c-Myc binds to human ribosomal DNA and stimulates transcription of rRNA genes by RNA polymerase I

Abstract

c-Myc coordinates cell growth and division through a transcriptional programme that involves both RNA polymerase (Pol) II- and Pol III-transcribed genes. Here, we demonstrate that human c-Myc also directly enhances Pol I transcription of ribosomal RNA (rRNA) genes. rRNA synthesis and accumulation occurs rapidly following activation of a conditional MYC-ER allele (coding for a Myc-oestrogen-receptor fusion protein), is resistant to inhibition of Pol II transcription and is markedly reduced by c-MYC RNA interference. Furthermore, by using combined immunofluorescence and rRNA-FISH, we have detected endogenous c-Myc in nucleoli at sites of active ribosomal DNA (rDNA) transcription. Our data also show that c-Myc binds to specific consensus elements located in human rDNA and associates with the Pol I-specific factor SL1. The presence of c-Myc at specific sites on rDNA coincides with the recruitment of SL1 to the rDNA promoter and with increased histone acetylation. We propose that stimulation of rRNA synthesis by c-Myc is a key pathway driving cell growth and tumorigenesis.

The balance between rRNA and ribosomal protein synthesis up- and downregulates the tumour suppressor p53 in mammalian cells

“…Insulin and IGF-1 stimulate the activity of polymerase I transcription by elevating both UBF protein level and phosphorylation (Hannan et al, 1998;Wu et al, 2005). Partial hepatectomy induces a progressive increase in rRNA synthesis (up to 24 h after operation) in regenerating rat hepatocytes (Sirri et al, 1995) very likely due to the induction of c-myc (Thompson et al, 1986), which controls the RNA polymerase I activity (Arabi et al, 2005;Grandori et al, 2005;Grewal et al, 2005). Cortisol at the dose used in the present experiments stimulated rRNA transcription in rat hepatocytes (Sirri et al, 1995) by activating the glycocorticoid receptor signalling (Glibetic et al, 1993), while inhibiting their proliferation (Nadal, 1995).…”

“…The mean DCT value of the control sample was used in each experiment to calculate the DDCT value of sample replicates. POLR1A, p21 and the internal control b-glucuronidase mRNAs were quantified with TaQMan Gene Expression Assays primers and probe kits (Applied Biosystems); primers and UPL probe (Roche Diagnostics, Milan, Italy) for rpL11 and rpL5 were chosen with the Roche online primer design tool, primers for SYBR Green real-time PCR analysis of human Bax, PUMA and rat p21, Bax, and PUMA were designed using the same online tool; primers for human and rat 45S rRNA have been already described by Grandori et al (2005)and Murayama et al (2008), respectively. All sequences are available upon request.…”

Pontin is localized in nucleolar fibrillar centers

“…ReChIP was essentially performed as the first ChIP. For the detection of rDNA initiator-and terminator-regions primer-sets H1 and H13 were used as described previously (Grandori et al 2005). The following primers were used for detection of the GAPDH promoter: Forward-5′-TACTAGCGGTTTTACGGGCG-3′ and reverse-5′-TCGAACAGGAGGAGCAGAGAGCGA-3′ giving a 166-bp PCR product.…”

“…Several lines of evidence suggest that Pontin may act in the nucleolus: (1) Pontin interacts with c-Myc, which regulates the activity of all three RNA polymerases including RNA polymerase I (Pol I; Arabi et al 2005;Grandori et al 2005), (2) Pontin is a part of the Uri complex that includes Rpb5, a protein associated with Pol I (Zaros et al 2007) and (3) Pontin is involved in the maturation of snoRNPs that mostly reside in the nucleolus. Indeed, Pontin was detected in nucleoli by extensive proteomic analysis (Leung et al 2006).…”

Molecular basis for the actions of Hsp90 inhibitors and cancer therapy

“…14,15 The c-Myc protein bound to TFIIIB, a RNA polymerase III-specific general transcription factor, directly activates pol III transcription, thereby stimulating ribosomal RNA production. 16,17 The tumor suppressors p53 and pRB repress TFIIIB expression. 17 The c-Myc protein itself is assumed to be necessary for c-Myc expression.…”