RESUMEN
Epithelial-mesenchymal transition (EMT) is a key event that is involved in the invasion and dissemination of cancer cells. Although typically considered as having tumour-suppressive properties, transforming growth factor (TGF)-ß signalling is altered during cancer and has been associated with the invasion of cancer cells and metastasis. In this study, we report a previously unknown role for the cytoplasmic promyelocytic leukaemia (cPML) tumour suppressor in TGF-ß signalling-induced regulation of prostate cancer-associated EMT and invasion. We demonstrate that cPML promotes a mesenchymal phenotype and increases the invasiveness of prostate cancer cells. This event is associated with activation of TGF-ß canonical signalling pathway through the induction of Sma and Mad related family 2 and 3 (SMAD2 and SMAD3) phosphorylation. Furthermore, the cytoplasmic localization of promyelocytic leukaemia (PML) is mediated by its nuclear export in a chromosomal maintenance 1 (CRM1)-dependent manner. This was clinically tested in prostate cancer tissue and shown that cytoplasmic PML and CRM1 co-expression correlates with reduced disease-specific survival. In summary, we provide evidence of dysfunctional TGF-ß signalling occurring at an early stage in prostate cancer. We show that this disease pathway is mediated by cPML and CRM1 and results in a more aggressive cancer cell phenotype. We propose that the targeting of this pathway could be therapeutically exploited for clinical benefit.
Asunto(s)
Transición Epitelial-Mesenquimal , Proteína de la Leucemia Promielocítica/metabolismo , Neoplasias de la Próstata/metabolismo , Factor de Crecimiento Transformador beta/metabolismo , Transporte Activo de Núcleo Celular , Línea Celular Tumoral , Movimiento Celular , Núcleo Celular/metabolismo , Citoplasma/metabolismo , Humanos , Immunoblotting , Estimación de Kaplan-Meier , Carioferinas/genética , Carioferinas/metabolismo , Masculino , Invasividad Neoplásica , Fosforilación , Proteína de la Leucemia Promielocítica/genética , Neoplasias de la Próstata/genética , Neoplasias de la Próstata/patología , Proteínas Serina-Treonina Quinasas/genética , Proteínas Serina-Treonina Quinasas/metabolismo , Interferencia de ARN , Receptor Tipo I de Factor de Crecimiento Transformador beta , Receptores Citoplasmáticos y Nucleares/genética , Receptores Citoplasmáticos y Nucleares/metabolismo , Receptores de Factores de Crecimiento Transformadores beta/genética , Receptores de Factores de Crecimiento Transformadores beta/metabolismo , Transducción de Señal , Proteína Smad2/metabolismo , Proteína smad3/metabolismo , Proteína Exportina 1RESUMEN
The tumour suppressor PML (promyelocytic leukaemia protein) regulates several cellular pathways involving cell growth, apoptosis, differentiation and senescence. PML also has an important role in the regulation of stem cell proliferation and differentiation. Here, we show the involvement of the helicase HAGE in the transcriptional repression of PML expression in ABCB5+ malignant melanoma-initiating cells (ABCB5+ MMICs), a population of cancer stem cells which are responsible for melanoma growth, progression and resistance to drug-based therapy. HAGE prevents PML gene expression by inhibiting the activation of the JAK-STAT (janus kinase-signal transducers and activators of transcription) pathway in a mechanism which implicates the suppressor of cytokine signalling 1 (SOCS1). Knockdown of HAGE led to a significant decrease in SOCS1 protein expression, activation of the JAK-STAT signalling cascade and a consequent increase of PML expression. To confirm that the reduction in SOCS1 expression was dependent on the HAGE helicase activity, we showed that SOCS1, effectively silenced by small interfering RNA, could be rescued by re-introduction of HAGE into cells lacking HAGE. Furthermore, we provide a mechanism by which HAGE promotes SOCS1 mRNA unwinding and protein expression in vitro. Finally, using a stem cell proliferation assay and tumour xenotransplantation assay in non-obese diabetic/severe combined immunodeficiency mice, we show that HAGE promotes MMICs-dependent tumour initiation and tumour growth by preventing the anti-proliferative effects of interferon-α (IFNα). Our results suggest that the helicase HAGE has a key role in the resistance of ABCB5+ MMICs to IFNα treatment and that cancer therapies targeting HAGE may have broad implications for the treatment of malignant melanoma.