Direct role of nucleotide metabolism in C-MYC-dependent proliferation of melanoma cells

Abstract

To identify C-MYC targets rate-limiting for proliferation of malignant melanoma, we stably inhibited C-MYC in several human metastatic melanoma lines via lentivirus-based shRNAs approximately to the levels detected in normal melanocytes. C-MYC depletion did not significantly affect levels of E2F1 protein reported to regulate expression of many S-phase specific genes, but resulted in the repression of several genes encoding enzymes rate-limiting for dNTP metabolism. These included thymidylate synthase (TS), inosine monophosphate dehydrogenase 2 (IMPDH2) and phosphoribosyl pyrophosphate synthetase 2 (PRPS2). C-MYC depletion also resulted in reduction in the amounts of deoxyribonucleoside triphosphates (dNTPs) and inhibition of proliferation. shRNA-mediated suppression of TS, IMPDH2 or PRPS2 resulted in the decrease of dNTP pools and retardation of the cell cycle progression of melanoma cells in a manner similar to that of C-MYC-depletion in those cells. Reciprocally, concurrent overexpression of cDNAs for TS, IMPDH2 and PRPS2 delayed proliferative arrest caused by inhibition of C-MYC in melanoma cells. Overexpression of C-MYC in normal melanocytes enhanced expression of the above enzymes and increased individual dNTP pools. Analysis of in vivo C-MYC interactions with TS, IMPDH2 and PRPS2 genes confirmed that they are direct C-MYC targets. Moreover, all three proteins express at higher levels in cells from several metastatic melanoma lines compared to normal melanocytes. Our data establish a novel functional link between C-MYC and dNTP metabolism and identify its role in proliferation of tumor cells.

Probing the Active Site of the Deoxynucleotide N-Hydrolase Rcl Encoded by the Rat Gene c6orf108

“…c-Myc directly activates genes involved in purine and pyrimidine biosynthesis, and a deregulation of c-Myc leads to an increase in nucleotide pools (38) (39). Paradoxically, c-Myc also activates rcl expression (1), whose product hydrolyzes dNMP.…”

Pharmacological targeting of guanosine monophosphate synthase suppresses melanoma cell invasion and tumorigenicity

“…7,33,34 A specific inhibitor of IMPDH enzymes, MPA has been used as an immunosuppressant during organ transplant. [35][36][37] A better bioavailable form of MPA is its prodrug MMF (over 200% improvement in bioavailability), 38 which has also been proposed as anti-cancer therapy.…”

“…[6][7][8][9] Recently, we have identified a fundamental connection between melanoma invasion and biosynthesis of guanylates, 8 suggesting that distortion of the guanylate metabolism facilitates melanoma progression.…”

c-MYC-Induced Genomic Instability

“…In MYC transgenic mouse livers, most of these target genes had increased expression on MYC induction. Also, when MYC was inhibited through lentivirus-based shRNAs in human metastatic melanoma cell lines, the genes encoding enzymes important for dNTP metabolism were repressed and the amount of dNTPs were reduced (Mannava et al 2008). Last, Myc controls the ATR DNA repair pathway that is activated in response to specific single-stranded DNA produced during replication stress (Schoppy et al 2012).…”