Ultraconserved region-containing Transformer 2β4 controls senescence of colon cancer cells.

K Kajita,K Masuda,Y Satake,K Rokutan,Y Akaike,K Kurokawa,S Kano,K Nishida,Y Kuwano

doi:10.1038/oncsis.2016.18

Abstract

Ultraconserved regions (UCRs) are >200 bp genomic segments with perfect human-to-rodent sequence identity. Transcribed UCRs constitute a new category of noncoding RNAs whose functions remain poorly understood. The human transformer 2β (TRA2B) gene contains a 419-bp UCR spanning the 276-bp exon 2 and its neighboring introns. TRA2B exon 2 has premature stop codons, whereas an exon 2-containing splice variant (TRA2β4) was expressed preferentially in the nuclei of human colon cancer cells. TRA2β4 knockdown p53-independently stimulated CDKN1A transcription and increased p21, resulting in the appearance of senescent cells. Biotin pull-down and RNA immunoprecipitation assays revealed that TRA2β4 interacted with Sp1 through a Sp1-binding sequence (485-GGGG-488) in a stem-loop structure of exon 2. Mutation of this sequence (485-AAGG-488) disrupted the stem-loop structure, blocked the interaction with Sp1 and increased CDKN1A transcription. Overexpression of TRA2β4 significantly decreased CDKN1A mRNA levels and accelerated cell growth, but the introduction of the mutation in the Sp1-binding sequence completely canceled these effects. Taken together, TRA2β4 may sequester Sp1 from occupying promoters of target genes including CDKN1A, promoting cell growth by interrupting the senescence-related gene expression program. This novel function of TRA2β4 may uncover an oncogenic function of transcribed UCRs.

Highlights

Alternative splicing of pre-mRNAs generates protein diversity from a limited number of genes.[1]
TRA2β4 levels were estimated to be 10–20% of those of TRA2β1 mRNA that encodes a full-length transformer 2β (Tra2β) protein
We show here that human colon cancer cells express significant amounts of a T-Ultraconserved regions (UCRs) (TRA2β4), which is transcribed from uc 281

Summary

Introduction

Alternative splicing of pre-mRNAs generates protein diversity from a limited number of genes.[1]. Human colon cancer (HCT116) cells expressed mainly TRA2β1 mRNA and increased TRA2β4 isoform production after exposure to sodium arsenite (Supplementary Figures S2b and c) as observed in gastric cancer cells.[13] It was of interest that TRA2β4 siRNA did not change TRA2β1 mRNA or Tra2β protein levels, but it did inhibit cell growth (Figure 3c).

Results

Conclusion