Signaling and antiproliferative effects mediated by GnRH receptors after expression in breast cancer cells using recombinant adenovirus.
GnRH receptors (GnRH-Rs) are found in human cancers, including those of the breast, and GnRH can inhibit the growth of cell lines derived from such cancers. Although pituitary and extrapituitary GnRH-R transcripts appear identical, their functional characteristics may differ. Most extrapituitary GnRH-Rs have low affinity for GnRH analogs and may not activate PLC or discriminate between agonists and antagonists in the same way as pituitary GnRH-Rs. Here we have assessed whether GnRH-Rs expressed exogenously in breast cancer cells differ from those in gonadotropes. We found no evidence for endogenous GnRH-Rs in MCF7 cells, but after infection with adenovirus expressing the GnRH-R (Ad GnRH-R) at a multiplicity of infection of 10 or greater, at least 80% expressed GnRH-Rs. These had high affinity (K(d) for [(125)I]buserelin, 1.4 nM) and specificity (rank order of potency, buserelin>GnRH>>chicken GnRH-II) and mediated stimulation of [(3)H]IP accumulation. Increasing viral titer [from multiplicity of infection, 3-300] increased receptor number (10,000-225,000 sites/cell) and [(3)H]IP responses. GnRH stimulated ERK2 phosphorylation in Ad GnRH-R-infected cells, and this effect, like stimulation of [(3)H]IP accumulation, was blocked by GnRH-R antagonists. GnRH also inhibited [(3)H]thymidine incorporation into Ad GnRH-R-infected cells (but not control cells). This effect was mimicked by agonist analogs and inhibited by two antagonists. Thus, when exogenous GnRH-Rs are expressed at density comparable to that in gonadotropes, they are functionally indistinguishable from the endogenous GnRH-Rs in gonadotropes, and increasing expression of high affinity GnRH-Rs can dramatically enhance the direct antiproliferative effect of GnRH agonists on breast cancer cells.
Everest
H M
HM
University Research Center for Neuroendocrinology, University of Bristol, Bristol, United Kingdom BS2 8HW.
Hislop
J N
JN
Harding
T
T
Uney
J B
JB
Flynn
A
A
Millar
R P
RP
McArdle
C A
CA
D000256:Adenoviridae; D001667:Binding, Competitive; D001943:Breast Neoplasms / Q000473:pathology / Q000503:physiopathology*; D002455:Cell Division / Q000502:physiology; D005260:Female; D018014:Gene Transfer Techniques; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011966:Receptors, LHRH / Q000502:physiology*; D011995:Recombination, Genetic; D015398:Signal Transduction / Q000502:physiology*; D013936:Thymidine / Q000037:antagonists & inhibitors; D014407:Tumor Cells, Cultured
D007295:Inositol Phosphates; D011966:Receptors, LHRH; D007987:Gonadotropin-Releasing Hormone; D019950:Mitogen-Activated Protein Kinase 1; D013936:Thymidine