Ribonucleotide reductase and thymidylate synthase or exogenous deoxyribonucleosides reduce DNA damage and senescence caused by C-MYC depletion

Abstract

The down-regulation of dominant oncogenes, including C-MYC, in tumor cells often leads to the induction of senescence via mechanisms that are not completely identified. In the current study, we demonstrate that MYC-depleted melanoma cells undergo extensive DNA damage that is caused by the underexpression of thymidylate synthase (TS) and ribonucleotide reductase (RR) and subsequent depletion of deoxyribonucleoside triphosphate pools. Simultaneous genetic inhibition of TS and RR in melanoma cells induced DNA damage and senescence phenotypes very similar to the ones caused by MYC-depletion. Reciprocally, overexpression of TS and RR in melanoma cells or addition of deoxyribo-nucleosides to culture media substantially inhibited DNA damage and senescence-associated phenotypes caused by C-MYC depletion. Our data demonstrate the essential role of TS and RR in C-MYC-dependent suppression of senescence in melanoma cells.

Identification of ribonucleotide reductase M2 as a potential target for pro-senescence therapy in epithelial ovarian cancer

“…1 and 2; Table 1), which corroborates with data from recent studies that show RRM2 is overexpressed in EOCs. 35,36 RRM2 upregulation is sufficient to overcome the senescence-associated cell growth arrest tumor suppression mechanism, [23][24][25][26] implying that RRM2 may drive proliferation of transformed cells. Indeed, we observed that RRM2 expression positively correlates with the expression of the cell proliferation marker Ki67 (Table 1).…”

“…16,22,42 These results are consistent with previous reports from our lab and others. [23][24][25][26] Cisplatin, which is the primary front-line chemotherapy used for EOC, 5 also induces DNA damage. 43 Therefore, it is interesting to speculate whether there might be synergism between RRM2 inhibition and cisplatin treatment to increase the DNA damage to a threshold beyond which senescence would occur.…”

“…This correlates with the changes in DNA damage response during senescence. [23][24][25][26] Interestingly, senescence induced by C-MYC depletion in melanoma cells suppresses RRM2 expression and the subsequent depletion of dNTP pools. 24 This raises the possibility that RRM2 is a bona fide target for driving cancer cells to undergo senescence and the associated stable cell growth arrest and, thus, represents a target for the development of pro-senescence therapies.…”

Deoxyribonucleotide metabolism, mutagenesis and cancer

“…This is a stable growth arrest that occurs when an activated oncogene is expressed in a normal cell. Mannava et al 96,97 found that human fibroblasts undergoing OIS induced by HRAS-G12V or MYC expression underexpressed both RNR and thymidylate synthase and contained low dNTP pools. Ectopic expression of the two enzymes restored dNTP pools and suppressed senescence-associated phenotypes.…”

Controversial aspects of oncogene-induced senescence

“…Interestingly, a similar role of dNTP pools in control of DNA damage and senescence phenotypes was shown in melanoma cells undergoing senescence due to depletion of C-MYC oncogene. 80 SSB engage serine/threonine-protein kinase ATR (ataxia telangiectasia and Rad3-related protein), which activates checkpoint kinase 1 (CHK1). CHK1, in turn, phosphorylates CDC25, one of the key regulators of cell cycle progression, causing its degradation.…”