human Insulin expressed in yeast

IC50: 5.01 nmol/L for insulin receptor

Insulin is a peptide hormone produced by beta cells in pancreas. Insulin has been found to stimulate glucose uptake into muscle and adipose tissue, which is central to the maintenance of whole body glucose homeostasis. Autoimmune destruction of the β-cells in pancreas leads to a lack of insulin production and the development of type I and II diabetes mellitus.

In vitro: Methotrexate (MTX) was found to be linked to insulin covalently. As effectively as insulin, insulin-MTX complex competed with 125I-insulin for insulin receptor. It was found that IC50 and Ki for insulin-MTX were 93.82 nM and 91.88 nM, respectively, whereas those for insulin were 5.01 nM and 4.85 nM, respectively [1].

In vivo: Previous study showed that insulin-stimulated glucose uptake in extensor muscles from SJL mice was reduced, but the basal uptake rates were not different. In another mouse study, knockdown of TC10α but not TC10β in 3T3-L1 adipocytes resulted in a inhibition of both insulin-stimulated glucose uptake and GLUT4 translocation [2].

Clinical trial: Clinical study shows that when insulin levels fails, diabetes mellitus can happen. Thus, insulin is medically used to treat some forms of diabetes mellitus. Biosynthetic human insulin for clinical use is manufactured by recombinant DNA technology. Insulin is often taken as subcutaneous injections . Morevoer, inhaled insulin is currently also available in U.S. market (https://en.wikipedia.org/wiki/Insulin#Medication_uses).

References:
[1] Ou X,Kuang A,Liang Z,Peng X,Zhong Y.  The binding characteristics of insulin-MTX to insulin receptor. Hua Xi Yi Ke Da Xue Xue Bao.2001 Dec;32(4):538-40.
[2] Leney SE,Tavaré JM.  The molecular basis of insulin-stimulated glucose uptake: signalling, trafficking and potential drug targets. J Endocrinol.2009 Oct;203(1):1-18.

A Lys27-to-Glu27 mutation in the human insulin-like growth factor-1 prevents disulfide linked dimerization and allows secretion of BiP when expressed in yeast.[Pubmed:1756863]

FEBS Lett. 1991 Dec 9;294(3):213-6.

Recombinant human insulin-like growth factor-1 (IGF1) secreted from yeast contains only 10-15% of the active monomer. A majority of the IGF1-like molecules are disulfide bonded dimers. These dimers are not formed in an IGF1 mutant where Lys27 has been replaced by glutamic acid. However, increased levels of secreted BiP (the yeast KAR2 gene product) are seen in cells expressing the mutant. These results imply that by preventing ionic interactions between two IGF1 molecules, intermolecular disulfide bonds do not form in yeast, and that in the mutant there is a structural change which induces BiP, allowing its secretion.

The molecular basis of insulin-stimulated glucose uptake: signalling, trafficking and potential drug targets.[Pubmed:19389739]

J Endocrinol. 2009 Oct;203(1):1-18.

The search for the underlying mechanism through which insulin regulates glucose uptake into peripheral tissues has unveiled a highly intricate network of molecules that function in concert to elicit the redistribution or 'translocation' of the glucose transporter isoform GLUT4 from intracellular membranes to the cell surface. Following recent technological advances within this field, this review aims to bring together the key molecular players that are thought to be involved in GLUT4 translocation and will attempt to address the spatial relationship between the signalling and trafficking components of this event. We will also explore the degree to which components of the insulin signalling and GLUT4 trafficking machinery may serve as potential targets for the development of orally available insulin mimics for the treatment of diabetes mellitus.

[The binding characteristics of insulin-MTX to insulin receptor].[Pubmed:12528542]

Hua Xi Yi Ke Da Xue Xue Bao. 2001 Dec;32(4):538-40.

OBJECTIVE: It has been reported that several kinds of tumors express increased insulin receptor and the molecules of insulin can be internalized in cells and may thence enter into the nuclei mediated by insulin receptor. In this study, we investigated the receptor binding characteristics of insulin-MTX for the possibility of using insulin as a carrier for carcinoma targeted therapy by receptor mediation. METHODS: MTX(methotrexate) was covalently linked to insulin directly. The insulin-MTX conjugate was purified by polyacrylamine agarose gel electrophoresis and analysed by high performance liquid chromatography and SDS- polyacrylamine agarose gel electrophoresis. Histologically confirmed human hepatocellular carcinoma specimens were obtained from patients at surgery and immediately frozen under -80 degrees C. Cell membrane fractions were isolated by sucrose density gradient centrifugation. Competitive displacement of 125I-insulin with insulin and insulin-MTX binding to insulin receptor were carried out and the values of IC50 and Ki were calculated so as to observe the characteristics of insulin-MTX binding to insulin receptor. RESULTS: Insulin-MTX competed as effectively as insulin with 125I-insulin for insulin receptor. The values of IC50 and Ki for insulin-MTX were 93.82 +/- 19.32 nmol/L and 91.88 +/- 16.86 nmol/L respectively, while the values of IC50 and Ki for insulin were 5.01 +/- 1.24 nmol/L and 4.85 +/- 1.12 nmol/L respectively. CONCLUSION: Insulin-MTX could bind with insulin receptor with high affinity. The result demonstrates us that there is a possibility of using insulin as a carrier for carcinoma targeted therapy by receptor mediation.

Age dependent changes of insulin receptors in rat tissues.[Pubmed:11220495]

J Physiol Pharmacol. 2000 Dec;51(4 Pt 2):871-81.

Aging is associated with insulin resistance but the exact molecular mechanism is still unknown. Tissue insulin resistance can be evoked by the decreased sensitivity to insulin, the decreased responsiveness to hormone or both. As the first step in insulin action is its binding to alfa subunits of the receptor we, therefore, studied the insulin binding kinetics in plasma membranes of the liver, heart and skeletal muscle in order to establish whether their ability to bind the hormone is altered with aging. Plasma membranes were prepared and purified according to Havrankowa and binding assay was performed using (125I)-iodoinsulin. The kinetic parameters of the hormone-receptor interaction were analysed by the method of Scatchard using the LIGAND-Pc v.3.1. computer program. The binding potency of insulin was calculated as IC50 using ALLFIT-Pc v.2.7. computer program. We have shown that there are striking differences in insulin binding kinetics in newborn and old rats, depending on kind of tissue tested. The liver plasma membranes ability for insulin binding, number of high (HAIR) and low (LAIR) affinity insulin receptors, values of the dissociation constants and products of association constants and number of insulin receptors, were almost the same, being not dependent on age of the rats. By contrast, there is less high affinity insulin receptors in skeletal muscle of the old animals. The most dramatic changes in insulin binding occur in the heart where both high and low affinity insulin receptors are greatly affected by aging. Our results indicate that the response of the three tissues tested to hyperglycemia and hyperinsulinemia, observed in the old rats, has not been identical and probably can be accounted for by the different distribution of insulin receptor isoforms in the liver, heart and skeletal muscles as shown recently by Vidal et al.