Claudin 1 overexpression increases invasion and is associated with aggressive histological features in oral squamous cell carcinoma

BACKGROUND. The authors have previously shown that overexpression of claudin 1 (CLDN1) is associated with advanced disease stage in oral squamous cell carcinomas (OSCCs). Their goal was to examine CLDN1 expression in a large series of primary OSCCs and to further investigate whether CLDN1 overexpression plays a role in invasion in OSCC. METHODS. CLDN1 gene expression levels were determined by quantitative real‐time reverse transcription polymerase chain reaction (QRT‐PCR) in 100 primary OSCCs. CLDN1 protein expression was examined by immunohistochemistry in 70 of 100 OSCCs. E‐Cadherin protein levels were also assessed in 58 OSCCs. The authors performed a transwell Matrigel invasion assay for assessment of the invasive potential of CLDN1 overexpressing oral carcinoma cells. Western blotting and QRT‐PCR were used to assess CLDN1 expression in transfected cells and controls. RESULTS. CLDN1 mRNA was increased (median = 18.5) in 79 of 100 OSCCs, compared with normal oral mucosa (expression = 1.0). CLDN1 overexpression was associated with angiolymphatic (P = .037) and perineural invasion (P = .051). CLDN1 was highly expressed in 48 of 70 (68%) OSCCs. E‐Cadherin was lost or underexpressed in 49 of 58 (84%) OSCCs. The invasion assay showed that cells overexpressing CLDN1 have increased invasive potential, whereas small interfering RNA–mediated depletion of CLDN1 decreased the invasive potential of cells. CONCLUSIONS. CLDN1 overexpression is associated with angiolymphatic and perineural invasion, consistent with aggressive tumor behavior. Overexpression of CLDN1 protein is associated with increased invasiveness of oral carcinoma cells. Cancer 2008. © 2008 American Cancer Society. This study is the first to show an association of overexpression of claudin 1, which encodes a tight junction protein, with aggressive histological features in oral squamous cell carcinomas. The authors also demonstrate the involvement of this protein in the invasive potential of oral carcinoma cells.