Anti-Neuronal Nuclei monoclonal antibody, clone 2C8

Activation of the telomere maintenance mechanism is a key hallmark of cancer. Human telomerase reverse transcriptase (hTERT) is the catalytic subunit of telomerase, which is highly expressed in more than 80% of tumors, including hepatocellular carcinoma (HCC). However, the exact mechanisms by which hTERT is up-regulated in HCCs and promotes tumor growth and progression is not fully understood. The aim of this study was to discover the novel molecular targets that modulate hTERT signaling and HCC growth. In this study, we pulled down and identified RBFOX3 (RNA binding protein fox-1 homolog 3) as a novel hTERT promoter-binding protein in HCC cells using biotin-streptavidin-agarose pull-down and proteomics approach, and validated it as a regulatory factor for hTERT signaling and tumor growth in HCCs. Knockdown of RBFOX3 suppressed the promoter activity and expression of hTERT and consequently inhibited the growth and progression of HCC cells in vitro and in vivo. The suppression of HCC growth mediated by RBFOX3 knockdown could be rescued by hTERT overexpression. Conversely, exogenous overexpression of RBFOX3 activated the promoter activity and expression of hTERT and promoted the growth and progression of HCC cells. Moreover, we found that RBFOX3 interacted with AP-2 beta to regulate the expression of hTERT. Furthermore, we demonstrated that RBFOX3 expression was higher in the tumor tissues of HCC patients compared to the corresponding paracancer tissues, and was positively correlated with hTERT expression. Kaplan-Meier analysis showed that the HCC patients with high levels of RBFOX3 and hTERT had poor prognosis. Collectively, our data indicate that RBFOX3 promotes HCC growth and progression and predicts a poor prognosis by activating the hTERT signaling, and suggest that the RBFOX3/hTERT pathway may be a potential therapeutic target for HCC patients.

Alternative premRNA splicing is a major mechanism to generate diversity of gene products. However, the biological roles of alternative splicing during development remain elusive. Here, we focus on a neuron-specific RNA-binding protein, Rbfox3, recently identified as the antigen of the widely used anti-NeuN antibody. siRNA-mediated loss-of-function studies using the developing chicken spinal cord revealed that Rbfox3 is required to promote neuronal differentiation of postmitotic neurons. Numb premRNA encoding a signaling adaptor protein was found to be a target of Rbfox3 action, and Rbfox3 repressed the inclusion of an alternative exon via binding to the conserved UGCAUG element in the upstream intron. Depleting a specific Numb splice isoform reproduced similar neuronal differentiation defects. Forced expression of the relevant Numb splice isoform was sufficient to rescue, in an isoform-specific manner, postmitotic neurons from defects in differentiation caused by Rbfox3 depletion. Thus, Rbfox3-dependent Numb alternative splicing plays an important role in the progression of neuronal differentiation during vertebrate development.