The Rho protein belongs to a subfamily member of the small G protein superfamily. So far, more than 20 members of the Rho family have been found. According to the degree of homology and function of the sequence, it is divided into four categories: RhoA, Racl, Cdc42 and lack of GTPase activity. Fifteen Rho proteins have been identified and divided into three subfamilies. The first contains Rho (A, B, C), the second contains Rnd 1-3, and the third contains Rac 1-3, RhoG, Cdc42Hs, Rho/TTF. TC10 and Chp. Rho acts as a molecular switch that can shut down various intracellular signaling pathways, such as ACK, PAK, MEKKs ROCK. Rho is active when bound to GTP and inactive when bound to GDP. It is also known to participate in many physiological activities, including cell migration, adhesion, cytokinesis, proliferation, differentiation, and apoptosis, and to extend cell transformation to a greater extent.

Figure 1. Rho protein.

Introductions

Rho family proteins are the earliest cloned proteins in the Ras superfamily. They are a group of guanosine triphosphate (GTP) binding proteins with a relative molecular mass of about 20 to 25 kD. They have GTPase activity. Called Rho GTPase, Rho GTPase plays an important role in the regulation of cytoskeleton recombination. Recent studies have found that Rho GTPase is highly expressed in a variety of malignant tumors and is closely related to tumorigenesis, invasion and metastasis.

Rho GTPase and tumor invasion and metastasis

The movement of tumor cells in the matrix consists of 4 reciprocating steps, namely the formation and extension of the pseudopodia in the head, the establishment of new adhesion sites, the contraction of the cell body, and the withdrawal of the tail. Before migration. The molecular mechanisms that precisely regulate this process are very complex, involving multiple intracellular signal transduction pathways. Among multiple signal cascade response pathways, Rho GTPases, especially RhoA, Rac1, and Cdc42, are key regulators. They are mainly involved in the regulation of cell morphology, cell-matrix adhesion, and cytoskeleton reorganization, and regulate the transfer process of tumor cell invasion.

Cytoskeleton reorganization

The continuous movement of invading and metastatic tumor cells depends on the tension fiber contraction and the extension of actin filaments to provide power. Rho GTPase can provide power for cell migration by regulating the reorganization of the cytoskeleton. Tension fiber is a stable, parallel-arranged microfilament structure in eukaryotic cells. It is composed of actin, myosin, tropomyosin, and so on. The contraction force produced by the relative movement of myosin is the driving force for cell migration. The main source. Rho and its downstream Rho associated coiledcoil forming protein kinase (ROCK) can increase the phosphorylation level of myosin light chain (MLC) and increase the contraction of actin-myosin Force promotes cell migration in the ECM. ROCK is an important effector molecule downstream of Rho, including Rho kinase and p160 ROCK. Activated ROCK increases the phosphorylation level of MLC through two pathways. On the one hand, ROCK phosphorylates its substrate, myosin light chain phosphatase (MLCP), and myosin binding subunit (MBS)., While inhibiting the phosphatase activity of MLCP, reducing the hydrolysis of MLC phosphate groups; on the other hand, ROCK can directly phosphorylate MLC and increase the phosphorylation level of MLC, thereby increasing the contractile force produced by cross-linking with actin filaments. Inhibition of the Rho/Rock pathway can inhibit the contraction and cell invasion of tumor cell tension fibers. Dominant active p160 ROCK plasmid-transfected human ovarian cancer cells have a stronger ability to invade and migrate, while p160 ROCK The ability of cancer cells treated with antisense oligonucleotides to invade and migrate can be significantly reduced. Rho can also act on another downstream important effector molecule, mDia (Mammalian Diaphanous related protein) protein. Activated mDia protein can join actin monomers to the ends of actin filaments, prevent the binding of capping proteins, induce elongation of actin filaments, and help cell migration.

Reference

1. Leung T; et al. The p160 RhoA-binding kinase ROK alpha is a member of a kinase family and is involved in the reorganization of the cytoskeleton. Molecular and Cellular Biology. 1996, 16 (10): 5313-27.