Nucleolar stress response pathway (NSR)

The p53 pathway via nucleolar surveillance, also known as the nucleolar stress response (NSR), is a vital cellular sensing mechanism that monitors the fidelity of ribosome biogenesis [Boulon et al., 2010]. Under normal conditions, the nucleolus is the primary site for ribosomal RNA (rRNA) synthesis and the assembly of ribosomal subunits. When this process is impaired by cellular stress, DNA damage, or specific inhibitors, the nucleolus undergoes structural disruption, a state termed nucleolar stress [Woods et al., 2015]. This disruption triggers the release of free ribosomal proteins, most notably RPL11 and RPL5, into the nucleoplasm where they interact with and inhibit the E3 ubiquitin ligase MDM2 [Pelletier et al., 2018]. Because MDM2 is the principal negative regulator of p53, its inhibition leads to the stabilization and accumulation of p53, which subsequently induces cell cycle arrest, senescence, or apoptosis [Quin et al., 2014]. In the context of cancer therapy, this pathway is targeted by small molecules like CX-5461 (Pimiciklib) that selectively inhibit RNA Polymerase I to activate p53-mediated tumor suppression, particularly in malignancies with high biosynthetic demands [Senhwa Biosciences].

Other names

Nucleolar surveillanceRibosomal stress responsep53-dependent nucleolar stress responseNucleolar stress-p53 axis

Drugs targeting this pathway typically inhibit RNA Polymerase I-mediated transcription of ribosomal DNA or disrupt ribosomal RNA processing. This disruption causes the nucleolus to release ribosomal proteins, specifically RPL5 and RPL11, which form a complex with 5S rRNA. This complex binds to the E3 ubiquitin ligase MDM2, blocking its ability to ubiquitinate p53. Consequently, p53 protein levels increase, leading to the transcriptional activation of genes involved in cell cycle arrest (e.g., p21) and apoptosis (e.g., PUMA, BAX) [Pelletier et al., 2018; Woods et al., 2015].