Increased expression of gap junction protein--connexin 32 in lymph node metastases of human ductal breast cancer.

Abstract

Gap junctions are specialized cell membrane channels composed of connexins (Cxs), which mediate the direct passage of small molecules between adjacent cells. They are involved in the regulation of cell cycle, cell signaling and differentiation as well as probably invasion and metastasis. Up to now, Cx32 status in human breast cancer has not been studied. Consequently, the aim of the present study was the evaluation of the expression of connexin 32 (Cx32) in primary breast tumors (PTs) and matched-paired metastases to lymph nodes (MLNs) in correlation with selected clinicopathological features. Tissue samples from 79 women were examined by immunohistochemistry, using the streptavidin-biotin-peroxidase complex technique for Cx32. Cytoplasmic expression of Cx32 was detected in 31 of 79 breast cancers (39.2%). Both epithelial and myoepithelial cells of normal ducts adjacent to the tumor did not express Cx32. Increased expression of studied Cx was observed in metastases to lymph nodes relative to primary tumors. Additionally, Cx32-negative primary tumors developed Cx32-positive metastases. Statistical comparisons of Cx32 expression in the matched pairs indicate that this protein significantly increased in lymph node metastases compared to primary tumors (p<0.001). The expression of Cx32 in primary breast cancer was not statistically associated with age of patients, tumor size, lymph node status, but we observed a tendency toward association between Cx32 expression and histological differentiation. In conclusion, transformed cells may have an ability to produce Cxs also atypical for normal cells. Increased expression of Cx32 in metastases to the lymph nodes might reflect alteration in connexin gene transcription during breast carcinogenesis and finally, it may be a sign of more malignant phenotype of cancerous cells.