Efecto del ácido retinoico sobre la apoptosis, proliferación y migración de células de cáncer de pulmón, a través de las vías PI3K-Akt y MAPK

El ATRA ha sido utilizado como agente anti-neoplásico por su capacidad de inducir diferenciación, principalmente en leucemias, mientras que en otros tipos de cáncer es capaz de promover la inhibición de la proliferación; sin embargo, en pacientes con cáncer de pulmón el efecto inhibitorio de proliferación no se puede apreciar en todos los casos y no se sabe a qué se debe esta resistencia al tratamiento con ATRA. Por otro lado, las vías de señalización PI3K-Akt y ERK se encuentran constitutivamente activas en células cancerosas promoviendo sobrevivencia, proliferación e invasión celular, sugiriendo su participación en la resistencia al tratamiento con ATRA en cáncer de pulmón. En este trabajo demostramos que el ATRA es capaz de activar a las vías de señalización PI3K-Akt y ERK por un mecanismo independiente de la transcripción y que, la activación de Akt y ERK está relacionada con el mecanismo de resistencia a ATRA, provocando efectos desfavorables, ya que promueve sobrevivencia y migración en células de cáncer de pulmón. La inhibición de estas vías de señalización restaura el efecto benéfico del ATRA, disminuyendo la proliferación, aumentando la apoptosis y evitando el proceso de migración celular. Por lo tanto, este trabajo propone el uso del ATRA en combinación con inhibidores de PI3K y ERK como posible tratamiento para ser evaluado en estudios clínicos para que, en un futuro, pueda ser usado como terapia en pacientes con cáncer de pulmón que son resistentes al tratamiento con ATRA

The regulatory role of ELK-1 ubiquitination in cell proliferation and prostate cancer

Early stage Prostate Cancer (PC) is usually androgen-dependent and androgen ablation therapies have been used with good results in the destruction of androgen-dependent cells. However, anti-androgens are associated with systemic side effects and selection for tumour cells that survive in the absence of androgens, leading to androgen-independent PC. ELK-1 is a member of the ETS-domain transcription factor family. In response to mitogens, ERKs phosphorylate and activate ELK-1 to stimulate the expression of Immediate Early Genes (IEGs) such as CFOS and EGR1, thereby promoting cell cycle entry and proliferation. In PC cells, ELK-1 expression is frequently up-regulated and androgen receptor (AR) was found to function as a constitutive coactivator for ELK-1, up-regulating a major subset of its target genes involved in cell proliferation and migration. Removal or inactivation of ELK-1 could therefore serve to suppress PC tumour growth. Mono-ubiquitination modulates ELK-1 activity. De-ubiquitination of ELK-1 by USP17, a de-ubiquitinase over-expressed in multiple tumour types, increases ELK-1 target gene expression and cell proliferation, indicating that mono-ubiquitination of ELK-1 suppresses its activity (Ducker et al., 2019). This project aims to identify the ubiquitin E3 ligase responsible for ELK-1 mono-ubiquitination and evaluate its role in PC. Using a combination of gene knockdown experiments and ubiquitination assays, as well as an in silico gene expression analysis to identify ubiquitin E3 ligases that were significantly down-regulated in PC cells, I have tested candidates including FBXW7, FBXO25, SPOP and UBR5, for their ability to modify ELK-1 and suppress its activity. Moreover, using the BioID screening I was able to identify ELK-1 partners under starved and mitogen-stimulated conditions. My findings suggest that an ubiquitin E3 ligase previously reported to target ELK-1 is unlikely to promote ELK-1 ubiquitination and transactivation. Furthermore, the BioID analysis found some potential E3 ligase candidates that need to be evaluated to elucidate their role in promoting ELK-1 ubiquitination. Additionally, the BioID analysis concluded that ELK-1 interacts with transcriptional regulators to modulate ELK-1 target genes expression

ELK-1 ubiquitination status and transcriptional activity are modulated independently of F-Box protein FBXO25

The mitogen-responsive, ETS-domain transcription factor ELK-1 stimulates the expression of immediate early genes at the onset of the cell cycle and participates in early developmental programming. ELK-1 is subject to multiple levels of posttranslational control, including phosphorylation, SUMOylation, and ubiquitination. Recently, removal of monoubiquitin from the ELK-1 ETS domain by the Ubiquitin Specific Protease USP17 was shown to augment ELK-1 transcriptional activity and promote cell proliferation. Here we have used coimmunoprecipitation experiments, protein turnover and ubiquitination assays, RNA-interference and gene expression analyses to examine the possibility that USP17 acts antagonistically with the F-box protein FBXO25, an E3 ubiquitin ligase previously shown to promote ELK-1 ubiquitination and degradation. Our data confirm that FBXO25 and ELK-1 interact in HEK293T cells and that FBXO25 is active toward Hand1 and HAX1, two of its other candidate substrates. However, our data indicate that FBXO25 neither promotes ubiquitination of ELK-1 nor impacts on its transcriptional activity and suggest that an E3 ubiquitin ligase other than FBXO25 regulates ELK-1 ubiquitination and function

The regulatory role of ELK-1 ubiquitination in cell proliferation and prostate cancer

Early stage Prostate Cancer (PC) is usually androgen-dependent and androgen ablation therapies have been used with good results in the destruction of androgen-dependent cells. However, anti-androgens are associated with systemic side effects and selection for tumour cells that survive in the absence of androgens, leading to androgen-independent PC. ELK-1 is a member of the ETS-domain transcription factor family. In response to mitogens, ERKs phosphorylate and activate ELK-1 to stimulate the expression of Immediate Early Genes (IEGs) such as CFOS and EGR1, thereby promoting cell cycle entry and proliferation. In PC cells, ELK-1 expression is frequently up-regulated and androgen receptor (AR) was found to function as a constitutive coactivator for ELK-1, up-regulating a major subset of its target genes involved in cell proliferation and migration. Removal or inactivation of ELK-1 could therefore serve to suppress PC tumour growth. Mono-ubiquitination modulates ELK-1 activity. De-ubiquitination of ELK-1 by USP17, a de-ubiquitinase over-expressed in multiple tumour types, increases ELK-1 target gene expression and cell proliferation, indicating that mono-ubiquitination of ELK-1 suppresses its activity (Ducker et al., 2019). This project aims to identify the ubiquitin E3 ligase responsible for ELK-1 mono-ubiquitination and evaluate its role in PC. Using a combination of gene knockdown experiments and ubiquitination assays, as well as an in silico gene expression analysis to identify ubiquitin E3 ligases that were significantly down-regulated in PC cells, I have tested candidates including FBXW7, FBXO25, SPOP and UBR5, for their ability to modify ELK-1 and suppress its activity. Moreover, using the BioID screening I was able to identify ELK-1 partners under starved and mitogen-stimulated conditions. My findings suggest that an ubiquitin E3 ligase previously reported to target ELK-1 is unlikely to promote ELK-1 ubiquitination and transactivation. Furthermore, the BioID analysis found some potential E3 ligase candidates that need to be evaluated to elucidate their role in promoting ELK-1 ubiquitination. Additionally, the BioID analysis concluded that ELK-1 interacts with transcriptional regulators to modulate ELK-1 target genes expression