Abstract 467: Hypertension and Cancer: Are They Related?
There are literature references supporting a link between hypertension and cancer. However, a mechanism for this association has not been defined. Key players in blood pressure regulation include the dopamine-1 receptor (D1R), G protein-coupled kinase type 4 (GRK4) and c-Myc, all found in renal proximal tubule cells (RPTC). c-Myc also regulates GRK4 in the breast cancer cell line MCF7. We hypothesized that the D1R would act as a tumor suppressor and both GRK4 and c-Myc as oncogenes in MCF7 cells. GRK4 is positively regulated transcriptionally by c-Myc, and GRK4 is negatively regulated by Caveolin-1 (CAV1) in RPTCs, so we tested if the same relationship occurs in this breast cancer model. SKF38393 (D1R agonist, 10μM, 18hr) reduced wild type MCF7 (WT-MCF7) cell motility (an index of aggressive growth) by 16.0% ± 3.2 SEM (n=9; p<0.005; 115393/137330 RFU), while the D1R antagonist LE300 (10μM, 18hr) increased cell motility 23.0% ± 7.0 SEM (n=9; p<0.05; 168955/137330 RFU). CAV1, a tumor suppressor and GRK4 kinase inhibitor, is missing in MCF7, so we transfected CAV1 into MCF7 cells (CAV-MCF7) and inhibited cell motility even further following SKF38393 stimulation (29.8% ± 2.8 SEM; n=11; p<0.005 vs.WT-MCF7; 105801/150766 RFU). CAV1 binding to GRK4 was verified by co-immunoprecipitation. CAV-MCF7 also showed higher levels of basal cell surface D1R (103.3% ± 35.9 SEM; n=10; p<0.01 vs WT-MCF7; 808/397 RFU) and D1R membrane recruitment post-fenoldopam stimulation (FEN, D1R agonist, 10μM, 30min) (increase of 65.5% ± 6.18 SEM; n=4; p<0.05 vs. WT-MCF7; 1.65/1.00 RFU). We verified that CAV-MCF7 showed decreased soft agar colony growth and decreased rates of cell proliferation. Because c-Myc increases GRK4 expression, cell proliferation after c-Myc knock down (KD-MCF7) was tested. KD-MCF7 showed decreased cell proliferation at 48 hr by 37.7% ± 7.6 SEM (n=3; p<0.05 vs WT-MCF7; 2752/4416 cells), while both knockdown of c-Myc and re-expression of GRK4 restored proliferation by 23.1% ± 13.4 SEM (n=10; p<0.05 vs KDMCF; 1346/1093 cells) at 96 hr. We therefore conclude that c-Myc activation of GRK4 inactivates the dopaminergic pathway in both the kidney and breast cancer progression which may be a common link between hypertension and breast cancer.
- © 2013 by American Heart Association, Inc.