ROCKs: multifunctional kinases in cell behaviour

Abstract

ROCKs, or Rho kinases, are serine/threonine kinases that are involved in many aspects of cell motility, from smooth-muscle contraction to cell migration and neurite outgrowth. Recent experiments have defined new functions of ROCKs in cells, including centrosome positioning and cell-size regulation, which might contribute to various physiological and pathological states.

Key Points

  • Rho effectors include two serine/threonine kinases that are known as ROCK I and ROCK II.

  • ROCKs phosphorylate various substrates, including myosin light chain phosphatase, myosin light chain, ezrin–radixin–moesin proteins and LIM (for Lin11, Isl1 and Mec3) kinases, and mediate the formation of actin stress fibres and focal adhesions in various cell types.

  • In smooth muscle, ROCKs are involved in agonist-induced Ca2+-sensitization in muscle contraction, possibly by phosphorylating the myosin-binding subunit of myosin light chain phosphatase, and thereby inhibiting the phosphatase activity.

  • ROCKs have an important role in cell migration by enhancing cell contractility. They are required for tail retraction of monocytes and cancer cells, and a ROCK inhibitor has been used to reduce tumour-cell dissemination in vivo.

  • ROCKs also have a role in other cellular responses that require actomyosin contractility, such as axonal growth and cytokinesis.

  • Recently, ROCKs have been linked to the control of cell size and regulation of distance between the two centrioles.

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Figure 1: Phylogenetic tree of kinases that are homologous to ROCKs.
Figure 2: The structure of ROCKs.
Figure 3: Regulation of ROCK function.
Figure 4: ROCK targets.
Figure 5: Signals affecting ROCK-induced myosin II and LIMK activity.
Figure 6: Schematic model of ROCK function in insulin signalling.

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Acknowledgements

K.R. is supported by a European Commission Marie Curie fellowship.

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DATABASES

LocusLink

Adducin

cofilin

CR3

Dia

eukaryotic elongation factor 1α

IGF-1

MBS

PP1c

profilin

Swiss-Prot

basic calponin

CD44

Cdc42

citron kinase

CRMP1

CRMP2

DMPK

E-cadherin

Gem

GFAP

Insulin receptor substrate-1

LIMK1

LIMK2

MARCKS

MLCK

MRCK

NF-L

NHE1

p190-B

RhoA

RhoB

RhoC

RhoE

ROCK I

ROCK II

vimentin

FURTHER INFORMATION

Anne J. Ridley's laboratory

Cell migration consortium

Movies from the cell migration consortium

Cytokinesis link with movies

Glossary

STRESS FIBRE

An axial bundle of F-actin and myosin that traverses the cytoplasm. The formation of stress fibres is typically induced by the activity of the GTPase RhoA.

FOCAL ADHESION

A cellular structure that links the extracellular matrix on the outside of the cell, through integrin receptors, to the actin cytoskeleton inside the cell.

PLECKSTRIN HOMOLOGY (PH) DOMAIN

A sequence of around 100 amino acids that is present in many signalling molecules, and in some cases binds to phosphatidylinositides. Pleckstrin is a protein of unknown function that was originally identified in platelets — it is a principal substrate of protein kinase C.

CLEAVAGE FURROW

A region of the plasma membrane in higher eukaryotic cells that ingresses to separate the two daughter cells at cytokinesis. Contraction in this region is driven by the interaction of actin and myosin filaments.

INTERMEDIATE FILAMENT

A cytoskeletal filament, typically 10 nm in diameter, that occurs in higher eukaryotic cells. The protein composition of intermediate filaments varies between cell types. Examples of intermediate-filament proteins are keratins, vimentin and desmin.

DOMINANT-NEGATIVE

A defective protein that retains some interaction abilities and so competes with normal proteins for interacting partners and/or substrates.

CASPASE

A cysteine endopeptidase that cleaves at specific aspartic acid residues. Caspases are typically activated during apoptosis.

GTPγS

A non-hydrolysable analogue of GTP.

PHORBOL ESTER

A polycyclic compound isolated from croton oil that is a potent co-carcinogen or tumour promoter. Phorbol esters are diacylglycerol analogues and irreversibly activate protein kinase C.

MICROVILLI

Small, finger-like projections (1–2 μm long and 100 nm wide) that occur on the exposed surfaces of epithelial cells to maximize the surface area.

LYSOPHOSPHATIDIC ACID

(LPA). Any phosphatidic acid that is deacylated at positions 1 or 2. LPA binds to a G-protein-coupled receptor, which results in the activation of the GTPase Rho and the induction of stress fibres.

GROWTH CONE

The motile tip of an axon or dendrite of a growing nerve cell, which spreads out into a large cone-shaped appendage.

CA2+ SENSITIZATION

Stimulation by an agonist results in increased myosin light chain phosphorylation and smooth-muscle-cell contraction at submaximal Ca2+ levels.

TIGHT JUNCTION

A belt-like region of adhesion between adjacent epithelial or endothelial cells. Tight junctions regulate paracellular flux, and contribute to the maintenance of cell polarity by stopping molecules from diffusing within the plane of the membrane.

ADHERENS JUNCTION

A cell–cell adhesion complex that is composed of cadherins and catenins that are attached to cytoplasmic actin filaments.

MACROPHAGE

Any cell of the mononuclear phagocyte system that is characterized by its ability to phagocytose foreign particulate and colloidal material.

ASTROCYTE

A star-shaped glial cell that carries out supportive and protective functions for the tissue of the central nervous system.

LAMELLIPODIUM

A thin sheet-like cell extension that is found at the leading edge of crawling cells or growth cones.

MONOCYTE

A large leukocyte with a horseshoe-shaped nucleus. Monocytes derive from pluripotent stem cells and become phagocytic macrophages when they enter tissues.

NATURAL KILLER CELLS

A class of lymphocytes that are crucial in the innate immune response. They exert a cytotoxic activity on target cells (such as virus-infected cells) that is enhanced by cytokines such as interferons.

BLEBBING

Protrusions from the plasma membrane that rapidly extend and retract in many regions, and can be shed as small vesicles containing cytoplasmic material. Blebbing is most commonly observed soon after the onset of apoptosis, and is believed to be driven by a strong contractile force that is generated by actin and myosin.

PC12 CELLS

A clonal line of rat adrenal pheochromocytoma cells that respond to nerve growth factor by extension of neurites and that can synthesize, store and secrete catecholamines, much like sympathetic neurons. PC12 cells contain small, clear synaptic-like vesicles and larger dense core granules.

RNA INTERFERENCE

The process by which an introduced double-stranded RNA specifically silences the expression of genes through degradation of their cognate messenger RNAs.

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