Cancer and Aging: Why Bother about Light at Night?

Shift work which causes circadian disruption is an established cancer risk factor. A large body of experimental and epidemiological data proves that exposure to light at night promotes carcinogenesis in various tissues and accelerates aging [1-3]. Artificial or natural light through master clock located in suprachiasmatic nuclei of hypothalamus suppresses night peak of melatonin synthesis in the pineal gland. Melatonin is known to exert antioxidant, antigonadotropic, immunostimulating and anticancer effects [4-6]. Except direct antioxidant action through free radicals scavenging melatonin works as a chronobiotic which tunes cellular clock. Exact molecular pathway by which melatonin regulates cellular clock is still not established. Melatonin is a ligand for two membrane-bound Gprotein coupled receptors, MT1 and MT2 [7]; in nucleus it interacts with members of retinoid-related orphan nuclear receptor family (RORalpha/RZRalpha) [8]. One of the latter, RORa, is a part of cellular clock machinery.