Ribosomal protein uL3 targets E2F1 and Cyclin D1 in cancer cell response to nucleolar stress

Abstract

Several experimental strategies in the treatment of cancer include drug alteration of cell cycle regulatory pathways as a useful strategy. Extra-ribosomal functions of human ribosomal protein L3 (uL3) may affect DNA repair, cell cycle arrest and apoptosis. In the present study, we demonstrated that uL3 is required for the activation of G1/S transition genes. Luciferase assays established that uL3 negatively regulates the activity of E2F1 promoter. Induced ribosome-free uL3 reduces Cyclin D1 mRNA and protein levels. Using protein/protein immunoprecipitation methods, we demonstrated that uL3 physically interacts with PARP-1 affecting E2F1 transcriptional activity. Our findings led to the identification of a new pathway mediated by uL3 involving E2F1 and Cyclin D1 in the regulation of cell cycle progression.

Role of uL3 in the Crosstalk between Nucleolar Stress and Autophagy in Colon Cancer Cells

“…The up-regulation of epithelial-mesenchymal transition (EMT) pathway, a migratory cellular program associated with tumor development and metastasis is in line with our previous data demonstrating that this pathway is activated in colon cancer cells in absence of uL3 [12]. A large number of gene sets were found significatively depleted (n = 13) in uL3∆HCT 116 p53−/− after Act D treatment compared to untreated cells, while there were only two positively enriched ( Figure 3B).…”

“…In the presence of Act D, we found up-regulation of uL3 expression and its translocation from the nucleolus in the nucleoplasm where it can exert its extra-ribosomal functions [12].…”

“…It has been largely accepted that autophagy is a mechanism for treatment failure in cancer [22]. On the basis of our previous findings [4,12,17], we hypothesized that uL3 might attenuate cancer cell response to drug treatment modulating autophagy.…”

“…Recently, a large number of studies conducted by our group focused on post-transcriptional regulation of r-protein synthesis [6][7][8] and on extra-ribosomal functions of some r-proteins [4]. In particular, we demonstrated that r-protein uL3 is a key mediator of nucleolar stress induced by several chemotherapeutic drugs as 5-fluorouracil (5-FU), Oxaliplatinum (OHP), Actinomycin D (Act D) and Niclosamide in p53-mutated lung and p53-deleted colon cancer cells [9][10][11][12]. Specifically, we identified a new nucleolar stress pathway activated upon cell treatment with chemotherapeutic drugs that is p53-independent and uL3-dependent [4].…”

“…We have previously demonstrated that the treatment of HCT 116 p53−/− cells with Act D induced a nucleolar stress pathway p53-independent but uL3-dependent. In fact, in condition of Act D treatment uL3 protein was up-regulated and as ribosome free form translocated to the nucleoplasm where it regulated key cellular processes such as cell cycle progression and apoptosis [11,12].…”