CDC42EP5/BORG3 modulates SEPT9 to promote actomyosin function, migration, and invasion.

Aaron J Farrugia,María Lucas,Fernando Calvo,Jose L Orgaz,Victoria Sanz-Moreno,Javier Rodríguez

doi:10.1083/jcb.201912159

Abstract

Fast amoeboid migration is critical for developmental processes and can be hijacked by cancer cells to enhance metastatic dissemination. This migratory behavior is tightly controlled by high levels of actomyosin contractility, but how it is coupled to other cytoskeletal components is poorly understood. Septins are increasingly recognized as novel cytoskeletal components, but details on their regulation and contribution to migration are lacking. Here, we show that the septin regulator Cdc42EP5 is consistently required for amoeboid melanoma cells to invade and migrate into collagen-rich matrices and locally invade and disseminate in vivo. Cdc42EP5 associates with actin structures, leading to increased actomyosin contractility and amoeboid migration. Cdc42EP5 affects these functions through SEPT9-dependent F-actin cross-linking, which enables the generation of F-actin bundles required for the sustained stabilization of highly contractile actomyosin structures. This study provides evidence that Cdc42EP5 is a regulator of cancer cell motility that coordinates actin and septin networks and describes a unique role for SEPT9 in melanoma invasion and metastasis.

Highlights

Malignant melanoma is a very aggressive type of skin cancer due to its highly metastatic behavior, which relies on the increased ability of melanoma cells to migrate and invade (Lo and Fisher, 2014)
Identification of CDC42EP5 as a regulator of melanoma migration, invasion, and metastasis To assess the relevance of Binder of Rho GTPases (Borg) proteins Cdc42ep1–Cdc42ep5 in cancer cell migration and invasion, we first analyzed transwell migration after RNAi silencing of individual genes in the murine melanoma model 690.cl2 (Dhomen et al, 2009; Kümper et al, 2016)
We found that CDC42EP5 was the only Borg gene whose expression was significantly correlated with cell roundness in a panel of 11 human melanoma cell lines of varying degrees of rounding

Summary

Introduction

Malignant melanoma is a very aggressive type of skin cancer due to its highly metastatic behavior, which relies on the increased ability of melanoma cells to migrate and invade (Lo and Fisher, 2014). Amoeboid behavior is prominent in the invasive fronts of melanomas in animal models (Herraiz et al, 2015; Sanz-Moreno et al, 2008, 2011) and human lesions (Georgouli et al, 2019; Orgaz et al, 2014; Sanz-Moreno et al, 2011) It has been associated with increased risk of metastasis and poorer prognosis (Georgouli et al, 2019), which underlies the need for a better mechanistic understanding of the process. Actomyosin contractility driven by the motor protein myosin II is critical for rounded migration (Tozluoglu et al, 2013) This process has been shown to be tightly controlled by RhoROCK signaling leading to increased phosphorylation of the regulatory myosin light chain 2 (MLC2; Vicente-Manzanares et al, 2009). How actin structures are organized and coordinated with other cytoskeletal components to enable their correct assembly and the formation of fully functional actomyosin networks is not well understood

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