These stimuli can be quite diverse in nature, comprising several distinct classes of biological molecules including hormones, growth factors, cytokines, toxins, organic inhibitors, osmotic stimuli as well as ultraviolet light. Differences in the nature and consequences of signaling initiated by such diverse agents and legends results from the differential modulation of multiple signaling elements in distinct combinations. Indeed, all known effects of signaling cascades can be regulated by more than one stimulus. Moreover, overlapping pathways can be activated by different stimuli, further contributing to the regulation of signaling specificity. To define the signaling mechanisms and their role in physiological events triggered by an extracellular stimulus, it is necessary to identify the signal transducers, their interactions and the time-course in which their activity and subcellular location are modulated.
Broken arrows indicate interactions that are less definitively established.
The JNK and p38 enzymes comprise two additional subfamilies, whose members are potently activated by a variety of stress-related stimuli. The cells then were either untreated or treated with anisomycin, a protein synthesis inhibitor isolated from Streptomyces . Note that the myc-tagged SAPKbeta enzyme runs at a higher molecular weight as compared to JNK1 or JNK2. Zanke, B.W. et al. Pena, L.A. et al.