Ahmet Doymaz

CUGBP1 and Calreticulin Can Bind Both a Long Non-Coding RNA and Full-Length Transcript of CDKN1A Gene Resulting in Post-Transcriptional Regulation of p21 Expression

Ahmet Doymaz, Anthony Ramadei, Michael R. Murphy and Frida E. Kleiman.
Chemistry Department, Hunter College, City University of New York, New York

Regulation of CDKN1A gene expression, and hence p21 protein levels, has long been studied. The tumor suppressor p21 is a CDK inhibitor that regulates cell-cycle progression to prevent aberrant transmission of damaged DNA. The expression of CDKN1A under normal conditions and during DNA damage response (DDR) is tightly regulated. Our studies show that CDKN1A undergoes intronic alternative polyadenylation (APA) during DDR, and the resulting transcript is a long non-coding RNA (lncRNA). Like p21, lncRNA levels increase following UV treatment. Our recent data indicate that the loss of this lncRNA through siRNA-mediated knockdown produces a significant decrease in p21 protein, without a change in CDKN1A full-length mRNA levels, suggesting a role for this lncRNA at the post-transcriptional level.

Previous studies showed that RNA binding proteins (RBPs) calreticulin (CTR) and CUGBP1 can bind the CDKN1A full-length mRNA and regulate p21 translation (Iakova et al. 2004). CUGBP1 is a p21 translational activator, whereas CTR blocks translation of p21 via stabilization of a stem–loop in CDKN1A mRNA. Using RNA-immunoprecipitation assays, we show that CTR and CUGBP1 binding to the CDKN1A full-length mRNA increases in cells depleted of CDKN1A lncRNA. Both RBPs can bind the CDKN1A lncRNA directly. Additionally, after UV damage, CTR binding to the lncRNA is favored over full-length mRNA, whereas CUGBP1 binding to the full-length is favored over the lncRNA. Together, these results suggest a new regulatory mechanism for p21 expression at the post-transcriptional level, whereby the CDKN1A lncRNA sequesters p21 translational regulators CUGBP1 and CTR at different stages of DDR.

Email questions and comments about this abstract to ahmet.doymaz@macaulay.cuny.edu.