RESUMEN
The DEAD-box RNA helicases p68 (DDX5) and p72 (DDX17) have been shown to act as transcriptional co-activators for a diverse range of transcription factors, including oestrogen receptor-alpha (ERalpha). Here, we show that, although both proteins interact with and co-activate ERalpha in reporter gene assays, small interfering RNA-mediated knockdown of p72, but not p68, results in a significant inhibition of oestrogen-dependent transcription of endogenous ERalpha-responsive genes and oestrogen-dependent growth of MCF-7 and ZR75-1 breast cancer cells. Furthermore, immunohistochemical staining of ERalpha-positive primary breast cancers for p68 and p72 indicate that p72 expression is associated with an increased period of relapse-free and overall survival (P=0.006 and 0.016, respectively), as well as being inversely associated with Her2 expression (P=0.008). Conversely, p68 shows no association with relapse-free period, or overall survival, but it is associated with an increased expression of Her2 (P=0.001), AIB-1 (P<0.001) and higher tumour grade (P=0.044). Our data thus highlight a crucial role for p72 in ERalpha co-activation and oestrogen-dependent cell growth and provide evidence in support of distinct but important roles for both p68 and p72 in regulating ERalpha activity in breast cancer.
Asunto(s)
Neoplasias de la Mama/patología , Proliferación Celular , ARN Helicasas DEAD-box/fisiología , Receptor alfa de Estrógeno/fisiología , Estrógenos/farmacología , Transcripción Genética , Animales , Neoplasias de la Mama/genética , Neoplasias de la Mama/metabolismo , Células COS , Proliferación Celular/efectos de los fármacos , Supervivencia Celular/efectos de los fármacos , Supervivencia Celular/genética , Chlorocebus aethiops , ARN Helicasas DEAD-box/metabolismo , Receptor alfa de Estrógeno/genética , Receptor alfa de Estrógeno/metabolismo , Estrógenos/metabolismo , Femenino , Regulación Neoplásica de la Expresión Génica , Humanos , Coactivador 1 de Receptor Nuclear/metabolismo , Coactivador 1 de Receptor Nuclear/fisiología , Unión Proteica , Transcripción Genética/efectos de los fármacos , Transcripción Genética/genética , Activación Transcripcional , Células Tumorales CultivadasRESUMEN
The nuclear-encoded Krebs cycle enzymes, fumarate hydratase (FH) and succinate dehydrogenase (SDHB, -C and -D), act as tumour suppressors. Germline mutations in FH predispose individuals to leiomyomas and renal cell cancer (HLRCC), whereas mutations in SDH cause paragangliomas and phaeochromocytomas (HPGL). In this study, we have shown that FH-deficient cells and tumours accumulate fumarate and, to a lesser extent, succinate. SDH-deficient tumours principally accumulate succinate. In situ analyses showed that these tumours also have over-expression of hypoxia-inducible factor 1alpha (HIF1alpha), activation of HIF1alphatargets (such as vascular endothelial growth factor) and high microvessel density. We found no evidence of increased reactive oxygen species in our cells. Our data provide in vivo evidence to support the hypothesis that increased succinate and/or fumarate causes stabilization of HIF1alpha a plausible mechanism, inhibition of HIF prolyl hydroxylases, has previously been suggested by in vitro studies. The basic mechanism of tumorigenesis in HPGL and HLRCC is likely to be pseudo-hypoxic drive, just as it is in von Hippel-Lindau syndrome.
Asunto(s)
Fumarato Hidratasa/genética , Mutación de Línea Germinal , Succinato Deshidrogenasa/genética , Succinato Deshidrogenasa/metabolismo , Carcinoma de Células Renales/metabolismo , Ciclo del Ácido Cítrico/fisiología , Femenino , Fumarato Hidratasa/metabolismo , Humanos , Leiomioma/genética , Leiomioma/metabolismo , Neoplasias/genética , Neoplasias/metabolismo , Paraganglioma/genética , Paraganglioma/metabolismo , Células Tumorales Cultivadas , Factor A de Crecimiento Endotelial Vascular/metabolismoRESUMEN
Germline mutations of the fumarate hydratase (FH, fumarase) gene are found in the recessive FH deficiency syndrome and in dominantly inherited susceptibility to multiple cutaneous and uterine leiomyomatosis (MCUL). We have previously reported a number of germline FH mutations from MCUL patients. In this study, we report additional FH mutations in MCUL and FH deficiency patients. Mutations can readily be found in about 75% of MCUL cases and most cases of FH deficiency. Some of the more common FH mutations are probably derived from founding individuals. Protein-truncating FH mutations are functionally null alleles. Disease-associated missense FH changes map to highly conserved residues, mostly in or around the enzyme's active site or activation site; we predict that these mutations severely compromise enzyme function. The mutation spectra in FH deficiency and MCUL are similar, although in the latter mutations tend to occur earlier in the gene and, perhaps, are more likely to result in a truncated or absent protein. We have found that not all mutation-carrier parents of FH deficiency children have a strong predisposition to leiomyomata. We have confirmed that renal carcinoma is sometimes part of MCUL, as part of the variant hereditary leiomyomatosis and renal cancer (HLRCC) syndrome, and have shown that these cancers may have either type II papillary or collecting duct morphology. We have found no association between the type or site of FH mutation and any aspect of the MCUL phenotype. Biochemical assay for reduced FH functional activity in the germline of MCUL patients can indicate carriers of FH mutations with high sensitivity and specificity, and can detect reduced FH activity in some patients without detectable FH mutations. We conclude that MCUL is probably a genetically homogeneous tumour predisposition syndrome, primarily resulting from absent or severely reduced fumarase activity, with currently unknown functional consequences for the smooth muscle or kidney cell.