alpha-catenin

a-Catenin

updated 20/5/'02

a-catenin is an actin-binding protein at the adherens junction, that has overall similarity to vinculin, another actin-binding protein present at adhesional complexes. It attaches the microfilaments ad associated proteins (vinculin, alpha-actinin) to the trans-membranous cell adhesion molecules (cadherins) via b-catenin. In addition to being an important physical connection, this system is also important in cell signalling. Free b-catenin is taken into the nucleus where it binds LEF-1 a transcription activator, this is the important Wnt pathway. b-catenin may also play a part in dendritic spines as it shuttles between the shafts and spines of neurons in a polarization sensitive manner (Murase et al, 2002).

Figure 1. a-catenin in relation to the other major components of the cell-cell adherent junction. This is a simplified diagram showing the major, but not all interconnections.

Protein	Function	Reference
actin	A cytoskeletal component.	Rimm et al, 1995
a-actinin	An actin filament bundling protein	Imamura et al, 1999
afadin	A component of cell-cell adhesion complexes.	Takahashi et al, 1999
b-catenin	A signalling molecule that is also part of the adhesion complex	Ozawa & Kemler, 1992
spectrin	Usually present as part of the sub-membranous cytoskeleton where it connects various membranous proteins to actin.	Pradham et al, 2001
vinculin	A component of focal contacts and some cell adhesions that binds actin and lipids.	Watabe-Uchida et al, 1998
ZO-1	A component of cell-cell adhesion complexes.	Itoh et al, 1997
ZO-2	Binds ZO-1 is a MAGUK family member, present at tight and adherens junctions. Binds occludin.	Itoh et al, 1999
Table 1 a-catenin-binding proteins

The structure of a-catenin
There are three regions of that are homologous to regions in vinculin (),

The actin-binding site of a-catenin
It appears that the last 42 amino-acids of a-catenin contains an actin-binding domain. This is a bit odd because it was expected that the actin-binding domain would be contained within one of the regions that is homologous to vinculin as it too binds actin. The last 42 amino-acids of a-catenin

a-catenin and disease
Mutations in a-catenin genes are known to produce proteins that break the all important links between cell adhesion molecules and cell signalling throught through Wnt pathway (Vanpoucke et al, 2002). Disruption of adhesions releases b-catenin into the nucleus to switch on genes, while the broken cell adhesion leaves cells free to invade by locomotion.

References:-

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