WAVE Regulatory Complex Play key role in cytoskeletal remodeling

The cytoskeleton of cells plays a crucial role in various cellular processes such as cell division, migration, and signaling. It is also essential for maintaining the shape and mechanical properties of cells. Alterations in cytoskeletal dynamics are associated with a wide range of human diseases, including cancer, cardiovascular diseases, and infectious diseases caused by bacterial, viral, and parasitic pathogens. In the context of infectious diseases, many pathogens exploit the host cell cytoskeleton to invade host cells and spread throughout the body. Therefore, understanding the molecular mechanisms of cytoskeletal remodeling is critical for developing new approaches to combat infectious diseases. One important cytoskeletal component is the actin cytoskeleton, which is highly dynamic and continuously re-arranged to enable cell migration and changes in cell shape. The WAVE Regulatory Complex (WRC) is a protein complex that assembles at the inner surface of the plasma membrane and plays a central role in actin cytoskeletal remodeling.

Recent research has provided new insights into the molecular mechanisms of WRC activation, specifically the role of the small GTPase Arf1. The study found that Arf1 binds to WRC and triggers its activation, leading to the formation of cytoskeletal protrusions called lamellipodia. This process is critical for cell migration and engulfment of extracellular particles. Importantly, previous studies have shown that Arf1 activation is involved in the invasion of host cells by pathogenic bacteria such as Salmonella. Therefore, interference with this particular Arf1 mode of action could potentially slow down actin remodeling and inhibit bacterial uptake, providing a new avenue for the development of antimicrobial strategies. In addition to infectious diseases, cytoskeletal remodeling plays a role in various other medical conditions. For example, abnormalities in the actin cytoskeleton are associated with cancer cell metastasis and tumor invasion. Therefore, understanding the molecular mechanisms of cytoskeletal dynamics could lead to new approaches for cancer treatment. In cardiovascular diseases, cytoskeletal remodeling is associated with changes in mechanical properties of the heart muscle, leading to heart failure. Additionally, abnormalities in the cytoskeleton of endothelial cells lining blood vessels can contribute to the development of atherosclerosis, a condition characterized by the buildup of plaque in the arterial walls.

Moreover, Bacteria like Salmonella, Shigella, and Listeria manipulate the host cell’s protein skeleton to spread throughout the host’s body. However, the molecular mechanisms underlying the assembly and remodeling of the host cell’s cytoskeleton are still unclear. Understanding these mechanisms could help develop new strategies to combat infectious diseases caused by these pathogens.

An international team of researchers led by Prof. Dr. Klemens Rottner, including members from the Helmholtz Center for Infection Research (HZI) in Braunschweig, has now uncovered the precise molecular mechanisms of activation of a key signaling unit in cytoskeletal remodeling. The results of this study have been published in the scientific journal Science Advances. The cytoskeleton in our body consists of a complex network of filaments that play specific roles in maintaining cell shapes and functions during various processes, such as embryonic development and migration of immune cells. Additionally, the cytoskeleton plays a crucial role in transport processes, both within cells and between neighboring cells.

Infectious agents have evolved numerous ways to exploit the cytoskeleton of their hosts, which allows them to enter host cells or move across them to infect deeper tissue layers. A better understanding of the cytoskeleton and its molecular mechanisms of formation could help develop more precise interventions with pathogenic processes. The researchers discovered new, fundamental details concerning the activation of the WAVE Regulatory Complex (WRC), a protein complex that assembles at the inner surface of the plasma membrane and operates like a central signaling unit. Upon activation, WRC triggers the formation of prominent cytoskeletal protrusions called lamellipodia, which are key structures that allow the cell to migrate and engulf extracellular particles.

The subpart of the cytoskeleton comprising actin filaments is highly dynamic, constantly re-arranged, and enables cells to develop locomotive forces to drive cell migration and change cell shape. Previously, it was shown that WRC is responsible for the assembly of actin filaments in lamellipodia downstream of the signaling switch Rac1, a small GTPase. The current study aimed to understand precisely how Arf1, another GTPase, docks onto WRC and what happens in the context of WRC activation upon Arf1 binding.

Using biochemical and structural biology approaches and cell biological studies using CRISPR/Cas9 technology, the team defined and characterized the Arf1 binding site on WRC and characterized its WRC-activating function. WRC harbors three binding sites for signaling switches, two specific for Rac1 that were already established, and a novel one for Arf1. The latter is positioned between the two Rac-binding sites. The researchers showed that Arf1 can only bind WRC after Rac1 binding to its so-called D-site on the complex.

Rac1-binding to the D-site enables a conformational change on WRC, allowing interaction with Arf1. The researchers also established that optimal WRC activation occurs upon occupancy of all three GTPase binding sites. Aside from Rac1 binding, Arf1 constitutes a crucial signaling switch on WRC, required for its optimal function. Such fundamental molecular insights, like the WRC regulation by Arf1, can be of potential interest for applied infection research. Previous studies have reported functions for Arf1 activation in host cell invasion by pathogenic bacteria, such as Salmonella, which was accompanied by increased actin remodeling enhancing by bacterial uptake. Arf1 or its binding site on WRC could thus constitute potential hubs for interfering with the pathogens’ invasion strategies. Specific interference with this particular Arf1 mode

In summary, cytoskeletal remodeling is a critical process in various cellular functions and plays an essential role in the pathogenesis of many human diseases, including infectious diseases, cancer, and cardiovascular diseases. A better understanding of the molecular mechanisms of cytoskeletal dynamics could lead to new approaches for the prevention and treatment of these conditions.