The Biological Function Of LITAF Gene In Carcinogenesis Of B-cell Lymphoma

LITAF (LPS-induced TNF a factor), as a transcription factor, which could bind to a sequence motif, CTCCC (-515to-511), within the TNF-α「promoter, activating transcription of TNF-a upon lipopolysaccharide (LPS) stimulation. It was initially identified as the P53-inducible gene7(Pig7). Recently, accumulating evidence have indicated that LITAF may be implicated as a tumour suppressor in different malignancies, such as prostate cancer, acute myloid leukaemia and breast cancer. In mature B-cell lymphoma cells, LITAF is inactivated by epigenetic mechanisms, but the biological function of LITAF in these cells remains unclear. As we all know, B cell non-Hodgkin’s lymphoma (B-NHL) are highly heterogeneous diseases with different biology and clinical outcome. So most people were focused on finding a biological target which is helpful in clinical diagnosis and therapy. This study aims to investigate the regulation role of LITAF in cell proliferation, apoptosis and differentiation.First, we detected the expression level of LITAF in six B-cell lymphoma cell lines with real time PCR and western blotting, respectively. Recombinant lentiviral LITAF-pLVX-IRES-ZsGreenl was infected into DLBCL lymphoma cell line OCI-ly6 and Burkitt’s lymphoma cell line Ramos. Recombinant lentiviral LITAF-pLKO.1-puro was infected into Burkitt’s lymphoma cell line Namalwa and DLBCL lymphoma cell line OCI-Ly3. Then apoptosis analysis showed that overexpressed LITAF could induce cell apoptosis which could be rescued by BCL-6. On the other hand, after treatment of hydrogen peroxide combined serum deprivation, the knockdown group inhibit apoptosis. Western blotting was performed to determine expression levels of apoptosis-related proteins. The results indicated that LITAF could increase the expression level of Bax, releasing the Cytochrome C, and activating PARP. Cell proliferation activity was evaluated by cell cycle and MTT assay. We found that LITAF could inhibit cell proliferation and slow down the cell cycle. And the NF-κB signaling was inhibited upon up-regulated LITAF. In addition, we investigated if LITAF could regulate BCL6and its target gene (like Blimp-1and C-myc), which played an important role in differentiation, survival and proliferation of B cell.Our experiment showed there were negative correlation between LITAF and BCL6in B-cell lymphoma. We found that LITAF could inhibit the activity of BCL6luciferase reporter. IF assay indicated that LITAF could entered into nucleus. Subsequently, the Co-Iimmunoprecipitation results showed that there were interaction between these two proteins in293T cell line. Furthermore, Blimp-1is a target of BCL6repression, and there is a feedback loop in which Blimp-1represses BCL6expression.Our research found that overexpressed LITAF could upregulate the expression of Blimp-1and decrease C-myc at mRNA level.On the contrary, konckdown of LITAF could downregulate Blimp-1and increase C-myc at mRNA level.In summery, LITAF gene probably act as an important role in cell apoptosis, proliferation and differentiation in B-cell lymphoma. In our study, LITAF could inhibit cell proliferation through repressing BCL6and NF-κ B signaling, and induce cell apoptosis by activating mitochondrial pathway. What’s more, LITAF may be involved in cell differentiation by regulating Blimp-1and C-myc. And important aspects of LITAF-dependent regulation remain to be discovered. The function in different subtypes of B-NHL need to be revealed through immunohistochemistry in clinical pathological samples. Altogether, LITAF may be a potential tumor suppressor gene in B-cell lymphoma, acting as a new biological target for clinical therapy.