Mark Yen-Ping Kuo

Connective Tissue Growth Factor Activates Pluripotency Genes and Mesenchymal–Epithelial Transition in Head and Neck Cancer Cells

The epithelial-mesenchymal transition (EMT) is a key mechanism in both embryonic development and cancer metastasis. The EMT introduces stem-like properties to cancer cells. However, during somatic cell reprogramming, mesenchymal-epithelial transition (MET), the reverse process of EMT, is a crucial step toward pluripotency. Connective tissue growth factor (CTGF) is a multifunctional secreted protein that acts as either an oncoprotein or a tumor suppressor among different cancers. Here, we show that in head and neck squamous cell carcinoma (HNSCC), CTGF promotes the MET and reduces invasiveness. Moreover, we found that CTGF enhances the stem-like properties of HNSCC cells and increases the expression of multiple pluripotency genes. Mechanistic studies showed that CTGF induces c-Jun expression through αvβ3 integrin and that c-Jun directly activates the transcription of the pluripotency genes NANOG, SOX2, and POU5F1. Knockdown of CTGF in TW2.6 cells was shown to reduce tumor formation and attenuate E-cadherin expression in xenotransplanted tumors. In HNSCC patient samples, CTGF expression was positively correlated with the levels of CDH1, NANOG, SOX2, and POU5F1. Coexpression of CTGF and the pluripotency genes was found to be associated with a worse prognosis. These findings are valuable in elucidating the interplay between epithelial plasticity and stem-like properties during cancer progression and provide useful information for developing a novel classification system and therapeutic strategies for HNSCC.

Genotoxic and Non-genotoxic Effects of Betel Quid Ingredients on Oral Mucosal Fibroblasts in vitro

To understand the role of betel quid (BQ) in the pathogenesis of oral submucous fibrosis (OSF) and oral cancer, we used DNA damage, cytotoxicity, and cell proliferation assays to study the pathobiological effects of aqueous extracts of three BQ constituents [betel nut (Areca catechu, BN), inflorescence of Piper betle (IPB), and lime], one BN alkaloid (arecoline), and one BN polyphenol [(+)-catechin] on cultured oral mucosal fibroblasts. Extracts of BN and IPB induced DNA strand break formation in a dose-dependent manner. Extracts of BN and IPB, (+)-catechin, and arecoline decreased cell survival and proliferation in a dose-dependent manner. However, aqueous extract of lime (50-800 μg/mL) increased cell proliferation by 20-40%. These results indicate that BQ contains not only genotoxic and cytotoxic agents, but also compounds which stimulate cell proliferation. These compounds may act synergistically in the pathogenesis of OSF and oral cancer in BQ chewers. In addition, five anti-oxidants [glutathione (GSH), cysteine, mannitol, catalase, and superoxide dismutase (SOD)] were tested for their protective effects against the cytotoxicity of BQ constituents. GSH (1.95 and 2.6 mmol/L) and cysteine (4 and 8 mmol/L) prevented the arecoline-induced cytotoxicity. In contrast, mannitol, catalase, and SOD did not decrease the arecoline-induced cytotoxicity. These results indicate that thiol depletion, but not the attack of oxygen free radicals, could be the mechanism for arecoline cytotoxicity. GSH could also protect cells from the cytotoxicity of IPB extract. Increasing dietary intake of GSH-rich foods or dietary supplements of GSH may have chemopreventive potential to reduce BQ-associated oral lesions.

Histone deacetylase 2 expression predicts poorer prognosis in oral cancer patients

Histone deacetylase 2 (HDAC2) has been implicated in the development and progression of several human tumors. We immunohistochemically examined the expression of HDAC2 protein in 20 cases of oral epithelial dysplasia (OED) and 93 cases of oral squamous cell carcinoma (OSCC). Positive HDAC2 nuclear staining was observed in 80 of the 93 (86.02%) cases of SCC and 11 of the 20 (55%) cases of ED. The labeling index (LI) for HDAC2 nuclear staining increased significantly from ED (25.8+/-26.5%) to SCCs (59.8+/-28.5%) (p<0.001). No significant correlation was found between the HDAC2 expression level and patients age, sex, oral habits in oral SCC patients. However, cancer with advanced stage, larger tumor size, or positive lymph node metastasis had higher level of HDAC2 protein expression. Kaplan-Meier curves showed oral SCC patients with high HDAC2 expression (LI>50%), advanced stage, larger tumor size, or positive lymph node metastasis had significantly shorter overall survival (p=0.0158, 0.0267, 0.0029 and 0.02514, respectively by log-rank test) than others. The results of this study show for the first time that overexpression of the HDAC protein is a frequent event in oral cancer and could be used as a prognostic factor in oral SCC.

Cytotoxicity of sodium fluoride on human oral mucosal fibroblasts and its mechanisms

Because sodium fluoride (NaF) is widely used for prevention of dental caries, pathobiological effects of NaF were investigated on human oral mucosal fibroblasts. The results showed that NaF was cytotoxic to oral mucosal fibroblasts at concentrations of 4 mmol/L or higher. Exposure of cells to NaF for 2 h also inhibited protein synthesis, cellular ATP level and functional mitochondrial activities in a dose-dependent manner. However, incubation of cells with NaF up to 12 mmol/L for 2 h depleted only 13% of cellular glutathione level. The IC50 of NaF on cellular ATP level was about 5.75 mmol/L. Preincubation of the cells with pyruvate and succinate did not protect cells from NaF-induced ATP depletion. At concentrations of 4 mmol/L, 8 mmol/L and 12 mmol/L, NaF inhibited 31%, 56% and 57% of mitochondrial functions, respectively, after 2 h incubation. No significant inhibition for NaF was found at concentrations lower than 2 mmol/L (40 ppm). These results indicate that NaF can be toxic to oral mucosal fibroblasts in vitro by its inhibition of protein synthesis, mitochondrial function and depletion of cellular ATP. Because of repeated and long-term usage of NaF, more detailed studies should be undertaken to understand its toxic effects in vitro and in vivo.

Eugenol Triggers Different Pathobiological Effects on Human Oral Mucosal Fibroblasts 1

Pathobiological effects of eugenol (4-allyl-2-methoxyphenol), a major constituent of betel quid (BQ), were studied on oral mucosal fibroblasts. At a concentration higher than 3 mmol/L, eugenol was cytotoxic to oral mucosal fibroblasts in a concentration-and time-dependent manner. Cell death was associated with intracellular depletion of glutathione (GSH). Most of the GSH was depleted prior to the onset of cell death. At concentrations of 3 mmol/L and 4 mmol/L, eugenol depleted about 45% and 77% of GSH after one-hour incubation. In addition, eugenol decreased cellular ATP level in a concentration- and time-dependent manner. Eugenol also inhibited lipid peroxidation. Inhibition of lipid peroxidation was partially explained by its dose-dependent inhibition of xanthine oxidase activity. The IC50 of eugenol on xanthine oxidase activity was about 0.3 mmol/L. No DNA strand break activity for eugenol was found at concentrations between 0.5 and 3 mmol/L. Taken together, frequent exposure of oral mucosa to a high concentration of eugenol during the chewing of BQ might be involved in the pathogenesis of oral submucous fibrosis and oral cancer via its cytotoxicity. In contrast, eugenol at a concentration less than 1 mmol/L might protect cells from the genetic attack of reactive oxygen species via inhibition of xanthine oxidase activity and lipid peroxidation.

Collagen gene expression in human dental pulp cell cultures

Pulp cells from human permanent molars were isolated and established in culture; 40% showed positive alkaline phosphatase staining. When incubated with 50 micrograms/ml of ascorbic acid and 10 mM of beta-glycerophosphate, the cells formed a mineralized extracellular matrix; they could thus have the potential to differentiate into odontoblast-like cells in vitro. Collagen synthesis was analysed by SDS interrupted gel electrophoresis, Northern blot and slot blot: the cells produced predominantly (approximately 99%) type I collagen and only trace amount of type III collagen. The ratio of alpha 1 (I) to alpha 2(I) procollagen chains was about 68:32, indicating that no significant amount of collagen type I trimer was synthesized in this system. The ratios of alpha 1(I), alpha 2(I) and alpha 1(III) procollagen mRNAs were about 61:25:1; these were compatible with the ratios of corresponding procollagen alpha chains. In addition, a novel 5.8 kb pro alpha 1(III) mRNA was detected. These observations indicate that collagen synthesis in these cultured pulp cells was regulated at the transcriptional level.

Collagen Biosynthesis in Human Oral Submucous Fibrosis Fibroblast Cultures

To investigate the mechanism of collagen accumulation in oral submucous fibrosis (OSF) tissues, we examined the biosynthesis of collagen in fibroblast cultures established from OSF lesions. Fibroblasts obtained from four of ten OSF specimens showed more than a 1.5-fold increase in the production of collagens compared with fibroblasts from age-, sex-, and passage-matched normal controls (p < 0.05). When the relative amounts of collagen synthesis were estimated by SDS polyacrylamide gel electrophoresis, it was found that both OSF and control cells produced about 85% type I collagen and 15% type III collagen. The ratio of α1(I) to a2(I) chains was about 3:1 in OSF cells instead of the 2:1 expected for type I collagen. The excess al(I) chains could mean that collagen type I trimer was synthesized by the fibroblasts. These findings suggest that collagen overproduction and a reduced degradation of the structure-stable collagen type I trimer synthesized by OSF fibroblasts might contribute to the accumulation of collagen in OSF lesions in vivo. The mechanism(s) of increased procollagen production were analyzed by Northern blot, slot blot, and Southern blot. The OSF fibroblast strains with elevated collagen production also contained higher-than-normal levels of procollagen mRNA, and the ratios of α1(I), a2(I), and α1(III) procollagen mRNAs were compatible with the results of corresponding procollagen a chains. The gene copy number of proa2(I) collagen gene in OSF fibroblasts was about 1.05. No gene amplification was found. These results indicate that expression of these procollagen genes in cultured fibroblasts is regulated at the transcriptional level.

Nuclear localization of annexin A1 is a prognostic factor in oral squamous cell carcinoma.

To investigate whether annexin A1 (ANXA1) expression is a marker in predicting the prognosis of oral cancer patients.

Nitric oxide promotes infectious bone resorption by enhancing cytokine-stimulated interstitial collagenase synthesis in osteoblasts

This experiment was undertaken to determine the role of macrophage‐derived nitric oxide (NO) in mediating lipopolysaccharide (LPS)‐induced bone resorption by using an in vitro co‐culture system and an in vivo model of infectious bone resorption. Our results demonstrated that LPS stimulated the expression of inducible nitric oxide synthase (iNOS) and tumor necrosis factor (TNF)‐α mRNAs and nitrite synthesis in the J774 mouse macrophage cell line but not in the UMR‐106 (rat) and MC3T3‐E1 (mouse) osteoblast cell lines. Conditioned media (CM) from LPS‐stimulated J774 triggered only low to moderate levels of iNOS mRNAs in MC3T3‐E1 and a trivial effect in UMR‐106. On the other hand, CM induced matrix metalloproteinase‐1 (MMP‐1) gene expression in both osteoblast cell lines. The NOS inhibitor NG‐monomethyl‐L‐arginine (L‐NMMA) did not alter this effect in MC3T3‐E1 and UMR‐106, whereas TNF‐α antibody diminished the CM‐induced MMP‐1 gene expression in both cell lines. Interestingly, SNAP, a NO donor, although by itself is not a MMP‐1 stimulator for UMR‐106, augmented the TNF‐α‐stimulated MMP‐1 mRNA production in UMR‐106. In a J774/UMR‐106 co‐culture system, LPS stimulated significant MMP‐1 gene expression in UMR‐106, and this upregulation was abolished by L‐NMMA and TNF‐α antibodies. Immunohistochemical analysis in a rat model of infectious bone resorption (periapical lesion) showed co‐distributions of iNOS+ macrophages and MMP‐1+ osteoblasts around the osteolytic areas. Administration of L‐NMMA markedly reduced the extent of bone loss and the percentage of MMP‐1‐synthesizing osteoblasts. These data suggest that NO derived from macrophages after LPS stimulation may enhance bone loss by augmenting the cytokine‐induced MMP‐1 production in osteoblasts.

Comparisons of norcantharidin cytotoxic effects on oral cancer cells and normal buccal keratinocytes

Norcantharidin (NCTD) is the demethylated analogue of cantharidin. In this study, multi-parameter assessments of morphological alterations, clonogenic efficiency, cell growth curves, DNA synthesis, and DNA strand break were employed to determine and compare the cytotoxic effects of NCTD on oral cancer KB cell line and normal buccal keratinocytes. The results showed NCTD induced significant cytotoxicity in KB cells after 24 h of exposure. Normal buccal keratinocytes were more resistant to NCTD induced cytotoxicity. The IC(50) of 24 h NCTD treatment for KB and keratinocytes were 15.06 and 216.29 microg/ml, respectively with a keratinocyte/KB selective index of 14.36. Anoikis and membrane blebbing, morphological characterization of apoptosis, were observed in about 90% of KB cells after exposure to 100 microg/ml of NCTD for 24 h compared to about 30% in keratinocytes. In addition, inhibition of colony formation was noted in KB cells even when exposed to low concentration of drug (5 microg/ml) for a short period of time (6 h). NCTD inhibited subsequent cell proliferation in KB but growth of normal keratinocytes was retarded only temporarily. NCTD inhibited DNA synthesis in both KB and normal keratinocytes. However, keratinocytes were more sensitive to DNA synthesis inhibition by low dose of NCTD. Significant DNA strand break was noted in KB cells only after cell viability was reduced to less than 60% of the control. In comparison, normal keratinocytes were resistant to NCTD induced DNA strand break. These results indicated KB cells were more sensitive to NCTD induced cytotoxicity compared to normal keratinocytes. NCTD may be of value in treating oral cancers. The underlying mechanisms of the differential actions of NCTD on these two cell types are worthy of further investigations.