Pathological p53 activation induced by disruption of ribosome biogenesis prevents normal expansion of erythroid progenitors, suggesting a regulatory role for ribosome biogenesis in normal erythroid development, according to the results of a study published in Blood.
Deletions and point mutations in ribosomal protein genes, which cause ribosomopathies, have been associated with erythroid defects in macrocytic anemia, including both Diamond-Blackfan anemia and 5q- syndrome.
To study the role of ribosome biogenesis in normal erythroid development, the investigators characterized ribosome biogenesis dynamics during human and murine erythropoiesis.
Human erythroblast cultures were assessed for normal ribosome biogenesis dynamics, and were studied after treatment with an RNA polI inhibitor, CX-5461. Cell differentiation was assessed by cytological examination and flow cytometry; ribosomal protein expression was measured using a variety of molecular assays and p53 chromatin immunoprecipitation (ChIP)-sequencing to assess p53 interactions with DNA. Confirmation experiments were conducted in murine erythroblast cultures and a TP53-deficient mouse model.
Treatment of human primary erythroblasts with CX-5461 interrupted ribosome biogenesis by reducing ribosomal DNA transcription and subsequent ribosomal protein neo-synthesis. Cell proliferation was significantly decreased following treatment.
Protein expression and p53 ChIP-seq analyses of treated and control human primary erythroblasts showed that p53 activation coincides with the decrease in ribosome biogenesis, and its activation upregulates a transcriptional program involved in cell cycle arrest, negative regulation of apoptosis, and DNA damage response. Similar results were confirmed in murine studies.
Electron microscopy revealed that CX-5461 disrupts the morphological features of the nucleoli in human primary erythroblasts, and protein phosphorylation assessments revealed concomitant activation of the ATR-CHK1-p53 pathway, suggesting this may be the mechanism for p53 activation.
“Our results imply that the timing of ribosome biogenesis extinction and p53 activation are crucial for erythroid development,” wrote the authors. “In ribosomopathies in which ribosome availability is altered by unbalanced production of ribosomal proteins, the threshold of ribosome biogenesis down-regulation could be prematurely reached and together with pathological p53 activation prevents a normal expansion of erythroid progenitors.”
Le Goff S, Boussaid I, Floquet C, et al. p53 activation during ribosome biogenesis regulates normal erythroid differentiation. Blood. Published online August 20, 2020. doi:10.1182/blood.2019003439