Regulatory role of rpL3 in cell response to nucleolar stress induced by Act D in tumor cells lacking functional p53

Abstract

Many chemotherapeutic drugs cause nucleolar stress and p53-independent pathways mediating the nucleolar stress response are emerging. Here, we demonstrate that ribosomal stress induced by Actinomycin D (Act D) is associated to the up-regulation of ribosomal protein L3 (rpL3) and its accumulation as ribosome-free form in lung and colon cancer cell lines devoid of p53. Free rpL3 regulates p21 expression at transcriptional and post-translational levels through a molecular mechanism involving extracellular-signal-regulated kinases1/2 (ERK1/2) and mouse double minute-2 homolog (MDM2). Our data reveal that rpL3 participates to cell response acting as a critical regulator of apoptosis and cell migration. It is noteworthy that silencing of rpL3 abolishes the cytotoxic effects of Act D suggesting that the loss of rpL3 makes chemotherapy drugs ineffective while rpL3 overexpression associates to a strong increase of Act D-mediated inhibition of cell migration. Taking together our results show that the efficacy of Act D chemotherapy depends on rpL3 status revealing new specific targets involved in the molecular pathways activated by Act D in cancers lacking of p53. Hence, the development of treatments aimed at upregulating rpL3 may be beneficial for the treatment of these cancers.

rpL3 promotes the apoptosis of p53 mutated lung cancer cells by down-regulating CBS and NFκB upon 5-FU treatment

“…In fact the loss of rpL3 makes chemotherapeutic drug ineffective. We have demonstrated that ectopic expression of rpL3 in cancer cells induces cell cycle arrest or apoptosis by positively modulating p21 expression at transcriptional and post-translational levels1617. Moreover, we found that rpL3 status was associated to chemoresistance since the loss of rpL3 makes chemotherapeutic drugs, such as 5-FU, oxaliplatin, actinomycin D and cisplatin ineffective41635.…”

“…2A shows that 5-FU treatment caused a decrease of CBS expression levels. Next, to investigate the role of rpL3, we performed analogous experiments in a cell clone namely rpL3ΔCalu-6 cells in which rpL3 is stably silenced16. In these cells, 5-FU failed to downregulate CBS expression levels (Fig.…”

“…Since we have recently demonstrated that after drug treatment the ribosome-free rpL3 behaves as a transcription factor416, we became interested to determine if the rpL3-mediated down-regulation of CBS protein levels occurred via inhibition of CBS gene transcription. To this aim, total RNA from untreated and 5-FU treated Calu-6 and rpL3ΔCalu-6 cells was isolated and analyzed by quantitative RT-PCR using primers specific for CBS.…”

The nucleolus, an ally, and an enemy of cancer cells

“…Consistently, RPL3-mediated positive regulation of p21 expression via ERK (extracellular-signal-regulated kinase) activation results in promotion of apoptosis as well as reduction of proliferation and migration of these cancer cells (Russo et al 2016a). In a similar experimental system, the use of 5-FU, DNA, and RNA synthesis inhibitor in combination with RPL3 overexpression considerably enhances sensitivity of 5-FU-resistant lung and colon cancer cells to this drug, and thereby, it strongly increases cytotoxic effect by means of the mitochondrial apoptotic cell response which prevents cell migration and invasion.…”

Synthetic nanoparticles for delivery of radioisotopes and radiosensitizers in cancer therapy

“…Chemotherapy drugs constitute another category of cell cycle regulators (Russo et al 2016; Li et al 2016), among which paclitaxel is widely used to treat various types of cancer (Pazdur et al 1993). Paclitaxel promotes the assembly of microtubules and inhibits their disassembly (Pazdur et al 1993).…”