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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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Evidence of another P-gp-CNTF-independent-regulation pathway. a) Addition of IFNγ at 300 U/ml in the culture medium induces an increase of the P-gp cellular level (+48.42% ± 30). This increase remains unchanged by the addition of the hLIF05, partial LIF receptor inhibitor at two concentrations (+69% ± 35 at 0.5 μg/ml and +76% ± 30 at 5 μg/ml). b) The same effect is observed in CNTF-deficient astrocyte culture. Addition of IFNγ at the same concentration induces a major significant increase of P-gp cellular level (+252% ± 68, factorial ANOVA significant at 95%, t-test p < 0.01**).
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Figure 6: Evidence of another P-gp-CNTF-independent-regulation pathway. a) Addition of IFNγ at 300 U/ml in the culture medium induces an increase of the P-gp cellular level (+48.42% ± 30). This increase remains unchanged by the addition of the hLIF05, partial LIF receptor inhibitor at two concentrations (+69% ± 35 at 0.5 μg/ml and +76% ± 30 at 5 μg/ml). b) The same effect is observed in CNTF-deficient astrocyte culture. Addition of IFNγ at the same concentration induces a major significant increase of P-gp cellular level (+252% ± 68, factorial ANOVA significant at 95%, t-test p < 0.01**).

Mentions: Besides the IL-6 family of cytokines, the only compound to trigger P-gp overexpression in astrocytes was IFNγ (Fig. 6a). This IFNγ effect was very likely direct since hLIF05, which inhibits the LIF receptor pathway, could not reverse it.


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)

Evidence of another P-gp-CNTF-independent-regulation pathway. a) Addition of IFNγ at 300 U/ml in the culture medium induces an increase of the P-gp cellular level (+48.42% ± 30). This increase remains unchanged by the addition of the hLIF05, partial LIF receptor inhibitor at two concentrations (+69% ± 35 at 0.5 μg/ml and +76% ± 30 at 5 μg/ml). b) The same effect is observed in CNTF-deficient astrocyte culture. Addition of IFNγ at the same concentration induces a major significant increase of P-gp cellular level (+252% ± 68, factorial ANOVA significant at 95%, t-test p < 0.01**).
© Copyright Policy
Related In: Results  -  Collection

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Figure 6: Evidence of another P-gp-CNTF-independent-regulation pathway. a) Addition of IFNγ at 300 U/ml in the culture medium induces an increase of the P-gp cellular level (+48.42% ± 30). This increase remains unchanged by the addition of the hLIF05, partial LIF receptor inhibitor at two concentrations (+69% ± 35 at 0.5 μg/ml and +76% ± 30 at 5 μg/ml). b) The same effect is observed in CNTF-deficient astrocyte culture. Addition of IFNγ at the same concentration induces a major significant increase of P-gp cellular level (+252% ± 68, factorial ANOVA significant at 95%, t-test p < 0.01**).
Mentions: Besides the IL-6 family of cytokines, the only compound to trigger P-gp overexpression in astrocytes was IFNγ (Fig. 6a). This IFNγ effect was very likely direct since hLIF05, which inhibits the LIF receptor pathway, could not reverse it.

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