Sequential protein kinase reactions controlling cell growth and differentiation

Anisomycin-activated protein kinases p45 and p55 but not mitogen-activated protein kinases ERK-1 and -2 are implicated in the induction of c-fos and c-jun

Independent of its ability to block translation, anisomycin intrinsically initiates intracellular signals and immediate-early gene induction [L. C. Mahadevan and D. R. Edwards, Nature (London) 349:747-749, 1991]. Here, we characterize further its action as a potent, selective signalling agonist. In-gel kinase assays show that epidermal growth factor (EGF) transiently activates five kinases: the mitogen-activated protein (MAP) kinases ERK-1 and -2, and three others, p45, p55, and p80. Anisomycin, at inhibitory and subinhibitory concentrations, does not activate ERK-1 and -2 but elicits strong sustained activation of p45 and p55, which are unique in being serine kinases whose detection is enhanced with poly-Glu/Tyr or poly-Glu/Phe copolymerized in these gels. Translational arrest using emetine or puromycin does not activate p45 and p55 but does prolong EGF-stimulated ERK-1 and -2 activation. Rapamycin, which blocks anisomycin-stimulated p70/85S6k activation without affecting nuclear responses, has no effect on p45 or p55 kinase. p45 and p55 are activable by okadaic acid or UV irradiation, and both kinases phosphorylate the c-Jun NH2-terminal peptide 1-79, putatively placing them within c-Jun NH2-terminal kinase/stress-activated protein kinase (JNK/SAPK) subfamily of MAP kinases. Thus, the EGF- and anisomycin-activated kinases p45 and p55 are strongly implicated in signalling to c-fos and c-jun, whereas the MAP kinases ERK-1 and -2 are not essential for this process.

MAPKs: new JNK expands the group

Mitogen-activated protein kinases (MAPKs) are activated by dual phosphorylation on threonine and tyrosine in response to a wide array of extracellular stimuli. In the yeast Saccharomyces cerevisiae, a series of extracellular stimuli. In the yeast Saccharomyces cerevisiae, a series of MAPK signal transduction pathways have been demonstrated to control many cellular functions. By contrast, mammalian MAPKs are more poorly understood. However, recent studies have established important roles for three separate groups of mammalian MAPKs, which are characterized by distinct dual phosphorylation motifs. Together, these protein kinases mediate signal transduction in mammalian tissues and control many aspects of cellular physiology.

Anisomycin-activated protein kinases p45 and p55 but not mitogen-activated protein kinases ERK-1 and -2 are implicated in the induction of c-fos and c-jun

Independent of its ability to block translation, anisomycin intrinsically initiates intracellular signals and immediate-early gene induction [L. C. Mahadevan and D. R. Edwards, Nature (London) 349:747-749, 1991]. Here, we characterize further its action as a potent, selective signalling agonist. In-gel kinase assays show that epidermal growth factor (EGF) transiently activates five kinases: the mitogen-activated protein (MAP) kinases ERK-1 and -2, and three others, p45, p55, and p80. Anisomycin, at inhibitory and subinhibitory concentrations, does not activate ERK-1 and -2 but elicits strong sustained activation of p45 and p55, which are unique in being serine kinases whose detection is enhanced with poly-Glu/Tyr or poly-Glu/Phe copolymerized in these gels. Translational arrest using emetine or puromycin does not activate p45 and p55 but does prolong EGF-stimulated ERK-1 and -2 activation. Rapamycin, which blocks anisomycin-stimulated p70/85S6k activation without affecting nuclear responses, has no effect on p45 or p55 kinase. p45 and p55 are activable by okadaic acid or UV irradiation, and both kinases phosphorylate the c-Jun NH2-terminal peptide 1-79, putatively placing them within c-Jun NH2-terminal kinase/stress-activated protein kinase (JNK/SAPK) subfamily of MAP kinases. Thus, the EGF- and anisomycin-activated kinases p45 and p55 are strongly implicated in signalling to c-fos and c-jun, whereas the MAP kinases ERK-1 and -2 are not essential for this process.

Examination of the natural protein substrates affected by staurosporine in the developing cerebral cortex

The protein substrates affected by staurosporine (SP), the most potent inhibitor of protein kinases yet described, are unknown. In order to approach this problem we incubated cerebral cortex tissue with 0, 20, 50 and 100 nM of SP using [32P]orthophosphate as radioactive precursor. The analysis of the phosphoproteins were made with a modified high resolution two dimensional gel electrophoresis, followed by autoradiography. We detected several proteins affected by SP. Specially noticeable was an approximately 55 kDa protein which strikingly diminished the intensity of phosphorylation. However, the reverse phenomenon was also observed. To the best of our knowledge this is the first examination of protein substrates affected by SP in intact tissue.

Signal transduction. Switching off MAP kinases

Protein phosphatases have recently been identified that inactivate MAP kinases and turn off intracellular signalling pathways. Their regulation may determine the response of cells to stimuli that signal via MAP kinases.