Anthony Ramadei

Regulation of p21 Expression in the DNA Damage Response by Calreticulin, CUGBP1, and a Long Non-Coding RNA Generated by Alternative Polyadenylation

Anthony Ramadei ^1,2, Amy Yu ¹, Ahmet Doymaz ¹, Devorah Natelson ^1,2, Michael R. Murphy ^1,2, and Frida E. Kleiman ^{1,2, 3}.

¹Chemistry Department, Hunter College, City University of New York (CUNY)
²Biology Program, Graduate Center, CUNY
³Biochemistry Program, Graduate Center, CUNY

The cyclin-dependent kinase inhibitor p21 functions in cell-cycle regulation, DNA damage response (DDR), and is at the center of “Therapy-induced senescence” (TIS). While high or low levels of p21 upon chemotherapeutic treatment leads to senescence, moderate levels enable a proliferative fate. Therefore, understanding mechanisms involved in regulating p21 dynamics in TIS is relevant in improving the efficacy of treatments, especially in triple negative breast cancer (TNBC) which undergoes frequent chemoresistance relapse by TIS.

There is a current gap in knowledge concerning the early mechanisms regulating expression of p21; a delay in p21 expression following cellular stress has been described despite p53 presence at the CDKN1A promoter, the gene that encodes p21. CDKN1A undergoes alternative polyadenylation (APA), a mechanism that generates alternative transcripts from the same gene. APA in CDKN1A occurs in the first intron after DNA damage generating a long non-coding RNA named APA-CDKN1A. APA-CDKN1A is expressed early in DDR before the induction of p21 expression. Interestingly, APA-CDKN1A depletion does not affect full-length CDKN1A mRNA levels, increases cell proliferation, and significantly decreases p21 protein levels, suggesting a translational regulatory role of APA-CDKN1A. Furthermore, the RNA-binding proteins (RNA-BP) and translational regulators of p21, calreticulin and CUGBP1, compete for binding to the same sequence in APA-CDKN1A and CDKN1A mRNA. My results indicate that changes in CDKN1A isoforms interaction to these RNA-BPs during DDR and in different BC will affect p21 expression levels and cellular functions, and this can be exploited for conditions where p21 levels are relevant, such as in TIS.