Effect of depletion of HuR on gene expression in mouse head and neck squamous cell carcinoma (mHNSCC) cells

RNA-binding protein HuR (Hu Antigen R, alias ELAVl1) is a primary post-transcriptional gene regulatory protein. Its overexpression promotes the progression of multiple cancers, including head and neck squamous cell carcinoma (HNSCC). Although HuR promotes cancer progression, the crosstalk between HuR and immune cells during oral tumorigenesis remains elusive. Here, we investigated the effects of HuR on oral tumors and immune cell functions in vitro and in vivo using a transgenic HuR knockout (KO) mouse model. We observed that CRISPR/Cas9 mediated knockout of HuR in murine oral carcinoma cells failed to form colonies and tumors. The HuR KO cells exhibited reduced tumor volume with high infiltration of CD8+ and fewer CD4+ T cells, demonstrating that HuR may control the immune response during oral cancer progression. Next, oral epithelial tissue-specific HuR KO failed to form neoplastic growth compared with the control 4NQO-induced tumor mice. The HuR KO mice show decreased Tregs and increased IFNg compared to WT tumor-bearing mice. The transcriptome obtained from RNA-Seq showed that multiple cancer pathways were altered between WT and HuR KO oral cancer cells. The HuR KO group showed significant negative regulation of transcription factors and positive regulation of extracellular matrix and cell adhesion pathways, demonstrating its significance in HNSCC. Specifically, positive regulation of HuR target mRNAs that encode proteins responsible for cancer stem cells associated with cell adhesion was observed and confirmed through mRNA half-life analysis. Finally, HuR inhibitor pyrvinium pamoate reduces the tumor burden through activation of CD8+ and reduction in CD4+ in tumors, demonstrating that anti-tumor functions were associated with HuR KO. Together, the results of this study indicate that HuR-mediated oral carcinogenesis, dependent on immune dysfunction and cell adhesion pathway, suggests that inhibition of HuR may enhance the anti-tumor potential for oral cancer therapeutics.