Role of Circadian Rhythm Gene Homolog PER3 in Breast Cancer

Institution: University of California, San Francisco
Investigator(s): Kuang-Yu Jen, M.D., Ph.D. -
Award Cycle: 2009 (Cycle 15) Grant #: 15FB-0099 Award: $45,000
Award Type: Postdoctoral Fellowship
Research Priorities
Biology of the Breast Cell>Pathogenesis: understanding the disease

Initial Award Abstract (2009)

Emerging evidence suggests that disruption of circadian rhythms (i.e., the 24-hour cycle involved in biochemical, physiological or behavioral processes) and underlying genes may play a significant role in cancer. Women with disrupted sleep cycles are more likely to develop breast cancer. In fact, Period 3 (PER3), a mammalian homolog of the Drosophila (fruit fly) circadian rhythm gene period, contains a coding polymorphism that is associated with an increased risk of breast cancer in younger women. Interestingly, Per3 is not required for central regulation of circadian rhythms in mice since targeted disruption of Per3 result in minimal circadian abnormalities. However, our preliminary data indicate that when Per3-deficient mice are exposed to carcinogens, they are more prone to develop cancer, in particular breast tumors. In addition, mice with Her2/neu overexpression have an accelerated course of developing malignant breast cancer when Per3 is also disrupted. We have found that low levels of PER3 correlate with poor prognosis in patients with estrogen receptor (ER) positive but not ER-negative invasive ductal carcinomas. Of note, in humans PER3 is located on the short arm of chromosome 1 (1p36), a locus that is commonly lost in human cancers including breast cancer.

Our research will further examine the mechanism by which loss of Per3 can lead to breast tumor formation in mice and determine whether Per3 is useful prognostic biomarker. To address these aims, we will: (1) Characterize the molecular defects that contribute to breast tumor development in Per3-deficient mice when exposed to genotoxic stresses (DNA damage); (2) evaluate the utility of PER3 expression as a prognostic marker for ER-positive invasive ductal carcinoma; and (3) determine the effects of PER3 expression on estrogen and tamoxifen sensitivity. Using mouse models, we will examine various aspects of the genotoxic stress response including proliferative activity, ability to elicit cell cycle arrest, extent of apoptosis, and ability to repair DNA and maintain genomic stability following DNA damage. Similar work will be performed in human breast cancer cell lines that either overexpress PER3 or have PER3 knocked-down by short hairpin RNA (shRNA) inhibition. Next, we will also determine the mRNA level of PER3 in a panel of approximately 400 primary human breast cancer specimens to validate whether PER3 expression is a prognostic marker in human ER-positive invasive ductal carcinoma. Finally, we will examine the effects of PER3 on hormone sensitivity in human breast cancer cell lines.

These studies will allow us to better understand PER3 function and its relationship to breast cancer, breast cancer prognosis, and hormone sensitivity in ER-positive breast tumors.

Final Report (2010)

Note: the PI resigned after 1-yr to pursue medical training.

Many environmental factors contribute to breast cancer susceptibility. It is increasingly apparent that disruption of day-night cycles (i.e. sleep disruption) leads to an increased breast cancer risk. For instance, women who work night-shifts exhibit higher incidences of breast cancer. Day-night cycles, termed circadian rhythms, are controlled by defined molecular pathways. Circadian rhythm genes show daily cycles in their gene expression and protein activity. We previously discovered that mice deficient in one of the circadian rhythm genes, known as Period3 (Per3), are more susceptible to developing breast tumors following exposure to carcinogens.

Therefore, we proceeded to better define the mechanism by which Per3 deficiency can lead to breast cancer formation. We discovered that a certain type of cell known as mouse embryonic fibroblasts (MEFs) taken from Per3 deficient mice grow slower than MEFs from normal mice. However, when we exposed these cells to radiation or chemical carcinogens, both of which cause DNA damage, we saw no difference in pathways related to DNA damage repair. Therefore, the cancer susceptibility in Per3-deficient mice is likely not attributed to their acute ability to repair DNA damage.

Future plans include determining whether more long term changes following DNA damage contribute to the observed increase in breast cancer susceptibly. We also showed that patients with breast cancers that express low amounts of PER3 are more likely to relapse to anti-hormone treatment. This data was recently published in the Journal of Clinical Oncology. As a next step, we propose to examine whether lowering PER3 levels in breast cancer cell lines can blunt their sensitivity to hormone inhibitors (i.e. tamoxifen). Thus far, we have successfully lowered PER3 levels in several breast cancer cell lines. We plan to test their sensitivities to tamoxifen in the near future. We also proposed to attempt to evaluate the utility of using PER3 levels in breast cancers from patients as a marker for prognosis. Unfortunately, our breast cancer samples were of poor quality. Therefore, we were not able to further pursue this endeavor.

Deletion of the PER3 gene on chromosome 1p36 in recurrent ER-positive breast cancer.
Periodical:Journal of Clinical Oncology
Index Medicus: J Clin Oncol
Authors: Climent J, Perez-Losada J, Quigley DA, Kim IJ, Delrosario R, Jen KY, et al, and Balmain A
Yr: 2010 Vol: 28 Nbr: 23 Abs: Pg:3770-8