p21, ccng1, foxo3b and fbxw7 contribute to p53-dependent cell-cycle arrest [MPNP 18hpf]

p53 is a transcription factor that plays a critical role in cancer prevention. However, the mechanisms by which p53 exerts its tumor-suppressive function is still unclear. While PUMA/BBC3 and NOXA/PMAIP1 are known to be important in p53-dependent apoptosis, and p21/CDKN1A is crucial for p53-dependent cell-cycle arrest, we demonstrate that zebrafish lacking puma, noxa, and p21 do not show a predisposition to cancer. This suggests that additional p53 transcriptional targets are sufficient for its tumor suppressive function. Contrary to the prevailing belief that p21 is the key regulator of p53-dependent cell-cycle arrest, we provide evidence that p53 can still induce cell-cycle arrest in the absence of p21, following DNA damage or loss of mdm2 (p53 activation in the absence of stress). This implies the involvement of other p53 transcriptional targets in mediating p53-dependent cell-cycle arrest. Since p53 tumor suppression is conserved across multiple vertebrate species, we conducted a cross-species comparative analysis of p53-dependent transcriptional profiles to identify a conserved set of 136 p53-upregulated transcripts. Our analysis stresses the importance of ortholog to paralog analysis across species, since in many cases the paralog but not ortholog in differing species is p53 dependent. Additionally, we performed a CRISPR/Cas9 G0 “crispant” screen in a genetic background lacking mdm2, puma, noxa, and p21 to identify key components involved in p53-dependent cell-cycle arrest. Our findings revealed that ccng1, fbxw7, and foxo3b play an important role in this process. RNA sequencing was performed on zebrafish quadruple knockouts of mdm2, puma, noxa, and p21 at 18 hours post-fertilization. Sibling controls from the same batch, including mdm2+/- (or mdm2+/+); puma-/-; noxa-/-; and p21-/- embryos, were also harvested to extract RNA for comparison.