Phorbol Myristate Acetate and 8‐Bromo‐Cyclic AMP‐Induced Phosphorylation of Glial Fibrillary Acidic Protein and Vimentin in Astrocytes: Comparison of Phosphorylation Sites

Harrison, Beth C.; Mobley, Philip L.

doi:10.1111/j.1471-4159.1991.tb02073.x

Cited by 41 publications

(22 citation statements)

References 22 publications

(14 reference statements)

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“…To determine the mechanism underlying the glutamate inhibition of glial stellation, we examined the effect of glutamate on CAMP formation. Our data indicated that the effect of glutamate was not a result of CAMP regulation since 1) glutamate only inhibited a small fraction of ISO-induced CAMP formation compared to NE and 2) glutamate also blocked the stellation induced by PMA which activates protein kinase C rather than CAMP-dependent protein kinase (Harrison and Mobley, 1991 ).…”

Section: Mechanism Of the Glutamate Inhibition Of Glial Stellationmentioning

confidence: 70%

Glutamate blocks astroglial stellation: Effect of glutamate uptake and volume changes

Shao

Enkvist

McCarthy

1994

Glia

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Neurotransmitters which increase intracellular cAMP levels can cause cultured astroglia to change from a flat, polygonal shape to a stellate morphology. Little is known about how glial stellation can be regulated by other transmitters. In the present study, we demonstrated that L-glutamate blocked isoproterenol (ISO) or dibutyryl-cAMP induced stellation in astroglia. The glutamate inhibition was concentration dependent, with its maximal effect on > 90% of cells at 500 microM. Glutamate also reversed glial stellation within a short period (< 30 min). Glutamate uptake analogues, D-glutamate and D-aspartate, rather than receptor agonists, kainate and quisqualate, mimicked the glutamate effect. Likewise, the glutamate uptake blocker, D-thero-beta-hydroxyaspartate, blocked the glutamate effect. The glutamate inhibition was not a result of inhibition of cAMP formation, since norepinephrine, which inhibited 80% of ISO-stimulated cAMP, also caused glial stellation. Increases in extracellular K+ to 50 mM also reduced glial stellation, whereas 25 mM K+ had little effect. Since 25 mM K+ caused much greater depolarization than 400 microM glutamate, it was unlikely that the effects of both glutamate and high [K+] on glial stellation were due to membrane depolarization. Hypotonic treatment (120 mOsm) enhanced, whereas hypertonic treatment (520 mOsm) prevented, the glutamate reversal of glial stellation. Thus, glial swelling appeared to be a primary mechanism for the inhibitory effect of glutamate and high [K+] on glial stellation. This mechanism could also explain the observation that glutamate inhibited stellation induced by PMA, a PKC activator. Our data suggest that glutamate released from neurons during neuronal activity or pathology can be taken up by astrocytes and alter their morphology. Changes in glial morphology may in turn affect the volume and composition of the extracellular space and, as a result, neuronal activity.

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Section: Mechanism Of the Glutamate Inhibition Of Glial Stellationmentioning

confidence: 70%

Glutamate blocks astroglial stellation: Effect of glutamate uptake and volume changes

Shao

Enkvist

McCarthy

1994

Glia

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“…The field of view for these images is 205 pm. glial fibrillary acidic protein (GFAP) and vimentin contain both unique and overlapping phosphorylation sites for both PKA and PKC (Harrison and Mobley, 1991), indicating that these cytoskeletal components may be important to the stellation response. However, GFAP may not be crucial to the stellation response since stellation occurs in LRM55 glioma cells (Shain et al, 1987), which do not express appreciable amounts of GFAP (Shain et al, unpublished observations).…”

Section: Introductionmentioning

confidence: 99%

Phorbol ester‐stimulated stellation in primary cultures of astrocytes from different brain regions

Davis

Turner

Szarowski

et al. 1994

Microscopy Res & Technique

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Stellation is the process by which astrocytes change from epithelial-like to process-bearing cells. Stellation occurs following activation of either cyclic AMP-dependent protein kinase or protein kinase C. This process occurs through tubulin-dependent rearrangement of the cytoskeleton. We have evaluated the ability of phorbol, 12-myristate, 13-acetate (PMA) to induce astrocyte stellation. Astrocytes from five brain regions (cerebellum, cerebral cortex, hippocampus, diencephalon, and brain-stem) were examined to determine if all astrocytes would exhibit similar responses to this activator of protein kinase C. Stellation was evaluated following cell fixation by either phase optics using conventional light microscopy, or scanning laser confocal light microscopy of cultures prepared using immunocytochemistry for tubulin and glial fibrillary acidic protein. Both the number of cells responding to PMA and the sensitivity to PMA varied for astrocytes from each brain region. PMA-induced stellation was most robust in cerebellar and brainstem astrocytes, with greater than 70% responding. Less than 40% of hippocampal and diencephalic astrocytes responded to PMA at the maximum dose (10(-5) M). PMA also induced different numbers of processes or branching patterns of processes on astrocytes from different brain regions. The protein kinase C induced stellation response in astrocytes supports the hypothesis that astrocytes contribute to neural plasticity.

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“…No phosphorylation was observed in the C-terminal fragment (1 5 kDa). In other studies in which GFAP was phosphorylated in intact cells, purified, and then cleaved with NTCB, only one band at 35 kDa was observed (Hamson and Mobley, 1991). It Tryptic peptide maps of GFAP (Fig.…”

Section: Fig 3 Tryptic Phosphopeptide Maps Of Gfap Phosphorylated Bmentioning

confidence: 85%

Phosphorylation of Glial Fibrillary Acidic Protein and Vimentin by Cytoskeletal‐Associated Intermediate Filament Protein Kinase Activity in Astrocytes

Harrison

Mobley

1992

Journal of Neurochemistry

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These studies describe a cytoskeletal-associated protein kinase activity in astrocytes that phosphorylated the intermediate filament proteins glial fibrillary acidic protein (GFAP) and vimentin and that appeared to be distinct from protein kinase C (PK-C) and the cyclic AMP-dependent protein kinase (PK-A). The cytoskeletal-associated kinase activity phosphorylated intermediate filament proteins in the presence of 10 mM MgCl2 and produced an even greater increase in 32P incorporation into these proteins in the presence of calcium/calmodulin. Tryptic peptide mapping of phosphorylated intermediate filament proteins showed that the intermediate filament protein kinase activity produced unique phosphopeptide maps, in both the presence and the absence of calcium/calmodulin, as compared to that of PK-C and PK-A, although there were some common sites of phosphorylation among the kinases. In addition, it was determined that the intermediate filament protein kinase activity phosphorylated both serine and threonine residues of the intermediate filament proteins, vimentin and GFAP. However, the relative proportion of serine and threonine residues phosphorylated varied depending on the presence or absence of calcium/calmodulin. The magnesium-dependent activity produced the highest proportion of threonine phosphorylation, suggesting that the calcium/calmodulin-dependent kinase activity acts mainly at serine residues. PK-A and PK-C phosphorylated mainly serine residues. Also, the intermediate filament protein kinase activity phosphorylated both the N-and the C-terminal domains of vimentin and the N-terminal domain of GFAP. In contrast, both PK-C and PK-A are known to phosphorylate the N-terminal domains of both proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

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Phorbol Myristate Acetate and 8‐Bromo‐Cyclic AMP‐Induced Phosphorylation of Glial Fibrillary Acidic Protein and Vimentin in Astrocytes: Comparison of Phosphorylation Sites

Cited by 41 publications

References 22 publications

Glutamate blocks astroglial stellation: Effect of glutamate uptake and volume changes

Glutamate blocks astroglial stellation: Effect of glutamate uptake and volume changes

Phorbol ester‐stimulated stellation in primary cultures of astrocytes from different brain regions

Phosphorylation of Glial Fibrillary Acidic Protein and Vimentin by Cytoskeletal‐Associated Intermediate Filament Protein Kinase Activity in Astrocytes

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