Juxtacrine

A mechanism of growth control and intercellular communication involving specific cell-to-cell contacts. These are established by the interaction of membrane-bound forms of growth factors that are normally secreted, with receptors on an adjacent cell and thus play an important role in developmental processes that have spatial restrictions. Membrane-bound forms of the growth factors then elicit the same spectrum of responses as the soluble factors. On the other hand it is known that the lack of membrane-associated forms of certain factors (for example, SCF ; kit ligand ) can have pathological consequences despite the presence of a soluble form of the same factor.

The membrane bound forms of cytokines frequently are incompletely processed biologically active precursors of the secreted form of the factor. They can be generated also by alternative splicing of the corresponding mRNA.

Juxtacrine growth control has been described to be elicited, among others, by membrane-anchored forms of AR (amphiregulin ), Betacellulin , EGF , GM-CSF , HB-EGF (heparin-binding EGF-like growth factor), M-CSF , SCF (stem cell factor ), SDGF (schwannoma-derived growth factor ), VGF , CD23 ligand, CD27 ligand , CD40 ligand , IL1 , TGF-alpha , and TNF-alpha .

Another mechanism of juxtacrine interaction involving extracellular matrix-associated (see: ECM ) rather than membrane-anchored forms of growth factors has been described for GM-CSF , IL3 , IFN-gamma , SCI (stem cell inhibitor ), and LIF .

Since these specific interactions constitute a controlled form of cell adhesion juxtacrine interactions are involved probably in many developmental processes requiring directed and specific cell-to-cell interactions. This form of interaction allows developmentally important signals to be transmitted specifically between neighboring cells.

Juxtacrine interactions are probably also involved in the control of Hematopoiesis , allowing specific interactions between hematopoietic cells and the surrounding stromal cells (see also: LTBMC (long-term bone marrow culture ), Stromal cell line ). Experimentally this form of specific cell interactions is accessible by introduction of genes encoding specific receptors into cells that normally do not express this receptor and the subsequent detection of engineered cells adhering to the stroma.

For other mechanisms of growth control involving diffusible growth factors rather than membrane-bound forms see also: autocrine , intracrine , paracrine , retrocrine .

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