Cell-to-Cell Interactions

Intracellular Signal
Transduction Systems
Multicellular organisms depend on communication
between cells to assure growth,
differentiation, specific functions in different
types of cells, and proper response to external
stimuli. Specific cell–cell interactions between
different types of cells have evolved. A common
leitmotif is the specific binding of an extracellular
signaling molecule (ligand) to a specific receptor
of the target cell to trigger a specific
functional response. The vast variety of
molecules involved in the many different types
of cells can be classified into families of related
structure and function (see Lodish et al., 2000;
Alberts et al., 1994). Two areas are selected
here: the main intracellular functions controlling
growth and the receptor tyrosine kinases.