Analysis of the level of mRNA expression of the membrane regulators of complement, CD59, CD55 and CD46, in breast cancer.

We have examined the relative mRNA expression of the complement (C) regulatory proteins CD59, CD55 and CD46 in RNA isolated from 50 primary breast cancer specimens using a semiquantitative RT-PCR approach. Having normalized the mRNA expression levels of the C regulators relative to actin, we subsequently correlated their expression with estrogen receptor (ER) and various clinical, pathologic and biochemical features of the disease. CD59 and CD46 were detected in all clinical biopsies, while CD55 mRNA was detected in the majority of samples. The comparative levels of expression between the 3 regulators analyzed, using Spearman rank correlation test, revealed a significant association (p = 0.01; r = 0.36) between CD46 and CD59. CD46 exhibited the most striking pattern of association, with increased levels of expression being associated with ER-positive samples and lower levels of expression associated with a loss of differentiation and epidermal growth factor receptor positivity. Application of Spearman rank correlation test revealed CD46 expression was significantly associated with expression of ER at the level of protein (p = 0.031; r = 0.31) and mRNA (p < 0.001; r = 0.52). CD46 expression also correlated with insulin-like growth factor receptor-positive samples using Spearman rank correlation test (p = 0.016; r = 0.34), but negatively associated with tumor samples either exhibiting histologic grade 3 when compared to grades 1 or 2 or displaying elevated levels of inflammatory cell infiltrate. Immunohistochemical analysis of a limited series (n = 8) of paraffin-embedded breast cancers indicated that the level of CD46 protein expression directly associates with that of the mRNA and, where prominent, is localized in the tumor epithelial cell population, including at the plasma membrane. These data provide new information on expression of these important regulators in breast cancer and suggest that CD46 should be evaluated as a novel prognostic indicator.