Circadian gating of epithelial-to-mesenchymal transition in breast cancer cells via melatonin-regulation of GSK3ß.

ABSTRACT

Disturbed sleep-wake cycle and circadian rhythmicity are associated with cancer, but the underlying mechanisms are unknown. Employing a tissue-isolated human breast xenograft tumor nude rat model, we observed that glycogen synthase kinase 3ß (GSK3ß), an enzyme critical in metabolism and cell proliferation/survival, exhibits a circadian rhythm of phosphorylation in human breast tumors. Exposure to light-at-night suppresses the nocturnal pineal melatonin synthesis, disrupting the circadian rhythm of GSK3ß phosphorylation. Melatonin activates GSK3ß by inhibiting the serine-threonine kinase Akt phosphorylation, inducing ß-catenin degradation and inhibiting epithelial-to-mesenchymal transition, a fundamental process underlying cancer metastasis. Thus, chronic circadian disruption by light-at-night via occupational exposure or age-related sleep disturbances may contribute to cancer incidence and the metastatic spread of breast cancer by inhibiting GSK3ß activity and driving epithelial-to-mesenchymal transition in breast cancer patients.