Date

9-19-2023

Department

School of Health Sciences

Degree

Doctor of Philosophy

Chair

Jeremiah Winter

Keywords

S6K-1, p300, IRS-1 regulation, Insulin, RPS6, HepG2 cells, phosphorylation of IRS-1, acetylation of IRS-1

Disciplines

Biology

Abstract

The study of IRS-1 has increased over the years due to the prevalence of cardiometabolic diseases. An increase in IRS-1 serine phosphorylation is often associated with the development of insulin resistance due to the downregulation bestowed upon it by different kinases such as p70 S6K-1. Recently, p300 has been shown to acetylate IRS-1 thus leading to its downregulation. However, studies have not looked into the relationship that exists between serine phosphorylation and lysine acetylation of IRS-1. In this study, insulin stimulated HepG2 cells were treated with either PF4708671, a selective p70 S6K-1 inhibitor, or C646, a selective p300 inhibitor. PF4708671 treatment led to the successful dose dependent decrease in the phosphorylation of S312, S636/639, and S1101 on IRS-1. Treatment with 10µM of C646 did successfully decrease p300 activity. By inhibiting p300 activity there was a decrease in S312 and S1101 phosphorylation. The inhibition of p300 also led to an exponential increase in the activation of insulin stimulated RPS6, thus meaning that there was an increase in IRS-1 insulin signaling. Thus, p300 inhibition prevents the phosphorylation of the negative regulatory sites S312 and S1101. In addition, p300 activity enhances the phosphorylation of S1101, while the overall phosphorylation by p70 S6K-1 enhances the overall acetylation of IRS-1. There is a connection that exists between the acetylation and serine phosphorylation of IRS-1 and further research will need to be done to narrow down the exact mechanism. Together we elucidate that the inability of p300 to acetylate IRS-1 leads to a decrease in the phosphorylation of IRS-1 S312 and S1101 in insulin stimulated HepG2.

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