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Volume 272, Number 17, Issue of April 25, 1997 pp. 11518-11525
©1997 by The American Society for Biochemistry and Molecular Biology, Inc.

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Bromocriptine Transcriptionally Activates the Multidrug Resistance Gene (pgp2/mdr1b) by a Novel Pathway

(Received for publication, November 11, 1996, and in revised form, February 10, 1997)

Katryn N. Furuya , Jaideep V. Thottassery ^¶ , Erin G. Schuetz ^¶ , Mohammed Sharif and John D. Schuetz ^¶

From the  Department of Pediatrics and The Research Institute, The Hospital for Sick Children, Toronto, Ontario, Canada M5G 1X and the Departments of ^¶ Pharmaceutical Sciences and  Molecular Pharmacology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105

The P-glycoprotein (Pgp) reversing agent, reserpine, induces MDR1 mRNA and PGP protein in human colon carcinoma cells (Schuetz, E. G., Beck, W. T., and Schuetz, J. D. (1996) Mol. Pharmacol. 49, 311-318) and in H35 rat hepatoma cells. Reserpine's interference with cellular dopamine utilization suggested that dopamine and dopaminergics might be important physiological regulators of PGP expression. Initial studies demonstrated that the H35 cells express the D2 dopamine receptor. Pgp protein and pgp2/mdr1b mRNA was increased (maximum of 10- and 8-fold, respectively) by the potent D2 dopamine receptor agonists bromocriptine, R()-propylnorapomorphine hydrochloride, and quinpirole, and Pgp protein induction was blocked by D2 receptor antagonists spiperone and clozapine. D2 receptor agonist induction of pgp2/mdr1b mRNA was paralleled by transcriptional activation of the pgp2/mdr1b promoter but blocked by pretreatment with the D2 dopamine receptor antagonists, spiperone, eticlopride, and clozapine. Co-transfection of a D2 dopamine receptor expression vector enhanced bromocriptine's transcriptional activation of the pgp2/mdr1b promoter. The G-protein, G_i2, is required for bromocriptine transcriptional activation because the G-protein inhibitor, pertussis toxin, suppressed bromocriptine's activation of pgp2/mdr1b transcription and co-transfection of a dominant negative G_i2 abrogated bromocriptine activation of pgp2/mdr1b. G_i proteins can transduce signals by activation of mitogen-activated protein kinases (MAPKs), and because Raf-1 is a known activator of MDR1, we tested for Raf-1 involvement. Co-transfection of a dominant negative Raf-1 failed to block bromocriptine induction of pgp2/mdr1b, and bromocriptine treatment caused no phosphorylation of the MAP kinase kinase substrates p42 and p44, demonstrating that the MAP kinase pathway was not involved. These are the first studies demonstrating transcriptional activation of an MDR gene by dopamine receptor agonists and that this activation occurs by a signal transduction pathway requiring the D2 dopamine receptor coupled to a functional G-protein.

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