Biomedical subjects

C Kroner

Publications and source records attributed to C Kroner.

8 recordsLinked to original sources

PubMed2000

Dual regulation of platelet protein kinase B.

Protein kinase B (PKB) is a serine/threonine kinase that is activated by growth hormones and implicated in prevention of apoptosis, glycogen metabolism, and glucose uptake. A key enzyme in PKB activation is phosphatidylinositide 3-kinase (PI-3K), which triggers the dual phosphorylation of PKB by phosphatidylinositol-dependent kinases (PDKs). Here we report that the major PKB subtype in platelets is PKBalpha, which is activated by phosphorylation of Thr(308) and Ser(473) and has a constitutively phosphorylated Thr(450) that does not contribute to PKB activation. alpha-Thrombin and thrombopoietin activate PKBalpha via PI-3K and trigger the concurrent phosphorylation of Thr(308) (via PDK1) and Ser(473) (via a not yet identified PDK2). In addition, alpha-thrombin activates a PI-3K-independent pathway involving phospholipase Cbeta and calcium-dependent protein kinase C subtypes (PKCalpha/beta). This route is specific for phosphorylation of Ser(473) and can be initiated by direct PKC activation with phorbol ester or purified active PKC catalytic fragment in platelet lysate. Different degrees of Ser(473) and Thr(308) phosphorylation correlate with different degrees of enzyme activity. These data reveal a PI-3K-independent PKB activation in which PKCalpha/beta regulates the phosphorylation of Ser(473) in PKBalpha. The independent control of the two phosphorylation sites may contribute to fine regulation of PKBalpha activity.

Blood Platelets↗

PubMed2000

Cyclic adenosine monophosphate signaling in the rat vomeronasal organ: role of an adenylyl cyclase type VI.

The present study indicates that male rat urinary components in female rat vomeronasal organ microvillar preparations not only induce a rapid and transient IP(3) signal, but in addition, the level of cAMP decreases with a delayed and sustained time course. This decrease seems to be a consequence of the preceding activation of the phosphoinositol pathway rather than the result of an enhanced phosphodiesterase activity or an inhibition of adenylyl cyclase (AC) via Galpha(i) or Galpha(o). This notion is supported by the finding that activation of the endogenous protein kinase C suppresses basal as well as forskolin-induced cAMP formation. Furthermore, it was observed that elevated levels of calcium inhibit cAMP formation in rat VNO microvillar preparations. These properties of cAMP signaling in the VNO of rats may be mediated by a calcium- and protein kinase C-inhibited AC VI subtype, which is localized in microvillar preparations of the VNO.

Adenylyl Cyclases↗

PubMed1998

Odorants selectively activate distinct G protein subtypes in olfactory cilia.

Chemoelectrical signal transduction in olfactory neurons appears to involve intracellular reaction cascades mediated by heterotrimeric GTP-binding proteins. In this study attempts were made to identify the G protein subtype(s) in olfactory cilia that are activated by the primary (odorant) signal. Antibodies directed against the alpha subunits of distinct G protein subtypes interfered specifically with second messenger reponses elicited by defined subsets of odorants; odor-induced cAMP-formation was attenuated by Galphas antibodies, whereas Galphao antibodies blocked odor-induced inositol 1,4, 5-trisphosphate (IP3) formation. Activation-dependent photolabeling of Galpha subunits with [alpha-32P]GTP azidoanilide followed by immunoprecipitation using subtype-specific antibodies enabled identification of particular individual G protein subtypes that were activated upon stimulation of isolated olfactory cilia by chemically distinct odorants. For example odorants that elicited a cAMP response resulted in labeling of a Galphas-like protein, whereas odorants that elicited an IP3 response led to the labeling of a Galphao-like protein. Since odorant-induced IP3 formation was also blocked by Gbeta antibodies, activation of olfactory phospholipase C might be mediated by betagamma subunits of a Go-like G protein. These results indicate that different subsets of odorants selectively trigger distinct reaction cascades and provide evidence for dual transduction pathways in olfactory signaling.

Acetates↗

PubMed1998

Identification of a phospholipase C beta subtype in rat taste cells.

From rat circumvallate papillae a novel phospholipase C (PLC) subtype has been cloned and identified as most closely related to human PLC beta2. The corresponding mRNA was only detected in sensory lingual tissue but not in non-taste lingual tissue or any other tissues examined by Northern blot analysis. In situ hybridization revealed that a subset of taste receptor cells of circumvallate papillae was specifically labeled. A functional involvement of this PLC beta subtype in taste signal transduction emerged from biochemical analysis monitoring the second messenger response in circumvallate preparations induced by denatonium benzoate. This bitter agent elicited a rapid and transient increase of the inositol 1,4,5-trisphosphate level; this response was blocked by U73122, a potent inhibitor of PLC, and by PLC beta2-specific antibodies. These data indicate that a phospholipase C beta2 isoform mediates a denatonium benzoate-induced second messenger response of taste sensory cells in the circumvallate papillae.

Amino Acid Sequence↗

PubMed1996

Pheromone-induced second messenger signaling in the hamster vomeronasal organ.

Compounds present in estrous hamster vaginal discharge modulate male attraction and mounting behavior. These compounds are differentially processed by chemosensory neurons in the main olfactory epithelium (MOE) and vomeronasal organ (VNO). The transduction cascade responsible for this processing is unclear in the VNO, although studies of the MOE suggest that the second messengers cAMP or IP3 may be involved. Here we demonstrate that purified aphrodisin, a hamster mounting pheromone, modulates IP3 production in male VNO membranes without altering cAMP production. Aphrodisin does not alter the concentration of either second messenger in membranes from the MOE. These results confirm the specificity of the VNO in the processing of mounting pheromones and establishes the importance of IP3 cascades in mammalian reproductive behavior.

Animals↗

PubMed1996

Phosphatase 2A regulates the responsiveness of olfactory cilia.

The odorant-induced second messenger response in olfactory cilia was monitored in the presence of phosphatase modulators. Okadaic acid, a phosphatase inhibitor, attenuated the odorant-induced cAMP-response in a dose-dependent manner, half maximal inhibition was obtained at 1.5 nM okadaic acid indicating that phosphatase 2A may be involved. Protamine, a selective activator of phosphatase 2A, led to significantly stronger cAMP-responses. Western blot and immunohistochemical analysis employing specific antibodies revealed that phosphatase 2A is present in olfactory tissues in particular in olfactory cilia. The results suggest that phosphatase 2A may play a regulatory role in governing the responsiveness of olfactory neurons.

Animals↗

PubMed1996

Regulation of olfactory signalling via cGMP-dependent protein kinase.

Strong odor stimuli elicit a slow and sustained increase of the cGMP concentration in isolated rat olfactory cilia. Elevated cGMP levels appear to attenuate the primary response to odorant stimulation. Incubating cilia with membrane-permeable cGMP derivates caused a significantly reduced cAMP signal in response to odorant stimulation. This inhibitory effect was mimicked by 8-(4-chlorophenlythio)-cGMP, a selective activator of cGMP-activated protein kinases; in contrast, a selective inhibitor, [8-(4-chlorophenylthio)-guanosine-3',5'-cyclic monophosphorothioate] of cGMP kinases enhanced the reactivity to odorant stimulation. The data suggest that the responsiveness of olfactory sensory cells is governed by a cGMP-dependent protein kinase. Western-blot analysis using subtype-specific antibodies indicated that cytosolic type-I cGMP kinase, but not the membrane-associated type-II cGMP kinase, is expressed in olfactory sensory neurons.

Animals↗

PubMed1996

Calcium controls second-messenger signalling in olfactory cilia.

The increase in intracellular calcium concentration elicited by odorant stimulation seems to be involved in down-regulating the responsiveness of olfactory neurons to subsequent stimuli. The present study suggests that this regulatory effect may be due to a calcium-dependent attenuation of the olfactory signalling cascade; the odor-induced cyclic adenosine monophosphate (cAMP) response in olfactory cilia is diminished by calcium in a dose-dependent manner. This reduced cAMP signal is not due to an activation of phosphodiesterases by elevated calcium levels, but rather seems to be mediated by the inhibition of adenylate cyclase by calcium ions.

1-Methyl-3-isobutylxanthine↗