Pttg1 Promotes Growth of Breast Cancer through P27 Nuclear Exclusion

Abstract

Background/Aims: A role of Pituitary Tumor Transforming Gene 1 (Pttg1) in the carcinogenesis has been shown in some cancers, but not in BC (BC). Methods: We compared the levels of Pttg1 in the resected BC tissue with the adjacent normal breast tissue from the same patient. We modified Pttg1 levels in a BC cell line, MCF7, by either a Pttg1 transgene, or a Pttg1 shRNA. The cell growth was measured in an MTT assay. The cell apoptosis was measured by apoptosis assay. The nuclear protein of cell-cycle-related genes was examined in Pttg1-modifed BC cells. Co-immunoprecipitation was performed to examine the association of Pttg1 and p27. Results: We detected significantly higher levels of Pttg1 in the resected BC tissue, compared to the adjacent normal breast tissue from the same patient. Overexpression or depletion of Pttg1 in MCF7 significantly increased or inhibited cell growth, respectively. Changes in Pttg1 levels, however, did not alter cell apoptosis, suggesting that Pttg1 increases cell growth through augmented cell proliferation, rather than decreased cell apoptosis. Among all examined cell-cycle-related proteins in Pttg1-modifed BC cells, only nuclear p27 levels were significantly affected. Further, co-immunoprecipitation showed that Pttg1 directly associated with p27. Conclusion: Pttg1 may increase BC cell growth through nuclear exclusion of p27, which highlights a novel molecular regulatory machinery in tumorigenesis of BC.