Le gène DLC1, cibler Rhoa dans le cancer de la prostate.

Mise à jour, l'article date de décembre 2015

Ras homolog gene family, member A (RhoA) has been reported as essential to the invasion process and aggressiveness of numerous cancers. However, there are only sparse data on the expression and activity of RhoA in clinically localised prostate cancer. In numerous cancers, tumour cells at the invasive front demonstrate more aggressive behaviour in comparison with the cells in the central regions. In the present study, the expression and activity of RhoA was evaluated in 34 paraffin‑embedded and 20 frozen prostate tissue specimens obtained from 45 patients treated with radical prostatectomy for clinically localised cancer. The expression patterns of RhoA were assessed by immunohistochemical staining and western blotting. Additional comparisons were performed between the tumour centre, tumour front and distant peritumoural tissue. RhoA activity was assessed by G‑LISA. Associations between RhoA expression and the clinical features and outcome of the patients were also analysed. The present study found an increasing gradient of expression from the centre to the periphery of index tumour foci. RhoA expression was significantly increased at the tumour front compared to the tumour centre, which was determined using immunohistochemistry (P=0.001). Increased RhoA expression was associated with poor tumour differentiation in the tumour front (P=0.044) and tumour centre (P=0.039). Subsequent to a median follow‑up period of 52 months, the rate of prostate‑specific antigen (PSA) relapse was increased in patients with higher RhoA expression at the tumour front when compared with patients with lower RhoA expres​sion(62.5 vs. 35.0%), although the difference was not significant (P=0.09). There was no association between RhoA expression and the PSA level or pathological stage in the present study. In conclusion, RhoA expression was increased at the tumour front and was associated with poor tumour differentiation in the tumour front and tumour centre, indicating the potential role of RhoA in prostate cancer. RhoA expression may also act as a prognostic factor in prostate cancer. The present data provide a foundation for novel therapeutic approaches by targeting RhoA in prostate cancer.

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La famille du gène homologue Ras, membre A (RhoA) a été rapporté comme essentielle pour le processus d'invasion et de l'agressivité de nombreux cancers. Cependant, il n'y a que des données éparses sur l'expression et l'activité de RhoA dans le cancer de la cliniquement localisé.

Dans de nombreux cancers, les cellules tumorales à l'avant démontrent un comportement plus agressif par rapport aux cellules dans les régions centrales. Dans la présente étude, l'expression et l'activité de RhoA a été évaluée dans 34 échantillons inclus en paraffine et 20 échantillons de tissus de la prostate congelés obtenus à partir de 45 patients traités par prostatectomie radicale pour cancer cliniquement localisé.

Les profils d'expression de RhoA ont été évaluées par coloration immunohistochimique et western blot. D'autres comparaisons ont été effectuées entre le centre de la tumeur, l'avant de la tumeur et les tissus péri-tumoral lointain. L'activité RhoA a été évaluée par G-LISA. Les associations entre l'expression de RhoA et les caractéristiques cliniques et les résultats des patients ont également été analysés. La présente étude a révélé un gradient croissant de l'expression à partir du centre vers la périphérie de foyers indice tumoral.

L'expression RhoA a été augmenté de façon significative à l'avant de la tumeur par rapport au centre de la tumeur, qui a été déterminée par immunohistochimie (P = 0,001). RhoA expression accrue a été associée à une mauvaise différenciation de la tumeur à l'avant de la tumeur (p = 0,044) et le centre de la tumeur (p = 0,039). Suite à une période médiane de suivi de 52 mois, le taux de l'antigène prostatique spécifique (PSA) et la rechute a été augmentée chez les patients atteints avec expression supérieure de RhoA à l'avant de la tumeur par rapport aux patients ayant une plus faible expression RhoA (62,5 vs 35,0%) , bien que la différence ne soit pas significative (P = 0,09). Il n'y avait pas d'association entre l'expression de RhoA et le niveau de PSA ou le stade pathologique dans la présente étude.

En conclusion, l'expression RhoA a été augmentée à l'avant de la tumeur et a été associé à la différenciation tumorale pauvres dans le centre-avant et tumeur tumeur, indiquant le rôle potentiel de RhoA dans le cancer de la prostate. L'expression de Rhoa peut également agir en tant que facteur pronostic dans le cancer de la prostate. Les données actuelles fournissent une base pour de nouvelles approches thérapeutiques en ciblant RhoA dans le cancer de la prostate.

Scientists at Cold Spring Harbor Laboratory (CSHL) have taken the search for cancer-causing genes an important step forward. In a newly published paper, they confirm that a gene called DLC1 is a tumor suppressor. They have demonstrated in living mice that its deletion, inactivation or loss precipitates events culminating in an aggressive type of liver cancer closely related to common human epithelial cancers of the liver (also known as hepatocellular carcinoma, or HCC).

Des scientifiques ont fait avancé la recherche des causes du cancer. Dans un nouvel article, ils ocnfirment que le gène appelé DLC1 est un suppresseur de tumeurs. Ils ont démontré chez les ouris vivantes que son effacement, son inactivation ou sa perte, précipites des évênements aboutissant à une forme agressive de cancer du foie ressemblant beaucoup à la forme de cancer du foie connue sous l'appellation de HCC.

The team's success in tracing the intricate pathway by which DLC1 functions in both healthy and pathological states suggests a highly specific new target for future anticancer drugs.

Le succès de l'équipe de chercheurs suggère l'invention de nouveaux médicaments.

Focusing on a Suspected Tumor Suppressor Tumor suppressor genes play a vital role in intracellular signaling networks that protect against uncontrolled cell growth and proliferation. Such genes can be rendered inactive by a variety of DNA alterations, including deletions, mutations and so-called epigenetic changes in DNA's chemical configuration. DLC1 -- a gene whose acronym reflects prior suspicions that it was "deleted in liver cancer" -- was known to be located in a region of chromosome 8 that has been observed to be missing in past studies of mammalian liver cancer cells.

"The region in question is a large one that may harbor more than one tumor suppressor," said Dr. Scott W. Lowe. "We set out to conclusively identify DLC1 as a tumor suppressor, which had not been done before, and to show at the molecular level how the absence of this gene produces pathology in cells that can lead to liver cancer. Interestingly, loss of DLC1 is observed in a range of epithelial cancers, which suggests that DLC1 may a play common role in many types of human cancer."

La perte de DLC1 est observée dans beaucoup de cancers et suggère que DLC1 peut jouer un rôle important dans plusieurs types de cancers.

In addition to corresponding author Lowe, the research team included five other laboratory heads at CSHL: Prof. Linda Van Aelst, Ph.D., and Prof. Michael Wigler, Ph.D.; Assoc. Prof. Scott Powers, Ph.D.; and Asst. Prof. Robert Lucito, Ph.D., and

Asst. Prof. Raffaella Sordella, Ph.D.; as well as Lars Zender, M.D., professor at the Helmholtz Center, Germany. Their collaborative paper, whose lead authors are Wen Xue, Ph.D., of the Lowe lab, and Alexander Krasnitz, Ph.D., of the Wigler lab, appears in the June 1 issue of Genes & Development.

Connecting the Gene to Liver Cancers

To prove that DLC1 was causally implicated in specific cancers, the team genetically engineered mouse liver cells in which the gene was not expressed. Short-hairpin RNAs (shRNAs) were designed to "knock down" DLC1 expression in vivo. When the DLC1 shRNAs are introduced into normal mouse liver cells, the production of DLC1 protein is blocked, or 'silenced.' The team observed that nearly all of the mice whose livers had been transplanted with the engineered cells developed liver cancer, and that the gene's reintroduction stopped the cancer. However, this was only the beginning of the experimental road, for it is not simply the absence of the DLC1 protein that causes tumorigenesis. In fact, abnormally low levels of the protein, or its complete absence, induces a complex series of interrelated events, as Dr. Lowe and colleagues demonstrated. The protein encoded by the DLC1 gene belongs to regulators of a large family of enzymes called small Rho GTPases that act as molecular switches.

Following the Signaling Pathway Using a mechanism called RNA interference to control the expression of specific genes, the team effectively turned the DLC1 "switch" on and off in living mice cells, and in so doing was able to isolate one particular signaling intermediary whose presence was both necessary and sufficient to set the cell on an uncontrolled growth path. This essential molecular intermediary is called RhoA. When the DLC1 gene is absent in a cell, RhoA is activated, effectively removing a brake on tumor initiation. Whether the experimenters knocked down the DLC1 gene or in separate experiments activated RhoA, the result was the same: the promotion of liver cancer.

Suivant le chemin cellulaire et utilisant un mécanisme appelé "interférence d'ARN" pour controler l'expression de gènes spécifiques, l'équipe a effectivement éteint et allumé le gène chez des souris vivantes et ce faisant a été capable d'isoler un élément intermédiare dont la présence était nécessaire et suffisante pour mettre la cellules sur le chemin d'une croissance incontrolable. Ce chemin essentiel est appelé Rhoa. quand le gène DLC1 est absent dans une cellule, Rhoa est activé et enlève un frein dans l'initiation de la tumeur. Si les chercheurs neutralisent le gène DCL1 ou active le le Rhoa, le résultat est le même : la promotion du cancer du foie.

Specifically, the team demonstrated that RhoA is required for maintaining the tumor-formation process stimulated by deletion of the DLC1 gene.

"This suggests an opportunity for molecularly targeted therapies," Dr. Lowe said. "For a variety of reasons, tumor suppressors like DLC1 are not amenable to direct therapeutic targeting. But we may be able to readily target cancer-promoting molecules like RhoA that are 'downstream' in the signaling cascade.

Nous pourrions être capcble de cibler Rhoa qui est en aval dans la cascade d'évênements qui mène au cancer.

"Our data show that RhoA is required for maintenance of at least some tumors driven by DLC1 loss, and also that cells with disabled DLC1 are particularly sensitive to inhibitors that target at least one of the molecular 'effectors' that renders RhoA active. We know that DLC1 is frequently lost in human epithelial cancers. This suggests that drug intervention in the signaling pathways modulated by DLC1 may have broad therapeutic utility."

'Nos données montrent que le Rhoa est requis pour le maintien d'au moins quelques tumeurs induites par la perte DLC1 et aussi que quelques cellules avec le DCL1 désactivé sont sensibles aux agents inhibiteurs qui ciblent au moins une molécule qui rend Rhoas active.
Nous savons que DLC1 est fréquemment perdu dans les cancers de type épithélial. tout cela suggère qu'un médicament qui ciblerait DLC1 pourrait avoir de larges utilités thérapeuhiques."