Circadian Alterations Increase with Progression in a Patient-Derived Cell Culture Model of Breast Cancer

Circadian rhythms are critical regulators of many physiological and behavioral functions; disruption of this time-tracking system can elicit the development of various diseases, including breast cancer. While multiple studies have used cell lines to study the correlation between altered circadian rhythms and cancer, these cells generally have different genetic backgrounds and do not mirror the changes that occur with disease development. Isogenic cell models can represent and recapitulate changes across cancer progression. Hence in the present study, a patient-derived breast cancer model, the 21T series, was used to evaluate changes to circadian oscillations of core clock protein transcription and translation as cells progress from normal to malignant states. Three cell lines from the series were used: H16N2, from normal breast epithelium; 21PT, from Atypical Ductal Hyperplasia; and 21MT, from Invasive Metastatic Carcinoma. Both of the cancerous cell lines are HER2 positive. We assessed the transcriptional profiles of two core circadian clock proteins, BMAL1 and PER2, which represent a positive and negative component of the molecular oscillator. In the normal H16N2 cells, BMAL1 and PER2 both possessed rhythmic mRNA oscillations with close to standard periods and the expected anti-phase relationship. However, in the cancerous cells, consistent changes were observed: both clock genes had periods that deviated farther from normal and did not have an anti-phase relationship. To provide a more complete understanding of circadian alterations in breast cancer, luciferase reporters and real-time luminometry should be used in future studies.