Insulin-like growth factor 1

Insulin-like growth factor 1 (somatomedin C)

PDB rendering based on 1bqt.
Identifiers
Symbols IGF1; IGF-I; IGF1A; IGFI
External IDs OMIM: 147440 MGI: 96432 HomoloGene: 515 GeneCards: IGF1 Gene
RNA expression pattern
More reference expression data
Orthologs
Species Human Mouse
Entrez 3479 16000
Ensembl ENSG00000017427 ENSMUSG00000020053
UniProt P05019 Q4VJC0
RefSeq (mRNA) NM_000618.3 NM_010512
RefSeq (protein) NP_000609.1 NP_034642
Location (UCSC) Chr 12:
102.79 – 102.87 Mb		 Chr 10:
87.32 – 87.4 Mb
PubMed search [1] [2]

Insulin-like growth factor 1 (IGF-1) also known as somatomedin C is a protein that in humans is encoded by the IGF1 gene.[1][2] IGF-1 has also been referred to as a "sulfation factor"[3] 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.[4]

IGF-1 consists of 70 amino acids in a single chain with three intramolecular disulfide bridges. IGF-1 has a molecular weight of 7649 daltons.

Contents

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 signalling 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.

In rat experiments the amount of IGF-1 mRNA in the liver was positively associated with dietary casein and negatively associated with a protein-free diet.[5]

Recently, an efficient plant expression system was developed to produce biologically active recombinant human IGF-I (rhIGF-I) in transgenic rice grains.[6]

Mechanism of action

Its primary action is mediated by binding to its specific receptor, the Insulin-like growth factor 1 receptor, abbreviated as ""IGF1R"", 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 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.

Deficiency of either growth hormone or IGF-1 therefore results in diminished stature. GH-deficient children are given recombinant GH to increase their size. IGF-1 deficient humans, who are categorized as having Laron syndrome, or Laron's dwarfism, are treated with recombinant IGF-1. In beef cattle, circulating IGF-I concentrations are related to reproductive performance.[7]

Receptors

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 0.1x 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 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.

Other 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 II receptor" (also called the mannose-6 phosphate receptor). The insulin 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.

Contribution to aging

It is now widely accepted that signaling through the insulin/IGF-1-like receptor pathway is a significant contributor to the biological aging process in many organisms. This avenue of research first achieved prominence with the work of Cynthia Kenyon, who showed that mutations in the daf-2 gene could double the lifespan of the roundworm C. elegans.[8] daf-2 encodes the worm's unified insulin/IGF-1-like receptor.

Insulin/IGF-1-like signaling is conserved from worms to humans. Subsequent to Kenyon's early work, mutations that reduce insulin/IGF-1 signaling have been shown to decelerate the degenerative aging process and extend lifespan in a wide range of organisms, including Drosophila melanogaster, mice,[9] and possibly humans.[10],[11],[12], [13] Reduced IGF-1 signaling is also thought to contribute to the "anti-aging" effects of Calorie restriction.[14]

Factors influencing the levels in the circulation

Factors that are known to cause variation in the levels of growth hormone (GH) and IGF-1 in the circulation include: 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.[15] The later inclusion of xenobiotic intake as a factor influencing GH-IGF status highlights the fact that the GH-IGF axis is a potential target for certain endocrine disrupting chemicals - see also endocrine disruptor.

Diseases of deficiency and resistance

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 -3SD. 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.

The IGF signaling pathway appears to play a crucial role in cancer. Several studies have shown that increased levels of IGF lead to an increased risk of cancer.[16] Studies done on lung cancer cells show that drugs inhibiting such signaling can be of potential interest in cancer therapy.[17]

Use as a diagnostic test

Reference ranges for IGF-1[18]
(in ng/mL)
Age Females Males
2.5th
centile		 97.5th
centile		 2.5th
centile		 97.5th
centile
20 111 423 156 385
25 102 360 119 343
30 94 309 97 306
35 86 271 84 275
40 79 246 76 251
45 73 232 71 233
50 68 228 66 221
55 64 231 61 214
60 61 237 55 211
65 59 241 49 209
70 57 237 46 207
75 55 219 48 202

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 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

Mecasermin (brand name Increlex) is a synthetic analog of IGF-1 which is approved for the treatment of growth failure.[19] IGF-1 has been manufactured recombinantly on a large scale using both yeast and E. coli.

Several companies have evaluated IGF-1 in clinical trials for a variety of additional indications, including type 1 diabetes, type 2 diabetes, amyotrophic lateral sclerosis (ALS aka "Lou Gehrig's Disease"), 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 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.

However, in the last few years, two additional companies Tercica and Insmed compiled enough clinical trial data to seek FDA approval in the United States. In August 2005, the FDA approved Tercica's IGF-1 drug, Increlex, as replacement therapy for severe primary IGF-1 deficiency based on clinical trial data from 71 patients. In December 2005, the FDA also approved Iplex, Insmed's IGF-1/IGFBP-3 complex. The Insmed drug is injected once a day versus the twice-a-day version that Tercica sells.

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.[20] To settle patent infringement charges and resolve all litigation between the two companies, Insmed in March 2007 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.[21]

By delivering Iplex in a complex, patients might get the same efficacy with regard to growth rates but experience fewer side effects with less severe hypoglycemia. This medication might emulate IGF-1's endogenous complexing, as in the human body 97-99% of IGF-1 is bound to one of six IGF binding proteins. IGFBP-3 is the most abundant of these binding proteins, accounting for approximately 80% of IGF-1 binding.

In a clinical trial of an investigational compound MK-677, which raises IGF-1 in patients, did not result in an improvement in patients' Alzheimer's symptoms.[22] Another clinical demonstrated that Cephalon's IGF-1 does not slow the progression of weakness in ALS patients. Previous shorter studies had conflicting results.[23]

IGFBP-3 is a carrier for IGF-1, meaning that IGF-1 binds IGFBP-3, creating a complex whose combined molecular weight and binding affinity allows the growth factor to have an increased half-life in serum. Without binding to IGFBP-3, IGF-1 is cleared rapidly through the kidney, due to its low molecular weight. But when bound to IGFBP-3, IGF-1 evades renal clearance. Also, since IGFBP-3 has a lower affinity for IGF-1 than IGF-1 has for its receptor, IGFR, its binding does not interfere with IGF-1 function. For these reasons, an IGF-1/IGFBP-3 combination approach was approved for human treatment... brought forward by a small company called Insmed. However, Insmed fell afoul patent issues, and was ordered to desist in this approach.

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.[24]

Interactions

Insulin-like growth factor 1 has been shown to bind and interact with all the IGF-1 Binding Proteins (IGFBPs), of which there are six (IGFBP1-6).

Specific references are provided for interactions with IGFBP3,[25][26][27][28][29][30] IGFBP4,[31][32] and IGFBP7.[33][34]

References

  1. ^ Höppener JW, de Pagter-Holthuizen P, Geurts van Kessel AH, Jansen M, Kittur SD, Antonarakis SE, Lips CJ, Sussenbach JS (1985). "The human gene encoding insulin-like growth factor I is located on chromosome 12". Hum. Genet. 69 (2): 157–60. doi:10.1007/BF00293288. PMID 2982726. 
  2. ^ Jansen M, van Schaik FM, Ricker AT, Bullock B, Woods DE, Gabbay KH, Nussbaum AL, Sussenbach JS, Van den Brande JL (1983). "Sequence of cDNA encoding human insulin-like growth factor I precursor". Nature 306 (5943): 609–11. doi:10.1038/306609a0. PMID 6358902. 
  3. ^ Salmon W, Daughaday W (1957). "A hormonally controlled serum factor which stimulates sulfate incorporation by cartilage in vitro". J Lab Clin Med 49 (6): 825–36. PMID 13429201. 
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  5. ^ Miura, Y.; Kato, H.; Noguchi, T. (2007). "Effect of dietary proteins on insulin-like growth factor-1 (IGF-1) messenger ribonucleic acid content in rat liver". British Journal of Nutrition 67 (2): 257. doi:10.1079/BJN19920029. PMID 1596498.  edit
  6. ^ Cheung SC, Liu LZ, Lan LL, Liu QQ, Sun SS, Chan JC, Tong PC.,"Glucose lowering effect of transgenic human insulin-like growth factor-I from rice: in vitro and in vivo studies." BMC Biotechnol. 2011;11:37
  7. ^ Yilmaz A, Davis ME, RCM Simmen RCM (1999). "Reproductive performance of bulls divergently selected on the basis of blood serum insulin-like growth factor I concentration". J Anim Sci 77 (4): 835–9. PMID 10328346. 
  8. ^ See publications documenting series of experiments at Cynthia Kenyon lab, in particular, Dorman JB, Albinder B, Shroyer T, Kenyon C (December 1995). "The Age-1 and Daf-2 Genes Function in a Common Pathway to Control the Lifespan of Caenorhabditis Elegans". Genetics 141 (4): 1399–406. PMC 1206875. PMID 8601482. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1206875. ; and Apfeld J, Kenyon C (October 1998). "Cell nonautonomy of C. elegans daf-2 function in the regulation of diapause and life span". Cell 95 (2): 199–210. doi:10.1016/S0092-8674(00)81751-1. PMID 9790527. 
  9. ^ Bartke, A (2011-01-12). "Single-gene mutations and healthy ageing in mammals". Philos Trans R Soc Lond B Biol Sc 366 (1561): 28–34. doi:10.1098/rstb.2010.0281. PMC 3001310. PMID 21115527. http://rstb.royalsocietypublishing.org/content/366/1561/28.long. Retrieved 2011-09-28. 
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  16. ^ Smith GD, Gunnell D, Holly J (2000). "Cancer and insulin-like growth factor-I : A potential mechanism linking the environment with cancer risk". British Medical Journal 321 (7265): 847–8. doi:10.1136/bmj.321.7265.847. PMC 1118665. PMID 11021847. http://www.bmj.com/content/321/7265/847.full. 
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  18. ^ Ranges estimated from quantile regression as shown in table 4 in: Friedrich, N.; Alte, D.; Volzke, H.; Spilckeliss, E.; Ludemann, J.; Lerch, M.; Kohlmann, T.; Nauck, M. et al. (2008). "Reference ranges of serum IGF-1 and IGFBP-3 levels in a general adult population: Results of the Study of Health in Pomerania (SHIP)". Growth Hormone & IGF Research 18 (3): 228–237. doi:10.1016/j.ghir.2007.09.005. PMID 17997337.  edit
  19. ^ Rosenbloom AL (August 2007). "The role of recombinant insulin-like growth factor I in the treatment of the short child". Curr. Opin. Pediatr. 19 (4): 458–64. doi:10.1097/MOP.0b013e3282094126. PMID 17630612. 
  20. ^ Pollack A (2007-02-17). "Growth Drug Is Caught Up in Patent Fight". The New York Times. http://www.nytimes.com/2007/02/17/business/17patent.html?_r=1&ref=health. Retrieved 2010-03-28. 
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  25. ^ Horton JK, Thimmaiah KN, Houghton JA, Horowitz ME, Houghton PJ (June 1989). "Modulation by verapamil of vincristine pharmacokinetics and toxicity in mice bearing human tumor xenografts". Biochem. Pharmacol. 38 (11): 1727–36. doi:10.1016/0006-2952(89)90405-X. PMID 2735930. 
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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, et al. (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. 
  • Trojan LA, Kopinski P, Wei MX, et al. (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, et al. (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. 243: 215–85. doi:10.1016/S0074-7696(05)43004-1. 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, et al. (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. PMID 17033263. 
  • Zakula Z, Koricanac G, Putnikovic B, et al. (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. 
  • Trojan J, Cloix JF, Ardourel MY, et al. (2007). "Insulin-like growth factor type I biology and targeting in malignant gliomas". Neuroscience 145 (3): 795–811. doi:10.1016/j.neuroscience.2007.01.021. PMID 17320297. 
  • Venkatasubramanian G, Chittiprol S, Neelakantachar N, Naveen MN, Thirthall J, Gangadhar BN, Shetty KT (October 2007). "Insulin and insulin-like growth factor-1 abnormalities in antipsychotic-naive schizophrenia". Am J Psychiatry 164 (10): 1557–60. doi:10.1176/appi.ajp.2007.07020233. PMID 17898347. 

External links

Fibroblast

FGF receptor ligands: FGF1/FGF2/FGF5 · FGF3/FGF4/FGF6 · KGF (FGF7/FGF10/FGF22) · FGF8/FGF17/FGF18 · FGF9/FGF16/FGF20

FGF homologous factors: FGF11 · FGF12 · FGF13 · FGF14

hormone-like: FGF19 · FGF21 · FGF23
EGF-like domain
TGF-α · EGF  · HB-EGF
TGFβ pathway
Insulin-like
IGF-1 · IGF-2
Platelet-derived
PDGFA · PDGFB · PDGFC · PDGFD
Vascular endothelial
VEGF-A · VEGF-B · VEGF-C · VEGF-D · PGF
Other
B trdu: iter (nrpl/grfl/cytl/horl), csrc (lgic, enzr, gprc, igsr, intg, nrpr/grfr/cytr), itra (adap, gbpr, mapk), calc, lipd; path (hedp, wntp, tgfp+mapp, notp, jakp, fsap, hipp, tlrp)