Cell contacts

Direct contact of cells in tissues. All multicellular organisms form temporary or permanent cell contacts.

The cell contacts are mainly formed by proteins, the cell adhesion molecules (CAM), which on the one hand protrude from the cell surfaces and on the other hand form a cytoplasmic plaque as intracellular anchor proteins.

Cell contacts have the task of holding the tissue together and enabling cells to communicate with each other. Many of the cell adhesion molecules are so-called transmembrane proteins, which protrude beyond the cell membrane on both sides, inside and outside.

Transmembrane proteins can transmit signals from outside, e.g. from other cells, into the interior of a cell, or they can transmit cell signals to a neighbouring cell. Especially structured transmembrane proteins(connexins) are transmembrane proteins that form channels (gap junctions).

Among the different types of cell contacts there are:

• Desmosomes (adhesive connections)
• Adherence Connections
• focal adhesions
• Tight junctions: closing connections
• Gap junctions: communicating connections (gap junctions, channel connections).

Gap junctions connect two cells pore-like and thus allow the exchange of substances.

• The two classical cell-cell connections in humans, the desmosomes and adherent connections (Zonulae adherentes) have one protein in common, the plakoglobin.
• In adherence compounds, beta-catenin, but also plakoglobin, represents the connection between the classical cadherins (e.g. N-cadherin, E-Cadherin) and alpha-catenin, thus enabling interaction with the actin cytoskeleton. Adherence compounds are evolutionarily older than desmosomes and are usually detected earlier in the development of an organism or organ.
• The protein claudin-1 plays an important role in tight junctions (see below Claudine).
• Mutations in the gene for claudin-1 lead to the clinical picture of neonatal dyosis sclerosing cholangitis syndrome. Here, the tight junctions of epidermal cells, hepatocytes and cholangocytes are affected. An overexpression of the isoform of claudin 18 can be detected in a large number of tumor cells.

1. Grosse B et al(2012) Claudin-1 involved in neonatal ichthyosis sclerosing cholangitis syndrome regulates hepatic paracellular permeability. Hepatology 55:1249-1259.