The Angiotensin II Type 1 Receptor Antagonist Losartan Affects NHE1-Dependent Melanoma Cell Behavior.

BACKGROUND/AIMS: The peptide hormone angiotensin II (ATII) plays a prominent role in regulating vasoconstriction and blood pressure. Its primary target is the angiotensin II receptor type 1 (AT1), the stimulation of which induces an increase in cytosolic [Ca2+] and calmodulin activation. Ca2+-bound (activated) calmodulin stimulates the activity of the Na+/ H+ exchanger isoform 1 (NHE1); and increased NHE1 activity is known to promote melanoma cell motility. The competitive AT1 receptor inhibitor losartan is often used to lower blood pressure in hypertensive patients. Since AT1 mediates ATII-stimulated NHE1 activity, we set out to investigate whether ATII and losartan have an impact on NHE1-dependent behavior of human melanoma (MV3) cells.

METHODS

ATII receptor expression was verified by PCR, F-actin was visualized using fluorescently labeled phalloidin, and cytosolic [Ca2+] and pH were determined ratiometrically using Fura-2 and BCECF, respectively. MV3 cell behavior was analyzed using migration, adhesion, invasion and proliferation assays.

RESULTS

MV3 cells express both AT1 and the angiotensin II receptor type 2 (AT2). Stimulation of MV3 cells with ATII increased NHE1 activity which could be counteracted by both losartan and the Ca2+/ calmodulin inhibitor ophiobolin-A. ATII stimulation induced a decrease in MV3 cell migration and a more spherical cell morphology accompanied by an increase in the density of F-actin. Independently of the presence of ATII, both NHE1 and migratory activity were reduced when AT1 was blocked by losartan. On the other hand, losartan clearly increased cell adhesion to, and the invasion of, a collagen type I substrate. The AT2 inhibitor PD123319 did not affect NHE1 activity, proliferation and migration, but increased adhesion and invasion.

CONCLUSION

Losartan inhibits NHE1 activity and the migration of human melanoma cells. At the same time, losartan promotes MV3 cell adhesion and invasion. The therapeutic use of AT1 antagonists (sartans) in hypertensive cancer patients should therefore be given critical consideration.