Aberrant Promoter Methylation of PTEN Gene among Indian Patients with Oral Squamous Cell Carcinoma

METTL3 modulates m6A modification of CDC25B and promotes head and neck squamous cell carcinoma malignant progression

BACKGROUND

N6-methyladenosine (m6A) RNA methylation and its methyltransferase METTL3 have been widely reported to be involved in different cancers by regulating RNA metabolism and function. Here, we aimed to explore the biological function and clinical significance of m6A modification and METTL3 in head and neck squamous cell carcinoma (HNSCC).

METHODS

The prognostic value of METTL3 expression was evaluated using tissue microarray and immunohistochemical staining analyses in a human HNSCC cohort. The biological role and mechanism of METTL3 in HNSCC tumour growth, metastasis and angiogenesis were determined in vitro and in vivo.

RESULTS

M6A levels and METTL3 expressions in HNSCC tissues were significantly increased compared with paired adjacent tissues. Meanwhile, METTL3 was an independent risk factor for the prognosis of HNSCC patients. Moreover, METTL3 overexpression promoted HNSCC cell proliferation, migration, invasion, and angiogenesis, while knockdown of METTL3 had an opposite effect in vivo and in vitro. Mechanistically, METTL3 enhanced the m6A modification of CDC25B mRNA, which maintained its stability and upregulated its expression, thereby activating G2/M phase of cell cycle and leading to HNSCC malignant progression.

CONCLUSIONS

METTL3 may be a potential prognostic biomarker and therapeutic target for HNSCC.

Epigenetic Modifications in Head and Neck Cancer

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common human malignancy in the world, with high mortality and poor prognosis for patients. Among the risk factors are tobacco and alcohol intake, human papilloma virus, and also genetic and epigenetic modifications. Many studies show that epigenetic events play an important role in HNSCC development and progression, including DNA methylation, chromatin remodeling, histone posttranslational covalent modifications, and effects of non-coding RNA. Epigenetic modifications may influence silencing of tumor suppressor genes by promoter hypermethylation, regulate transcription by microRNAs and changes in chromatin structure, or induce genome instability through hypomethylation. Moreover, getting to better understand aberrant patterns of methylation may provide biomarkers for early detection and diagnosis, while knowledge about target genes of microRNAs may improve the therapy of HNSCC and extend overall survival. The aim of this review is to present recent studies which demonstrate the role of epigenetic regulation in the development of HNSCC.

Allelic loss at PTEN locus leads to progression of colorectal carcinoma among North Indian patients

We evaluated the loss of heterozygosity (LOH) at 10q^23.3 locus of microsatellite markers; D10S198, D10S192, and D10S541 of PTEN gene in 223 North Indian colorectal cancer (CRC) specimens. DNA was isolated and microsatellite-specific markers polymerase chain reaction was performed. Out of total 223 cases 102 showed LOH for at least one of the locus. In addition, thereto a significant association was found with the clinicopathologic features like grade of differentiation, clinical stage, invasion, lymph node invasion, and the clinical outcome (p < 0.05). These data argue that the given markers to check the possible LOH of PTEN gene at locus 10q^23.3 could be considered as one of the diagnostic markers in CRC.

PTEN and p16 genes as epigenetic biomarkers in oral squamous cell carcinoma (OSCC): a study on south Indian population

Phosphatase and tensin homolog (PTEN) and p16INK4a (p16) genes are tumor suppressor genes, associated with epigenetic alterations. PTEN and p16 promoter hypermethylation is a major epigenetic silencing mechanism leading to cancer. The cooperation between PTEN and p16 in pathogenesis of cancers suggest that their combination might be considered as potential molecular marker for specific subgroups of patients. Hence, the present study aimed to investigate whether PTEN and p16 promoter methylations were involved in oral squamous cell carcinoma (OSCC) in south Indian subjects. DNA methylation quantitative analyses of the two candidate tumor suppressor genes PTEN and p16 were performed by methylation-specific polymerase chain reaction (MSP). Fifty OSCC biopsy samples and their corresponding non-malignant portions as controls were studied comparatively. The methylation status was correlated with the clinical manifestations. Twelve out of 50 patients (24 %) were found to be methylated for PTEN gene, whereas methylation of the p16 gene occurred in 19 out of 50 cases (38 %). A statistically significant result was obtained (P = <0.0001 and 0.017) for both PTEN and p16 genes. PTEN and p16 promoter methylation may be the main mechanism leading to the low expression of PTEN and p16 genes indicating the progress of tumor development. Our data suggest that a low PTEN and p16 expression due to methylation may contribute to the cancer progression and could be useful for prognosis of OSCC. Therefore, analysis of promoter methylation in such genes may provide a biomarker valuable for early detection of oral cancer.

Podocalyxin-like 1 is associated with tumor aggressiveness and metastatic gene expression in human oral squamous cell carcinoma

Metastasis-mediated death remains a major challenge in cancer treatment due to the lack of identifiable biomarkers for early diagnosis. Identifying tumor-specific biomarkers is critical for the development of diagnostic and therapeutic tools. In the present study, we found that podocalyxin-like 1 (PODXL), a cell surface glycoprotein, was overexpressed in cancer tissues and was upregulated in lymph node metastatic tumor cells. The expression of PODXL was associated with the migratory ability of human oral squamous cell carcinoma (OSCC). Knockdown of PODXL by small hairpin RNA in the SAS OSCC cell line reduced tumor migration and invasion, and inhibited cell proliferation and colony formation. Suppression of PODXL resulted in downregulation of focal adhesion kinase (FAK) and paxillin phosphorylation. PODXL silencing inhibited filopodia formation, and suppressed F-actin and cortactin colocalization. In addition, PODXL expression was associated with the DNA methylation status, and treatment with the DNA methyltransferase inhibitor 5-aza-deoxycytidine increased the PODXL transcriptional level. Moreover, DNA microarray analysis data revealed that suppression of PODXL significantly affected subsets of genes associated with extracellular matrix organization, the epithelial-mesenchymal transition, and the expression of metastasis-related cytokines. Collectively, these data showed that the overexpression of PODXL may be associated with tumor aggressiveness and that PODXL could be a diagnostic biomarker for metastatic OSCC.