Upregulation of KLF4 Expression in Pediatric B-NHL Lymphomas and Its Association with Low EFS and Poor Survival Following Treatment with Chemotherapy

Abstract 5184

Krüppel-like factor 4 (KLF4) is a transcription factor expressed in a variety of tissues in humans and has been implicated in several physiologic processes including development, differentiation, and tissue homeostasis. KLF4 is a bi-functional transcription factor that can either activate or repress transcription depending on the target gene. Human KLF4 is a protein of 470 amino acids with a 55 kDa. It contains three C-terminal C₂H₂-type zinc fingers that bind DNA. It is divided into three separate domains, namely, an N-terminal activation domain, a central repression domain and a C-terminal DNA-binding domain. For instance, KLF4 acts as a tumor suppressor gene in several cancers (colon, gastric, esophageal, bladder, and NSCLC) or as an oncogene (laryngeal carcinoma, squamous cell carcinoma, ductal carcinoma of the breast). However, the role of KLF4 in hematologic malignancies is still poorly understood. Reported studies in leukemia suggested that KLF4 may be a tumor suppressor. The goal of this study was to investigate the expression and the clinical significance of KLF4 in B-Non-Hodgkin's lymphomas (B-NHLs). Both B-NHL cell lines and patient-derived tumor tissues (TMA) were examined by western blot and immunohistochemistry, respectively. The expression of KLF4 was calculated based on the intensity and the percentage of the area stained, and scoring was corroborated by two pathologists. The complete absence of KLF4 expression was considered as KLF4 negative. Normal peripheral blood mononuclear cells expressed low levels of KLF4, in contrast, there was a significant overexpression of KLF4 in Ramos and Raji (Burkitt's lymphoma) and 2F7 (AIDS lymphoma) B-NHL cell lines. However, the DHL4 (DBLCL) cell line showed similar expression to normal cells. Among the 73 childhood lymphomas studied, 13/23 (57%) of lymphoblastic lymphoma, 7/20 (35%) of large B-cell lymphoma, 4/4 (100%) of anaplastic large cell lymphoma and 5/6 NHL not otherwise specified were KLF4 positive. Noteworthy, 18/18 (100%) Burkitt's lymphoma was KLF4 positive. In addition, the nuclear expression of KLF4 was significantly higher in Burkitt's lymphoma (n=18) compared to the remaining subtypes (lymphoblastic lymphoma, n=23, large B-cell lymphoma n=20 and others). All patients were treated with chemotherapy and the majority of the patients that were KLF4 positive had a stage 3–4 disease. Analysis of the EFS demonstrated that patients' tumors that were KLF4 negative had significantly higher EFS as compared to tumors that were KLF4 positive. Likewise, there was significant prolongation of survival in patients with tumors that were KLF4 negative. We suggest that the expression of KLF4 and poor response to chemotherapy may be attributed to its role in resistance via its regulation by the resistance factor Notch3¹ . In contrast, the absence of KLF4 and good response to chemotherapy may be due to shifting p53 activity from cellular repair to cell death² . The present findings demonstrate that KLF4 may be considered as an oncogene in Burkitt's lymphoma and subsets of other types of lymphoma. The findings also suggest that the expression of KLF4 may be a potential prognostic factor, though, this need to be validated in a large cohort of patients. We propose that KLF4 may be a therapeutic target in patients with B-NHL lymphomas.