CGN (gene)
Encyclopedia
Cingulin is a protein
that in humans is encoded by the CGN gene
.
s.
, which is also detected at adheren
s-type junctions in non-epithelial cells. During early Xenopus
embryo development, cingulin is detected at a cortical localization, and then accumulates at apical junctions, unlike ZO-1 and other junctional proteins, that are targeted to the new regions of cell-cell contact via the lateral domain. Cingulin interacts with ZO-1 and several other tight junction proteins, in addition to interacting with actin and myosin. A conserved sequence in the N-terminal region of cingulin is required for junctional recruitment and interaction with ZO-1. The notion that that ZO-1 recruits cingulin to tight junctions is confirmed by the observation that epithelial cells lacking ZO-1 lose cingulin junctional staining.
The function of cingulin has been studied by knockout
and knockdown
approaches. Embryoid bodies derived from embryonic stem cells where one or both cingulin alleles were targeted by homologous recombination show apparently normal tight junctions, but changes in the expression of a large number of genes, including tight junction protein genes (claudin-2
, claudin-6
, claudin-7
and occludin
) and transcription factors (GATA4
). Changes in the expression of claudin-2 and ZO-3 are also observed in cultured kidney cells (MDCK) depleted of cingulin by shRNA
. These effects of cingulin depletion on gene expression are thought to be mediated at least in part by the regulation of RhoA
activity by cingulin, snce they can be reversed by dominant-negative RhoA. Indeed, cingulin interacts with the RhoA exchange factor GEF-H1
, and inactivates it by recruiting it to junctions when cells reach confluence. It was therefore hypothesized that the accumulation of cingulin at mature junctions of confluent monolayers is one mechanism to down-regulate RhoA activity once cells reach confluence. Cells depleted of cingulin also show increased density and proliferation, indicating that cingulin contributes to regulating cell proliferation. Cingulin is also implicated in the junctional recruitment of the RhoGEF p114RhoGEF, which activates RhoA at tight junctions and is required for junction assembly (Terry et al, Nat. Cell Biol. 2011). Cingulin is expressed in some but not all human carcinomas, for example its expression is strongly downregulated in epidermoid carcinomas of the lung. Histone deacetylase inhibitors such as sodium butyrate strongly up-regulate cingulin expression in some cultured cells, indicating that cingulin is a marker of epithelial differentiation.
). Unlike cingulin, paracingulin is detected both at tight and adherens junctions. The function of paracingulin was clarified when it was discovered that epithelial cells depleted of paracingulin show increased RhoA activation at confluence, and delayed tight junction assembly in the experimental model of the "calcium switch". The delay in junction assembly correlates with decreased Rac1 activation. In fact, similarly to cingulin, paracingulin contributes to recruiting and inactivating the RhoA guanine exchange factor GEF-H1 to junctions. In addition, paracingulin interacts with and recruits to junctions the Rac1 guanine exchange factor Tiam1
.
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
that in humans is encoded by the CGN gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
.
Discovery
Cingulin was originally discovered at the MRC Laboratory of Molecular Biology (Cambridge, UK) by Dr. Sandra Citi, as a protein present in chicken intestinal epithelial cells, that co-purified with nonmuscle myosin II, and was specifically localized at tight junctionTight junction
Tight junctions, or zonula occludens, are the closely associated areas of two cells whose membranes join together forming a virtually impermeable barrier to fluid. It is a type of junctional complex present only in vertebrates...
s.
Structure
Cingulin is a homodimer, each subunit containing a globular "head" domain, a long coiled-coil "rod" domain, and a small globular "tail". This domain organization is conserved throughout vertebrate species. However, cingulin homologs have not been detected in invertebrate species.Function
Cingulin is specifically localized at tight junctions in epithelial cells, unlike ZO-1Tight junction protein 1
Tight junction protein ZO-1 is a protein that in humans is encoded by the TJP1 gene.-Interactions:Tight junction protein 1 has been shown to interact with F11 receptor, Gap junction protein, alpha 1, MLLT4, Occludin, TJP3, GJA3, KIRREL, Tight junction protein 2 and GJA8.-Further reading:...
, which is also detected at adheren
Adherens junction
Adherens junctions are protein complexes that occur at cell–cell junctions in epithelial tissues, usually more basal than tight junctions...
s-type junctions in non-epithelial cells. During early Xenopus
Xenopus
Xenopus is a genus of highly aquatic frogs native to Sub-Saharan Africa. There are 19 species in the Xenopus genus...
embryo development, cingulin is detected at a cortical localization, and then accumulates at apical junctions, unlike ZO-1 and other junctional proteins, that are targeted to the new regions of cell-cell contact via the lateral domain. Cingulin interacts with ZO-1 and several other tight junction proteins, in addition to interacting with actin and myosin. A conserved sequence in the N-terminal region of cingulin is required for junctional recruitment and interaction with ZO-1. The notion that that ZO-1 recruits cingulin to tight junctions is confirmed by the observation that epithelial cells lacking ZO-1 lose cingulin junctional staining.
The function of cingulin has been studied by knockout
Gene knockout
A gene knockout is a genetic technique in which one of an organism's genes is made inoperative . Also known as knockout organisms or simply knockouts, they are used in learning about a gene that has been sequenced, but which has an unknown or incompletely known function...
and knockdown
Gene knockdown
Gene knockdown refers to techniques by which the expression of one or more of an organism's genes is reduced, either through genetic modification or by treatment with a reagent such as a short DNA or RNA oligonucleotide with a sequence complementary to either an mRNA transcript or a gene...
approaches. Embryoid bodies derived from embryonic stem cells where one or both cingulin alleles were targeted by homologous recombination show apparently normal tight junctions, but changes in the expression of a large number of genes, including tight junction protein genes (claudin-2
CLDN2
Claudin-2 is a protein that in humans is encoded by the CLDN2 gene. It belongs to the group of claudins. -Function:Claudin-2 is expressed in cation-leaky epithelia such as that of the kidney proximal tubule. Mice that are deficient in claudin-2 have reduced reabsorption of Na+ in the proximal...
, claudin-6
CLDN6
Claudin-6 is a protein that in humans is encoded by the CLDN6 gene. It belongs to the group of claudins.-Further reading:...
, claudin-7
CLDN7
Claudin-7 is a protein that in humans is encoded by the CLDN7 gene. It belongs to the group of claudins.-Further reading:...
and occludin
Occludin
Occludin is a protein that in humans is encoded by the OCLN gene.Occludin is a 65-kDa integral plasma-membrane protein located at the tight junctions, described for the first time in 1993 by Shoichiro Tsukita...
) and transcription factors (GATA4
GATA4
Transcription factor GATA-4 is a protein that in humans is encoded by the GATA4 gene.-Interactions:GATA4 has been shown to interact with NKX2-5, TBX5, ZFPM2, Serum response factor and HAND2.HDAC2- External links :...
). Changes in the expression of claudin-2 and ZO-3 are also observed in cultured kidney cells (MDCK) depleted of cingulin by shRNA
Small hairpin RNA
A small hairpin RNA or short hairpin RNA is a sequence of RNA that makes a tight hairpin turn that can be used to silence gene expression via RNA interference. shRNA uses a vector introduced into cells and utilizes the U6 or H1 promoter to ensure that the shRNA is always expressed...
. These effects of cingulin depletion on gene expression are thought to be mediated at least in part by the regulation of RhoA
RHOA
Ras homolog gene family, member A is a small GTPase protein known to regulate the actin cytoskeleton in the formation of stress fibers. In humans, it is encoded by the gene RHOA....
activity by cingulin, snce they can be reversed by dominant-negative RhoA. Indeed, cingulin interacts with the RhoA exchange factor GEF-H1
ARHGEF2
Rho guanine nucleotide exchange factor 2 is a protein that in humans is encoded by the ARHGEF2 gene.-Further reading:...
, and inactivates it by recruiting it to junctions when cells reach confluence. It was therefore hypothesized that the accumulation of cingulin at mature junctions of confluent monolayers is one mechanism to down-regulate RhoA activity once cells reach confluence. Cells depleted of cingulin also show increased density and proliferation, indicating that cingulin contributes to regulating cell proliferation. Cingulin is also implicated in the junctional recruitment of the RhoGEF p114RhoGEF, which activates RhoA at tight junctions and is required for junction assembly (Terry et al, Nat. Cell Biol. 2011). Cingulin is expressed in some but not all human carcinomas, for example its expression is strongly downregulated in epidermoid carcinomas of the lung. Histone deacetylase inhibitors such as sodium butyrate strongly up-regulate cingulin expression in some cultured cells, indicating that cingulin is a marker of epithelial differentiation.
Homologs
In 2004, a protein homologous to cingulin was discovered and named JACOP (also known as paracingulin, or cingulin-like 1 protein; CGNL1Cingulin-like 1
Cingulin-like 1 is a protein which in humans is encoded by the CGNL1 gene.-Function:The mouse homolog of CGNL1 has been designated JACOP . JACOP is recruited to the junctional complex in epithelial cells and to cell-cell contacts in fibroblasts...
). Unlike cingulin, paracingulin is detected both at tight and adherens junctions. The function of paracingulin was clarified when it was discovered that epithelial cells depleted of paracingulin show increased RhoA activation at confluence, and delayed tight junction assembly in the experimental model of the "calcium switch". The delay in junction assembly correlates with decreased Rac1 activation. In fact, similarly to cingulin, paracingulin contributes to recruiting and inactivating the RhoA guanine exchange factor GEF-H1 to junctions. In addition, paracingulin interacts with and recruits to junctions the Rac1 guanine exchange factor Tiam1
T-cell lymphoma invasion and metastasis-inducing protein 1
T-cell lymphoma invasion and metastasis-inducing protein 1 is a protein that in humans is encoded by the TIAM1 gene.- Structure :TIAM1 is tightly associate with BAIAP2 as a subunit...
.