cAMP-mediated Growth Inhibition in Fibroblasts Is Not Mediated via Mitogen-activated Protein (MAP) Kinase (ERK) Inhibition. cAMP-DEPENDENT PROTEIN KINASE INDUCES A TEMPORAL SHIFT IN GROWTH FACTOR-STIMULATED MAP KINASES (original) (raw)
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cAMP abrogates the p21ras-mitogen-activated protein kinase pathway in fibroblasts
The mechanism by which CAMP inhibits growth factor-induced DNA synthesis in fibroblasts is not understood. Here we show that in Rat-1 fibroblasts, C A M Praising agents inhibit p21"mediated mitogenactivated protein ( M A P ) kinase activation induced by either epidermal growth factor or lysophosphatidic acid. Under the same conditions, however, epidermal growth factoror lysophosphatidic acid-induced protein tyrosine phosphorylation, Ca2+ mobilization, and activation of Na+M+ exchange are not attenuated. In ras-transformed Rat-1 cells, 8-bromo-CAMP rapidly deactivates constitutively active MAP kinase without reducing p21".GTP levels; long term 8-bromo-CAMP treatment of these cells leads to growth arrest and reversion of the transformed phenotype. These results show that elevation of intracellular CAMP levels abrogates the p21-MAP kinase pathway at a step downstream of p21" activation. This finding provides a molecular basis for the growth-inhibitory action of CAMP in normal and transformed fibroblasts.
British journal of cancer, 1999
The growth factor-activated mitogenic pathways are often disregulated in tumour cells and, therefore, they can provide specific molecular targets for novel anti-tumour approaches. 8-Chloro-cAMP (8-Cl-cAMP), a synthetic cAMP analogue, is a novel anti-tumour agent that has recently undergone clinical evaluation. We investigated the effects of 8-Cl-cAMP on the epidermal growth factor (EGF)/EGF receptor (EGF-R) signalling in human epidermoid cancer KB cells, which are responsive to the mitogenic stimulus of EGF. We found that the growth-promoting activity of EGF was completely abolished when EGF treatment was performed in combination with 8-Cl-cAMP. The inhibition of the EGF-induced proliferation by 8-Cl-cAMP was paralleled by the blockade of the EGF-stimulated activation of mitogen-activated protein kinases (MAPK), ERK-1 and ERK-2. Conversely, we found an increase of EGF-R expression and EGF-R tyrosine phosphorylation when KB cells were growth inhibited by 8-Cl-cAMP. Moreover, the acti...
cAMP stimulates protein kinase B in a Wortmannin‐insensitive manner
FEBS Letters, 1997
Activation of protein kinase B (PKB) by growth factors has been demonstrated to proceed via phosphatidylinositol 3‐kinase (PI3‐kinase). Here, we show that agents which raise intracellular cAMP can also stimulate PKB. However, this effect is not sensitive to wortmannin, indicating that it is PI3‐kinase independent. This activation does not appear to result from direct phosphorylation by protein kinase A (PKA) since GST–PKB is not an effective PKA substrate. In addition, the activation pathway of PKB by cAMP seems to be linked to that of growth factors, albeit downstream of PI3‐kinase. Evidence for this is that a constitutive active PKB, T308D, S473D, containing activating mutations in the serine and threonine residues which are phosphorylated subsequent to PI3‐kinase activation, cannot be further stimulated by cAMP elevations. Hence, these data suggest that, in addition to growth factors, cAMP can also lead to activation of PKB. This cAMP stimulatory action appears to require phospho...
Endocrinology, 1997
The mitogen-activated protein kinase (MAP kinase) is a key participant in growth factor-stimulated intracellular events such as proliferation and differentiation. We and others have previously described a cross-talk between the MAP kinase pathway and the cAMP pathway. Indeed, in several cell lines and, in particular in fibroblasts, an increase in the level of cAMP produced an inhibition of MAP kinase together with decreased cell proliferation. In contrast, in PC12 cells, cAMP induced an increase in the NGF-induced activation of MAP kinase concomitantly with augmented NGF-induced differentiation. Therefore, it has been proposed that the cellular context is important for the nature of the cAMP effects on growth factor-stimulated MAP kinase activity. Here we show that the type of tyrosine kinase receptor stimulated also participates in the nature of the cAMP effect. Thus, in NIH3T3 fibroblasts expressing NGF receptors (NIH3T3/trk cells) we found that cAMP potentiates NGF-stimulated ERK1 and MEK1
Febs Letters, 1995
In PC12 cells, cAMP stimulates the MAP kinase pathway by an unknown mechanism. Firstly, we examined the role of calcium ion mobilization and of protein kinase C in cAMPstimulated MAP kinase activation. We show that cAMP stimulates p44 mapk independently of these events. Secondly, we studied the role of B-Raf in this process. We observed that NGF, PMA and cAMP induce the phosphorylation of B-Raf as well as an upward shift in its electrophoretic mobility. We show that B-Raf is activated following NGF and PMA treatment of PC12 cells, and that it can phosphorylate and activate MEK-1. However, cAMP inhibits B-Raf autokinase activity as well as its ability to phosphorylate and activate MEK-1. This inhibition is likely to be due to a direct effect since we found that PKA phosphorylates B-Raf in vitro. Further, we show that B-Raf binds to p21 ras, but more important, this binding to p21 ras is virtually abolished with B-Raf from PCI2 cells treated with CPT-cAMP. Hence, these data indicate that the PKA-mediated phosphorylation of B-Raf hampers its interaction with p21 ras, which is responsible for the PKA-mediated decrease in B-Raf activity. Finally, our work suggests that in PC12 cells, cAMP stimulates MAP kinase through the activation of an unidentified MEK kinase and/or the inhibition of a MEK phosphatase.