Cell contact

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As cell contacts or cell connections (engl. Cell junctions ) direct contact points are of cells in tissues indicated. All multicellular living things form temporary or permanent cell contacts. The cell contacts are essentially formed by proteins , the cell adhesion molecules , which on the one hand protrude from the cell surfaces and, on the other hand, form a cytoplasmic plaque as intracellular anchor proteins . Their job is to hold the tissue together and enable cells to communicate with one another. Many of the cell adhesion molecules are transmembrane proteins that protrude beyond the cell membrane on both sides, inside and outside . These proteins can transmit signals from outside, for example from other cells, to the inside, or transmit signals from the cell to the neighboring cells. Cell adhesion molecules mediate contacts between cells as well as between cells and the extracellular matrix . The channel-forming transmembrane proteins of the gap junctions , the connexins and innexins, are a specialty . From a certain cell density onwards, cell contact inhibits cell contact . Cell contacts can be detected using a cell adhesion test.

Differentiation of cell contacts

Schematic representation of various cell contacts

Cell contacts can be roughly divided into adhesive, locking or connecting contacts according to their task.

Closing connections

Closing connections ( engl .: Occluding junctions ), also barriers contacts or opaque compounds , bringing the cell spaces in close contact and control the flow of ions and molecules across the cell gap.

Adhesive connections

Adhesive connections , also adhesion connections (English: Adhering junctions ), adhesion contacts or anchor connections (English: Anchoring junctions ), connect the cells mechanically. In this way, they allow intercellular cohesion, also known as (cell) coherence . A distinction is made between two functional groups:

  1. Cell-cell contacts ( desmosome in the broader sense)
    • Macula adhaerens (spot desmosome = desmosome in the narrower sense)
    • Adherens junctions (ger .: adherens junctions)
      • Zonula adhaerens (belt desmosome)
      • Punctum adhaerens (point desmosome)
      • Fascia adhaerens (striped desmosome)
    • Adhaerens complex
  2. Cell-matrix contacts

Communicating connections

Communicating compounds (engl .: Communicating junctions ) or communication contacts permit the free flow of chemical or electrical signals ( ions and small molecules ). A distinction is made between:

Task and function

The cohesion and communication between cells are the basic requirements for the development of more complex organisms. Only then is it possible to differentiate between cells and thereby specialize tissues into organs . The lipid bilayers of the biomembranes are thin and therefore cannot transmit the great forces that are exerted on a cell structure. Cell anchorages (engl .: Anchoring junctions ) solve this problem by the cytoskeleton connect inside a cell with other cells or with the extracellular matrix.

Proteins involved

The cell contacts are mediated , among other things, by cell adhesion molecules . These include the selectins , the cadherins , the integrins and the immunoglobulin superfamily. In addition to the cell adhesion molecules, anchor proteins such as claudins and channel proteins such as connexins also occur in cell contacts .

Selectins are involved in various inflammatory processes, such as the rolling of neutrophils along a vessel wall . There are three selectins: L-selectin, P-selectin and E-selectin. L-selectin occurs on lymphocytes , monocytes, and neutrophils, P-selectin on platelets and endothelial cells, and E-selectin on endothelial cells. Their extracellular protein domain consists of an N-terminal lectin , followed by an EGF -like region and short repeating units for binding to other proteins.

Cadherins are calcium-dependent homophilic (equal binding) cell adhesion molecules, which in complex with catenin to the actin - microfilaments of the cytoskeleton bind adherens junctions form and embryonic development are used.

In addition to their function in cell adhesion, integrins are also receptors with the following signal transduction .

The immunoglobulin superfamily binds both homophilically to other proteins in the family and heterophilically to integrins.

Individual evidence

  1. ↑ a b c Detlev Drenkhahn and Wolfgang Zenker (eds.): Benninghoff Anatomie Volume 1. 15th edition, Urban and Schwarzenberg, Vienna / Munich / Baltimore 1994 ,; Pp. 25-32, ISBN 3-541-00245-X
  2. ^ Schmelz, M. & Franke, WW: "Complexus Adhaerentes, A New Group of Desmoplakin-Containing Junctions in Endothelial Cells - the Syndesmos Connecting Retothelial Cells of Lymph-Nodes." In: European Journal of Cell Biology 61, 1993, p 274-289
  3. ↑ Lodish et al .: Molecular Cell Biology , 6th. Edition, WH Freeman and Company, 2007, ISBN 1429203145 , p. 803.
  4. ↑ Tedder TF, Steeber DA, Chen A, Engel P: The selectins: vascular adhesion molecules . In: FASEB J. . 9, No. 10, July 1995, pp. 866-73. PMID 7542213 .
  5. ^ Bevilacqua MP, Nelson RM: Selectins . In: J. Clin. Invest. . 91, No. 2, February 1993, pp. 379-87. doi : 10.1172 / JCI116210 . PMID 7679406 . PMC 287934 (free full text).
  6. ^ Rowlands ™, Symonds JM, Farookhi R, Blaschuk OW: Cadherins: crucial regulators of structure and function in reproductive tissues . In: Rev. Reprod. . 5, No. 1, January 2000, pp. 53-61. PMID 10711736 .
  7. ↑ Brembeck FH, Rosário M, Birchmeier W: Balancing cell adhesion and Wnt signaling, the key role of β-catenin . In: Curr. Opin. Genet. Dev. . 16, No. 1, February 2006, pp. 51-9. doi : 10.1016 / j.gde.2005.12.007 . PMID 16377174 .
  8. ↑ Hynes RO: Integrins: bidirectional, allosteric signaling machines . In: Cell . 110, No. 6, September 2002, pp. 673-87. doi : 10.1016 / S0092-8674 (02) 00971-6 . PMID 12297042 .
  9. ↑ Wai Wong C, Dye DE, Coombe DR: The role of immunoglobulin superfamily cell adhesion molecules in cancer metastasis . In: Int J Cell Biol . 2012, 2012, p. 340296. doi : 10.1155 / 2012/340296 . PMID 22272201 . PMC 3261479 (free full text).

literature

  • Alberts, B. et al .: Molecular Biology of the Cell . Garland Science, 4th edition, 2002. ISBN 0815340729 .
  • Detlev Drenkhahn and Wolfgang Zenker (eds.): Benninghoff Anatomie Volume 1. 15th edition, Urban and Schwarzenberg, Vienna / Munich / Baltimore 1994. ISBN 3-541-00245-X

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