Emerging evidence indicates that Orai1, a key calcium channel for store-operated Ca2+ entry, is associated with human cancer. However, the underlying mechanism by which Orai1 regulates cancer progression remains unknown. Here we report that intracellular level of Orai1 is increased in a stepwise manner during oral/oropharyngeal carcinogenesis and highly expressed in cancer stem-like cell (CSC)-enriched populations of human oral/oropharyngeal squamous cell carcinoma (OSCC). Ectopic Orai1 expression converted non-tumorigenic immortalized oral epithelial cells to malignant cells that showed CSC properties, e.g., self-renewal capacity, increased ALDH1HIGH cell population, increased key stemness transcription factors, and enhanced mobility. Conversely, inhibition of Orai1 suppressed tumorigenicity and CSC phenotype of OSCC, indicating that Orai1 could be an important element for tumorigenicity and stemness of OSCC. Mechanistically, Orai1 activates its major downstream effector molecule, NFATc3. Knockdown of NFATc3 in the Orai1-overexpressing oral epithelial cells abrogates the effect of Orai1 on CSC phenotype. Moreover, antagonist of NFAT signaling also decreases CSC phenotype, implying the functional importance of Orai1/NFAT axis in OSCC CSC regulation. Our study identifies Orai1 as a novel molecular determinant for OSCC progression by enhancing cancer stemness, suggesting that inhibition of Orai1 signaling may offer an effective therapeutic modality against OSCC.

Cancer stem cells (CSCs) are defined as a small subpopulation of cancer cells within a tumor and responsible for initiation and maintenance of tumor growth. Thus, understanding of molecular regulators of CSCs is of paramount importance for the development of effective cancer therapies. Here, we identified jumonji domain-containing protein 6 (JMJD6) as a novel molecular regulator of oral CSCs. JMJD6 is highly expressed in CSC-enriched populations of human oral squamous cell carcinoma (OSCC) cell lines. Moreover, immunohistochemical staining revealed significantly high level of JMJD6 in OSCC tissues compared to normal human oral epithelia, suggesting that expression of JMJD6 positively correlates with oral carcinogenesis. Subsequent functional analysis showed that knockdown of endogenous JMJD6 in OSCC strongly suppressed self-renewal capacity, a key characteristic of CSCs, and anchorage-independent growth. Conversely, ectopic expression of JMJD6 enhanced CSC characteristics including self-renewal, ALDH1 activity, migration/invasion and drug resistance. Expression of CSC-related genes was also markedly affected by modulating JMJD6 expression. Mechanistically, JMJD6 induces interleukin 4 (IL4) transcription by binding to its promoter region. IL4 rescues self-renewal capacity in JMJD6- knocked down OSCC cells, suggesting the importance of JMJD6-IL4 axis in oral CSCs. Our studies identify JMJD6 as a molecular determinant of CSC phenotype, suggesting that inhibition of JMJD6 may offer an effective therapeutic modality against oral cancer.

High-risk human papillomaviruses (e. g., HPV16, HPV18) are closely associated with the development of head and neck cancers including oral/oropharyngeal squamous cell carcinoma (OSCC). We previously demonstrated immortalization of normal human oral keratinocytes by introducing high-risk HPV whole genome, suggesting that HPV infection plays an important role in the early stage of oral carcinogenesis. Although HPV infection may occur in different stages of cancer development, roles of HPV in exacerbating malignant phenotypes in already-transformed cells in the context of cancer stemness are not clearly defined. In this study, we investigated the role of HPV16 in promoting the virulence of HPV-negative OSCC. Introducing HPV16 whole genome in HPV-negative OSCC increased malignant growth and self-renewal capacity, a key characteristic of cancer stem cells (CSCs). HPV16 also enhanced other CSC properties, including aldehyde dehydrogenase 1 (ALDH1) activity, migration/invasion, and CSC-related factor expression. Mechanistically, we found that HPV16 inhibited the expression of miR-181a and miR-181d (miR-181a/d) at the transcriptional level. Ectopic expression of miR-181a/d decreased anchorage independent growth and CSC phenotype of HPV16-transfected OSCC. Furthermore, silencing of miR-181a/d target genes, i. e., K-ras and ALDH1, abrogated the effects of HPV16 in HPV16-transfected OSCC, supporting the functional importance of HPV16/miR-181a/d axis in HPV-mediated oral carcinogenesis. Our study suggests that high-risk HPV infection further promotes malignancy in HPV-negative OSCC by enhancing cancer stemness via miR-181a/d regulation. Consequently, miR-181a/d may represent a novel therapeutic agent for the treatment of HPV-positive OSCC.