Characterization of hypoxia effect in the expression of abnormal mRNAs containing premature termination codon

Abstract

mRNAs containing premature termination codon (PTC) are generally degraded by the nonsense-mediated mRNA decay (NMD) pathway, a well-known RNA surveillance mechanism. PTCs are generated by nonsense or frameshift mutation at coding mononucleotide repeats (cMNR) in high microsatellite instability (MSI-H) colon cancers. These PTC-containing abnormal mRNAs are identified as relevant substrates of NMD, and therefore suspected to be putative tumor target genes. Although aberrant mRNAs are degraded by NMD, this NMD has also been inhibited in several conditions. Hypoxia is one of the NMD inhibiting conditions and common in many tumors, especially in the tumor cells located at the center.In this study, the effect of hypoxic change in the genes containing PTC was characterized through mimicking the tumor microenvironment. It was firstly confirmed that NMD was inhibited in hypoxic conditions using mutant β-globin genes. Then, PTC-containing mRNAs were selected by analyzing the status of frameshift mutations in 5 MSI colon cancer cell lines. 19 PTC-containing mRNAs were profiled by quantitative RT-PCR in 5 MSI-H colon cancer cell lines. Hypoxia exposure and treating hypoxic mimetic drugs in vitro were utilized. Specifically, highly up-regulated targets, RAPGEF6, TBC1D23, SPAG9, HDAC2, SLC35F5, and SMG7, in hypoxic conditions might affect tumor progression. This characterization of PTC-containing genes in hypoxic effects might give clues to the biological effect of NMD in vivo, and play a role in tumor progression