Melatonin down‐regulates MDM2 gene expression and enhances p53 acetylation in MCF‐7 cells

Abstract

Compelling evidence demonstrated that melatonin increases p53 activity in cancer cells. p53 undergoes acetylation to be stabilized and activated for driving cells destined for apoptosis/growth inhibition. Over-expression of p300 induces p53 acetylation, leading to cell growth arrest by increasing p21 expression. In turn, p53 activation is mainly regulated in the nucleus by MDM2. MDM2 also acts as E3 ubiquitin ligase, promoting the proteasome-dependent p53 degradation. MDM2 entry into the nucleus is finely tuned by two different modulations: the ribosomal protein L11, acts by sequestering MDM2 in the cytosol, whereas the PI3K-AkT-dependent MDM2 phosphorylation is mandatory for MDM2 translocation across the nuclear membrane. In addition, MDM2-dependent targeting of p53 is regulated in a nonlinear fashion by MDM2/MDMX interplay. Melatonin induces both cell growth inhibition and apoptosis in MCF7 breast cancer cells. We previously reported that this effect is associated with reduced MDM2 levels and increased p53 activity. Herein, we demonstrated that melatonin drastically down-regulates MDM2 gene expression and inhibits MDM2 shuttling into the nucleus, given that melatonin increases L11 and inhibits Akt-PI3K-dependent MDM2 phosphorylation. Melatonin induces a 3-fold increase in both MDMX and p300 levels, decreasing simultaneously Sirt1, a specific inhibitor of p300 activity. Consequently, melatonin-treated cells display significantly higher values of both p53 and acetylated p53. Thus, a 15-fold increase in p21 levels was observed in melatonin-treated cancer cells. Our results provide evidence that melatonin enhances p53 acetylation by modulating the MDM2/MDMX/p300 pathway, disclosing new insights for understanding its anticancer effect.

Melatonin, an inhibitory agent in breast cancer

“…Since the early apoptosis is a caspase independent response, it is triggered by an Apoptotic Induce Factor (AIF) and independent of BCL-2 protein family, it was shown that exposing breast cancer cells to 1 nM concentration of melatonin within 3 h induces apoptosis through downregulation of MDM2 (murine double minute 2) and sirt1 (silent mating type information regulation 1 homolog), leading to alteration of the p53-MDM2 balance. In contrast, after a 96 h incubation of the breast cancer cells, TGF-b, caspase7, caspase9 and PARP could be considered as the main contributors of the late apoptosis [63]. Notably the cytotoxic potency of melatonin had been observed in the triple negative breast cancer cell line MDA-MB361 as well.…”

“…Several lines of evidence have shown that both melatonin cytostatic and cytotoxic actions are coupled with enhancing p53 pathway by targeting different molecules [63,66,67]. Noteworthy, the PI3 K/Akt signaling pathway is involve in DNA damage response and p53 inhibition through phosphoactivation of MDM2 (murine double minute 2), a p53 ubiquitination regulator.…”

“…Noteworthy, the PI3 K/Akt signaling pathway is involve in DNA damage response and p53 inhibition through phosphoactivation of MDM2 (murine double minute 2), a p53 ubiquitination regulator. On this basis, it was shown that melatonin not only inhibits MDM-2 transcriptional activity, but also prevents MDM-2 phosorylation through reducing the pAkt/Akt ratio, leading to elevated transactivating and acetylation of p53 in melatonin-treated breast cancer cells [63,66,67]. Moreover, due to the fundamental role of sirt1(silent mating type information regulation 1 homolog) in p53 inactivation via downregulating p300, some studies found a simultaneous decrease in sirt1 expression and p300 upregulation in response to melatonin treatment, leading to p53 acetylation and activation [63].…”

“…On this basis, it was shown that melatonin not only inhibits MDM-2 transcriptional activity, but also prevents MDM-2 phosorylation through reducing the pAkt/Akt ratio, leading to elevated transactivating and acetylation of p53 in melatonin-treated breast cancer cells [63,66,67]. Moreover, due to the fundamental role of sirt1(silent mating type information regulation 1 homolog) in p53 inactivation via downregulating p300, some studies found a simultaneous decrease in sirt1 expression and p300 upregulation in response to melatonin treatment, leading to p53 acetylation and activation [63]. By and large, an increase in the p53/MDM2 ratio guides the melatonin-treated breast cancer cells toward cell cycle arrest or apoptosis by altering the transcriptional activity of p53 downstream target genes [67].…”

“…The melatonin-induced apoptosis response is affected through both early and late apoptosis due to the incubating time [63]. Since the early apoptosis is a caspase independent response, it is triggered by an Apoptotic Induce Factor (AIF) and independent of BCL-2 protein family, it was shown that exposing breast cancer cells to 1 nM concentration of melatonin within 3 h induces apoptosis through downregulation of MDM2 (murine double minute 2) and sirt1 (silent mating type information regulation 1 homolog), leading to alteration of the p53-MDM2 balance.…”