Chloride intracellular channel 4 (CLIC4) is a broadly expressed protein that has been implicated in multiple cellular processes, including cellular differentiation and apoptosis. As a soluble factor, CLIC4 translocates to the nucleus following exposure to a variety of stimuli, including TGF-β, TNF-α, and etoposide. Nuclear CLIC4 potentiates TGF-β signaling by preventing the dephosphorylation of phospho-SMAD2 and 3 and promotes growth arrest. Although its primary function is as a tumor suppressor, CLIC4 expression is progressively diminished during cancer progression and CLIC4 protein is excluded from the nucleus of many human epithelial neoplasms and squamous cell carcinoma (SCC) cell lines. To date, no gene deletions or mutations have been identified to account for this phenomenon; thus, identifying the mechanism of CLIC4 loss is our primary focus. To determine if epigenetic gene silencing is responsible, we evaluated the methylation status of the CLIC4 promoter in a progression panel (normal, papilloma, SCC) of epithelial cell lines by performing bisulfite sequencing. No differential promoter methylation was found between the cell lines, suggesting that the regulation may be post-transcriptional or post-translational. Because microRNAs (miRNAs) are known to regulate gene expression by mediating the degradation or translational repression of target mRNAs, we performed a bioinformatic analysis of the CLIC4 3’ UTR, which revealed a large number of putative targeting miRNAs. One such miRNA, miR-142-3p, has been predicted to target CLIC4 by multiple algorithms and has been shown to interact with the CLIC4 3’ UTR by high-throughput sequencing and crosslinking immunoprecipitation. We confirmed the functional activity of miR-142-3p against the CLIC4 3’ UTR by using a 3’ UTR luciferase reporter assay and a miR-142-3p mimic. miR-142-3p is high in the tumor tissue and plasma of patients with head and neck SCC and is correlated with worse prognosis, where CLIC4 expression is known to be low. Thus, miR-142-3p may be responsible for mediating CLIC4 loss in squamous lesions and warrants further investigation.
Citation Format: Brandi L. Carofino, Stuart H. Yuspa. miR-142-3p is a candidate mediator of chloride intracellular channel 4 (CLIC4) loss during squamous cancer progression. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1924.