title: Period-2: a tumor suppressor gene in breast cancer.
abstract: Previous reports have suggested that the ablation of the Period 2 gene (Per 2) leads to enhanced development of lymphoma and leukemia in mice. Employing immunoblot analyses, we have demonstrated that PER 2 is endogenously expressed in human breast epithelial cell lines but is not expressed or is expressed at significantly reduced level in human breast cancer cell lines. Expression of PER 2 in MCF-7 breast cancer cells significantly inhibited the growth of MCF-7 human breast cancer cells, and, when PER 2 was co-expressed with the Crytochrome 2 (Cry 2) gene, an even greater growth-inhibitory effect was observed. The inhibitory effect of PER 2 on breast cancer cells was also demonstrated by its suppression of the anchorage-independent growth of MCF-7 cells as evidenced by the reduced number and size of colonies. A corresponding blockade of MCF-7 cells in the G1 phase of the cell cycle was also observed in response to the expression of PER 2 alone or in combination with CRY 2. Expression of PER 2 also induced apoptosis of MCF-7 breast cancer cells as demonstrated by an increase in PARP [poly (ADP-ribose) polymerase] cleavage. Finally, our studies demonstrate that PER 2 expression in MCF-7 breast cancer cells is associated with a significant decrease in the expression of cyclin D1 and an up-regulation of p53 levels.
authors.affiliation: Department of Structural and Cellular Biology, Tulane University Health Sciences Center, New Orleans, LA 70112, USA. smhill@tulane.edu.
authors.forename: Shulin
authors.initials: S
authors.lastname: Xiang
authors.forename: Seth B
authors.initials: SB
authors.lastname: Coffelt
authors.forename: Lulu
authors.initials: L
authors.lastname: Mao
authors.forename: Lin
authors.initials: L
authors.lastname: Yuan
authors.forename: Qi
authors.initials: Q
authors.lastname: Cheng
authors.forename: Steven M
authors.initials: SM
authors.lastname: Hill