Regulation of the human IGF2 gene displays multiple layers of control, which secures a genetically and epigenetically predetermined gene expression pattern throughout embryonal growth and postnatal life. These predominantly nuclear regulatory mechanisms converge on the function of the IGF2-H19 gene cluster on Chromosome 11 and ultimately affect IGF2 gene expression. Deregulation of such control checkpoints leads to the enhancement of IGF2 gene transcription and/or transcript stabilization, ultimately leading to IGF-II peptide overproduction. This type of anomaly is responsible for the effects observed in terms of both abnormal fetal growth and increased cell proliferation, typically observed in pediatric overgrowth syndromes and cancer. We performed a review of relevant experimental work on the mechanisms affecting the human IGF2 gene at the epigenetic, transcriptional and transcript regulatory levels. The result of our work, indeed, provides a wider and diversified scenario for IGF2 gene activation than previously envisioned by shedding new light on its extended regulation. Overall, we focused on the functional integration between the epigenetic and genetic machinery driving its overexpression in overgrowth syndromes and malignancy, independently of the underlying presence of loss of imprinting (LOI). The molecular landscape provided at last strengthens the role of IGF2 in cancer initiation, progression and malignant phenotype maintenance. Finally, this review suggests potential actionable targets for IGF2 gene- and regulatory protein target-degradation therapies.
Keywords: (IGF2/H19) IG-DMR, intergenic differentially methylated region; BWS, Beckwith–Wiedemann syndrome; CCD, centrally conserved domain; CNV, copy number variation; CTCF, CCCTC binding factor; DMD, differentially methylated domain; DMR, differentially methylated region; GOM, gain of methylation; ICR1, imprinting control region 1; IGF-II, insulin-like growth factor-2 peptide; IGF2, insulin-like growth factor 2 gene; LOI, loss of imprinting; LOM, loss of methylation; MOI, maintenance of imprinting; SRS, Silver Russel Syndrome; TF: transcription factor; UPD, uniparental disomy; WT1, Wilms Tumor protein 1; mRNA transcript; p0–p4: IGF2 promoters 0–4.