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Typus
Verschleierung
Bearbeiter
Graf Isolan
Gesichtet
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Untersuchte Arbeit:
Seite: 19, Zeilen: 4-30
Quelle: Hapel and Stanley 2006
Seite(n): 3, Zeilen: 26-48
1.3.3. Tyrosine kinase receptor and cell signalling

Many cytokines such as CSF-1, SCF and FL are homodimeric that share some sequence homology and are structurally similar to one another. These three cytokines/ growth factors have complex patterns of expression due to alternative mRNA splicing. This allows them to be expressed as either membrane-spanning, cell-surface or secreted glycoproteins. All three growth factors are widely expressed in all tissues and two of them, SCF and CSF-1, also affect non-haematopoietic as well as haematopoietic cells.

The receptors for the above cytokines are members of the platelet derived growth factor (PDGF) receptor family. Each receptor possesses an extra-cellular domain, consisting of a five immunoglobulin (Ig) like repeat. These repeats are: a heavily glycosylated with N-linked sugars, a trans-membrane domain, intra-cellular domains containing a juxta-membrane region, a src-related tyrosine kinase domain that is interrupted by a kinase insert domain, and a carboxy-terminal tail. The three amino terminal Ig-like domains incorporate the ligand binding domains of the SCF and CSF-1 receptors. Binding of this type of dimeric receptor to its cognate ligand stabilizes the non-covalent association between the two chains of the receptor at the cell surface and permits the trans-phosphorylation of the intra-cellular domain of one chain by the other.

Tyrosine phosphorylation in response to cytokine binding is not restricted to those proteins that are stably associated with the receptor. Regions containing tyrosines that are phosphorylated as a consequence of receptor activation act as docking sites for src-homology region 2 (SH2) domains of signaling and adaptor proteins. These proteins in turn may interact with plasma membrane associated proteins. An example is the association of recruited Grb2/Sos with Ras, which leads to their activation. The associated proteins may themselves become tyrosine phosphorylated.

Tyrosine Kinase Receptors

CSF-1, SCF and FL are homodimeric cytokines that share some sequence homology and structurally are similar to one another.36-40 All three cytokines have complex patterns of expression due to alternative mRNA splicing. This allows them to be expressed as either membrane-spanning, cell-surface or secreted glycoproteins. All three growth factors are widely expressed in all tissues and at least two of them, SCF and CSF-1, affect non-haematopoietic as well as haematopoietic cells.

The receptors for the above cytokines are members of the PDGF receptor family.39-42 Each receptor possesses an extra-cellular domain comprising five Ig-like repeats which are heavily glycosylated with N-linked sugars, a trans-membrane domain, and intra-cellular domains containing a juxta-membrane region, a src-related tyrosine kinase domain that is interrupted by a kinase insert domain, and a carboxy-terminal tail. The three amino terminal Ig-like domains incorporate the ligand binding domains of the SCF and CSF-1 receptors.

Binding of this type of dimeric receptor to its cognate ligand stabilises the non-covalent association between the two chains of the receptor at the cell surface and permits the trans-phosphorylation of the intra-cellular domain of one chain by the other.

Tyrosine phosphorylation in response to cytokine binding is not restricted to those proteins that are stably associated with the receptor. Regions containing tyrosines that are phosphorylated as a consequence of receptor activation act as docking sites for src homology region 2 (SH2) domains of signalling and adaptor proteins. These proteins in turn may interact with plasma membrane associated proteins. An example is the association of recruited Grb2/Sos with Ras, which leads to their activation. Or the associated proteins may themselves become tyrosine phosphorylated.


36. Anderson DM, Williams DE, Tushinski R et al. Alternate splicing of mRNA encoding human mast cell growth factor and localisation of the gene to chromosome 12q22-24. Cell Growth Differ 1991; 2:373-378.

37. Bazan JF. Genetic and structural homology of stem cell factor and macrophage colony stimulating factor. Cell 1991; 65:9-10.

38. Flanagan JG, Chan DC, Leder P. Transmembrane form of the kit ligand growth factor is determined by alternative splicing and is missing in the Sld mutant. Cell 1991; 64:1025-1035.

39. Lyman SD, Jacobsen SEW. c-kit ligand and flt-3 ligand : stem cell factors with overlapping yet distinct activities. Blood 1998; 91:1101–1134.

40. Stanley ER. CSF-1. In: Oppenheim JJ, Feldmann M, eds. Cytokine Database. London: Academic 2000:913–934.

41. Qui F, Ray P, Brown K et al. Primary structure of c-kit: relationship with the CSF1/PDGF receptor kinase family - oncogenic activation of v-kit involves deletion of extracellular domain and C terminus. EMBO J 1988; 7:1003-1011.

42. Coussens L, van Beveren C, Smith D et al. Structural alteration of viral homologue of receptor proto oncogene fms at carboxy-terminus. Nature 1986; 32:277-280.

Anmerkungen

A literal copy except for minute details, without any part of it marked as a citation. No source given.

Sichter
(Graf Isolan) Agrippina1

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