Role of insulin receptor isoform A in breast cancer

Abstract

Insulin like growth factor II (IGF-II) binds to Insulin Receptor isoform A (IR-A) to sustain cell growth and proliferation. This autocrine loop exists in many human carcinomas and provides an additional proliferation and survival pathway to the type 1 insulin-like growth factor (IGF-1R) signalling pathway. In addition, activation of the IGF-II/IR-A autocrine loop provides a mechanism of resistance drugs target the type 1 insulin-like growth factor (IGF- 1R). However, the mechanism of how IGF-II/IR-A differentiates itself from the IGF-II/IGF- 1R pathway is still unclear. Additionally, a novel phosphorylation site Thr¹¹⁴⁸ (numbered in IR-A) of IR was found in response to insulin stimulation and its phosphorylation in the absence of any Tyr¹¹⁴⁶, Tyr¹¹⁵⁰, and Tyr¹¹⁵¹ phosphorylation. We thus hypothesis that the The phosphorylation of Thr¹¹⁴⁸ inhibits the phosphorylation of Tyr¹¹⁴⁶, Tyr¹¹⁵⁰, and Tyr¹¹⁵¹ of the activation loop, which is possibly due to steric hindrance and electrostatic repulsion of the phosphate group on Thr¹¹⁴⁸ preventing interaction of the activation loop with the tyrosine kinase. The key areas of investigation included: 1. Investigate the role of Thr¹¹⁴⁸ phosphorylation in IR-A by overexpress the wild-type IR-A and its mutants Thr¹¹⁴⁸Ala and Thr¹¹⁴⁸Asp in R⁻ (Mouse fibroblast cells with IGF- 1R KO). 2. Knock down the IR and IGF-1R separately in MDA-MB-231 and MCF-7 cells using inducible expressed miR30 shRNA and measure their characteristics (proliferation, migration, epithelial–mesenchymal transition) in response to insulin, IGF-I, and IGFII stimulation separately. 3. Quantitative phosphoproteomics was conducted to compare the insulin/IR-A and IGFII/ IR-A signalling pathway with MDA MB 231 IGF-1RKD cell. The key findings from this work included: included: 1. Thr¹¹⁴⁸Ala and Thr¹¹⁴⁸Asp inhibit the insulin sensitivity of IR-A, which indicate the Thr¹¹⁴⁸ phosphorylation inhibits the IR activation. 2. IRKD has no effect on proliferation of MCF-7 cells and the migration of MDA-MB- 231 cells, but increases the proliferation of MDA-MB-231 cells. 3. IGF-1RKD inhibits the proliferation of both MCF-7 cells and MDA-MB-231 cells, but increases the migration of MDA-MB-231 cells. 4. IGF-1R increases the insulin sensitivity of MDA-MB-231 cells, shown by the Akt activation. 5. Insulin and IGF-II are confirmed to induce different signalling pathways confirmed by quantitative phosphoproteomics study. IGF-II is preferentially regulates the migration and stemness of MDA-MB-231 IGF-1RKD cells. Many markers are identified but verifications are still needed. Drug developed on the verified markers can be used to treat the patients who are resistant to anti-IGF-1R inhibitor.