Estudi molecular i funcional del receptor d'insulina en síndromes de resistència a la insulina

Abstract

Insulin was discovered by Banting & Best in 1922, since then a great progress has been made in the knowledge and comprehension of its chemicals, physiology and function (1). All the insulin actions, including the metabolic and mitogenic ones, take place through its receptor. Insulin receptor is a heterotetrameric membrane protein with two extracellular a subunits that bind insulin, and two transmembrane b subunits. The intracellular portions of these b subunits have an intrinsic enzymatic tyrosine kinase activity (5). Insulin binding to its receptor is the first step in insulin signalling and it has been considered that insulin receptor mutations are responsible for disrupting the insulin signal and consequently giving rise to insulin resistance. There are three insulin resistant genetic syndromes associated with insulin receptor mutations: Leprechaunism, Rabson-Mendenhall syndrome and Type A Insulin Resistance syndrome, although some mutations in obese and Lipodystrophic patients have been described. Eighteen insulin resistant patients have been studied in the present work. The molecular study of its insulin receptor gene by means of PCR and automatic sequencing revealed three novel mutations in heterozigote state in three Type A insulin resistant patients (A1 patient Leu140/splicing acceptor-1239Stop, A2 patient splicing acceptor-1239Stop/WT and A3 patient Val1028/WT). Two previously described mutations in a Rabson Mendenhall patient (Lys15/Stop1000), and a variation in a control subject (Val985Met), as well as some polymorphisms. Functional studies of the mutant receptors showed that the Leu140 receptor expresses less than the Wt receptor, binds less insulin and has a decreased tyrosine kinase activity. Val1028 mutation affects the consensus sequence for ATP binding and abolishes tyrosine kinase activity. The splicing acceptor-1239Stop mutation gives rise to two abnormal and different mRNAs, but the resultant protein of both is the same: the receptor lacks the C-terminal domain (exon 22). This mutant receptor expresses as a WT receptor, binds a 50% less insulin than WT and lacks tyrosine kinase activity. In conclusion we can say that the insulin resistance of the patients is due to the mutations present in their insulin receptors.

Date of Award	27 Jun 2001
Original language	Catalan
Supervisor	Antonio Carrascosa Lezcano (Director), N. Potau (Director) & Maria del Carme Nogues Sanmiquel (Tutor)