IFITM1 modulates circadian rhythm by regulating CRY1 dtability

Circadian rhythm, generated by the central and peripheral clocks, regulates nearly all physiological and behavioral processes by synchronizing internal time to the earth's rotation within a period of 24 hours. Hence, disruption of circadian rhythm causes different types of diseases such as cancer, cognitive impairments, metabolic diseases, psychiatric illnesses, and immune system-related disorders. At the molecular level, the circadian clock is controlled by the interlocking of positive and negative transcriptional- translational feedback loops (TTFL). In the positive loop, BMAL1 and CLOCK form a heterodimer and initiate the transcription of clock-controlled genes (CCG), including Per and Cry, by binding E-BOX elements. In the negative loop of TTFL, Later, a heterodimer of CRY and PER interact with casein kinase Ie (CKIe) and translocates to the nucleus to repress the transactivation of BMAL1:CLOCK, thus transcription of CCG. In this thesis, I demonstrated that IFITM1, a transmembrane protein taking a role in the immune defense under viral attack and identified by machine learning, functionally interacts with CRY1 through the C-terminal domain of CRY1 in the nucleus. Knockout of IFITM1 by CRISPR/Cas9 in U2-OS Bmal1-dluc cells leads to period lengthening by 1.28 h and dampening of the amplitude. Further, biochemical studies showed that IFITM1 increases the half-life of CRY1 significantly and represses the BMAL1:CLOCK-driven transcription, hence modulating circadian rhythmicity. Moreover, treatment of U2OS cells with poly (I: C) result in an increased level of IFITM1 and a change in circadian period length. This suggests that IFITM1-CRY1 interaction may be important for regulating cellular circadian physiology and circadian clock-driven immune system regulation.