A RAC-GEF network critical for early intestinal tumourigenesis

Karen Pickering ,M Bain,Bryan W Miller ,William Clark ,Kathryn Gilroy ,Andrew D Campbell ,Kevin Myant ,Saskia M Brachmann ,Catherine Nixon ,Ann Hedley ,Jan Paul Medema ,Arafath K Najumudeen ,Sigrid K Fey ,Luís Serrano ,Martin J Drysdale ,Elçin Ünal ,Kurt I Anderson ,Joel Johansson ,Volker M Stucke ,Robert Fordham ,Laura M Machesky ,David F Vincent ,James W Cassidy ,Angeliki Malliri ,Lucas B Zeiger ,Anna‐Karin Johnsson ,Douglas Strathdee ,Martin Turner ,Christina Kiel ,Ewan J Mcghee ,S.r Van Hoof ,Owen J Sansom

doi:10.1038/s41467-020-20255-4

Abstract

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.

Highlights

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
We show that Rac[1] deletion throughout the intestinal epithelium causes defects in intestinal homeostasis, loss of VAV2, VAV3 and TIAM1 is sufficient to strongly suppress cancer phenotypes and tumourigenesis induced by APC loss, whilst leaving the normal intestinal epithelium unperturbed
We demonstrate that oncogenic mutation of KRAS, a feature of ~40% of human colorectal cancers[41], and key driver of resistance to current clinical therapeutic approaches, while remaining sensitive to RAC depletion, drives profound resistance to deletion of VAV2, VAV3 and TIAM1 in the absence of compensatory RACGEF expression in vivo

Summary

Introduction

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. Given the upregulation of transcription of Vav[2] and the high expression following loss of TIAM1 alongside APC, we reasoned that VAV2 might compensate for TIAM1 and generated Vav2−/− Vav3−/− Tiam1−/− triple-GEF whole body knockout mice (V2V3T).

Results

Conclusion