Quercetin Induces Cell Cycle Arrest and Apoptosis in YD10B and YD38 Oral Squamous Cell Carcinoma Cells.

OBJECTIVE: Oral squamous cell carcinoma (OSCC) exhibits the highest lethality among head and neck cancers. Treatment for OSCC is limited due to diverse side effects. Quercetin is a natural flavonoid compound found in many kinds of plants and foods. Quercetin has been reported to be a modulator of proliferation and survival in various types of cancers due to its cytotoxic effects. We aimed to investigating chemopreventative roles of quercetin in YD10B and YD38 OSCC cells. METHODS: For our study, two different types of OSCC cells were used. YD10B cells are tongue SCC cells with the p53 mutation and YD38 cells are lower gingiva SCC cells without the p53 mutation, respectively. The anticancer effects of quercetin were examined by cell viability, cell cycle, annexin-PI staining, and western blot. RESULT: Our results showed that quercetin decreased cell viability and induced G1 cell cycle arrest in YD10B and YD38 OSCC cells. Moreover, quercetin remarkably decreased the expression of cell cycle upregulating proteins and increased the expression of a CDK inhibitor. Quercetin also significantly increased the number of annexin-V-positive cells in a dose-dependent manner in both types of OSCC cells. This apoptotic potential of quercetin triggered cleavage of PARP followed by activation of p38 MAPK signaling pathway. CONCLUSION: In conclusion, this study demonstrates that quercetin shows different anti-cancer responses in OSCC with and without p53 mutation, respectively. Despite different p53 status in OSCC cells, quercetin led to apoptotic signals in both cells. Quercetin repressed cell proliferation with G1 cell cycle arrest and apoptosis by activating the p38 signaling pathway in two OSCC cells with different p53 status. These findings might provide new strategy for OSCC therapy by quercetin.

A novel TGF-ß receptor II mutation (I227T/N236D) promotes aggressive phenotype of oral squamous cell carcinoma via enhanced EGFR signaling.

BACKGROUND: Transforming growth factor-ß (TGF-ß) signaling is a double-edged sword in cancer development and progression. TGF-ß signaling plays a tumor suppressive role during the early stages of tumor development but promotes tumor progression in later stages. We have previously identified various mutations of TGF-ß receptor II (TßRII) in human oral squamous cell carcinoma (OSCC) samples. In the present study we analyzed I227T/N236D mutation of TßRII, which was detected in the metastatic lymph node of an OSCC patient. METHODS: The effect of I227T/N236D TßRII mutation on transcriptional activities was measured using DR26 cells, which lack functional TßRII. HSC2 human OSCC cells stably expressing wild-type and I227T/N236D mutant TßRII were generated and used to examine the effect of I227T/N236D TßRII mutation on xenograft tumor growth, in vitro cell proliferation, apoptosis, migration, and invasion. RESULTS: The I227T/N236D mutation of TßRII upregulated TGF-ß signaling and promoted xenograft tumor growth when compared with the wild-type, without affecting the in vitro proliferative capacities. To delineate the differences in proliferative capacities in vivo and in vitro, the apoptotic and survival signals were analyzed following curcumin treatment. Concomitant with apoptotic induction, epidermal growth factor receptor (EGFR) activation was observed upon curcumin treatment, which was further activated in I227T/N236D mutant transfectant cells when compared with wild-type cells. Enhanced EGFR activation correlated with cell survival and apoptotic resistance. Enhanced migratory and invasive capabilities of I227T/N236D mutant cells also depended on EGFR signaling. CONCLUSIONS: These results suggest that enhanced EGFR signaling via upregulated TGF-ß signaling shifted the balance toward survival and promoted cell migration and invasion in I227T/N236D mutant cells, elucidating the role of I227T/N236D mutation of TßRII in OSCC progression.

Areca nut exposure increases secretion of tumor-promoting cytokines in gingival fibroblasts that trigger DNA damage in oral keratinocytes.

Molecular crosstalk between cancer cells and fibroblasts has been an emerging hot issue in understanding carcinogenesis. As oral submucous fibrosis (OSF) is an inflammatory fibrotic disease that can potentially transform into squamous cell carcinoma, OSF has been considered to be an appropriate model for studying the role of fibroblasts during early stage carcinogenesis. In this sense, this study aims at investigating whether areca nut (AN)-exposed fibroblasts cause DNA damage of epithelial cells. For this study, immortalized hNOF (hTERT-hNOF) was used. We found that the levels of GRO-α, IL-6 and IL-8 increased in AN-exposed fibroblasts. Cytokine secretion was reduced by antioxidants in AN-exposed fibroblasts. Increase in DNA double strand breaks (DSB) and 8-oxoG FITC-conjugate was observed in immortalized human oral keratinocytes (IHOK) after the treatment of cytokines or a conditioned medium derived from AN-exposed fibroblasts. Cytokine expression and DNA damage were also detected in OSF tissues. The DNA damage was reduced by neutralizing cytokines or antioxidant treatment. Generation of reactive oxygen species (ROS) and DNA damage response, triggered by cytokines, were abolished when NADPH oxidase (NOX) 1 and 4 were silenced in IHOK, indicating that cytokine-triggered DNA damage was caused by ROS generation through NOX1 and NOX4. Taken together, this study provided strong evidence that blocking ROS generation might be a rewarding approach for cancer prevention and intervention in OSF.

A distinct role for interleukin-6 as a major mediator of cellular adjustment to an altered culture condition.

Tissue microenvironment adjusts biological properties of different cells by modulating signaling pathways and cell to cell interactions. This study showed that epithelial-mesenchymal transition (EMT)/ mesenchymal-epithelial transition (MET) can be modulated by altering culture conditions. HPV E6/E7-transfected immortalized oral keratinocytes (IHOK) cultured in different media displayed reversible EMT/MET accompanied by changes in cell phenotype, proliferation, gene expression at transcriptional, and translational level, and migratory and invasive activities. Cholera toxin, a major supplement to culture medium, was responsible for inducing the morphological and biological changes of IHOK. Cholera toxin per se induced EMT by triggering the secretion of interleukin 6 (IL-6) from IHOK. We found IL-6 to be a central molecule that modulates the reversibility of EMT based not only on the mRNA level but also on the level of secretion. Taken together, our results demonstrate that IL-6, a cytokine whose transcription is activated by alterations in culture conditions, is a key molecule for regulating reversible EMT/MET. This study will contribute to understand one way of cellular adjustment for surviving in unfamiliar conditions.

RUNX3 confers sensitivity to pheophorbide a-photodynamic therapy in human oral squamous cell carcinoma cell lines.

Photodynamic therapy (PDT) with photosensitizer is one of the promising modalities for cancer treatment. For clinical use of PDT, screening process should be preceded to enhance sensitivity to PDT. Thus, we investigated a molecular biomarker to determine the sensitivity to pheophorbide a (Pa)-PDT in immortalized human oral keratinocytes (IHOK) and oral squamous cell carcinoma (OSCC) cell lines. Two IHOK and several OSCC cell lines were used. After Pa-PDT, cell viability was reduced by more than 50%, and reactive oxygen species were generated in IHOK and OSCC cell lines. Additionally, apoptosis occurred in PDT-treated cells. IHOK(S) and IHOK(P), the two IHOK cell lines derived from the same source, showed a difference in cytotoxicity after Pa-PDT. To explain this difference in cytotoxicity, we looked at the expression of Wnt signaling-related genes in these two cell lines, for the morphology of IHOK(S) which was spindle like and elongated and distinct from IHOK(P) and the parent cell. Among the relevant genes, runt-related transcription factor 3 (RUNX3), an apoptosis-related gene, was selected as a potential marker that confers sensitivity to PDT. We found that the cytotoxicity by Pa-PDT was proportional to RUNX3 expression in OSCC cell lines. Additionally, knockdown of RUNX3 expression reduced cytotoxicity by Pa-PDT, suggesting that RUNX3 might be a biomarker to determine sensitivity to Pa-PDT. This was the first study to find a new target molecule that enhances Pa-PDT effects in IHOK and OSCC cell lines. Hence, the development of a PDT-dependent biomarker could provide a novel approach to improve the effects of PDT on oral precancerous and cancerous lesions.

A novel gain-of-function mutation of TGF-ß receptor II promotes cancer progression via delayed receptor internalization in oral squamous cell carcinoma.

We present a novel gain-of-function mutation of TGF-ß receptor II (TßRII) found in human oral squamous cell carcinoma (OSCC). Expression of E221V/N238I mutant TßRII enhanced TGF-ß signaling. Mutation of TßRII conferred cells higher migratory and invasive capabilities and MMP-2 activity. In mouse tumor model, mutant tumors exhibited poor differentiation and E-cadherin relocalization to the cytosol. Lipid-raft-dependent endocytosis of TßRII was attenuated in mutant TßRII, suggesting that enhancement of TGF-ß signaling by this mutation is due to delayed TßRII internalization. Taken together, our results show a novel gain-of-function TßRII mutation, which enhances TGF-ß signaling leading to more invasive phenotypic changes in human OSCC.