Post-transcriptional regulatory strategies and extraribosomal functions of human rpL3

Comprensione del ruolo di alcuni putativi interattori proteici di rpL3 e del suo trascritto primario identificati mediante spettrometria di massa sui prodotti di esperimenti di “GST Pull Down” e “RNA Pull Down”, quali hnRNP H1, NPM e KHSRP, nella regolazione post-trascrizionale del gene di rpL3

Oncogenic Alternative Splicing Switches: Role in Cancer Progression and Prospects for Therapy

Alterations in the abundance or activities of alternative splicing regulators generate alternatively spliced variants that contribute to multiple aspects of tumor establishment, progression and resistance to therapeutic treatments. Notably, many cancer-associated genes are regulated through alternative splicing suggesting a significant role of this post-transcriptional regulatory mechanism in the production of oncogenes and tumor suppressors. Thus, the study of alternative splicing in cancer might provide a better understanding of the malignant transformation and identify novel pathways that are uniquely relevant to tumorigenesis. Understanding the molecular underpinnings of cancer-associated alternative splicing isoforms will not only help to explain many fundamental hallmarks of cancer, but will also offer unprecedented opportunities to improve the efficacy of anti-cancer treatments

Human rpL3 induces mitochondrial apoptosis in Calu-6 cells through activation of p21 expression.

It has recently reported that some ribosomal proteins may regulate the cell cycle and apoptosis in response to nucleolar stress through extraribosomal functions. Defects of ribosome assembly promote the binding of some ribosomal proteins to MDM2, activating p53 and p21 to induce cell cycle arrest or apoptosis, depending on the cellular context. Several proteins involved in ribosome assembly, such as Nucleophosmin (NPM), have been proposed as positive regulators of p53-independent p21 expression. We have previously reported that NPM binds to rpL3 in the context of rpL3 expression autoregulatory circuit. We wondered whether this interaction could occur also in the regulation of p21 expression. To verify this hypothesis, we first analyzed changes in p21 protein levels in p53-null Calu-6 cells upon rpL3 overexpression. We observed that the enforced expression of the rpL3 protein resulted in an increase of p21 protein levels. Interestingly, we detected that the rpL3-mediated p21 upregulation activates mitochondrial apoptosis in Calu-6 cells, abrogated by p21 silencing. These data indicate that the mitochondrial apoptosis activated by rpL3 overexpression could be p21-dependent

Oncogenic alternative splicing switches: role in cancer progression and prospects for therapy

Alterations in the abundance or activities of alternative splicing regulators generate alternatively spliced variants that contribute to multiple aspects of tumor establishment, progression and resistance to therapeutic treatments. Notably, many cancer-associated genes are regulated through alternative splicing suggesting a significant role of this post-transcriptional regulatory mechanism in the production of oncogenes and tumor suppressors. Thus, the study of alternative splicing in cancer might provide a better understanding of the malignant transformation and identify novel pathways that are uniquely relevant to tumorigenesis. Understanding the molecular underpinnings of cancer-associated alternative splicing isoforms will not only help to explain many fundamental hallmarks of cancer, but will also offer unprecedented opportunities to improve the efficacy of anti-cancer treatments

A novel extraribosomal function of human rpL3 involves antitumoral activity in Calu-6 cells through p21-dependent mitochondrial apoptosis

Surveillance of ribosome assembly plays an important role in the regulation of cell growth and defects in ribosome biogenesis can lead to cell cycle arrest or apoptosis. Mounting evidences show that several ribosomal proteins may be involved in this regulation through extraribosomal function. A main outcome of the impairment of the ribosome synthesis is the nucleolus destruction and the p53 stabilization through the inhibitory interaction between some ribosomal proteins and MDM2. The effects of p53 activation are mainly mediated by upregulation of p21 which promotes cell cycle arrest or apoptosis, depending on the cellular context. In addition to p53, several other proteins are able to activate p21 expression. It has been demonstrated that various protein factors involved in ribosome biogenesis such as nucleophosmin (NPM) can regulate p21 expression p53-independently at transcriptional and post-translational levels. In a previous study, we have reported a direct protein-protein interaction between NPM and the ribosomal protein rpL3, required for the autoregulatory circuit of the rpL3 expression. We wondered whether this interaction could occur also in another context and whether rpL3 could be involved in the regulation of p21 expression. In order to verify this hypothesis, we first analyzed changes in p21 protein levels in p53-null Calu-6 cells upon alteration of rpL3 production. We performed transient transfection experiments of a construct encoding for the recombinant protein HA-rpL3 in the aforementioned cell lines. We observed that the enforced expression of the HA-rpL3 protein resulted in a dose-dependent increasing of p21 protein amount. In addition, the rpL3-mediated p21 upregulation was associated with cell cycle arrest in Calu-6 cells. The results of these experiments will be discussed

Novel extraribosomal function of human ribosomal protein rpL3

The nucleolus appears to be involved in additional cellular functions that may not be directly related to ribosome subunit biogenesis. In fact, perturbation of ribosome assembly has recently emerged as a relevant cell cycle arrest or apoptosis promoting pathway, relying on the dynamic sequestration or release of proteins in response to stress stimuli. In particular, it has been reported that upon nucleolar stress a subset of ribosomal proteins can be delocalized in the nucleoplasm where they can bind to MDM2, activating therefore p53 and its major target p21 to promote cell cycle arrest or apoptosis depending on the particular stress and cellular conditions. An increasing number of proteins have been proposed as positive regulators of p21 expression. It has been demonstrated that various protein factors involved in ribosome biogenesis such as nucleophosmin (NPM) can regulate p21 expression p53-independently at transcriptional and post-translational levels. In a previous study, we have reported a direct protein-protein interaction between NPM and the ribosomal protein rpL3, required for the autoregulatory circuit of the rpL3 expression. We wondered whether this interaction could occur also in another context and whether rpL3 could be involved in the regulation of p21 expression. In order to verify this hypothesis, we first analyzed changes in p21 protein levels in p53-null Calu-6 cells upon alteration of rpL3 production. We observed that the enforced expression of the rpL3 protein resulted in a dose-dependent increasing of p21 protein amount. In addition, we found that the rpL3 overexpression, associated with p21 upregulation, activates the apoptotic pathway through mitochondria in Calu-6 cells. Interestingly, we detected that the induction of apoptosis upon rpL3 overexpression was abrogated by p21 silencing, indicating that the mitochondrial apoptosis activated by rpL3 overexpression could be p21-dependent. The results of these experiments will be discussed

Human rpL3 induces mitochondrial apoptosis in Calu-6 cells through activation of p21 expression

It has recently reported that some ribosomal proteins may regulate the cell cycle and apoptosis in response to nucleolar stress through extraribosomal functions. Defects of ribosome assembly promote the binding of some ribosomal proteins to MDM2, activating p53 and p21 to induce cell cycle arrest or apoptosis, depending on the cellular context. Several proteins involved in ribosome assembly, such as Nucleophosmin (NPM), have been proposed as positive regulators of p53-independent p21 expression. We have previously reported that NPM binds to rpL3 in the context of rpL3 expression autoregulatory circuit. We wondered whether this interaction could occur also in the regulation of p21 expression. To verify this hypothesis, we first analyzed changes in p21 protein levels in p53-null Calu-6 cells upon rpL3 overexpression. We observed that the enforced expression of the rpL3 protein resulted in an increase of p21 protein levels. Interestingly, we detected that the rpL3-mediated p21 upregulation activates mitochondrial apoptosis in Calu-6 cells, abrogated by p21 silencing. These data indicate that the mitochondrial apoptosis activated by rpL3 overexpression could be p21-dependent

A novel extraribosomal function of human rpL3 involves antitumoral activity in Calu-6 cells through p21-dependent mitochondrial apoptosis.

Surveillance of ribosome assembly plays an important role in the regulation of cell growth and defects in ribosome biogenesis can lead to cell cycle arrest or apoptosis. Mounting evidences show that several ribosomal proteins may be involved in this regulation through extraribosomal function. A main outcome of the impairment of the ribosome synthesis is the nucleolus destruction and the p53 stabilization through the inhibitory interaction between some ribosomal proteins and MDM2. The effects of p53 activation are mainly mediated by upregulation of p21 which promotes cell cycle arrest or apoptosis, depending on the cellular context. In addition to p53, several other proteins are able to activate p21 expression. It has been demonstrated that various protein factors involved in ribosome biogenesis such as nucleophosmin (NPM) can regulate p21 expression p53-independently at transcriptional and post-translational levels. In a previous study, we have reported a direct protein-protein interaction between NPM and the ribosomal protein rpL3, required for the autoregulatory circuit of the rpL3 expression. We wondered whether this interaction could occur also in another context and whether rpL3 could be involved in the regulation of p21 expression. In order to verify this hypothesis, we first analyzed changes in p21 protein levels in p53-null Calu-6 cells upon alteration of rpL3 production. We performed transient transfection experiments of a construct encoding for the recombinant protein HA-rpL3 in the aforementioned cell lines. We observed that the enforced expression of the HA-rpL3 protein resulted in a dose-dependent increasing of p21 protein amount. In addition, the rpL3-mediated p21 upregulation was associated with cell cycle arrest in Calu-6 cells. The results of these experiments will be discussed

Novel extraribosomal function of human ribosomal protein rpL3

Surveillance of ribosome assembly plays an important role in the regulation of cell growth and defects in ribosome biogenesis can lead to cell cycle arrest or apoptosis. Mounting evidences show that several ribosomal proteins may be involved in this regulation through extraribosomal function. A main outcome of the impairment of the ribosome synthesis is the nucleolus destruction and the p53 stabilization through the inhibitory interaction between some ribosomal proteins and MDM2. The effects of p53 activation are mainly mediated by upregulation of p21 which promotes cell cycle arrest or apoptosis, depending on the cellular context. In addition to p53, several other proteins are able to activate p21 expression. It has been demonstrated that various protein factors involved in ribosome biogenesis such as nucleophosmin (NPM) can regulate p21 expression p53-independently at transcriptional and post-translational levels. In a previous study, we have reported a direct protein-protein interaction between NPM and the ribosomal protein rpL3, required for the autoregulatory circuit of the rpL3 expression. We wondered whether this interaction could occur also in another context and whether rpL3 could be involved in the regulation of p21 expression. In order to verify this hypothesis, we first analyzed changes in p21 protein levels in p53-null Calu-6 cells upon alteration of rpL3 production. We performed transient transfection experiments of a construct encoding for the recombinant protein HA-rpL3 in the aforementioned cell lines. We observed that the enforced expression of the HA-rpL3 protein resulted in a dose-dependent increasing of p21 protein amount. In addition, the rpL3-mediated p21 upregulation was associated with cell cycle arrest in Calu-6 cells. The results of these experiments will be discusse