Molecular Characterisation of Long-Acting Insulin Analogues in Comparison with Human Insulin, IGF-1 and Insulin X10

AIMS/HYPOTHESIS: There is controversy with respect to molecular characteristics of insulin analogues. We report a series of experiments forming a comprehensive characterisation of the long acting insulin analogues, glargine and detemir, in comparison with human insulin, IGF-1, and the super-mitogenic insulin, X10. METHODS: We measured binding of ligands to membrane-bound and solubilised receptors, receptor activation and mitogenicity in a number of cell types. RESULTS: Detemir and glargine each displayed a balanced affinity for insulin receptor (IR) isoforms A and B. This was also true for X10, whereas IGF-1 had a higher affinity for IR-A than IR-B. X10 and glargine both exhibited a higher relative IGF-1R than IR binding affinity, whereas detemir displayed an IGF-1R:IR binding ratio of ≤ 1. Ligands with high relative IGF-1R affinity also had high affinity for IR/IGF-1R hybrid receptors. In general, the relative binding affinities of the analogues were reflected in their ability to phosphorylate the IR and IGF-1R. Detailed analysis revealed that X10, in contrast to the other ligands, seemed to evoke a preferential phosphorylation of juxtamembrane and kinase domain phosphorylation sites of the IR. Sustained phosphorylation was only observed from the IR after stimulation with X10, and after stimulation with IGF-1 from the IGF-1R. Both X10 and glargine showed an increased mitogenic potency compared to human insulin in cells expressing many IGF-1Rs, whereas only X10 showed increased mitogenicity in cells expressing many IRs. CONCLUSIONS: Detailed analysis of receptor binding, activation and in vitro mitogenicity indicated no molecular safety concern with detemir

Class III PI-3-kinase activates phospholipase D in an amino acid–sensing mTORC1 pathway

In response to amino acid availability, the class III PI-3-kinase hVps34 activates the phospholipase PLD and mTORC1 signaling to regulate mammalian cell size

Engineering of Insulin Receptor Isoform-Selective Insulin Analogues

BACKGROUND: The insulin receptor (IR) exists in two isoforms, A and B, and the isoform expression pattern is tissue-specific. The C-terminus of the insulin B chain is important for receptor binding and has been shown to contact the IR just adjacent to the region where the A and B isoforms differ. The aim of this study was to investigate the importance of the C-terminus of the B chain in IR isoform binding in order to explore the possibility of engineering tissue-specific/liver-specific insulin analogues. METHODOLOGY/PRINCIPAL FINDINGS: Insulin analogue libraries were constructed by total amino acid scanning mutagenesis. The relative binding affinities for the A and B isoform of the IR were determined by competition assays using scintillation proximity assay technology. Structural information was obtained by X-ray crystallography. Introduction of B25A or B25N mutations resulted in analogues with a 2-fold preference for the B compared to the A isoform, whereas the opposite was observed with a B25Y substitution. An acidic amino acid residue at position B27 caused an additional 2-fold selective increase in affinity for the receptor B isoform for analogues bearing a B25N mutation. Furthermore, the combination of B25H with either B27D or B27E also resulted in B isoform-preferential analogues (2-fold preference) even though the corresponding single mutation analogues displayed no differences in relative isoform binding affinity. CONCLUSIONS/SIGNIFICANCE: We have discovered a new class of IR isoform-selective insulin analogues with 2-4-fold differences in relative binding affinities for either the A or the B isoform of the IR compared to human insulin. Our results demonstrate that a mutation at position B25 alone or in combination with a mutation at position B27 in the insulin molecule confers IR isoform selectivity. Isoform-preferential analogues may provide new opportunities for developing insulin analogues with improved clinical benefits

Involvement of Phospholipase D2 in Lysophosphatidate-induced Transactivation of Platelet-derived Growth Factor Receptor-β in Human Bronchial Epithelial Cells

Lysophosphatidate (LPA) mediates multiple cellular responses via heterotrimeric G protein coupled LPA-1, LPA-2, and LPA-3 receptors. Many G protein-coupled receptors stimulate ERK following tyrosine phosphorylation of growth factor receptors; however, the mechanism(s) of transactivation of receptor tyrosine kinases are not well defined. Here, we provide evidence for the involvement of phospholipase D (PLD) in LPA-mediated transactivation of platelet-derived growth factor receptor-beta (PDGF-R beta). In primary cultures of human bronchial epithelial cells (HBEpCs), LPA stimulated tyrosine phosphorylation of PDGF-R beta and threonine/tyrosine phosphorylation of ERK1/2. The LPA-mediated activation of ERK and tyrosine phosphorylation of PDGF-R beta was attenuated by tyrphostin AG 1296, an inhibitor of PDGF-R kinase, suggesting transactivation of PDGF-R by LPA. Furthermore, LPA-, but not PDGF beta-chain homodimer-induced tyrosine phosphorylation of PDGF-R beta was partially blocked by pertussis toxin, indicating coupling of LPA-R(s) to Gi. Exposure of HBEpCs to LPA activated PLD. Butan-1-ol, which acts as an acceptor of phosphatidate generated by the PLD pathway, blocked LPA-mediated transactivation of PDGF-R beta. This effect was not seen with butan-3-ol, suggesting PLD involvement. The role of PLD1 and PLD2 in the PDGF-R beta transactivation by LPA was investigated by infection of cells with adenoviral constructs of wild type and catalytically inactive mutants of PLD. LPA activated both PLD1 and PLD2 in HBEpCs; however, infection of cells with cDNA for wild type PLD2, but not PLD1, increased the tyrosine phosphorylation of PDGF-R beta in response to LPA. Also, the LPA-mediated tyrosine phosphorylation of PDGF-R beta was attenuated by the catalytically inactive mutant mPLD2-K758R. Infection of HBEpCs with adenoviral constructs of wild type hPLD1, mPLD2, and the inactive mutants of hPLD1 and mPLD2 resulted in association of PLD2 wild type and inactive mutant proteins with the PDGF-R beta compared with PLD1. These results show for the first time that transactivation of PDGF-R beta by LPA in HBEpCs is regulated by PLD2

Pseudoacromegaly

© 2018 Elsevier Inc. Individuals with acromegaloid physical appearance or tall stature may be referred to endocrinologists to exclude growth hormone (GH) excess. While some of these subjects could be healthy individuals with normal variants of growth or physical traits, others will have acromegaly or pituitary gigantism, which are, in general, straightforward diagnoses upon assessment of the GH/IGF-1 axis. However, some patients with physical features resembling acromegaly – usually affecting the face and extremities –, or gigantism – accelerated growth/tall stature – will have no abnormalities in the GH axis. This scenario is termed pseudoacromegaly, and its correct diagnosis can be challenging due to the rarity and variability of these conditions, as well as due to significant overlap in their characteristics. In this review we aim to provide a comprehensive overview of pseudoacromegaly conditions, highlighting their similarities and differences with acromegaly and pituitary gigantism, to aid physicians with the diagnosis of patients with pseudoacromegaly.PM is supported by a clinical fellowship by Barts and the London Charity. Our studies on pituitary adenomas and related conditions received support from the Medical Research Council, Rosetrees Trust and the Wellcome Trust

IGF1 and IGF2 specificities to the two insulin receptor isoforms are determined by insulin receptor amino acid 718.

METHODS:Alanine scan of insulin receptor (IR)-B exon 11 and site-directed mutagenesis of amino acid 718 in human IR-A and IR-B were performed. Ligand affinities to wild type and mutated receptors were studied by displacement of radioactive insulin in binding assay on secreted soluble midi receptors or solubilized semi-purified full length receptors stably expressed in Baby Hamster Kidney cells. Phosphorylation of IR in response to insulin, IGF1 and IGF2 was measured using ELISA. RESULTS:Insulin, insulin detemir and insulin glargine maximally showed two fold differences in affinity for human IR-A and IR-B, but IGF1 and IGF2 had up to 10 fold preference for IR-A. Alanine scan of exon 11 revealed that position 718 is important for low IGF1 affinity to IR-B. Mutational analysis of amino acid residue 718 in IR-A and IR-B demonstrated that charge is important for IGF1 and IGF2 affinity but not important for insulin affinity. The affinity of IGF1 and IGF2 for the mutant IR-A P718K was comparable to the wild type IR-B whereas the affinity of IGF1 and IGF2 for the mutant IR-B K718P was comparable to the wild type IR-A. Changes in affinity were also reflected in the IR activation pattern. CONCLUSION:Mutating position 718 in human IR-B to the proline found at position 718 in human IR-A increased IGF1 and IGF2 affinity to a level comparable to IR-A and mutating position 718 in IR-A to the lysine found at position 718 in IR-B decreased IGF1 and IGF2 affinity to a level comparable to IR-B, whereas a negatively charged glutamate did not. These changes in the affinities were also reflected in the IR phosphorylation pattern, meaning that position 718 is important for both affinity and activation of the receptor. It should be emphasized that none of the mutations affected insulin affinity, indicating that the mutations did not alter the overall receptor structure and that the effect is ligand specific