Claudin-7 down-regulation is an important feature in oral squamous cell carcinoma

Lourenço S V, Coutinho‐Camillo C M, Buim M E C, de Carvalho A C, Lessa R C, Pereira C M, Vettore A L, Carvalho A L, Fregnani J H, Kowalski L P & Soares F A (2010) Histopathology57, 689–698 Claudin‐7 down‐regulation is an important feature in oral squamous cell carcinoma Aims: Claudins, a large family of essential tight junction (TJ) proteins, are abnormally regulated in human carcinomas, especially claudin‐7. The aim of this study was to investigate claudin‐7 expression and alterations in oral squamous cell carcinoma (OSCC). Methods and results: Expression of claudin‐7 was analysed in 132 cases of OSCC organized in a tissue microarray. Claudin‐7 mRNA transcript was evaluated using real‐time polymerase chain reaction and the methylation status of the promoter was also assessed. Claudin‐7 was negative in 58.3% of the cases. Loss of claudin‐7 protein expression was associated with recurrence (P = 0.019), tumour size (P = 0.014), clinical stage of OSCC (P = 0.055) and disease‐free survival (P = 0.015). Down‐regulation of the claudin‐7 mRNA transcripts was observed in 78% of the cases, in accordance with immunoexpression. Analysis of the methylation status of the promoter region of claudin‐7 revealed that treatment of O28 cells (that did not express claudin‐7 mRNA transcripts) with 5‐Aza‐2′‐Deoxycytidine (5‐Aza‐dC) led to the re‐expression of claudin‐7 mRNA transcript. Conclusion: Loss of claudin‐7 expression is associated with important subcellular processes in OSCC with impact on clinical parameters.