ROCK1 is a protein serine/threonine kinase also known as rho-associated, coiled-coil-containing protein kinase 1. Other common names are ROKβ and P160ROCK. ROCK1 is a major downstream effector of the small

GTPase GTPases are a large family of hydrolase enzymes that bind to the nucleotide guanosine triphosphate (GTP) and hydrolyze it to guanosine diphosphate (GDP). The GTP binding and hydrolysis takes place in the highly conserved P-loop "G domain", a ...

RhoA Transforming protein RhoA, also known as Ras homolog family member A (RhoA), is a small GTPase protein in the Rho family of GTPases that in humans is encoded by the ''RHOA'' gene. While the effects of RhoA activity are not all well known, it is ...

and is a regulator of the

actomyosin Myofilaments are the three protein filaments of myofibrils in muscle cells. The main proteins involved are myosin, actin, and titin. Myosin and actin are the ''contractile proteins'' and titin is an elastic protein. The myofilaments act toget ...

cytoskeleton The cytoskeleton is a complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells, including those of bacteria and archaea. In eukaryotes, it extends from the cell nucleus to the cell membrane and is compos ...

which promotes contractile force generation. ROCK1 plays a role in cancer and in particular

cell motility Motility is the ability of an organism to move independently using metabolism, metabolic energy. This biological concept encompasses movement at various levels, from whole organisms to cells and subcellular components. Motility is observed in ...

metastasis Metastasis is a pathogenic agent's spreading from an initial or primary site to a different or secondary site within the host's body; the term is typically used when referring to metastasis by a cancerous tumor. The newly pathological sites, ...

, and

angiogenesis Angiogenesis is the physiological process through which new blood vessels form from pre-existing vessels, formed in the earlier stage of vasculogenesis. Angiogenesis continues the growth of the vasculature mainly by processes of sprouting and ...

Gene and expression

ROCK1 is also the name of the gene that encodes the protein ROCK1, a serine/threonine kinase. ROCK1 is activated when bound to the GTP-bound form of RhoA. The human ROCK1 gene is located on human

chromosome 18 Chromosome 18 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 18 spans about 80 million base pairs (the building material of DNA) and represents about 2.5 percent of the total DNA in ...

with specific location of 18q11.1. The location of the base pair starts at 18,529,703 and ends at 18,691,812 bp and

translates Translation is the communication of the semantics, meaning of a #Source and target languages, source-language text by means of an Dynamic and formal equivalence, equivalent #Source and target languages, target-language text. The English la ...

into 1354

amino acids Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the Proteinogenic amino acid, 22 α-amino acids incorporated into p ...

. ROCK1 has a ubiquitous tissue distribution, but subcellularly it is thought to colocalize with the

centrosomes In cell biology, the centrosome (Latin centrum 'center' + Greek sōma 'body') (archaically cytocentre) is an organelle that serves as the main microtubule organizing center (MTOC) of the animal cell, as well as a regulator of cell-cycle progre ...

. This is consistent with its function as a key modulator of

, tumor cell invasion, and

actin Actin is a family of globular multi-functional proteins that form microfilaments in the cytoskeleton, and the thin filaments in muscle fibrils. It is found in essentially all eukaryotic cells, where it may be present at a concentration of ...

cytoskeleton organization. In rats, ROCK1 is expressed in the lung, liver, spleen, kidney, and testis.

Structure and regulation

The ROCK1 structure is a serine/threonine kinase with molecular weight of 158 kDa. It is a homodimer composed of a catalytic kinase domain (residues76-338) located at the amino or

N-terminus The N-terminus (also known as the amino-terminus, NH2-terminus, N-terminal end or amine-terminus) is the start of a protein or polypeptide, referring to the free amine group (-NH2) located at the end of a polypeptide. Within a peptide, the amin ...

of the protein, a

coiled-coil A coiled coil is a structural motif in proteins in which two to seven alpha-helices are coiled together like the strands of a rope. ( Dimers and trimers are the most common types.) They have been found in roughly 5-10% of proteins and have a v ...

region (residues 425-1100) containing the Rho-binding domain, and a pleckstrin-homology domain (residues 1118-1317) with a cysteine-rich domain. When a substrate is absent, ROCK1 is an autoinhibited loop structure. Enzyme activity of ROCK1 is inhibited when the pleckstrin-homology and Rho-binding domains in the

C-terminus The C-terminus (also known as the carboxyl-terminus, carboxy-terminus, C-terminal tail, carboxy tail, C-terminal end, or COOH-terminus) is the end of an amino acid chain (protein Proteins are large biomolecules and macromolecules that comp ...

independently bind to the N-terminus kinase domain. When a substrate such as GTP-bound RhoA binds to the Rho-binding region of the coiled-coil domain, the interactions between the N-terminus and the C-terminus are disrupted, thus activating the protein. Cleavage of the C-terminal inhibitory domain by caspase-3 during

apoptosis Apoptosis (from ) is a form of programmed cell death that occurs in multicellular organisms and in some eukaryotic, single-celled microorganisms such as yeast. Biochemistry, Biochemical events lead to characteristic cell changes (Morphology (biol ...

can also activate the kinase. This view of autoinhibition released by RhoA binding has been challenged by low resolution electron microscopy data showing ROCK to be a constitutive linear dimer 120 nm in length. According to this new data ROCK does not need to be activated by RhoA or

phosphorylation In biochemistry, phosphorylation is described as the "transfer of a phosphate group" from a donor to an acceptor. A common phosphorylating agent (phosphate donor) is ATP and a common family of acceptor are alcohols: : This equation can be writ ...

because it is always active, and whether ROCK will phosphorylate its substrates (e.g. myosin regulatory light chain) depends only on their subcellular localization. There is one other isoform of ROCK known as ROCK2. ROCK2 is located at 2p24 and is highly homologous with ROCK1 with an overall amino acid sequence identity of 65%. The identity in the Rho-binding domain is 58% and approximately 92% in the kinase domain. The ROCK isoforms are encoded by two different identified genes and are ubiquitously expressed. GTPase-RhoA binding can increase the activity of ROCK1 by 1.5-2-fold. Without RhoA binding, lipids such as

arachidonic acid Arachidonic acid (AA, sometimes ARA) is a polyunsaturated omega−6 fatty acid 20:4(ω−6), or 20:4(5,8,11,14). It is a precursor in the formation of leukotrienes, prostaglandins, and thromboxanes. Together with omega−3 fatty acids an ...

or sphingosine phosphorylcholine can increase ROCK1 activity 5- to 6-fold. These two lipids interact with the pleckstrin-homology domain, thus disrupting its ability to inhibit ROCK1.

G-protein G proteins, also known as guanine nucleotide-binding proteins, are a family of proteins that act as molecular switches inside cells, and are involved in transmitting signals from a variety of stimuli outside a cell to its interior. Their ...

RhoE binds to the N-terminus of ROCK1 and inhibits its activity by preventing RhoA binding. Small G-proteins, Gem and Rad, have been shown to bind and inhibit ROCK1 function, but their mechanism of action is unclear.

Substrates and interactions

ROCK1 phosphorylation sites are at RXXS/T or RXS/T. More than 15 ROCK1 substrates have been identified and activation from these substrates most often leads to actin filament formation and cytoskeleton rearrangements. MYPT-1 is involved in a pathway for

smooth muscle Smooth muscle is one of the three major types of vertebrate muscle tissue, the others being skeletal and cardiac muscle. It can also be found in invertebrates and is controlled by the autonomic nervous system. It is non- striated, so-called bec ...

contraction. When ROCK1 is activated by binding of GTPase RhoA it produces multiple signaling cascades. For example, RhoA is one of the downstream signaling cascades activated by vascular endothelial growth factor (

VEGF Vascular endothelial growth factor (VEGF, ), originally known as vascular permeability factor (VPF), is a signal protein produced by many cells that stimulates the formation of blood vessels. To be specific, VEGF is a sub-family of growth factors ...

). ROCK1 acts as a negative regulator of VEGF

endothelial cell The endothelium (: endothelia) is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and th ...

activation and angiogenesis. ROCK1 activation by RhoA also promotes stabilization of

F-actin Actin is a family of globular multi-functional proteins that form microfilaments in the cytoskeleton, and the thin filaments in muscle fibrils. It is found in essentially all eukaryotic cells, where it may be present at a concentration of ...

, phosphorylation of regulatory

myosin light chain A myosin light chain is a light chain (small polypeptide subunit) of myosin. Myosin light chains were discovered by Chinese biochemist Cao Tianqin (Tien-chin Tsao) when he was a graduate student at the University of Cambridge in England. Struc ...

(MLC) and an increase in contractility, which plays a crucial role in tumor cell migration and metastasis. This activated ROCK1 also activates LIM kinase, which, phosphorylates

cofilin ADF/cofilin is a family of actin-binding proteins associated with the rapid depolymerization of Actin, actin microfilaments that give actin its characteristic dynamic instability. This dynamic instability is central to actin's role in muscle cont ...

, inhibiting its actin-depolymerizing activity. This depolymerization results in stabilization of actin filaments and decreased branching which promotes contraction. Cardiac

troponin Troponin, or the troponin complex, is a complex of three regulatory proteins (troponin C, troponin I, and troponin T) that are integral to muscle contraction in skeletal muscle and cardiac muscle, but not smooth muscle. Measurements of cardiac-spe ...

is another ROCK1 substrate that upon phosphorylation causes reduction in tension in cardiac

myocytes A muscle cell, also known as a myocyte, is a mature contractile cell in the muscle of an animal. In humans and other vertebrates there are three types: skeletal, smooth, and cardiac (cardiomyocytes). A skeletal muscle cell is long and threadli ...

. ROCK1 also acts as a suppressor of inflammatory cell migration by regulating PTEN phosphorylation and stability.

Function

ROCK1 has a diverse range of functions in the body. It is a key regulator of actin-myosin contraction, stability, and

cell polarity Cell polarity refers to spatial differences in shape, structure, and function within a cell. Almost all cell types exhibit some form of polarity, which enables them to carry out specialized functions. Classical examples of polarized cells are de ...

. These contribute to many progresses such as regulation of morphology, gene transcription, proliferation, differentiation, apoptosis and oncogenic transformation. Other functions involve smooth muscle contraction, actin cytoskeleton organization, stress fiber and focal adhesion formation,

neurite A neurite or neuronal process refers to any projection from the cell body of a neuron. This projection can be either an axon or a dendrite. The term is frequently used when speaking of immature or developing neurons, especially of cells in culture ...

retraction,

cell adhesion Cell adhesion is the process by which cells interact and attach to neighbouring cells through specialised molecules of the cell surface. This process can occur either through direct contact between cell surfaces such as Cell_junction, cell junc ...

and motility. These functions are activated by phosphorylation of

DAPK3 Death-associated protein kinase 3 is an enzyme that in humans is encoded by the ''DAPK3'' gene. Function Death-associated protein kinase 3 (DAPK3) induces morphological changes in apoptosis when overexpressed in mammalian cells. These result ...

, GFAP,

LIMK1 LIM domain kinase 1 is an enzyme that in humans is encoded by the ''LIMK1'' gene. Function There are approximately 40 known eukaryotic LIM proteins, so named for the LIM domains they contain. LIM domains are highly conserved cysteine-rich str ...

, LIMK2, MYL9/MLC2, PFN1 and

PPP1R12A Protein phosphatase 1 regulatory subunit 12A is an enzyme that in humans is encoded by the ''PPP1R12A'' gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nuc ...

. Additionally, ROCK1 phosphorylates FHOD1 and acts synergistically with it to promote SRC-dependent non-apoptotic plasma membrane

blebbing In cell biology, a bleb (or snout) is a bulge of the plasma membrane of a cell, characterized by a spherical, "blister-like", bulky morphology. It is characterized by the decoupling of the cytoskeleton from the plasma membrane, degrading the inte ...

. It is also required for centrosome positioning and centrosome-dependent exit from mitosis.

Interactions

ROCK1 has been shown to interact with: *

, * MLC, * MYPT1, * PFN2, and *

RHOA Transforming protein RhoA, also known as Ras homolog family member A (RhoA), is a small GTPase protein in the Rho family of GTPases that in humans is encoded by the ''RHOA'' gene. While the effects of RhoA activity are not all well known, it is ...

Clinical significance

In humans, the main function of ROCK1 is actomyosin contractility. As mentioned before, this contributes to many proximal progresses such as regulation of morphology, motility, and cell–cell and cell–matrix adhesion. In addition, ROCK kinases influence more distal cellular processes including gene transcription, proliferation, differentiation, apoptosis and oncogenic transformation. Given this diverse range of functions, it is not surprising that ROCK1 has been implicated in numerous aspects of cancer.

Role in cancer

Recent studies have explored the role of ROCK1 in cancer with particular attention focused on cell motility, metastasis, and angiogenesis. Rho GTPases such as RhoA are highly involved in morphologic changes in cells. When a tumor progresses from invasive to metastatic form it requires that they undergo these dramatic morphologic changes. Therefore, increased expression of RhoA and its downstream effector ROCK1 is often observed in human cancers. These cancers are typically more invasive and metastatic phenotypes.

Angiogenesis

Increased expression of RhoA and ROCK1 in endothelial cell migration pathways can cause an increase in angiogenesis and metastatic behavior in tumor cells. It has been suggested that ROCK1 either regulates the expression of angiogenic factors or ROCK1 activation facilitates angiogenesis by increasing the plasticity of the tumor. By reducing the strength of cell-cell interactions and aiding the movement of tumor cells, ROCK1 may enable endothelial cells to penetrate the tumor mass more easily.

ROCK1 inhibitors in cancer therapy

ROCK1 inhibitors might be used in cancer therapy for: *targeting of

stromal Stromal cells, or mesenchymal stromal cells, are differentiating cells found in abundance within bone marrow but can also be seen all around the body. Stromal cells can become connective tissue cells of any organ, for example in the uterine muco ...

rather than

tumor cells A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

*concomitant blocking of ROCK and

proteasome Proteasomes are essential protein complexes responsible for the degradation of proteins by proteolysis, a chemical reaction that breaks peptide bonds. Enzymes that help such reactions are called proteases. Proteasomes are found inside all e ...

activity in K‐Ras‐driven lung cancers *treating haematological malignancies such as

chronic myelogenous leukemia Chronic myelogenous leukemia (CML), also known as chronic myeloid leukemia, is a cancer of the white blood cells. It is a form of leukemia characterized by the increased and unregulated growth of myeloid cells in the bone marrow and the accumula ...

(CML) ROCK1 inhibition for cancer treatment has not been approved for standard therapy use. Y27632 and Fasudil are examples of ROCK1 inhibitors. Both inhibit ROCK1 by competing with ATP for the kinase activation site. Experiments with Y27632 show it is a promising candidate as a therapeutic

antihypertensive agent Antihypertensives are a class of medication, drugs that are used to treat hypertension (high blood pressure). Antihypertensive therapy seeks to prevent the complications of high blood pressure, such as stroke, heart failure, kidney failure and myo ...

. Fasudil has been used to characterize the role of ROCK1 in vascular function in clinical studies and has been approved for use in Japan for treatment of

cerebral vasospasm Cerebral vasospasm is the prolonged, intense vasoconstriction of the larger conducting arteries in the subarachnoid space which is initially surrounded by a clot. Significant narrowing of the blood vessels in the brain develops gradually over the ...

following

subarachnoid hemorrhage Subarachnoid hemorrhage (SAH) is bleeding into the subarachnoid space—the area between the arachnoid (brain), arachnoid membrane and the pia mater surrounding the human brain, brain. Symptoms may include a thunderclap headache, severe heada ...

Other diseases

The ROCK1 signaling plays an important role in many diseases including

diabetes Diabetes mellitus, commonly known as diabetes, is a group of common endocrine diseases characterized by sustained high blood sugar levels. Diabetes is due to either the pancreas not producing enough of the hormone insulin, or the cells of th ...

neurodegenerative diseases A neurodegenerative disease is caused by the progressive loss of neurons, in the process known as neurodegeneration. Neuronal damage may also ultimately result in their death. Neurodegenerative diseases include amyotrophic lateral sclerosis, mul ...

such as

Parkinson's disease Parkinson's disease (PD), or simply Parkinson's, is a neurodegenerative disease primarily of the central nervous system, affecting both motor system, motor and non-motor systems. Symptoms typically develop gradually and non-motor issues become ...

and

amyotrophic lateral sclerosis Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND) or—in the United States—Lou Gehrig's disease (LGD), is a rare, Terminal illness, terminal neurodegenerative disease, neurodegenerative disorder that results i ...

(ALS), and

pulmonary hypertension Pulmonary hypertension (PH or PHTN) is a condition of increased blood pressure in the pulmonary artery, arteries of the lungs. Symptoms include dypsnea, shortness of breath, Syncope (medicine), fainting, tiredness, chest pain, pedal edema, swell ...

References

External links

ROCK1
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