THE CIRCADIAN EXPRESSION OF c-MYC IS MODULATED BY THE HISTONE DEACETYLASE INHIBITOR TRICHOSTATIN A IN SYNCHRONIZED MURINE NEUROBLASTOMA CELLS

Abstract

Circadian clocks govern the mammalian physiology in a day/night-dependent manner. The circadian oscillator of peripheral organs is composed of the same elements as the central pacemaker at the suprachiasmatic nucleus (SCN). The interaction between the circadian clock and several cell cycle components has been established in recent years, since many key regulators of cell cycle and growth control were proved to be rhythmically expressed. In particular, the proto-oncogene c-Myc has been documented to be under circadian regulation. Given that it is overexpressed in many malignancies, the study of c-Myc mRNA and c-MYC protein regulation by the circadian clock is of great interest. Thus, the aim of this work was to: (a) analyze in detail the circadian oscillations of c-Myc steady-state mRNA levels and to investigate whether c-MYC protein levels display any oscillating pattern, and (b) ascertain whether circadian time is important for reducing c-MYC levels after drug application. For this purpose, we selected trichostatin A (TSA), since it is known that long (>or=12 h) treatment durations negatively influence the expression levels of c-Myc and short 2 h treatments up regulate the expression of the central oscillator gene Per1 resulting in the resetting of its rhythm. TSA is a specific inhibitor of histone deacetylases (HDACs), and its application results in increased acetylation levels of histone and non-histone proteins. Our results, using the murine neuroblastoma cell line N2A, show that Per1 and c-Myc steady-state mRNA levels oscillate with the same phase. Moreover, a short 2 h TSA treatment causes a phase-dependent decrease of oscillating c-Myc transcript levels only when applied at the trough of its mRNA rhythm, where a general decrease of c-MYC protein levels is also observed. At the peak of its rhythm, no apparent changes can be observed. These experiments demonstrate for the first time that a significant decrease in c-Myc transcript and protein levels can be achieved after a short TSA treatment applied only at specific circadian times. This is also followed by a reduction in the proliferation rate of the cell population.

Circadian Epigenomic Remodeling and Hepatic Lipogenesis: Lessons from HDAC3

“…The present study suggests potential side effects of these small molecules due to disruption of circadian rhythm and derangement of metabolism. In line with this notion, HDAC inhibitors have been shown to alter expression of circadian genes (Repouskou et al 2010; Sanchis-Segura et al 2009). On the other hand, these epigenetic drugs could also be useful in manipulating the circadian rhythm in a beneficial way (Perreau-Lenz et al 2007).…”

Coffee and caffeine potentiate the antiamyloidogenic activity of melatonin via inhibition of Aβ oligomerization and modulation of the Tau-mediated pathway in N2a/APP cells

“… 88 – 90 It has also been shown that there is a circadian clock in N2a cells and that treatments were only effective at specific circadian times. 91 Abnormal and disturbed circadian rhythms are common in AD. 30 , 46 Chronotherapeutic approaches aimed at bolstering weakened circadian rhythms in AD produce beneficial outcomes.…”

The Circadian Clock in Cancer Development and Therapy

“…Deregulation of c-Myc in cooperation with loss of function in p53 promotes neoplastic transformation, tumor initiation, maintenance and metastasis 205 . In addition to clock-controlled chromatin remodeling, BMAL1/CLOCK and BMAL1/NPAS2 directly regulate c-Myc transcription via the two E-boxes in the P1 promoter of c-Myc 124,149,206. Disruption of circadian rhythm leads to deregulation of c-Myc which is coupled with increased neoplastic growth in mice, suggesting that the control of G1 cell cycle initiation is one of the key mechanisms for circadian control of tumor suppression 29,124,149 .…”

“…Disruption of circadian rhythm leads to deregulation of c-Myc which is coupled with increased neoplastic growth in mice, suggesting that the control of G1 cell cycle initiation is one of the key mechanisms for circadian control of tumor suppression 29,124,149 . Many key cell cycle regulators, such as Cdk4, Itga6, Wnt3, LHx2, Tcf4, Sox 9, Smad7 and Wee1 are also directly regulated at the transcriptional level by BMAL1/CLOCK heterodimer via E-box-mediated interaction in the gene promoters 126,167,206 . p53 and MDM2 are controlled indirectly by the Per genes via the tumor suppressor ataxia-telangiectasia mutated (ATM) at the post-transcriptional level 29,98 .…”