IGF-2
IGF-2 (Insulin-like Growth Factor 2) is a 67 amino acid peptide hormone critical for fetal growth and development, regulated by genomic imprinting. It signals through IGF-1R, insulin receptor isoform A, and its own IGF-2R (mannose-6-phosphate receptor), with roles in cancer biology, metabolism, and tissue repair.
IGF-2 (Insulin-like Growth Factor 2) is a 67 amino acid single-chain peptide hormone with structural homology to both IGF-1 and insulin. It is the primary growth factor driving fetal and placental development, with expression regulated by one of the best-characterized examples of genomic imprinting in mammals: the IGF2 gene is expressed exclusively from the paternally inherited allele, while the maternally inherited allele is silenced by the adjacent H19 locus.
Overview
IGF-2 was first identified in the late 1970s as a second insulin-like growth factor distinct from IGF-1 (then called somatomedin-C). While IGF-1 is the dominant postnatal growth mediator regulated by growth hormone, IGF-2 is the principal mitogenic factor during embryonic and fetal development. Circulating IGF-2 concentrations in adult humans (~400-800 ng/mL) are approximately three-fold higher than IGF-1 levels, yet IGF-2's postnatal functions remain less well understood.
The IGF2 gene resides within the imprinted 11p15.5 region alongside the H19 long non-coding RNA gene. Imprinting is established by differential methylation of an imprinting control region (ICR) between IGF2 and H19. On the maternal allele, the unmethylated ICR binds CTCF insulator protein, blocking IGF2 access to downstream enhancers and allowing H19 expression. On the paternal allele, ICR methylation prevents CTCF binding, silences H19, and permits IGF2 transcription. This monoallelic expression pattern is conserved across mammals and reflects an evolutionary conflict between parental genomes over offspring growth -- the "kinship theory" of imprinting proposed by Haig & Graham (1991).
Unlike IGF-1, which signals almost exclusively through IGF-1R, IGF-2 has a more complex receptor pharmacology. It binds IGF-1R to activate mitogenic and anti-apoptotic signaling, the insulin receptor isoform A (IR-A, which lacks exon 11) with mitogenic rather than metabolic signaling, and its own dedicated receptor IGF-2R (identical to the cation-independent mannose-6-phosphate receptor), which functions primarily as a clearance receptor that sequesters and degrades IGF-2 to limit its bioavailability.
Mechanism of Action
IGF-2 signals through multiple receptors with distinct downstream effects:
IGF-1R Activation: IGF-2 binds the IGF-1 receptor (IGF-1R) with approximately 2-10 fold lower affinity than IGF-1. Upon binding, IGF-1R undergoes autophosphorylation and activates the canonical RAS-MAPK/ERK and PI3K/AKT signaling cascades, promoting cell proliferation, survival, and differentiation. DeChiara et al. (1990) demonstrated through knockout studies that IGF-2's growth-promoting effects during development are mediated primarily through IGF-1R.
Insulin Receptor Isoform A (IR-A): IGF-2 binds IR-A with high affinity, comparable to insulin. IR-A is the predominant insulin receptor isoform in fetal tissues and many cancers. Unlike IR-B (which mediates classical metabolic insulin signaling), IGF-2/IR-A activation preferentially drives mitogenic signaling through the RAS-MAPK pathway rather than metabolic signaling through IRS-1/PI3K. Frasca et al. (1999) characterized this differential signaling, demonstrating that IGF-2/IR-A promotes cell proliferation and survival in cancer cells.
IGF-2R/Mannose-6-Phosphate Receptor (Clearance): The IGF-2 receptor (IGF-2R) is a large, single-transmembrane glycoprotein identical to the cation-independent mannose-6-phosphate receptor. It binds IGF-2 at a distinct site from mannose-6-phosphate-tagged lysosomal enzymes and mediates IGF-2 internalization and lysosomal degradation. IGF-2R functions as a tumor suppressor by limiting IGF-2 bioavailability. Loss of IGF-2R expression or function leads to IGF-2 accumulation and enhanced mitogenic signaling. Lau et al. (1994) showed that IGF-2R is imprinted reciprocally to IGF2 (maternally expressed) in mice.
IGFBP Modulation: In circulation, >99% of IGF-2 is bound to IGF binding proteins (primarily IGFBP-3 and IGFBP-5 in a ternary complex with acid-labile subunit), which extend IGF-2 half-life from minutes to hours and regulate tissue bioavailability.
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IGF-2
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Research
Genomic Imprinting and Growth Disorders
The IGF2/H19 locus is the paradigmatic example of genomic imprinting in mammals. Disruption of normal imprinting produces two clinically recognized syndromes:
Beckwith-Wiedemann Syndrome (BWS): Characterized by fetal and postnatal overgrowth, macroglossia, organomegaly, omphalocele, and increased risk of embryonal tumors (Wilms tumor, hepatoblastoma). BWS results from IGF-2 overexpression through multiple mechanisms: loss of maternal allele silencing (biallelic IGF2 expression), paternal uniparental disomy of 11p15, or gain-of-function mutations. Weksberg et al. (2010) provided a comprehensive review of BWS molecular mechanisms and genotype-phenotype correlations.
Silver-Russell Syndrome (SRS): Characterized by intrauterine growth restriction, postnatal growth failure, body asymmetry, and feeding difficulties. Approximately 40-60% of SRS cases involve hypomethylation of the ICR1 controlling IGF2, resulting in biallelic H19 expression and loss of IGF2 transcription. Gicquel et al. (2005) identified ICR1 hypomethylation as the major molecular etiology of SRS.
Comparison with IGF-1
While IGF-1 and IGF-2 share structural homology and overlapping receptor binding, their biological roles differ substantially:
| Feature | IGF-1 | IGF-2 |
|---|---|---|
| Primary role | Postnatal growth | Fetal/placental growth |
| GH regulation | Strongly GH-dependent | Largely GH-independent |
| Expression timing | Postnatal predominant | Fetal predominant (but persists) |
| Circulating levels (adult) | ~150-350 ng/mL | ~400-800 ng/mL |
| Imprinting | Not imprinted | Paternally expressed |
| IR-A binding | Low affinity | High affinity |
| Primary receptor | IGF-1R | IGF-1R, IR-A, IGF-2R |
Metabolic Regulation
Despite structural similarity to insulin, IGF-2's metabolic effects are primarily mediated through IR-A rather than the classical metabolic IR-B isoform. IGF-2 can lower blood glucose through IR-A activation, a phenomenon exploited pathologically in NICTH. The role of IGF-2 in normal glucose homeostasis and metabolic syndrome is an area of active investigation, with some evidence suggesting that IGF-2 levels correlate with insulin sensitivity and metabolic health.
Muscle Hypertrophy
IGF-2 plays an important autocrine/paracrine role in skeletal muscle differentiation and regeneration. During myogenesis, IGF-2 expression is upregulated as myoblasts differentiate into myotubes, and this autocrine IGF-2 signaling is required for terminal differentiation. Florini et al. (1991) demonstrated that IGF-2 is a critical autocrine differentiation factor in L6A1 myoblasts, with antisense oligonucleotides blocking IGF-2 expression preventing myotube formation.
In adult muscle, IGF-2 contributes to satellite cell activation and muscle regeneration after injury. The muscle-specific enhancer of IGF2 is activated during regeneration, and IGF-2 cooperates with IGF-1 to promote muscle protein synthesis through mTOR signaling. Research in livestock genetics has identified IGF2 polymorphisms (particularly the IGF2-intron3-G3072A mutation in pigs) that significantly increase muscle mass, confirming IGF-2's myogenic potential.
Wound Healing
IGF-2 promotes wound healing through stimulation of fibroblast proliferation, collagen synthesis, and re-epithelialization. It acts synergistically with other growth factors including PDGF and HGF in orchestrating the wound repair cascade. In fetal wounds, which heal without scarring, IGF-2 is abundantly expressed, suggesting a role in the scarless healing phenotype. Hu et al. (2014) demonstrated that IGF-2 promotes dermal fibroblast migration and wound closure through PI3K/AKT signaling.
Cancer Biology
Loss of imprinting (LOI) at the IGF2 locus -- resulting in biallelic IGF2 expression and elevated IGF-2 levels -- is one of the most common epigenetic alterations in human malignancy. LOI has been identified in colorectal cancer, Wilms tumor, hepatocellular carcinoma, ovarian cancer, and rhabdomyosarcoma. Cui et al. (2003) demonstrated that IGF2 LOI in normal colonic mucosa is associated with a 3-5 fold increased risk of colorectal cancer, suggesting it may serve as an early biomarker for cancer predisposition.
Non-islet cell tumor hypoglycemia (NICTH) is a paraneoplastic syndrome caused by tumor secretion of incompletely processed "big IGF-2" (pro-IGF-2 forms of 10-18 kDa) that cannot form normal ternary complexes with IGFBP-3 and ALS, resulting in elevated free IGF-2 that activates insulin receptors and causes severe hypoglycemia. Dynkevich et al. (2013) characterized the IGF-2 processing defect underlying NICTH.
IGF-2 autocrine/paracrine signaling through IR-A is increasingly recognized as a driver of cancer cell proliferation and resistance to targeted therapies. Several IGF-1R-targeted antibodies failed in clinical trials partly because they did not block IGF-2/IR-A signaling. Pollak (2012) reviewed the complex roles of the insulin and IGF system in cancer and the challenges of therapeutic targeting.
Safety Profile
IGF-2 is an endogenous growth factor with well-characterized developmental functions. Key safety considerations include:
- Oncogenic potential: IGF-2 overexpression is associated with multiple cancers. Exogenous IGF-2 administration could theoretically promote tumor growth through IGF-1R and IR-A signaling
- Hypoglycemia: High-dose IGF-2, particularly "big IGF-2" forms, can cause severe hypoglycemia through insulin receptor activation
- Imprinting disruption: Therapeutic manipulation of IGF-2 levels must consider the tightly regulated imprinting system
- Fetal effects: Given IGF-2's central role in fetal growth, use during pregnancy could theoretically produce macrosomia or BWS-like features
- Limited human data: No approved IGF-2 therapeutics exist; safety data derive primarily from preclinical studies and observations in imprinting disorders
Pharmacokinetic Profile
IGF-2 — Pharmacokinetic Curve
Subcutaneous injection, IV (research)Quick Start
- Route
- Subcutaneous injection, IV (research)
Research Indications
Metabolic & Endocrine
IGF-2 promotes development of fetal pancreatic beta cells and may serve as an alternative therapeutic approach for diabetes. Pro-IGF-II variants and preptin derivatives show promise in T2DM management.
Research supports investigating pro-IGF-II variants for treatment of osteoporosis and complicated fractures through stimulation of bone cell growth and differentiation.
IGF-2 plays roles in muscle cell proliferation and differentiation, with therapeutic potential for enhancing muscle regeneration in injury and degenerative conditions.
Neuropsychiatric
Fear extinction-induced IGF-2/IGFBP7 signaling promotes survival of newborn hippocampal neurons, suggesting therapeutic strategies enhancing IGF-2 may treat excessive fear memory disorders.
IGF-2 is a major fetal growth factor with roles in neural development. Dysregulation is implicated in neurodevelopmental and neurodegenerative conditions.
Research Protocols
subcutaneous Injection
- Preclinical dosing: 1-10 mcg/kg subcutaneous or local injection in rodent wound healing and muscle regeneration models.
| Goal | Dose | Frequency | Duration |
|---|---|---|---|
| Preclinical dosing | 1-10 mcg | Per protocol | —(Route: Subcutaneous Injection) |
Interactions
Peptide Interactions
While IGF-1 and IGF-2 share structural homology and overlapping receptor binding, their biological roles differ substantially: | Feature | IGF-1 | IGF-2 | |---------|-------|-------| | Primary role | Postnatal growth | Fetal/placental growth | | GH regulation | Strongly GH-dependent | Largely GH-...
What to Expect
What to Expect
Rapid onset expected; half-life of ~10-15 minutes (free); hours (IGFBP-bound) indicates fast-acting pharmacokinetics
Due to short half-life (~10-15 minutes (free); hours (IGFBP-bound)), effects are expected per-dose; consistent daily administration maintains...
Regular administration schedule required; effects are dose-dependent and do not persist between doses
Quality Indicators
What to look for
- Extensive peer-reviewed research base
Caution
- Limited human data available
- Evidence primarily from preclinical studies
Frequently Asked Questions
References (14)
- [13]Bergman D, Halje M, Norber M, et al Insulin-like growth factor 2 in development and disease: a mini-review Gerontology (2013)
- [4]Lau MM, Stewart CE, Liu Z, et al Loss of the imprinted IGF2/cation-independent mannose 6-phosphate receptor results in fetal overgrowth and perinatal lethality Genes Dev (1994)
- [5]Frasca F, Pandini G, Scalia P, et al Insulin receptor isoform A, a newly recognized, high-affinity insulin-like growth factor II receptor in fetal and cancer cells Mol Cell Biol (1999)
- [1]Haig D, Graham C Genomic imprinting and the strange case of the insulin-like growth factor II receptor Cell (1991)
- [2]DeChiara TM, Efstratiadis A, Robertson EJ A growth-deficiency phenotype in heterozygous mice carrying an insulin-like growth factor II gene disrupted by targeting Nature (1990)
- [6]Cui H, Cruz-Correa M, Giardiello FM, et al Loss of IGF2 imprinting: a potential marker of colorectal cancer risk Science (2003)
- [7]Gicquel C, Rossignol S, Cabrol S, et al Epimutation of the telomeric imprinting center region on chromosome 11p15 in Silver-Russell syndrome Nat Genet (2005)
- [8]
- [9]Pollak M The insulin and insulin-like growth factor receptor family in neoplasia: an update Nat Rev Cancer (2012)
- [10]Dynkevich Y, Rother KI, Whitford I, et al Tumors, IGF-2, and hypoglycemia: insights from the clinic, the laboratory, and the historical archive Endocr Rev (2013)
- [12]
- [14]Constancia M, Hemberger M, Hughes J, et al Placental-specific IGF-II is a major modulator of placental and fetal growth Nature (2002)
- [11]Hu L, Zhao B, Li Q, et al IGF-2 promotes wound healing through PI3K/Akt signaling pathway Biomed Pharmacother (2014)
- [3][Florini JR, Magri KA, Ewton DZ, et al. (1991). Spontaneous J Biol Chem (1991)
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