Since the identification of the first RNA demethylase and the establishment of methylated RNA immunoprecipitationsequencing methodology 6 to 7 years ago, RNA methylation has emerged as a widespread phenomenon and a critical regulator of transcript expression. This new layer of regulation is termed "epitranscriptomics." The most prevalent RNA methylation, N 6-methyladenosine (m 6 A), occurs in approximately 25% of transcripts at the genome-wide level and is enriched around stop codons, in 5 0-and 3 0-untranslated regions, and within long internal exons. RNA m 6 A modification regulates RNA splicing, translocation, stability, and translation into protein. m 6 A is catalyzed by the RNA methyltransferases METTL3, METTL14, and METTL16 (writers), is removed by the demethylases FTO and ALKBH5 (erasers), and interacts with m 6 A-binding proteins, such as YTHDF1 and IGF2BP1 (readers). RNA methyltransferases, demethylases, and m 6 Abinding proteins are frequently upregulated in human cancer tissues from a variety of organ origins, increasing oncotranscript and oncoprotein expression, cancer cell proliferation, survival, tumor initiation, progression, and metastasis. Although RNA methyltransferase inhibitors are not available yet, FTO inhibitors have shown promising anticancer effects in vitro and in animal models of cancer. Further screening for selective and potent RNA methyltransferase, demethylase, or m 6 A-binding protein inhibitors may lead to compounds suitable for future clinical trials in cancer patients.

Gene expression and deacetylase activity of the class III histone deacetylase SIRT1 are up-regulated in cancer cells due to oncogene overexpression or loss of function of tumor suppressor genes. SIRT1 induces histone deacetylation and methylation, promoter CpG island methylation, transcriptional repression, and deacetylation of tumor suppressor proteins. SIRT1 may play a critical role in tumor initiation, progression, and drug resistance by blocking senescence and apoptosis, and promoting cell growth and angiogenesis. SIRT1 inhibitors have shown promising anticancer effects in animal models of cancer. Further screening for more potent SIRT1 inhibitors may lead to compounds suitable for clinical trials in patients.

The N-Myc oncoprotein is a critical factor in neuroblastoma tumorigenesis which requires additional mechanisms converting a low-level to a high-level N-Myc expression. N-Myc protein is stabilized when phosphorylated at Serine 62 by phosphorylated ERK protein. Here we describe a novel positive feedback loop whereby N-Myc directly induced the transcription of the class III histone deacetylase SIRT1, which in turn increased N-Myc protein stability. SIRT1 binds to Myc Box I domain of N-Myc protein to form a novel transcriptional repressor complex at gene promoter of mitogen-activated protein kinase phosphatase 3 (MKP3), leading to transcriptional repression of MKP3, ERK protein phosphorylation, N-Myc protein phosphorylation at Serine 62, and N-Myc protein stabilization. Importantly, SIRT1 was up-regulated, MKP3 down-regulated, in pre-cancerous cells, and preventative treatment with the SIRT1 inhibitor Cambinol reduced tumorigenesis in TH-MYCN transgenic mice. Our data demonstrate the important roles of SIRT1 in N-Myc oncogenesis and SIRT1 inhibitors in the prevention and therapy of N-Myc–induced neuroblastoma.

RNA N6-methyladenosine (m6A) modification occurs in approximately 25% of mRNAs at the transcriptome-wide level. RNA m6A is regulated by the RNA m6A methyltransferases methyltransferase-like 3 (METTL3), METTL14, and METTL16 (writers), demethylases FTO and ALKBH5 (erasers), and binding proteins YTHDC1–2, YTHDF1–3, IGF2BP1–3, and SND1 (readers). These RNA m6A modification proteins are frequently upregulated or downregulated in human cancer tissues and are often associated with poor patient prognosis. By modulating pre-mRNA splicing, mRNA nuclear export, decay, stability, and translation of oncogenic and tumor suppressive transcripts, RNA m6A modification proteins regulate cancer cell proliferation, survival, migration, invasion, tumor initiation, progression, metastasis, and sensitivity to anticancer therapies. Importantly, small-molecule activators of METTL3, as well as inhibitors of METTL3, FTO, ALKBH5, and IGF2BP1 have recently been identified and have shown considerable anticancer effects when administered alone or in combination with other anticancer agents, both in vitro and in mouse models of human cancers. Future compound screening and design of more potent and selective RNA m6A modification protein inhibitors and activators are expected to provide novel anticancer agents, appropriate for clinical trials in patients with cancer tissues harboring aberrant RNA m6A modification protein expression or RNA m6A modification protein–induced resistance to cancer therapy.

Our data demonstrate the important roles of lncUSMycN and NonO in regulating N-Myc expression and neuroblastoma oncogenesis and provide the first evidence that amplification of long noncoding RNA genes can contribute to tumorigenesis.