Suppression of CUL4B Induces G1 Cell Cycle Arrest through the Modulation of AKT Signaling Pathway

Abstract

IntroductionT-cell lymphomas (TCL) are a heterogeneous group and one of the more aggressive of non-Hodgkin lymphomas. Previous studies have illustrated the poor prognosis in major propotion of patients due to refractory and recurrent TCL. CUL4B, a member of the CUL4B-RING E3 ubiquitin ligase complex, has been demonstrated to be involved in tumorigenesis and correlated to poor survival, contributing to tumor progression via several mechanisms, including epigenetic silencing of tumor suppressors. Although CUL4B was recently identified as a novel oncogene in several solid malignancies, the potential functional role of CUL4B in TCL are poorly understood to data. Hence, the aim of this study was to determine the pro-tumor function and mechanism of CUL4B in TCL.MethodsThe paraffin-embedded lymph node samples were collected from 30 newly diagnosed cases of T-cell lymphoma and 20 normal lymph nodes with approval in our hospital. TCL samples and purified normal T cells (including CD4+, CD8+, HLA-DR+, and HLA-DR-cells) (Pier Paolo Piccaluga et al., 2007) were evaluated for CUL4B expression. Peripheral blood mononuclear cells (PBMCs) were isolated from healthy donors. Expression levels of CUL4B mRNA and protein in TCL cells was detected by RT-PCR and western blot assay. Lentiviral vectors were used to transfected TCL cells to stably silence CULB. To evaluate the effects of CULB on cell proliferation and cycle, cell counting kit-8 and Propidium iodide staining were assessed respectively.ResultsWe found that the expression levels of CUL4B were elevated in TCL samples compared with purified normal T cells via analyzing previously published gene expression data (Pier Paolo Piccaluga et al., 2007) (Fig. 1A). IHC assay indicated that CUL4B was higher expressed compared to normal lymph nodes (Fig. 1B). Moreover, RT-PCR and western blotting assays confirmed the elevated expression level of CUL4B in TCL cells compared with PBMCs in agreement with ICH assay (Fig. 1C-D). The function of cell viability maintenance of CUL4B as well as correlation with poor outcome has been reported previously in solid tumor. In consistent with previous studies in solid malignancies, knockdown CUL4B in TCL cells inhibited cell proliferation, induced G1/S phase arrest (Fig. 1E). Additionally, loss-of-function assay showed that the expression of phosphorylated AKT were reduced in TCL cells. Besides, p21 and p27 were observed in TCL cells (Fig. 1F).ConclusionOur investigations firstly identified the elevated expression levels and the oncogenic role of CUL4B in TCL tumorigenesis. Expression of CUL4B was upregulated in TCL. Targeting CUL4B with shRNA interference exerted therapeutic potential in abrogating cell survival, inducing cell cycle arrest through regulating the AKT signaling pathway. Taken together, targeting the expression of CUL4B may provide a novel approach to TCL therapy. DisclosuresNo relevant conflicts of interest to declare.