinogenesis and its development.We selected PLZF and DACH1 to study their putative roles in non-small cell lung cancer (NSCLC), since few references come out about their functions in lung cancer.Promyelocytic leukaemia zinc finger (PLZF), also known as zinc finger and BTB domain containing 16 (ZBTB16), was initially identified by virtue of its fusion with the gene RARa as a result of a variant t(11;17) chromosomal translocation that occurs in a small subset of acute promyelocytic leukaemia (APL) patient. In this genetic aberration, PLZF is fused to retinoic acid receptor a (RARa) producing PLZF-RARa and RARa-PLZF fusion products. PLZF, as a transcription repressor, plays an important role in cell growth and differentiation of hematopoietic cells, limb and axial skeletal patterning, development of neural system. Although PLZF was classically considered as a protein mainly involved in non-solid tumors since its discovery, some researches start to come out about its role on solid tumors. PLZF has different functions in different tumors.In this study, PLZF was found down-regulated by 62.8%(95%CI= 50.2%-75.3%, P<0.0001) in 87.1% of 155 Non-Small Cell Lung Cancer (NSCLC) tissues compared to the corresponding normal lung tissues and it was associated with patient gender (P=0.029). The result of immunohistochemistry also indicated that PLZF protein expression was down-regulated in cancer tissues. TUNEL assay showed that apoptosis was reduced in cancer, suggesting that PLZF was correlated with apoptosis. Moreover, the promoter region of PLZF was found highly methylated in lung cancer cell lines by Bisulfite sequencing PCR (BSP). Demethylation analysis validated that hypermethylation in the promoter region resulted in reduced expression level of PLZF. In addition, PLZF promoter methylation was confirmed in 36.8% of the NSCLC samples tested by Methylation specific PCR (MSP). Over-expression of PLZF in the A549 cells inhibited cell growth, reduced cells in S phase and induced cell apoptosis. These results suggest that low expression of PLZF may contribute to the tumorigenesis of NSCLC.The dachshund (dac) gene was initially described as a mutant phenotype in flies featuring extremely short legs relative to their body length. The dac gene plays a key role in metazoan development, regulating ocular, limb, brain, and gonadal development. DACH1 is one of the vertebrate homologues of dac gene. Recent studies demonstrated altered DACH1 expression in hormone responsive cancers and that DACH1 regulates hormone-dependent signaling.In this study, DACH1 was found downregulated by 50.1% (95%CI= 34.3%-65.5%, P<0.0001) in 74.8% of lung cancer samples. The immunohistochemistry results suggested that DACH1 protein expression was associated with tumor classification (P= 0.032). BSP asssay indicated that the CpG island located in the first intron of DACH1 was not methylated. Thus, the low expression of DACH1 was not due to the methylation of CpG island. DACH1 was up-regulated in A549 cells with low concentration of TGF-β. DACH1 was down-regulated when TGF-β concentration rose up. These results suggest that altered DACH1 expression was related to the tumorigenesis and TGF-β signaling may regulate its expression.