BMAL1 knockdown triggers different colon carcinoma cell fates by altering the delicate equilibrium between AKT/mTOR and P53/P21 pathways.

Yuan Zhang,Aurore Devocelle,Julien Giron-Michel,Christophe Desterke,Annabelle Ballesta,Rachel Sherrard,Lucas Souza,Sabrina Tenreira Bento,Yunhua Chang,Adlen Foudi,Rene Adam

doi:10.18632/aging.103124

Abstract

Dysregulation of the circadian timing system (CTS) frequently appears during colorectal cancer (CRC) progression. In order to better understand the role of the circadian clock in CRC progression, this study evaluated in vitro how knockdown of a core circadian protein BMAL1 (BMAL1-KD) influenced the behavior of two primary human CRC cell lines (HCT116 and SW480) and a metastatic CRC cell line (SW620).Unexpectedly, BMAL1-KD induced CRC cell-type specific responses rather than the same phenomenon throughout. First, BMAL1-KD increased AKT/mTOR activation in each CRC cell line, but to different extents. Second, BMAL1-KD-induced P53 activation varied with cell context. In a wild type P53 background, HCT116 BMAL1-KD cells quickly underwent apoptosis after shBMAL1 lentivirus transduction, while surviving cells showed less P53 but increased AKT/mTOR activation, which ultimately caused higher proliferation. In the presence of a partially functional mutant P53, SW480 BMAL1-KD cells showed moderate P53 and mTOR activation simultaneously with cell senescence. With a moderate increased AKT but unchanged mutant P53 activation, SW620 BMAL1-KD cells grew faster.Thus, under different CRC cellular pathological contexts, BMAL1 knockdown induced relatively equal effects on AKT/mTOR activation but different effects on P53 activation, which finally triggered different CRC cell fates.

Highlights

The circadian timing system (CTS) exists in most living organisms with a basic molecular frame preserved from fungi to Drosophila and humans
Our results revealed that BMAL1-KD activated AKT/mTOR in the three colorectal cancer (CRC) cell lines (HCT116, SW480 or SW620), but had different effects on P53 activation. mTOR signaling is an evolutionarily conserved nutrient sensing pathway and a central regulator of mammalian metabolism
BMAL1 expression was significantly decreased compared to control at mRNA (Figure 1A, Quantitative RT-PCR (qRT-PCR)) and protein levels (Figure 1B, Western blot) in all three BMAL1-KD cell lines, despite the fact that the two primary CRC cell lines exhibited much higher BMAL1 expression than the metastatic CRC cell line SW620

Summary

Introduction

The circadian timing system (CTS) exists in most living organisms with a basic molecular frame preserved from fungi to Drosophila and humans. This system coordinates behavior of the whole organism, including physiology and metabolism, with environmental cycles of 24h. The suprachiasmatic nuclei of the hypothalamus coordinate circadian rhythms via peripheral molecular clocks composed of at least fifteen genes that are expressed in every cell. Expression of these clock gene is regulated by transcription factors organized in positive (BMAL1 and CLOCK) or negative (PER and CRY) feedback loops. BMAL1 is central to circadian timing and is the only clock gene whose deletion causes an immediate loss of behavioral circadian rhythmicity [1, 3]

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Discussion

Conclusion