Benzo (a) pyrene induced tumorigenesity of human immortalized oral epithelial cells: transcription profiling:

Role of WDHD1 in Human Papillomavirus-Mediated Oncogenesis Identified by Transcriptional Profiling of E7-Expressing Cells

The E7 oncoprotein of the high-risk human papillomavirus (HPV) plays a major role in HPV-induced carcinogenesis. E7 abrogates the G1 cell cycle checkpoint and induces genomic instability, but the mechanism is not fully understood. In this study, we performed RNA sequencing (RNA-seq) to characterize the transcriptional profile of keratinocytes expressing HPV 16 (HPV-16) E7. At the transcriptome level, 236 genes were differentially expressed between E7 and vector control cells. A subset of the differentially expressed genes, most of them novel to E7-expressing cells, was further confirmed by real-time PCR. Of interest, the activities of multiple transcription factors were altered in E7-expressing cells. Through bioinformatics analysis, pathways altered in E7-expressing cells were investigated. The upregulated genes were enriched in cell cycle and DNA replication, as well as in the DNA metabolic process, transcription, DNA damage, DNA repair, and nucleotide metabolism. Specifically, we focused our studies on the gene encoding WDHD1 (WD repeat and high mobility group [HMG]-box DNA-binding protein), one of the genes that was upregulated in E7-expressing cells. WDHD1 is a component of the replisome that regulates DNA replication. Recent studies suggest that WDHD1 may also function as a DNA replication initiation factor as well as a G1 checkpoint regulator. We found that in E7-expressing cells, the steady-state level of WDHD1 protein was increased along with the half-life. Moreover, downregulation of WDHD1 reduced E7-induced G1 checkpoint abrogation and rereplication, demonstrating a novel function for WDHD1. These studies shed light on mechanisms by which HPV induces genomic instability and have therapeutic implications.

IMPORTANCE

The high-risk HPV types induce cervical cancer and encode an E7 oncoprotein that plays a major role in HPV-induced carcinogenesis. However, the mechanism by which E7 induces carcinogenesis is not fully understood; specific anti-HPV agents are not available. In this study, we performed RNA-seq to characterize transcriptional profiling of keratinocytes expressing HPV-16 E7 and identified more than 200 genes that were differentially expressed between E7 and vector control cells. Through bioinformatics analysis, pathways altered in E7-expressing cells were identified. Significantly, the WDHD1 gene, one of the genes that is upregulated in E7-expressing cells, was found to play an important role in E7-induced G1 checkpoint abrogation and rereplication. These studies shed light on mechanisms by which HPV induces genomic instability and have therapeutic implications.

Repression of Biotin-Related Proteins by Benzo[a]Pyrene-Induced Epigenetic Modifications in Human Bronchial Epithelial Cells

Benzo[a]pyrene (B[a]P) exposure has been associated with the alteration in epigenetic marks that are involved in cancer development. Biotinidase (BTD) and holocarboxylase synthetase (HCS) are 2 major enzymes involved in maintaining the homeostasis of biotinylation, and the deregulation of this pathway has been associated with a number of cancers. However, the link between B[a]P exposure and the dysregulation of BTD/HCS in B[a]P-associated tumorigenesis is unknown. Here we showed that the expression of both BTD and HCS was significantly decreased upon B[a]P treatment in human bronchial epithelial (16HBE) cells. Benzo[a]pyrene exposure led to the global loss of DNA methylation by immunofluorescence, which coincided with the reduction in acetylation levels on histones H3 and H4 in 16HBE cells. Consistent with decreased histone acetylation, histone deacetylases (HDACs) HDAC2 and HDAC3 were significantly upregulated in a dosage-dependent manner. When DNA methylation or HDAC activity was inhibited, we found that the reduction in BTD and HCS was separately regulated through distinct epigenetic mechanisms. Together, our results suggested the potential link between B[a]P toxicity and deregulation of biotin homeostasis pathway in B[a]P-associated cancer development.

Growth differentiation factor 15 as a radiation-induced marker in oral carcinoma increasing radiation resistance

BACKGROUND

Growth differentiation factor 15 (GDF15) is involved in tumor pathogenesis of oral squamous cell carcinoma (OSCC). The aim of this study was an investigation of the potential influence of GDF15 on radioresistance of OSCC cells in vitro.

METHODS

Oral squamous cell carcinoma cell lines were irradiated with 0, 2, or 6 Gy, and GDF15 expression in the supernatant per survived cell colony was examined with ELISA. Non-irradiated and OSCC cell lines irradiated with 6 Gy were evaluated for GDF15 expression using immunofluorescent staining. For further investigation of GDF15 effects on radioresistance, a GDF15 knockdown model in a human OSCC cell line was established, and apoptotic activity after radiation was measured using the Caspase-Glo 3/7 system.

RESULTS

ELISA and immunofluorescent staining indicated an increased GDF15 expression in 5 OSCC cell lines compared with human gingival epithelial cells. Irradiation with two and six gray resulted in a significant elevation of GDF15 expression per survived cell colony in the irradiated OSCC cell lines (P < 0.001). Furthermore, a dose-dependent expression of GDF15 was seen. Immunofluorescent staining confirmed an elevated GDF15 expression in irradiated OSCC cell lines (n = 10; P ≤ 0.001). Apoptotic activity was significantly increased after irradiation in the GDF15 knockdown group compared with control cells (n = 24; P < 0.001).

CONCLUSION

This study describes for the first time the vital role of GDF15 both in tumorigenesis and in radioresistance of OSCC cells. With its anti-apoptotic effects, GDF15 possibly promotes tumor progression and might protect carcinoma cells against irradiation effects. Consequently, GDF15 may be a promising therapeutic target in oral cancer.

Elevated level of serum growth differentiation factor 15 is associated with oral leukoplakia and oral squamous cell carcinoma

BACKGROUND

Although molecular mechanism of growth differentiation factor 15 (GDF15) in tumorigenesis of oral squamous cell carcinoma (OSCC) is not clear, the diagnostic and prognostic value of serum GDF15 detection has been noticed. However, serum GDF15 levels in patients with oral leukoplakia and GDF15 as a potential predictive biomarker for response to induction chemotherapy in patients with OSCC have not been reported.

METHODS

Pretreatment serum GDF15 concentration was detected using an enzyme-linked immunosorbent assay in 30 healthy persons, 24 patients with oral leukoplakia, and 60 patients with OSCC.

RESULTS

Serum GDF15 concentration was significantly higher in patients with oral leukoplakia and OSCC, compared with healthy controls (F = 13.701, df = 2, P < 0.001). From a diagnostic standpoint, a cutoff value of 346.9 ng/l of serum GDF15 concentration was calculated using receiver operating characteristic curve, with a sensitivity of 0.750, specificity of 0.867, Youden's Index of 0.617, and area under curve of 0.863. From a prognostic standpoint, patients with serum GDF15 concentration <346.9 ng/l had an improved 3-year disease-free survival rate (64.3% vs 56.5%) compared with those above 346.9 ng/l, but the difference was not statistically significant. A decreased concentration of GDF15 (<346.9 ng/l) showed a predictive trend toward an improved response to induction chemotherapy compared with elevated concentration with clinical response rates of 100% and 71.4%, respectively, but the difference was not significant.

CONCLUSION

Elevated GDF15 level may be not only a diagnostic biomarker for oral leukoplakia, but also a prognostic/predictive biomarker associated with decreased survival and diminished response to induction chemotherapy for patients with OSCC.

Yes-associated protein promotes cell proliferation by activating Fos Related Activator-1 in oral squamous cell carcinoma

In our previous study, we established an in vitro cellular carcinogenesis model of oral squamous cell carcinoma (OSCC), including a human immortalized oral epithelial cell (HIOEC) and a cancerous cell line (HB96). Microarray analysis showed that the gene encoding Yes-associated protein (YAP) was significantly increased in HB96 cells compared with HIOEC cells. But the underlying mechanism of YAP on oncogenesis, especially its downstream targets, are still not clear. YAP expression in OSCC cell lines and tissue specimens were investigated by using real-time PCR, western blotting and immunohistochemistry staining. YAP put-back plasmid with four mutation sites after YAP-siRNA interference was constructed by site-directed mutagenesis. Cell growth and colony formation were observed after YAP-siRNA interference or YAP put-back again in CAL27 cells. YAP expression was increased in the cellular carcinogenesis models and the clinical samples from primary OSCC patients. Inhibition of YAP by siRNA interference in CAL27 cells significantly inhibited cell proliferation and colony formation in soft agar, but these abilities were rescued when YAP was put-back again. At the same time, Fos Related Activator-1 (Fra-1) was down-regulated when YAP was inhibited by siRNA interference while Fra-1 was rescued when YAP was put-back again. Immunohistochemistry results also indicated that higher levels of YAP were significantly associated with Fra-1 overexpression in OSCC clinical samples. YAP could promote cell proliferation by activating transcription factor Fra-1 in oral squamous cell carcinoma.