Expression profiling of mammary carcinoma cell lines: correlation of in vitro invasiveness with expression of CD24.

Invasiveness and the capacity of tumor cells to form distant metastases are important cellular characteristics associated with a poor prognosis in breast cancer patients. In an approach to find genes that are potentially involved in these processes, RNA species showing different abundance in RNA pools from 12 invasive and 13 noninvasive mammary carcinoma-derived cell lines have been identified by hybridization to cDNA microarrays. CD24, keratin 19, keratin 8, GOB-4 and ezrin-radixin-moesin-binding phosphoprotein 50 were found to be preferentially expressed by noninvasive cells whereas vimentin was confirmed as a characteristic of invasive cells. Only differences in expression higher than 3-fold evident in three independent hybridization experiments were considered significant. For all cell lines, expression of mRNA coding for the adhesion molecule CD24, previously suggested to play an important role during tumor progression to more invasive phenotypes, has been quantified by real-time RT-PCR. Flow-cytometric analyses confirmed that CD24 mRNA reflects the amount of cell surface CD24 (Spearman R = 0.88, p = 10(-6)). CD24 mRNA was found to be absent or weakly expressed in 9/12 (75%) invasive cell lines compared to 3/13 (23%) noninvasive cell lines. The correlation between CD24 expression and invasiveness was calculated to be highly significant with chi2 = 6.74 and p = 0.0094. Future analyses of primary breast carcinomas are warranted to define the role of CD24 in future diagnostic and therapeutic approaches.