ROLES OF HUNTINGTIN ASSOCIATED PROTEIN-1 IN INSULIN-SECRETING CELLS

Abstract

Huntingtin associated protein-1 (HAP1) is a novel protein found in the patient of Huntington¿s disease. Some reports show that it might act as a scaffold in the assembly of protein complexes and participate in intracellular trafficking. Furthermore, there is evidence that HAP1 is expressed in pancreatic islet ß-cells.

In my project, I knocked down the HAP1 expression by RNAi technique in INS-1 cells (a insulin secreting cell line from rat insulinoma). In insulin secretion experiment, the knockdown cells secreted less insulin upon the stimulation by high concentrations of glucose compared with the control cells treated with scramble siRNA. In addition, high KCl-induced insulin secretion was also inhibited. However, my results indicated that HAP1 knockdown did not affect glucose metabolism and, glucose-induced membrane potential depolarization and intracellular Ca2+ elevation. On the other hand, HAP1 knockdown reduced INS-1 cell growth and affected cell cycle by arresting them at G2/M phase. However, apoptosis was not induced by HAP1 knockdown in INS-1 cells.

Thus, it can be concluded that HAP1 knockdown not only reduced glucose-stimulated insulin section by interfering with the step beyond [Ca2+]i rise in the secretion process cascade, but also slowed down the growth of INS-1 cells without induction of apparent apoptosis. These data suggest that HAP1 may participate in the regulation of insulin secretion and growth of pancreatic islet ß-cells.