Molecular Differences in Sporadic Breast Cancer in Young Women (≤ 35-Year Old): Analysis of TGFBI, DDB2 and MCM5

The aim of this study was to investigate mRNA and protein expression of three genes (Transforming Growth Factor Beta Induced (TGFBI), Damaged-Specific DNA Binding (DDB2) and Minichromosomal Maintenance-5 (MCM5)) in breast cancers. Q-RT-PCR (36 cancers, 8 normal/benign tissues and 9 organoid samples), western blotting (6 cell lines, 6 cancers and 4 normal/benign tissues) and immunohistochemistry (67 breast cancers) were performed, and for TGFBI functional assays (viability, apoptosis and invasion) were carried out in two cell lines (ZR-75-1 and MDA-MB-468) after transient transfection with recombinant TGFBI and vector controls. TGFBI showed reduced mRNA and protein expression in all cancer cell lines relative to HBL-100. The mRNA levels were also significantly lower in breast cancers compared to normal/benign tissues. Immunohistochemistry results showed that 46 / 67 breast cancers were negative or had <1% nuclear staining. There was a significant correlation between TGFBI mRNA levels and patient age; with lower levels expressed in younger women (p=0.04). Higher expression of DDB2 mRNA was observed in ER/PR positive (MCF-7, T47-D and ZR-75-1) compared to ER/PR negative (HBL-100, MDA-MB-231 and MDA-MB-468) cell lines. Higher DDB2 mRNA levels was significantly correlated with ER positive (p=0.04) and grade II (p=0.02) tumours; lower levels were associated with younger patient age (p=0.025). In addition, higher DDB2 protein expression was associated with ER (p=0.001) and PR (p=0.004). Elevated MCM5 mRNA and protein levels were observed in MCF-7 and MDA-MB-231. MCM5 immunoreactivity was significantly correlated with low grade (p=0.02) and ER/PR positive (ER p=0.04 and PR p=0.01) tumours. Transfection with TGFBI had no effect on viability, apoptosis and invasion of ZR-75-1 and MDA-MB-468 cells. In conclusion, the results fail to support the hypothesis of this study, namely that expression of TGFBI, DDB2 and MCM5 could contribute to the more aggressive features of sporadic breast cancers in younger women.