Insulin-like growth factor 1

IGF1
Available structures PDB Ortholog search: PDBe RCSB List of PDB id codes 1B9G, 1GZR, 1GZY, 1GZZ, 1H02, 1H59, 1IMX, 1PMX, 1TGR, 1WQJ, 2DSR, 2GF1, 3GF1, 3LRI, 1BQT, 4XSS
Identifiers
Aliases	IGF1, IGF-I, IGF1A, IGFI, MGF, insulin like growth factor 1
External IDs	OMIM: 147440 MGI: 96432 HomoloGene: 515 GeneCards: IGF1
Gene ontology Molecular function • hormone activity • insulin receptor binding • growth factor activity • integrin binding • protein binding • insulin-like growth factor receptor binding Cellular component • extracellular region • extracellular space • exocytic vesicle • insulin-like growth factor binding protein complex • platelet alpha granule lumen • insulin-like growth factor ternary complex • alphav-beta3 integrin-IGF-1-IGF1R complex • plasma membrane Biological process • positive regulation of transcription regulatory region DNA binding • skeletal system development • positive regulation of glucose import • movement of cell or subcellular component • muscle organ development • positive regulation of Ras protein signal transduction • positive regulation of tyrosine phosphorylation of Stat5 protein • response to heat • positive regulation of cardiac muscle hypertrophy • positive regulation of smooth muscle cell migration • DNA replication • positive regulation of insulin-like growth factor receptor signaling pathway • phosphatidylinositol 3-kinase signaling • positive regulation of DNA binding • Ras protein signal transduction • cell proliferation • positive regulation of mitotic nuclear division • positive regulation of trophectodermal cell proliferation • positive regulation of glycogen biosynthetic process • positive regulation of protein import into nucleus, translocation • positive regulation of fibroblast proliferation • ERK1 and ERK2 cascade • negative regulation of extrinsic apoptotic signaling pathway • cell activation • negative regulation of oocyte development • positive regulation of transcription, DNA-templated • bone mineralization involved in bone maturation • positive regulation of peptidyl-tyrosine phosphorylation • positive regulation of MAPK cascade • proteoglycan biosynthetic process • positive regulation of activated T cell proliferation • positive regulation of epithelial cell proliferation • negative regulation of release of cytochrome c from mitochondria • protein stabilization • myotube cell development • positive regulation of DNA replication • myoblast proliferation • skeletal muscle satellite cell maintenance involved in skeletal muscle regeneration • positive regulation of protein secretion • positive regulation of glycoprotein biosynthetic process • regulation of gene expression • phosphatidylinositol-mediated signaling • positive regulation of smooth muscle cell proliferation • cellular protein metabolic process • muscle hypertrophy • protein kinase B signaling • regulation of multicellular organism growth • positive regulation of cell migration • platelet degranulation • positive regulation of calcineurin-NFAT signaling cascade • positive regulation of phosphatidylinositol 3-kinase signaling • myoblast differentiation • glycolate metabolic process • positive regulation of glycolytic process • negative regulation of smooth muscle cell apoptotic process • signal transduction • positive regulation of transcription from RNA polymerase II promoter • positive regulation of cell growth involved in cardiac muscle cell development • activation of MAPK activity • positive regulation of cell proliferation • positive regulation of osteoblast differentiation • activation of protein kinase B activity • insulin-like growth factor receptor signaling pathway • negative regulation of apoptotic process Sources:Amigo / QuickGO
RNA expression pattern
More reference expression data
Orthologs
Species	Human	Mouse
Entrez	3479	16000
Ensembl	ENSG00000017427	ENSMUSG00000020053
UniProt	P05019	P05017
RefSeq (mRNA)	NM_000618 NM_001111283 NM_001111284 NM_001111285	NM_001111274 NM_001111275 NM_001111276 NM_010512 NM_184052 NM_001314010
RefSeq (protein)	NP_000609.1 NP_001104754.1	NP_001104745.1 NP_001300939.1 NP_034642.2
Location (UCSC)	Chr 12: 102.4 – 102.48 Mb	Chr 10: 87.86 – 87.94 Mb
PubMed search	[1]	[2]
Wikidata

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View/Edit Mouse

Insulin-like growth factor 1 (IGF-1), also called somatomedin C, is a protein that in humans is encoded by the IGF1 gene.^[3][4] IGF-1 has also been referred to as a "sulfation factor"^[5] and its effects were termed "nonsuppressible insulin-like activity" (NSILA) in the 1970s.

IGF-1 is a hormone similar in molecular structure to insulin. It plays an important role in childhood growth and continues to have anabolic effects in adults. A synthetic analog of IGF-1, mecasermin, is used for the treatment of growth failure.^[6]

IGF-1 consists of 70 amino acids in a single chain with three intramolecular disulfide bridges. IGF-1 has a molecular weight of 7,649 Dalton.^[7]

Synthesis and circulation

IGF-1 is produced primarily by the liver as an endocrine hormone as well as in target tissues in a paracrine/autocrine fashion. Production is stimulated by growth hormone (GH) and can be retarded by undernutrition, growth hormone insensitivity, lack of growth hormone receptors, or failures of the downstream signaling pathway post GH receptor including SHP2 and STAT5B. Approximately 98% of IGF-1 is always bound to one of 6 binding proteins (IGF-BP). IGFBP-3, the most abundant protein, accounts for 80% of all IGF binding. IGF-1 binds to IGFBP-3 in a 1:1 molar ratio. IGFBP-1 is regulated by insulin.

IGF-1 is produced throughout life. The highest rates of IGF-1 production occur during the pubertal growth spurt. The lowest levels occur in infancy and old age.

3-d model of IGF-1

Protein intake increases IGF-1 levels in humans, independent of total calorie consumption.^[8] Factors that are known to cause variation in the levels of growth hormone (GH) and IGF-1 in the circulation include: insulin levels, genetic make-up, the time of day, age, sex, exercise status, stress levels, nutrition level and body mass index (BMI), disease state, race, estrogen status and xenobiotic intake.^[9]

Mechanism of action

Its primary action is mediated by binding to its specific receptor, the insulin-like growth factor 1 receptor (IGF1R), which is present on many cell types in many tissues. Binding to the IGF1R, a receptor tyrosine kinase, initiates intracellular signaling; IGF-1 is one of the most potent natural activators of the AKT signaling pathway, a stimulator of cell growth and proliferation, and a potent inhibitor of programmed cell death . IGF-1 binds to at least two cell surface receptors: the IGF-1 receptor (IGF1R), and the insulin receptor. The IGF-1 receptor seems to be the "physiologic" receptor – it binds IGF-1 at significantly higher affinity than the IGF-1 that is bound to the insulin receptor. Like the insulin receptor, the IGF-1 receptor is a receptor tyrosine kinase – meaning it signals by causing the addition of a phosphate molecule on particular tyrosines. IGF-1 activates the insulin receptor at approximately 0.1 times the potency of insulin. Part of this signaling may be via IGF1R/Insulin Receptor heterodimers (the reason for the confusion is that binding studies show that IGF1 binds the insulin receptor 100-fold less well than insulin, yet that does not correlate with the actual potency of IGF1 in vivo at inducing phosphorylation of the insulin receptor, and hypoglycemia).

IGF-1 is a primary mediator of the effects of growth hormone (GH). Growth hormone is made in the anterior pituitary gland, is released into the blood stream, and then stimulates the liver to produce IGF-1. IGF-1 then stimulates systemic body growth, and has growth-promoting effects on almost every cell in the body, especially skeletal muscle, cartilage, bone, liver, kidney, nerves, skin, hematopoietic cell, and lungs. In addition to the insulin-like effects, IGF-1 can also regulate cell growth and development, especially in nerve cells, as well as cellular DNA synthesis.^[10]

Insulin-like growth factor 1 receptor (IGF-1R) and other tyrosine kinase growth factor receptors signal through multiple pathways. A key pathway is regulated by phosphatidylinositol-3 kinase (PI3K) and its downstream partner, the mammalian target of rapamycin (mTOR). Rapamycins complex with FKBPP12 to inhibit the mTORC1 complex. mTORC2 remains unaffected and responds by upregulating Akt, driving signals through the inhibited mTORC1. Phosphorylation of eukaryotic initiation factor 4e (eif-4E) [4EBP] by mTOR inhibits the capacity of 4EBP to inhibit eif-4E and slow metabolism.

Insulin-like growth factor 1 has been shown to bind and interact with all the IGF-1 binding proteins (IGFBPs), of which there are seven: IGFBP1, IGFBP2, IGFBP3, IGFBP4, IGFBP5, IGFBP6, and IGFBP7. Some IGFBPs are inhibitory. For example, both IGFBP-2 and IGFBP-5 bind IGF-1 at a higher affinity than it binds its receptor. Therefore, increases in serum levels of these two IGFBPs result in a decrease in IGF-1 activity.

Related growth factors

IGF-1 is closely related to a second protein called "IGF-2". IGF-2 also binds the IGF-1 receptor. However, IGF-2 alone binds a receptor called the "IGF-2 receptor" (also called the mannose-6 phosphate receptor). The insulin-like growth factor-II receptor (IGF2R) lacks signal transduction capacity, and its main role is to act as a sink for IGF-2 and make less IGF-2 available for binding with IGF-1R. As the name "insulin-like growth factor 1" implies, IGF-1 is structurally related to insulin, and is even capable of binding the insulin receptor, albeit at lower affinity than insulin.

A splice variant of IGF-1 sharing an identical mature region, but with a different E domain is known as mechano-growth factor (MGF).^[11]

Clinical significance

Dwarfism

Rare diseases characterized by inability to make or respond to IGF-1 produce a distinctive type of growth failure. One such disorder, termed Laron dwarfism does not respond at all to growth hormone treatment due to a lack of GH receptors. The FDA has grouped these diseases into a disorder called severe primary IGF deficiency. Patients with severe primary IGFD typically present with normal to high GH levels, height below 3 standard deviations (SD), and IGF-1 levels below 3 SD. Severe primary IGFD includes patients with mutations in the GH receptor, post-receptor mutations or IGF mutations, as previously described. As a result, these patients cannot be expected to respond to GH treatment.

People with Laron syndrome have strikingly low rates of cancer and diabetes.^[12]

Acromegaly

Acromegaly is a syndrome that results when the anterior pituitary gland produces excess growth hormone (GH). A number of disorders may increase the pituitary's GH output, although most commonly it involves a tumor called pituitary adenoma, derived from a distinct type of cell (somatotrophs). It leads to anatomical changes and metabolic dysfunction caused by elevated GH and insulin-like growth factor 1 (IGF-1) levels.^[13]

Diagnostic test

IGF-1 levels can be measured in the blood in 10-1000 ng/ml amounts. As levels do not fluctuate greatly throughout the day for an individual person, IGF-1 is used by physicians as a screening test for growth hormone deficiency and excess in acromegaly and gigantism.

Interpretation of IGF-1 levels is complicated by the wide normal ranges, and marked variations by age, sex, and pubertal stage. Clinically significant conditions and changes may be masked by the wide normal ranges. Sequential management over time is often useful for the management of several types of pituitary disease, undernutrition, and growth problems.

As a therapeutic agent

Patients with severe primary insulin-like growth factor-1 deficiency (IGFD), called laron syndrome, may be treated with either IGF-1 alone or in combination with IGFBP-3.^[14] Mecasermin (brand name Increlex) is a synthetic analog of IGF-1 which is approved for the treatment of growth failure.^[14] IGF-1 has been manufactured recombinantly on a large scale using both yeast and E. coli.

Research

Aging

Signaling through the insulin/IGF-1-like receptor pathway is a significant contributor to biological aging in many organisms. Cynthia Kenyon showed that mutations in the daf-2 gene double the lifespan of the roundworm, C. elegans.^[15][16] Daf-2 encodes the worm's unified insulin/IGF-1-like receptor. Despite the impact of IGF1-like on C. elegans longevity, direct application to mammalian aging is not as clear as mammals lack dauer developmental stages. It is also inconsistent with evidence in humans.^[17]

There are mixed reports that IGF-1 signaling modulates the aging process in humans and about whether the direction of its effect is positive or negative.^[17]

Neuropathy

Therapeutic administration of neurotrophic proteins (IGF-1) is associated with potential reversal of degeneration of spinal cord motor neuron axons in certain peripheral neuropathies.^[18]

Cancer

The IGF signaling pathway is implicated in some cancers.^[19][20] People with Laron syndrome have a lessened risk of developing cancer.^[21] Dietary interventions and modifications such as vegan diets shown to downregulate IGF-1 activity, has been associated with lower risk of cancer.^[22] However, despite considerable research, perturbations specific to cancer are incompletely delineated^[23][24] and clinical drug trials have been unsuccessful.^[20][25]

Stroke

IGF-1 has also been shown to be effective in animal models of stroke when combined with erythropoietin. Both behavioural and cellular improvements were found.^[26]

Clinical trials

Recombinant protein

Several companies have evaluated IGF-1 in clinical trials for a variety of indications, including type 1 diabetes, type 2 diabetes, amyotrophic lateral sclerosis (ALS aka "Lou Gehrig's Disease"),^[27] severe burn injury and myotonic muscular dystrophy (MMD). Results of clinical trials evaluating the efficacy of IGF-1 in type 1 diabetes and type 2 diabetes showed great promise in reducing hemoglobin A1C levels, as well as daily insulin consumption. However, the sponsor, Genentech, discontinued the program due to an exacerbation of diabetic retinopathy^[28] in patients coupled with a shift in corporate focus towards oncology. Cephalon and Chiron conducted two pivotal clinical studies of IGF-1 for ALS, and although one study demonstrated efficacy, the second was equivocal, and the product has never been approved by the FDA.

Small molecules that upregulate IGF-1

In a clinical trial of an investigational compound ibutamoren, which raises IGF-1 in patients, did not result in an improvement in patients' Alzheimer's symptoms.^[29] Another clinical demonstrated that Cephalon's IGF-1 does not slow the progression of weakness in ALS patients, but other studies have shown strong beneficial effects of IGF-1 replacement therapy in ALS patients,^[30] and therefore IGF-1 may have the potential to be an effective and safe medicine against ALS,^[31] however other studies had conflicting results.^[32]

Society and culture

Insmed was found to infringe on patents licensed by Tercica, which then sought to get a U.S. district court judge to ban sales of Iplex.^[33] To settle patent infringement charges and resolve all litigation between the two companies, in March 2007 Insmed agreed to withdraw Iplex from the U.S. market, leaving Tercica's Increlex as the sole version of IGF-1 available in the United States.^[34]

Numerous sources have claimed that Deer Antler Spray, purportedly extracted from cervid sources, contains IGF-1.^{[35][36][37][38]} Credence to this claim comes from the fact that deer's antlers grow extremely rapidly and that the associated cellular factors can similarly aid in skeletal healing in humans. IGF-1 is currently banned by various sporting bodies. However, sprays and pills claiming to be 'deer antler velvet extracts' are freely available on the market.^[39] As IGF-1 is a protein, it cannot be absorbed orally since it is rapidly broken down in the gastrointestinal tract.^[40] In September 2013, the headquarters of SWATS, a well-known distributor of deer antler spray and other controversial products, was raided and ordered to shut down by Alabama's attorney general citing "numerous serious and willful violations of Alabama’s deceptive trade practices act".^[41][42]

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Further reading

• Butler AA, Yakar S, LeRoith D (2002). "Insulin-like growth factor-I: compartmentalization within the somatotropic axis?". News Physiol. Sci. 17: 82–5. PMID 11909998.
• Maccario M, Tassone F, Grottoli S, Rossetto R, Gauna C, Ghigo E (2002). "Neuroendocrine and metabolic determinants of the adaptation of GH/IGF-I axis to obesity". Ann. Endocrinol. (Paris). 63 (2 Pt 1): 140–4. PMID 11994678.
• Camacho-Hübner C, Woods KA, Clark AJ, Savage MO (2003). "Insulin-like growth factor (IGF)-I gene deletion". Reviews in endocrine & metabolic disorders. 3 (4): 357–61. doi:10.1023/A:1020957809082. PMID 12424437.
• Dantzer B, Swanson EM (2012). "Mediation of vertebrate life histories via insulin-like growth factor-1". Biological Reviews. 87 (2): 414–429. doi:10.1111/j.1469-185X.2011.00204.x. PMID 21981025.
• Trojan LA, Kopinski P, Wei MX, Ly A, Glogowska A, Czarny J, Shevelev A, Przewlocki R, Henin D, Trojan J (2004). "IGF-I: from diagnostic to triple-helix gene therapy of solid tumors". Acta Biochim. Pol. 49 (4): 979–90. PMID 12545204.
• Winn N, Paul A, Musaró A, Rosenthal N (2003). "Insulin-like growth factor isoforms in skeletal muscle aging, regeneration, and disease". Cold Spring Harb. Symp. Quant. Biol. 67: 507–18. doi:10.1101/sqb.2002.67.507. PMID 12858577.
• Delafontaine P, Song YH, Li Y (2005). "Expression, regulation, and function of IGF-1, IGF-1R, and IGF-1 binding proteins in blood vessels". Arterioscler. Thromb. Vasc. Biol. 24 (3): 435–44. doi:10.1161/01.ATV.0000105902.89459.09. PMID 14604834.
• Trejo JL, Carro E, Garcia-Galloway E, Torres-Aleman I (2004). "Role of insulin-like growth factor I signaling in neurodegenerative diseases". J. Mol. Med. 82 (3): 156–62. doi:10.1007/s00109-003-0499-7. PMID 14647921.
• Rabinovsky ED (2004). "The multifunctional role of IGF-1 in peripheral nerve regeneration". Neurol. Res. 26 (2): 204–10. doi:10.1179/016164104225013851. PMID 15072640.
• Rincon M, Muzumdar R, Atzmon G, Barzilai N (2005). "The paradox of the insulin/IGF-1 signaling pathway in longevity". Mech. Ageing Dev. 125 (6): 397–403. doi:10.1016/j.mad.2004.03.006. PMID 15272501.
• Conti E, Carrozza C, Capoluongo E, Volpe M, Crea F, Zuppi C, Andreotti F (2005). "Insulin-like growth factor-1 as a vascular protective factor". Circulation. 110 (15): 2260–5. doi:10.1161/01.CIR.0000144309.87183.FB. PMID 15477425.
• Wood AW, Duan C, Bern HA (2005). "Insulin-like growth factor signaling in fish". Int. Rev. Cytol. International Review of Cytology. 243: 215–85. doi:10.1016/S0074-7696(05)43004-1. ISBN 9780123646477. PMID 15797461.
• Sandhu MS (2005). "Insulin-like growth factor-I and risk of type 2 diabetes and coronary heart disease: molecular epidemiology". Endocrine development. Endocrine Development. 9: 44–54. doi:10.1159/000085755. ISBN 3-8055-7926-8. PMID 15879687.
• Ye P, D'Ercole AJ (2006). "Insulin-like growth factor actions during development of neural stem cells and progenitors in the central nervous system". J. Neurosci. Res. 83 (1): 1–6. doi:10.1002/jnr.20688. PMID 16294334.
• Gómez JM (2006). "The role of insulin-like growth factor I components in the regulation of vitamin D". Current pharmaceutical biotechnology. 7 (2): 125–32. doi:10.2174/138920106776597621. PMID 16724947.
• Federico G, Street ME, Maghnie M, Caruso-Nicoletti M, Loche S, Bertelloni S, Cianfarani S (2006). "Assessment of serum IGF-I concentrations in the diagnosis of isolated childhood-onset GH deficiency: a proposal of the Italian Society for Pediatric Endocrinology and Diabetes (SIEDP/ISPED)". J. Endocrinol. Invest. 29 (8): 732–7. doi:10.1007/bf03344184. PMID 17033263.
• Zakula Z, Koricanac G, Putnikovic B, Markovic L, Isenovic ER (2007). "Regulation of the inducible nitric oxide synthase and sodium pump in type 1 diabetes". Med. Hypotheses. 69 (2): 302–6. doi:10.1016/j.mehy.2006.11.045. PMID 17289286.
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External links

• Insulin-Like Growth Factor I at the US National Library of Medicine Medical Subject Headings (MeSH)
• IGF-1 at Lab Tests Online
• IGF-1 recombinant GFP labeled at Protean Ltd.