RESUMO
Previous studies have established that expression of plakoglobin is down-regulated during malignant transformation. The aim of this study was to evaluate for the first time the expression of plakoglobin at the mRNA and protein levels in primary oropharyngeal squamous cell carcinomas (SCCs) and determine the extent to which the patterns of expression correlated with clinical parameters. Plakoglobin expression was evaluated in 37 new tumor cases and normal oral epithelium using immunofluorescence, reverse transcriptase-polymerase chain reaction (RT-PCR), and Northern and Western blotting analysis. The results indicated that the steady-state levels of plakoglobin protein were down-regulated in all tumors compared with normal epithelium. Furthermore, in 87.1% of the tumors, plakoglobin immunoreactivity displayed an abnormal cytoplasmic localization that was inversely correlated with tumor size and directly correlated with a poor clinical outcome for the patient. Northern blotting analysis revealed that down-regulation of mRNA expression occurred in only 65.6% of the tumors, with plakoglobin mRNA levels similar to normal epithelium in the remaining cases. In the tumors expressing mRNA levels similar to those of normal tissue, a 3.7-kb transcript was detected in addition to the expected 3.4-kb transcript observed in normal epithelium. RT-PCR analysis of the 3' untranslated region of the 3.7-kb plakoglobin mRNA transcript identified a 297-base insertion from +2369 to +2666 that had been previously reported only in transformed cell lines (GenBank M23410). Interestingly, the prognosis was poor for patients with tumors expressing both RNA transcripts. These results are consistent with the concept that complex regulation of plakoglobin expression and intracellular routing may contribute to malignant transformation. The study also shows evidence that the level of expression and intracellular localization of plakoglobin may be useful in predicting the course of disease in patients with oropharyngeal SCC.
