Regulación de la expresión de KLF-4 (Krüppel-like factor 4) a través del factor de transcripción Ying- Yang 1 en linfoma No-Hodgkin

Abstract

Cancer is the second cause of death in México and the rest of the world. The Non-Hodgkin Lymphoma (NHL) is a group of different type of cancers that emerged as a clonal proliferation of B and T cells at different stages of differentiation. More than 90% of the NHL is B cells. The pathogenesis of NHL is not well understood, it has been associated with infectious organisms and some genetic aberrations. It is important to know the transcription factors implicated in the development of NHL because of their implication in the therapy of diverse hematological malignancies, such as leukemia and lymphoma. Krüppel like factor 4 (KLF-4) is a transcription factor expressed in a variety of tissues in humans. It has been implicated in several physiologic processes including development, differentiation, and tissue homeostasis. KLF-4 is bi-functional and can either activate or repress transcription depending on the target gene. For instance, KLF-4 acts as a tumor suppressor gene (colon, gastric, esophageal, bladder) or as an oncogene (laryngeal carcinoma, squamous cell carcinoma, ductal carcinoma o the breast). However, the role in hematological malignances and the mechanisms that regulated its expression is still poorly understood. Besides, the transcription factor YY-1 has also a bi-functional role depending of the tissue, and it has been associated whit tumorogenesis. YY-1 is up-regulated in lymphoma-We found by bioinformatics analysis that the promoter of KLF-4 has five possible binding sites for YY-1. So, it is highly possible that KLF-4 is transcriptionally regulated by YY-1. The aim of this study was to search the role of YY-1 in the regulation of the expression of KLF-4, and the possible implication of this factor on the malignancy of B cell NHL. Both B-NHL cell lines and patient-derived tumor tissues (TMA) were analyzed. A significant overexpression of KLF-4 and YY-1 in B-NHL particularly in Burkitt´s cell lines (Ramos and Raji) compared whit prostatic cancer cell line (PC3) was observed. The expression of these factors had a positive correlation. By in silico analysis of the KLF-4 promoter it was identified the presence of five putative binding sites for YY-1. We confirmed that the position-298is a binding site for YY-1 in Ramos cell line (ChIP). In order to corroborate transcriptional regulation of KLF-4 by YY-1, we inhibited the expression of YY-1 by the transfection whit YY-1 siRNA. This strategy demonstrated that the expression of KLF-4 was also down regulated. Furthermore the expression of KLF-4 and YY-1 was analyzed on TMA. Notably, Burkitt´s lymphoma were KLF-4 and YY-1 positive compared whit lymphoblastic lymphoma and other indolent subtypes, and also it was found correlation between the expression of these factors in Burkitt´s lymphoma, suggesting that YY-1 regulates KLF-4 in vivo. The present findings confirmed that KLF-4 is upregulated in lymphoma and it is transcriptionally regulated by YY-1.We showed that KLF-4 may have implication in lymphomagenesis and it correlates whit poor survival, which suggest that KLF-4 may be a prognostic factor.