H-89 inhibits collagenase induction by phorbol ester through a mechanism that does not involve protein kinase A

Identification of clustered phosphorylation sites in PKD2L1: how PKD2L1 channel activation is regulated by cyclic adenosine monophosphate signaling pathway

Polycystic kidney disease 2-like-1 (PKD2L1), or polycystin-L or TRPP2, formerly TRPP3, is a transient receptor potential (TRP) superfamily member. It is a calcium-permeable non-selective cation channel that regulates intracellular calcium concentration and thereby calcium signaling. PKD2L1 has been reported to take part in hedgehog signaling in renal primary cilia and sour tasting coupling with PKD1L3. In addition to the previous reports, PKD2L1 is recently found to play a crucial role in localization with β2-adrenergic receptor (β2AR) on the neuronal primary cilia. The disruption of PKD2L1 leads to the loss of β2AR on the primary cilia and reduction in intracellular concentration of cyclic adenosine monophosphate (cAMP). Since the role of cAMP and PKA is frequently mentioned in the studies of PKD diseases, we investigated on the mechanism of cAMP regulation in relation to the function of PKD2L1 channel. In this study, we observed the activity of PKD2L1 channel increased by the downstream cascades of β2AR and found the clustered phosphorylation sites, Ser-682, Ser-685, and Ser-686 that are significant in the channel regulation by phosphorylation.

Opposite effects of two PKA inhibitors on cAMP inhibition of IGF-I-induced oligodendrocyte development: a problem of unspecificity?

The stimulatory effect of insulin-like growth factor I (IGF-I) on myelin basic protein (MBP) expression, a parameter for oligodendrocyte development, is mediated by the MAPK and PI3K signaling pathways. We have previously shown that the second messenger cAMP inhibits IGF-I-induced MAPK activation as well as MBP expression. We also showed that the PKA inhibitor Rp-cAMPS reverted the cAMP effect on IGF-I-induced MBP without affecting the cAMP effect on IGF-I-induced MAPK activation. Here we report that, in contrast to Rp-cAMPS, H89 (a PKA inhibitor structurally non-related to Rp-cAMPS) enhances both the inhibitory effect of cAMP on IGF-I-induced MBP expression and the inhibitory effect of cAMP on IGF-I-induced MAPK activation. Likewise, H89 is capable of inhibiting the IGF-I-induced MAPK activation in the absence of PKA stimulation. Thus, we hypothesize that an unspecific action of H89 on a target located upstream MAPK could account for the discrepancies between the effects elicited by Rp-cAMPS and H89.

The many faces of H89: a review

H89 is marketed as a selective and potent inhibitor of protein kinase A (PKA). Since its discovery, it has been used extensively for evaluation of the role of PKA in the heart, osteoblasts, hepatocytes, smooth muscle cells, neuronal tissue, epithelial cells, etc. Despite the frequent use of H89, its mode of specific inhibition of PKA is still not completely understood. It has also been shown that H89 inhibits at least 8 other kinases, while having a relatively large number of PKA-independent effects which may seriously compromise interpretation of data. Thus, while recognizing its kinase inhibiting properties, it is advised that H89 should not be used as the single source of evidence of PKA involvement. H-89 should be used in conjunction with other PKA inhibitors, such as Rp-cAMPS or PKA analogs.

Activation of stimulatory heterotrimeric G proteins increases glutathione and protects neuronal cells against oxidative stress

Oxidative glutamate toxicity in the neuronal cell line HT22 is a model for cell death by oxidative stress, where an excess of extracellular glutamate inhibits import of cystine, a building block of the antioxidant glutathione. The subsequent decrease in glutathione then leads to the accumulation of reactive oxygen species (ROS) and programmed cell death. We used pharmacological compounds known to interact with heterotrimeric G-protein signalling and studied their effects on cell survival, morphology, and intracellular events that ultimately lead to cell death. Cholera toxin and phorbol esters were most effective and prevented cell death through independent pathways. Treating HT22 cells with cholera toxin attenuated the glutamate-induced accumulation of ROS and calcium influx. This was, at least in part, caused by an increase in glutathione due to improved uptake of cystine mediated by the induction of the glutamate/cystine-antiporter subunit xCT or, additionally, by the up-regulation of the antiapoptotic protein Bcl-2. Gs activation also protected HT22 cells from hydrogen peroxide or inhibition of glutathione synthesis by buthionine sulfoximine, and immature cortical neurones from oxidative glutamate toxicity. Thus, this pathway might be more generally implicated in protection from neuronal death by oxidative stress.

Inhibition of 12-O-tetradecanoylphorbol-13-acetate induction of c-fos mRNA by the protein kinase A inhibitor N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinoline sulfonamide

The tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) can induce expression of many immediate-early genes, such as c-fos and c-jun. In this study, TPA increased c-fos mRNA, cellular cyclic AMP, and protein kinase A (PKA) activity in the first 30 min with similar inductive time courses. Treatment of NIH 3T3 cells with N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinoline sulfonamide (H-89), a PKA specific inhibitor, suppressed TPA induction of PKA activity and c-fos mRNA in a concentration-dependent manner, but did not inhibit serum-induced transcription. H-89 did not inhibit TPA and serum induction of c-jun mRNA. H-89 interfered with TPA-stimulated serum-responsive element-binding activity in a concentration-dependent manner, but did not inhibit TPA-induced mitogen-activated protein kinase 1/2 activity or Elk-1 phosphorylation. TPA stimulation of a c-fos promoter reporter construct was inhibited by overexpression of the dominant negative regulatory protein of PKA. In deletion studies, the H-89 inhibitory element was found to be localized between -563 and -379 in the c-fos promoter region. These results suggest that H-89 will be very useful for investigating the molecular mechanism of TPA induction of c-fos.

Signal transduction in fibroblasts stably transformed by [Val12]Ras--the activities of extracellular-signal-regulated kinase and Jun N-terminal kinase are only moderately increased, and the activity of the delta-inhibitor of c-Jun is not alleviated

Ras-transformed cells often show high levels of expression of activating protein-1 and Ets and of genes regulated by these transcription factors. In analogy with the effects of transient stimulation of Ras, it is assumed that the increase in transcription-factor transactivation in stably transformed cells is due to Ras-induced constitutive activation of mitogen-activated protein kinases. However, this has not been extensively studied. Using specific substrate peptides, we have examined here the activities of two types of mitogen-activated protein kinase, extracellular-signal-regulated kinase (ERK) and Jun N-terminal kinase (JNK), in [Val12]Ras-transformed rat embryo fibroblast cell lines. These activities were elevated 2-3-fold in Ras-transformed cells compared with non-transformed cells with a similar growth rate. Increased ERK activity was not necessarily accompanied by a similar increase in JNK activity. In transformed cells, ERK and JNK activities could be stimulated fourfold and ninefold by phorbol ester and ultraviolet-light treatment, respectively, indicating that only a fraction of these enzymes were constitutively activated in these cells. It has been suggested that inactive JNK downregulates c-Jun transcriptional activity by binding to the c-Jun delta-domain. No decrease in delta-inhibitor activity could be demonstrated in Ras-transformed cells compared with control cells, consistent with the presence of mainly inactive JNK in transformed cells. Treatment of transformed cells wih benzodiazepine 5B, an inhibitor of Ras farnesylation, decreased ERK and JNK activities, and concomitantly caused morphological reversion, reduced growth rate, and normalization of transformation-related gene expression. We conclude that in stably Ras-transformed cells the moderately increased ERK/JNK activities are not coregulated, and that ERK rather than JNK activity correlated with transformation-related gene expression.