Enhanced expression of PP1γ1, a catalytic subunit isoform of protein phosphatase type 1, in invasive ductal carcinoma of the breast

Breast cancer is one of the most common malignancies of women. Assessing the biological parameters of malignant tumors may facilitate predictions of clinical outcome. The expression of the three catalytic subunits of protein phosphatase (PP) type 1, PP1α, PP1γ1 and PP1δ, as well as the one catalytic subunit of PP type 2, PP2AC, were examined in ten cases of mammary dysplasia, ten cases of fibroadenoma and 12 cases of invasive ductal carcinoma, using immunohistochemical analysis. Moreover, we measured the S-phase fraction of the cell cycle for use as a marker value of cell growth, using flow cytometric analysis. The percentage of proliferating cells that stained positive with antisera against PP1γ1 was significantly higher in invasive ductal carcinoma than in mammary dysplasia and fibroadenoma. Furthermore, invasive ductal carcinoma showed a markedly high number of tumor cells in the S-phase of the cell cycle, as compared to mammary dysplasia and fibroadenoma. Our results indicate that PP1γ1 may be involved in the accelerated growth of malignant cells in breast tumors.