Period-2: a tumor suppressor gene in breast cancer

Shulin Xiang¹ , Seth B Coffelt² , Lulu Mao¹ , Lin Yuan¹ , Qi Cheng¹ and Steven M Hill¹^,3

¹Department of Structural and Cellular Biology, Tulane University Health Sciences Center, New Orleans, LA 70112, USA

²Department of Microbiology and Immunology, Tulane University Health Sciences Center, New Orleans, LA 70112, USA

³Tulane Cancer Center, Tulane University Health Sciences Center, New Orleans, LA 70112, USA

author email corresponding author email

Journal of Circadian Rhythms 2008, 6:4doi:10.1186/1740-3391-6-4


Published:	11 March 2008

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.