GDF15 contributes to radioresistance and cancer stemness of head and neck cancer by regulating cellular reactive oxygen species via a SMAD-associated signaling pathway.

Radiotherapy is an integral part for the treatment of head and neck cancer (HNC), while radioresistance is a major cause leads to treatment failure. GDF15, a member of the TGF-ß superfamily, is hypothesized to participate in various types of homeostasis. However, the potential role of this molecule in regulation of radiosensitivity remains unclear. In this study, we demonstrated that GDF15 contributed to radioresistance of HNC, as determined by both gain- and lost-of-functional experiments. These results were achieved by the induction of mitochondrial membrane potential and suppression of intracellular reactive oxygen species (ROS). We further showed that GDF15 facilitated the conversion of cancer stemness, as assessed by the promotion of CD44+ and ALDH1+ cell populations and spheroid cell formation. At molecular level, GDF15 conferred to these cellular functions was through phosphorylated SMAD1 proteins to elite downstream signaling molecules. These cellular results were further confirmed in a tumor xenograft mouse study. Taken together, our results demonstrated that GDF15 contributed to radioresistance and cancer stemness by regulating cellular ROS levels via a SMAD-associated signaling pathway. GDF15 may serve as a prediction marker of radioresistance and a therapeutic target for the development of radio-sensitizing agents for the treatment of refractory HNC.

Proteomics Analysis Reveals Involvement of Krt17 in Areca Nut-Induced Oral Carcinogenesis.

The areca nut is a known carcinogen that causes oral cancer in individuals in Southeast Asia, but the molecular mechanism that leads to this malignancy is still unclear. To mimic the habit of areca nut chewing, our laboratory has established four oral cancer cell sublines (SAS, OECM1, K2, C9), which have been chronically exposed to areca nut extract (ANE). To elucidate the molecular basis of areca nut-induced oral carcinogenesis, the differential proteomes between oral cancer cells and the ANE-treated sublines were determined using isobaric mass tag (iTRAQ) labeling and multidimensional liquid chromatography-mass spectrometry (LC-MS/MS). Over 1000 proteins were identified in four sublines, and 196 proteins were found to be differentially expressed in at least two ANE-treated sublines. A bioinformatic analysis revealed that these proteins participate in several pathways, and one of the most prominent pathways was the regulation of epithelial to mesenchymal transition (EMT). In all, 24 proteins including Krt17 were confirmed to be differentially expressed in the ANE-treated sublines. To reveal additional information on the mechanism of ANE-induced carcinogenesis, Krt17 was further investigated. Krt17 knockdown significantly suppressed ANE-induced cell migration and invasion and modulated the EMT process. Furthermore, in a murine model of carcinogen-induced (arecoline cocktail, an active compound of ANE) oral cancer, Krt17 was significantly up-regulated in all hyperplastic tissues and in carcinoma tissues (p < 0.001). In conclusion, we have identified a proteome of oral cancer cells that is associated with chronic areca nut exposure. Krt17 was demonstrated to contribute to areca nut-induced oral malignancy. The results of this study contribute to risk assessment, disease prevention and other clinical applications associated with areca nut-induced oral cancer.

Areca nut contributes to oral malignancy through facilitating the conversion of cancer stem cells.

Oral cancer is one of the most frequent malignant diseases worldwide, and areca nut is a primary carcinogen causing this cancer in Southeast Asia. Previous studies to examine the effects of this carcinogen often used short-term and high-dose treatment of area nut extract as a research model, which do not recapitulate the conditions of patients with long-term and habitual use of this substance. To approach authentic mechanism of areca nut-induced oral carcinogenesis that occurs in human, we established four isogenic sublines of oral cells which were chronic exposed to areca nut extract. Without eliciting cytotoxicity or senescence, these four sublines cells exhibited significant increase in invasive ability, along with epithelial-mesenchymal transition. These cells also showed resistance to chemotherapeutic drug and irradiation, accompanying with the augmentation of ABCG2 protein efflux and increased ROS clearance. Moreover, these sublines possessed the characteristics of cancer stemness, as demonstrated by enriched CD24-/CD44+ and CD133+ sub-populations, enhanced spheroid cell formation, and induced expressions of pluripotent stemness regulators, including Gp96, Grp78, Slug, Sox9, Snail, and Foxc2. These stemness regulators were further shown up-regulations in oral cancer patients with areca nut-chewing habit, and were statistically correlated with CD44 expression, a stemness marker. In conclusion, our findings suggested that areca nut contributes to oral malignancy through facilitating the conversion of cancer stem cells. This study may further contribute to clinical applications in disease prevention, risk assessment or molecular therapeutics on areca nut- associated diseases.

OncomiR-196 promotes an invasive phenotype in oral cancer through the NME4-JNK-TIMP1-MMP signaling pathway.

BACKGROUND: MicroRNA-196 (miR-196), which is highly up-regulated in oral cancer cells, has been reported to be aberrantly expressed in several cancers; however, the significance of miR-196 in oral cancer has not yet been addressed. METHODS: Cellular functions in response to miR-196 modulation were examined, including cell growth, migration, invasion and radio/chemosensitivity. Algorithm-based studies were used to identify the regulatory target of miR-196. The miR-196 target gene and downstream molecular mechanisms were confirmed by RT-qPCR, western blot, luciferase reporter and confocal microscopy analyses. miR-196 expression was determined in paired cancer and adjacent normal tissues from oral cancer patients. RESULTS: Both miR-196a and miR-196b were highly over-expressed in the cancer tissue and correlated with lymph node metastasis (P = 0.001 and P = 0.006, respectively). Functionally, miR-196 actively promoted cell migration and invasion without affecting cell growth. Mechanistically, miR-196 performed it's their function by inhibiting NME4 expression and further activating p-JNK, suppressing TIMP1, and augmenting MMP1/9. CONCLUSION: miR-196 contributes to oral cancer by promoting cell migration and invasion. Clinically, miR-196a/b was significantly over-expressed in the cancer tissues and correlated with lymph node metastasis. Thus, our findings provide new knowledge of the underlying mechanism of cancer metastasis. miR-196 may serve as a promising marker for better oral cancer management.