The delicate balance and spatiotemporal regulation of Rho GTPase activity determine the type and extent of protrusions formed, playing a central role in the migratory and invasive behavior of cancer cells. These GTPases activate downstream effectors such as Rho-associated protein kinases (ROCK1/2) that facilitate the phosphorylation of myosin light chains (MLC), leading to increased actomyosin contractility. Simultaneously, LIM kinases (LIMK) phosphorylate cofilin (p-cofilin), which prevents actin filament depolymerization, thus stabilizing the cytoskeleton. Meanwhile, proteins like mDia2 and N-WASP, in conjunction with the Arp2/3 complex, promote actin nucleation, a process fundamental to the polymerization of actin filaments, giving rise to the dynamic restructuring of the cytoskeleton. Concurrently, the cell coordinates the trafficking and releasing of matrix metalloproteinases (MMPs) via molecules such as IQGAP. MMPs are proteolytic enzymes that degrade components of the extracellular matrix, clearing a path through the tissue and enabling the invasive behavior of the tumor cell [49].

The proteins WASP and WASP-family Verprolin-homologous protein (WAVE), integral to Rho GTPase signaling, are key regulators of the actin cytoskeleton, playing crucial roles in the formation of lamellipodia and filopodia. They are activated by Rho family GTPases, such as Rho, Rac1, and Cdc42, leading to the formation of cellular protrusions essential for cell motility. In cancer, this mechanism becomes pivotal, as the dynamic rearrangement of the actin cytoskeleton facilitates invasive and metastatic behaviors of tumor cells. These proteins serve as critical activators of the actin cytoskeleton, which plays a central role in the morphological and motile capabilities of cancer cells. The activation of specific Rho GTPases - Rho, Rac1, and Cdc42 - by WASP and WAVE leads to the formation of actin stress fibers, membrane ruffles, lamellipodia, and filopodia. These actin structures are not merely components of cellular architecture but are actively involved in the directional motility of cancer cells, a key process in the invasion of surrounding tissues and the progression to metastasis. The actin cytoskeleton’s dynamic reorganization, facilitated by these proteins, enables cancer cells to form cellular protrusions essential for their movement and interaction with the extracellular matrix. This interaction is particularly important for the cells’ ability to degrade barriers, a prerequisite for invasive behavior. Moreover, these structures enable the cells to navigate complex extracellular environments, aiding in their metastatic spread. Furthermore, by influencing the actin dynamics and cell motility, these proteins emerge as potential targets for therapeutic interventions aimed at mitigating cancer metastasis [50,51].

Colorectal cancer, the third leading cause of cancer-related deaths globally, has been linked to WAVE2 expression. Studies indicate WAVE2’s association with liver metastasis, disease progression, and the activation of TGF-β1 and YAP1 signaling pathways in colorectal cancer. WAVE2’s role is critical in colorectal liver metastasis, particularly through its regulation by TGF-β1 in the cancer immune microenvironment. In cervical cancer, which predominantly affects women aged 35-44, overexpression of SH3BP1 has been found to increase Rac1 and WAVE2 activity, enhancing invasion, migration, and chemoresistance. WAVE2 has also been implicated in the invasiveness and motility of pancreatic cancer cells. It is shown that WAVE2 interacts with alpha-actinin 4 (ACTN4), affecting cell movement and invasiveness. Prostate cancer research indicates the involvement of WAVE2 in cell invasion and metastasis, particularly through its interaction with PIP3 and Rac1-induced actin reorganization. WAVE2 is also significant in breast cancer, the most common cancer among women worldwide. It contributes to the formation of lamellipodial protrusions in cancer cells and is associated with aggressive cancer types like triple-negative breast cancer (TNBC). The binding of WAVE2 to the Arp2/3 complex plays a crucial role in breast cancer cell migration and invasion, with implications for potential therapeutic targets [51].

Integrins, transmembrane receptors that link the ECM to the actin cytoskeleton, also play a pivotal role in regulating lamellipodia and filopodia dynamics [29,52]. Integrin engagement with the ECM initiates signaling cascades that influence focal adhesion formation and cytoskeletal rearrangements. Integrins activate focal adhesion kinase (FAK) and Src kinases, initiating downstream signaling events that regulate the activity of Rho GTPases. Focal adhesions serve as anchoring points for actin filaments and contribute to the stability of lamellipodia and filopodia [53]. The turnover of these focal adhesions is essential for dynamic cell movement. The interplay between integrins, focal adhesion signaling, and Rho GTPases coordinates the adhesive and protrusive forces required for effective cell migration and invasion in the tumor microenvironment [16].