ABS 053: PDCD-2 knockout inhibition of colony formation is independent of p53

Esha Kamath ¹ ², Niele Dias Mendes ¹, Cindy Song ¹, Hsin-Ching Lin ¹, Arnold B. Rabson ¹

¹ Child Health Institute of New Jersey, Rutgers Robert Wood Johnson Medical School (RWJMS), New Brunswick, NJ
² School of Environmental and Biological Sciences, Rutgers University, New Brunswick, NJ

The Van Wickle Journal (2026) Volume 2, ABS053

Introduction: Programmed Cell Death Domain 2 (PDCD2) is highly a conserved protein present in all eukaryotes. To study PDCD2 function, our laboratory developed a mouse strain in which PDCD2 exon 2 is flanked by loxP sites. Deletion of exon 2 was an effective knockout (KO) of PDCD2. This mouse was mated to a mouse expressing CRE under the control of Tamoxifen (TAM) allowing induction of PDCD2 knockout by Tamoxifen. Using this TAM-induced PDCD2 KO, we previously observed loss of cell proliferation in Mouse Embryo Fibroblasts (MEFs), with a block in entry into cell cycle S phase. We are interested in how PDCD2 KO leads to loss of proliferation. PDCD2 binds to ribosomal proteins and is essential for assembly of the small ribosomal subunit. PDCD2 inhibition by TAM-induced KO caused a marked reduction in 18S rRNA (Pestov, Lin et al, unpublished). Defects in ribosome assembly are known to activate p53, a tumor suppressor gene that induces cell cycle arrest and apoptosis.  We hypothesized that PDCD2 causes significant ribosomal stress inducing p53 and proliferation arrest. We compared wild-type p53 cells and CRISPR-induced p53 KO MEFs to determine whether there is a difference in their ability to form colonies in response to TAM-induced PDCD2 KO. In wild type p53 cells, TAM-treated cells formed fewer colonies than PDCD2 wild-type cells. The CRISPR knockouts of p53 did not rescue the proliferation arrest observed in TAM-induced PDCD2 knockouts. PCR of genomic DNA and Western blot of proteins from the few colonies that grew following p53 knockout and TAM treatment, showed that all colonies failed to knockout PDCD2. These data suggest that p53 is not responsible for the loss of colony formation in PDCD2-KO cells. We are now examining whether PDCD2 KO induces the integrated stress response as a mediator of PDCD2 KO effects on cell proliferation.