CHK Methylation Is Elevated in Colon Cancer Cells and Contributes to the Oncogenic Properties.

Shudong Zhu,Yi Zhang,Yan Zhu,Qiuwen Wang,Xialing Guo

doi:10.3389/fcell.2021.708038

Abstract

Src is an important oncogene that plays key roles in multiple signal transduction pathways. Csk-homologous kinase (CHK) is a kinase whose molecular roles are largely uncharacterized. We previously reported expression of CHK in normal human colon cells, and decreased levels of CHK protein in colon cancer cells leads to the activation of Src (Zhu et al., 2008). However, how CHK protein expression is downregulated in colon cancer cells has been unknown. We report herein that CHK mRNA was decreased in colon cancer cells as compared to normal colon cells, and similarly in human tissues of normal colon and colon cancer. Increased levels of DNA methylation at promotor CpG islands of CHK gene were observed in colon cancer cells and human colon cancer tissues as compared to their normal healthy counterparts. Increased levels of DNA methyltransferases (DNMTs) were also observed in colon cancer cells and tissues. DNA methylation and decreased expression of CHK mRNA were inhibited by DNMT inhibitor 5-Aza-CdR. Cell proliferation, colony growth, wound healing, and Matrigel invasion were all decreased in the presence of 5-Aza-CdR. These results suggest that increased levels of DNA methylation, possibly induced by enhanced levels of DNMT, leads to decreased expression of CHK mRNA and CHK protein, promoting increased oncogenic properties in colon cancer cells.

Highlights

Src is an important oncogene that plays key roles in multiple signal transduction pathways (Yeatman, 2004)
The results suggest that increased levels of DNA methylation, possibly induced by enhanced levels of DNA methyltransferases (DNMTs), leads to decreased expression of c-Src tyrosine kinase (Csk)-homologous kinase (CHK) mRNA and CHK protein, promoting increased oncogenic properties, revealing an important CHK regulatory mechanism in contributing to the tumorigenesis of colon cancer
To explore if transcriptional regulation led to this downregulation of CHK protein, we examined the mRNA levels of CHK in various colon cell lines using qPCR

Summary

Introduction

Src is an important oncogene that plays key roles in multiple signal transduction pathways (Yeatman, 2004). Csk-homologous kinase (CHK) sharing 53% amino acid identity with c-Src tyrosine kinase (Csk). CHK has been reported to be expressed primarily in brain and hematopoietic cells (Chow et al, 1994). Unlike Csk, which phosphorylates and inhibits Src effectively, CHK is not capable of phosphorylating Src Y530 effectively (Advani et al, 2017). The molecular and functional roles of CHK are largely uncharacterized. We previously reported that CHK expression was not restricted to brain and hematopoietic cells, instead, CHK is expressed in normal colon cells and its protein levels were decreased in colon

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