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Astroglial expression of the P-glycoprotein is controlled by intracellular CNTF.

Monville C, Fages C, Feyens AM, D'Hondt V, Guillet C, Vernallis A, Gascan H, Peschanski M - BMC Cell Biol. (2002)

Bottom Line: Surprisingly, most factors that are known to induce astroglial activation in astroglial cultures failed to increase P-gp expression.The only effective proteins were IFNgamma and those belonging to the IL-6 family of cytokines (IL-6, LIF, CT-1 and CNTF).These results reveal two different pathways regulating P-gp expression and activity in reactive astrocytes, one of which depends upon the intracellular concentration of CNTF.

View Article: PubMed Central - HTML - PubMed

Affiliation: INSERM U421/IM3, Créteil, France. monvillec@cf.ac.uk

ABSTRACT

Background: The P-glycoprotein (P-gp), an ATP binding cassette transmembrane transporter, is expressed by astrocytes in the adult brain, and is positively modulated during astrogliosis. In a search for factors involved in this modulation, P-gp overexpression was studied in long-term in vitro astroglial cultures.

Results: Surprisingly, most factors that are known to induce astroglial activation in astroglial cultures failed to increase P-gp expression. The only effective proteins were IFNgamma and those belonging to the IL-6 family of cytokines (IL-6, LIF, CT-1 and CNTF). As well as P-gp expression, the IL-6 type cytokines (but not IFNgamma) stimulated the expression of endogenous CNTF in astrocytes. In order to see whether an increased intracellular level of CNTF was necessary for induction of P-gp overexpression by IL-6 type cytokines, by the same cytokines analysis was carried out on astrocytes obtained from CNTF knockout mice. In these conditions, IFNgamma produced increased P-gp expression, but no overexpression of P-gp was observed with either IL-6, LIF or CT-1, pointing to a role of CNTF in the intracellular signalling pathway leading to P-gp overexpression. In agreement with this suggestion, application of exogenous CNTF (which is internalised with its receptor) produced an overexpression of P-gp in CNTF-deficient astrocytes.

Conclusion: These results reveal two different pathways regulating P-gp expression and activity in reactive astrocytes, one of which depends upon the intracellular concentration of CNTF. This regulation of P-gp may be one of the long searched for physiological roles of CNTF.

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Potentiation of IL-6 effects on P-gp expression by adding its specific α receptor subunits. Addition of soluble IL-6R induced a major potentiation of rmIL-6 whatever the concentration of the factor used.
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Figure 3: Potentiation of IL-6 effects on P-gp expression by adding its specific α receptor subunits. Addition of soluble IL-6R induced a major potentiation of rmIL-6 whatever the concentration of the factor used.

Mentions: Among the agents known to activate astrocytes ("astrogliotic factors") that were tested for modulating P-gp expression, most failed to alter it (Table 1). This was in particular the case for dBcAMP, IL-1β, LPS, NGF, RA, rhIFNα, rhTGFα and TNFα. In contrast, all the cytokines that belong to the IL-6 family induced a 50% or more increase in expression of P-gp in long-term astrocyte culture. This effect was dose-dependent and was modulated by α receptor subunits, when relevant. For instance, rrCNTF was inefficient when used alone at 30 ng/ml in long-term cultures. However, an increase in the cellular content of P-gp was observed in a significant and reproducible manner when 100, and even further 250 ng/ml of rCNTF were used (Fig. 2a). As previously described for the effects of rCNTF on other astroglial markers of differentiation [25], addition of 200 ng/ml of c-myc-sCNTFRα induced a potentiation of the effects, and an increase of P-gp cellular content was then observed with the lowest concentration of rCNTF studied (10 ng/ml), and maintained for all other concentrations used (data not shown). Addition of rhLIF and rhCT-1, in the culture medium provoked an increase of about 1.5 to 2-fold of P-gp cellular content (Fig. 2b). Addition of rmIL-6 at concentrations below 40 ng/ml in the culture medium was inefficient, but a significant increase of P-gp intracellular content was observed when this concentration was used (Fig. 2c). Addition of rhsIL-6Rα to the culture medium induced a major potentiation of the effects, since, in these conditions, all concentrations used triggered a significant increase in P-gp content (Fig. 3).


Astroglial expression of the P-glycoprotein is controlled by intracellular CNTF.

Monville C, Fages C, Feyens AM, D'Hondt V, Guillet C, Vernallis A, Gascan H, Peschanski M - BMC Cell Biol. (2002)

Potentiation of IL-6 effects on P-gp expression by adding its specific α receptor subunits. Addition of soluble IL-6R induced a major potentiation of rmIL-6 whatever the concentration of the factor used.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC117802&req=5

Figure 3: Potentiation of IL-6 effects on P-gp expression by adding its specific α receptor subunits. Addition of soluble IL-6R induced a major potentiation of rmIL-6 whatever the concentration of the factor used.
Mentions: Among the agents known to activate astrocytes ("astrogliotic factors") that were tested for modulating P-gp expression, most failed to alter it (Table 1). This was in particular the case for dBcAMP, IL-1β, LPS, NGF, RA, rhIFNα, rhTGFα and TNFα. In contrast, all the cytokines that belong to the IL-6 family induced a 50% or more increase in expression of P-gp in long-term astrocyte culture. This effect was dose-dependent and was modulated by α receptor subunits, when relevant. For instance, rrCNTF was inefficient when used alone at 30 ng/ml in long-term cultures. However, an increase in the cellular content of P-gp was observed in a significant and reproducible manner when 100, and even further 250 ng/ml of rCNTF were used (Fig. 2a). As previously described for the effects of rCNTF on other astroglial markers of differentiation [25], addition of 200 ng/ml of c-myc-sCNTFRα induced a potentiation of the effects, and an increase of P-gp cellular content was then observed with the lowest concentration of rCNTF studied (10 ng/ml), and maintained for all other concentrations used (data not shown). Addition of rhLIF and rhCT-1, in the culture medium provoked an increase of about 1.5 to 2-fold of P-gp cellular content (Fig. 2b). Addition of rmIL-6 at concentrations below 40 ng/ml in the culture medium was inefficient, but a significant increase of P-gp intracellular content was observed when this concentration was used (Fig. 2c). Addition of rhsIL-6Rα to the culture medium induced a major potentiation of the effects, since, in these conditions, all concentrations used triggered a significant increase in P-gp content (Fig. 3).

Bottom Line: Surprisingly, most factors that are known to induce astroglial activation in astroglial cultures failed to increase P-gp expression.The only effective proteins were IFNgamma and those belonging to the IL-6 family of cytokines (IL-6, LIF, CT-1 and CNTF).These results reveal two different pathways regulating P-gp expression and activity in reactive astrocytes, one of which depends upon the intracellular concentration of CNTF.

View Article: PubMed Central - HTML - PubMed

Affiliation: INSERM U421/IM3, Créteil, France. monvillec@cf.ac.uk

ABSTRACT

Background: The P-glycoprotein (P-gp), an ATP binding cassette transmembrane transporter, is expressed by astrocytes in the adult brain, and is positively modulated during astrogliosis. In a search for factors involved in this modulation, P-gp overexpression was studied in long-term in vitro astroglial cultures.

Results: Surprisingly, most factors that are known to induce astroglial activation in astroglial cultures failed to increase P-gp expression. The only effective proteins were IFNgamma and those belonging to the IL-6 family of cytokines (IL-6, LIF, CT-1 and CNTF). As well as P-gp expression, the IL-6 type cytokines (but not IFNgamma) stimulated the expression of endogenous CNTF in astrocytes. In order to see whether an increased intracellular level of CNTF was necessary for induction of P-gp overexpression by IL-6 type cytokines, by the same cytokines analysis was carried out on astrocytes obtained from CNTF knockout mice. In these conditions, IFNgamma produced increased P-gp expression, but no overexpression of P-gp was observed with either IL-6, LIF or CT-1, pointing to a role of CNTF in the intracellular signalling pathway leading to P-gp overexpression. In agreement with this suggestion, application of exogenous CNTF (which is internalised with its receptor) produced an overexpression of P-gp in CNTF-deficient astrocytes.

Conclusion: These results reveal two different pathways regulating P-gp expression and activity in reactive astrocytes, one of which depends upon the intracellular concentration of CNTF. This regulation of P-gp may be one of the long searched for physiological roles of CNTF.

Show MeSH