SRSF3, a Splicer of the PKM Gene, Regulates Cell Growth and Maintenance of Cancer-Specific Energy Metabolism in Colon Cancer Cells.

Yuki Kuranaga,Kohei Taniguchi,Tomoyoshi Soga,Nobuhiko Sugito,Yukihiro Akao,Yuko Ito,Kazumasa Komura,Haruka Shinohara,Takuya Tsujino

doi:10.3390/ijms19103012

Abstract

Serine and arginine rich splicing factor 3 (SRSF3), an SR-rich family protein, has an oncogenic function in various kinds of cancer. However, the detailed mechanism of the function had not been previously clarified. Here, we showed that the SRSF3 splicer regulated the expression profile of the pyruvate kinase, which is one of the rate-limiting enzymes in glycolysis. Most cancer cells express pyruvate kinase muscle 2 (PKM2) dominantly to maintain a glycolysis-dominant energy metabolism. Overexpression of SRSF3, as well as that of another splicer, polypyrimidine tract binding protein 1 (PTBP1) and heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1), in clinical cancer samples supported the notion that these proteins decreased the Pyruvate kinase muscle 1 (PKM1)/PKM2 ratio, which positively contributed to a glycolysis-dominant metabolism. The silencing of SRSF3 in human colon cancer cells induced a marked growth inhibition in both in vitro and in vivo experiments and caused an increase in the PKM1/PKM2 ratio, thus resulting in a metabolic shift from glycolysis to oxidative phosphorylation. At the same time, the silenced cells were induced to undergo autophagy. SRSF3 contributed to PKM mRNA splicing by co-operating with PTBP1 and hnRNPA1, which was validated by the results of RNP immunoprecipitation (RIP) and immunoprecipitation (IP) experiments. These findings altogether indicated that SRSF3 as a PKM splicer played a positive role in cancer-specific energy metabolism.

Highlights

Most differentiated cells produce ATP efficiently by using both the tricarboxylic acid (TCA) cycle in mitochondria in the presence of oxygen and glycolysis under the condition of a relatively lower oxygen level
We showed that gene silencing of polypyrimidine tract binding protein 1 (PTBP1), heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1), and Serine and arginine rich splicing factor 3 (SRSF3), which for coding proteins is known as the splicing factor, induced a partial PKM switching from pyruvate kinase muscle 2 (PKM2) dominant to Pyruvate kinase muscle 1 (PKM1) dominant, followed by a metabolic shift from glycolysis to oxidative phosphorylation (OXPHOS) in the TCA cycle in the cancer cells tested
The cancer cells produced a certain amount of Reactive Oxygen Species (ROS), which resulted in the induction of mitophagy and/or autophagic cell death

Summary

Introduction

Most differentiated cells produce ATP efficiently by using both the tricarboxylic acid (TCA) cycle in mitochondria in the presence of oxygen and glycolysis under the condition of a relatively lower oxygen level. Most cancer cells use glycolysis frequently even when enough oxygen is present [1] This phenomenon, termed “the Warburg effect” or “aerobic glycolysis”, was first observed by Otto Heinrich Warburg in 1924 and is referred to as “the Warburg hypothesis” [2,3]. PKL and PKR are encoded by the same single gene, PKL, and the expression of these isoforms is controlled by tissue-specific promoters [8]. PKM1 and PKM2 are encoded in the same single PKM gene: PKM1 lacks exon and PKM2, exon, by alternative splicing (AS) to form their mature PKM mRNA [6]. SRSF3 is known as one of the splicing factors of PKM gene, and it binds to ESE on PKM exon 10 [17]

Methods

Results

Conclusion