Avaliação dos níveis de expressão de genes HOX e potenciais mecanismos de regulação da expressão gênica em carcinoma epidermoide de esôfago

Abstract

Esophageal cancer (EC) is the seventh most incident cancer and the sixth leading cause of cancer death worldwide. Esophageal squamous cell carcinoma (ESCC) represents more than 90% of cases of EC. However, the molecular mechanisms involved in the initiation, promotion, and ESCC progression are poorly understood, creating a dark scenario. In this landscape, studies aimed at improving both the early diagnosis and the prognosis of patients with ESCC are necessary. HOX genes family are members of transcription factors (TFs) characterized by consensus sequence that encodes the homeodomain called homeobox. HOX genes play a fundamental role in embryogenesis, organ development, and cell differentiation. Deregulation of HOX gene expression has been reported in some tumors; however, few studies in ESCC have evaluated these genes deregulation. Therefore, our objective is to evaluate the expression profile and the possible regulatory mechanisms for HOX genes expression. The microarray technique initially identified the HOX gene expression, and then the selected targets were validated using real-time PCR. For this purpose, 41 ESCC and non-malignant tissues matched from the adjacent mucosa and ten esophageal biopsies from healthy volunteers were selected and associated with clinical-pathological and epidemiological data. HOXA5 was down-regulated in the tumor compared to healthy and adjacent mucosa, whereas HOXA7, HOXC9, HOXC10, HOXC13, HOXD8, HOXD10 and HOXD13 were up-regulated in the tumor mucosa compared to healthy and adjacent samples to the tumor. After Cox regression analysis, we found that increased expression of HOXA7 and HOXC10 were associated with low survival, while high expression of HOXD10 was associated with better survival. Then, we analyzed possible mechanisms that could regulate gene expressions, such as DNA methylation and transcription factors. Using data from our methylome, we evaluated the methylation profile of these genes and, later, through in silico analysis, a correlation between expression and methylation was performed. Although a different methylation profile was observed in tumors concerning adjacent mucosa and/or healthy tissue, the correlations between methylation and HOX gene expression are controversial. In addition, through the TRRUST database, we researched the TFs that could be targets and regulators of the HOX genes. Then, we analyzed the correlation of these TFs with HOX genes. We found a correlation between HOXA7 and PCGF2, which could activate or suppress HOXA7 in ESCC. Together, these data suggest the role of HOX genes in esophageal carcinogenesis, but methylation and known TFs do not appear to be the main mechanisms of HOX gene regulation