RESUMEN
RAC1 activity is critical for intestinal homeostasis, and is required for hyperproliferation driven by loss of the tumour suppressor gene Apc in the murine intestine. To avoid the impact of direct targeting upon homeostasis, we reasoned that indirect targeting of RAC1 via RAC-GEFs might be effective. Transcriptional profiling of Apc deficient intestinal tissue identified Vav3 and Tiam1 as key targets. Deletion of these indicated that while TIAM1 deficiency could suppress Apc-driven hyperproliferation, it had no impact upon tumourigenesis, while VAV3 deficiency had no effect. Intriguingly, deletion of either gene resulted in upregulation of Vav2, with subsequent targeting of all three (Vav2-/- Vav3-/- Tiam1-/-), profoundly suppressing hyperproliferation, tumourigenesis and RAC1 activity, without impacting normal homeostasis. Critically, the observed RAC-GEF dependency was negated by oncogenic KRAS mutation. Together, these data demonstrate that while targeting RAC-GEF molecules may have therapeutic impact at early stages, this benefit may be lost in late stage disease.
Asunto(s)
Carcinogénesis/metabolismo , Carcinogénesis/patología , Factores de Intercambio de Guanina Nucleótido/metabolismo , Intestinos/patología , Transducción de Señal , Proteína de Unión al GTP rac1/metabolismo , Proteína de la Poliposis Adenomatosa del Colon/metabolismo , Animales , Carcinogénesis/genética , Homeostasis , Intestinos/ultraestructura , Ratones Noqueados , Mutación/genética , Especificidad de Órganos , Fenotipo , Proteínas Proto-Oncogénicas c-vav/metabolismo , Proteínas Proto-Oncogénicas p21(ras)/genética , Proteína 1 de Invasión e Inducción de Metástasis del Linfoma-T/metabolismo , Regulación hacia Arriba , Vía de Señalización WntRESUMEN
Many epithelial stem cell populations follow a pattern of stochastic stem cell divisions called 'neutral drift'. It is hypothesised that neutral competition between stem cells protects against the acquisition of deleterious mutations. Here we use a Porcupine inhibitor to reduce Wnt secretion at a dose where intestinal homoeostasis is maintained despite a reduction of Lgr5+ stem cells. Functionally, there is a marked acceleration in monoclonal conversion, so that crypts become rapidly derived from a single stem cell. Stem cells located further from the base are lost and the pool of competing stem cells is reduced. We tested whether this loss of stem cell competition would modify tumorigenesis. Reduction of Wnt ligand secretion accelerates fixation of Apc-deficient cells within the crypt leading to accelerated tumorigenesis. Therefore, ligand-based Wnt signalling influences the number of stem cells, fixation speed of Apc mutations and the speed and likelihood of adenoma formation.
