Bazı Farmakolojik Şaperonların Mutant AVPR2 Proteinlerinde Gözlemlenen Fonksiyon Kayıpları Üzerine Etkilerinin Araştırılması

Abstract

Faults in protein folding cause production of abnormal or immature proteins. Misfolded proteins accumulate in aggregates and have toxic effect in endoplasmic reticulum. This process results in conformational diseases caused by mutations in related genes which disrupt protein homeostasis. Various research groups proved that small cell-permeable molecules, called pharmacological chaperones, have therapeutic effects on conformational diseases. These small compounds stabilize misfolded proteins, allowing them to fold in their natural form, thus create a structure which helps them regain their three-dimensional molecular forms and their functions.

Mutations in AVPR2 and related genes cause NDI which is the X-linked; a conformational disease. Mutations in AVPR2 gene - that cause NDI - can cause formation of receptors in different phenotypes. However, in vitro AVPR2 expression studies show that these intracellular receptors, which are misfolded as a result of the mutation and caught in quality control system of endoplasmic reticulum, can fulfill their functions when they reach the apical membrane. Purpose of this study is to investigate R68W, R67_G69/G107W (Compound heterozygote) and T273M mutant AVPR2 proteins which causes NDI disease and loss of functions, through pharmacological chaperone application; and observe if they are released from quality control mechanism and reach the apical membrane where they fulfill their functions. In experimental studies conducted for this purpose, plasmids used in previous studies, containing wild-type and mutant AVPR2 gene sequences, were transferred into COS-7 cells by transient transfection method. Three different pharmacological chaperones, non-peptide antagonists OPC41061 (Tolvaptan), OPC31260 (Mozavaptan) and OPC21268 were applied to transfected mutant and wild-type COS-7 cells. Cell surface ELISA and total ELISA methods were applied to determine intracellular and cell surface expression of mutant and wild-type AVPR2. Pharmacological chaperone effect was observed by comparing the results of function loss performed in previous studies to ELISA results after pharmacological chaperone application. Additionally, in order to determine the location of mutant and wild-type AVPR2s in the cells after pharmacological chaperone application, imaging studies in florescence microscope were performed after ER-tracker and Golgi apparatus-tracer dyeing method. All experimental studies proved, pharmacological chaperones of OPC41061, OPC31260 and OPC21268 were successful on R68W, R67_G69/G107W (Compound heterozygote) and T273M mutant AVPR2 proteins. Observations showed that ratio of mutant proteins reaching cell surface and their intracellular quantities are higher compared to control group mutant proteins.

Keywords: Pharmacological Chaperones, Quality Control Systems, Nephrogenic Diabetes Insipidus, AVPR2 Mutations