PKC

The induction of hepatic CYP1A by selected polycyclic aromatic hydrocarbons (PAHs) was followed in Atlantic salmon (Salmo salar) by measurement of CYP1A messenger RNA (mRNA), CYP1A protein levels, and catalytically by the measurement of 7-ethoxyresorufin-O-deethylase activity. There was clear correspondence between all three methods of measurement both in terms of the specificity of response to five- and some four-ring PAHs and in terms of the dose-response relationship to methyl-cholanthrene. The level of induction was compared with that measured in salmon confined in sea pens around Shetland and exposed to crude oil spilled from the Braer in January 1993. This oil was rapidly dispersed by the extreme weather (turbulence) at the time of the spill. The time course of the hepatic CYP1A induction was followed and related to the levels of oil measured in water and the concentration of PAHs determined in the flesh of the fish. Again there was a good correspondence between the different methods of measuring CYP1A expression, and the results show a rapid induction response in fish at the most contaminated sites and small, insignificant changes occurring at the reference stations. There was a clear concentration response between CYP1A and catalytic activity and between the exposure observed.

Background and purpose:  Protein kinase (PK) A and the ε isoform of PKC (PKCε) are involved in the development of hypernociception (increased sensitivity to noxious or innocuous stimuli) in several animal models of acute and persistent inflammatory pain. The present study evaluated the contribution of PKA and PKCε to the development of prostaglandin E2 (PGE2)-induced mechanical hypernociception.Experimental approach:  Prostaglandin E2-induced mechanical hypernociception was assessed by constant pressure rat paw test. The activation of PKA or PKCε was evaluated by radioactive enzymic assay in the dorsal root ganglia (DRG) of sensory neurons from the hind paws.Key results:  Hypernociception induced by PGE2 (100 ng) by intraplantar (i.pl.) injection, was reduced by i.pl. treatment with inhibitors of PKA [A-kinase-anchoring protein St-Ht31 inhibitor peptide (AKAPI)], PKCε (PKCεI) or adenylyl cyclase. PKA activity was essential in the early phase of the induction of hypernociception, whereas PKC activity was involved in the maintenance of the later phase of hypernociception. In the DRG (L4-L5), activity of PKA increased at 30 min after injection of PGE2 but PKC activity increased only after 180 min. Moreover, i.pl. injection of the catalytic subunit of PKA induced hypernociception which was markedly reduced by pretreatment with an inhibitor of PKCε, while the hypernociception induced by paw injection of PKCε agonist was not affected by an inhibitor of PKA (AKAPI).Conclusions and implications:  Taken together, these findings are consistent with the suggestion that PKA activates PKCε, which is a novel mechanism of interaction between these kinases during the development of PGE2-induced mechanical hypernociception.

Butyrate, produced in the colon by fermentation of dietary fibre, induces apoptosis in colon adenoma and cancer cell lines, which may contribute to protection against colorectal cancer. However, butyrate is present in the colon along with other dietary factors, including unconjugated bile acids, which are tumour promoters. We have shown previously that the proapoptotic effects of butyrate on AA/C1 human adenoma cells were reduced in the presence of bile acids. To determine the cellular basis of this interaction, we examined the effects of butyrate and the secondary bile acid ursodeoxycholic acid (UDCA) on signalling pathways known to regulate apoptosis using AA/C1 cells. Butyrate activated PKC-delta and p38 MAP (mitogen-activated protein) kinase, whereas UDCA activated PKC-alpha and p42/44 MAP kinase. Butyrate treatment also resulted in the caspase-3-mediated proteolysis of PKC-delta. Butyrate-induced apoptosis was reduced by inhibitors of PKC-delta (Rottlerin), p38 MAP kinase (SB20...

Nitric oxide (NO) plays an important role in innate host defense and inflammation. In response to infection, NO is generated by inducible nitric oxide synthase (iNOS), a gene product whose expression is highly modulated by different stimuli, including lipopolysaccharide (LPS) from gram-negative bacteria. We reported recently that LPS from Pseudomonas aeruginosa altered Na+ transport in alveolar epithelial cells via a suramin-dependent process, indicating that LPS activated a purinergic response in these cells. To further study this question, in the present work, we tested whether iNOS mRNA and protein expression were modulated in response to LPS in alveolar epithelial cells. We found that LPS induced a 12-fold increase in iNOS mRNA expression via a transcription-dependent process in these cells. iNOS protein, NO, and nitrotyrosine were also significantly elevated in LPS-treated cells. Ca2+ chelation and protein kinase C (PKCα-β1) inhibition suppressed iNOS mRNA induction by LPS, imp...

Several protein kinase C (PKC) isozymes were analyzed by immunoblot and immunocytochemistry in cultures of hippocampal neurones at several stages of differentiation. Our findings reveal the existence of two distinct patterns of expression. Firstly, conventional PKC isozymes α, β and γ, that are expressed at very low levels during the initial stages and then increase continuously with time of culture. Secondly, novel PKC isozymes δ, ϵ and ζ, whose contents increase very early to reach a maximum after three days of culture and then progressively decline. Specific proteolysis for PKC isozymes β and γ was observed throughout the period studied. The developmental profile obtained for the different PKC isozymes is discussed in relation to the differentiation of hippocampal neurones in culture.

Protein kinase C (PKC) is involved in a wide array of cellular processes such as cell proliferation, differentiation and apoptosis. Phosphorylation of both turn motif (TM) and hydrophobic motif (HM) are important for PKC function. Here, we show that the mammalian target of ...

Besides being involved in analgesia, δ-opioid receptors have recently been shown to exert antidepressant-like and neuroprotective effects. Glycogen synthase kinase-3β (GSK-3β), a key enzyme involved in cellular apoptosis and in mood disorders, may constitute a molecular target of δ-opioid receptors. However, relatively little is known on how δ-opioid receptors affect the multiple signaling pathways regulating GSK-3β. In the present study, we show that activation of human δ-opioid receptors stably expressed in Chinese hamster ovary (CHO) cells induced a rapid GSK-3β phosphorylation on Ser9 and a significant inhibition of the kinase activity. This effect was dependent on G proteins Gi/Go, unaffected by cell transfection with the Gβγ scavenger transducin, required the Src non-receptor tyrosine kinase and the specific involvement of the α isoform of phosphatidylinositol 3-kinase. δ-Opioid agonists activated the protein kinase Akt in a Src-dependent manner and chemical inhibition of Akt or stable expression of a dominant negative Akt1 mutant reduced the stimulation of GSK-3β phosphorylation. Moreover, δ-opioid receptor regulation of Akt and GSK-3β was dependent on transphosphorylation and transactivation of platelet-derived growth factor and insulin-like growth factor-1 receptor tyrosine kinases. AMP-activated protein kinase (AMPK) activity was also required, as δ-opioid effects on Akt and GSK-3β were mimicked by the AMPK activator A-769662 and reduced by the AMPK inhibitor Compound C. Conversely, inhibition of protein kinase C isoforms, extracellular signal-regulated protein kinases 1/2 and mammalian target of rapamycin was without effect, although the latter two kinases were activated by δ-opioid agonists. The results identify Src-dependent transactivation of receptor tyrosine kinases as a key process in δ-opioid receptor inhibitory control of GSK-3β and reveal a novel δ-opioid regulatory mechanism mediated by AMPK.This article is part of a Special Issue entitled ‘Trends in Neuropharmacology: In Memory of Erminio Costa’.► We show that δ-opioid receptors (DOR) cause GSK-3β phosphorylation and inactivation. ► The effect is dependent on Gi/Go and requires the activity of Src and PI3Kα. ► Inhibition of PDGF and IGF-1 receptor tyrosine kinases (RTK) impair the DOR effect. ► The AMPK inhibitor Compound C also attenuates DOR regulation of GSK-3β. ► We conclude that DOR-induced GSK-3β inhibition involves RTK transactivation and AMPK.