β3-adrenergic receptor activity modulates melanoma cell proliferation and survival through nitric oxide signaling

We have recently shown in B16F10 melanoma cells that blockade of beta 3-adrenergic receptors (beta 3-ARs) reduces cell proliferation and induces apoptosis, likely through the involvement of nitric oxide (NO) signaling. Here, we tested the hypothesis that the effects of beta 3-AR blockade on melanoma cells are mainly mediated by a decrease in the activity of the NO pathway, possibly due to reduced expression of inducible NO synthase (iNOS). B16F10 cells were used. Nitrite production, iNOS expression, cell proliferation, and apoptosis were evaluated. beta 3-AR blockade with L-748,337 reduced basal nitrite production, while beta 3-AR stimulation with BRL37344 increased it. The effects of beta 3-AR blockade were prevented by NOS activation, while the effects of beta 3-AR activation were prevented by NOS inhibition. Treatments increasing nitrite production also increased iNOS expression, while treatments decreasing nitrite production reduced iNOS expression. Among the different NOS isoforms, experiments using L-748,337 or BRL37344 with activators or inhibitors targeting specific NOS isoforms demonstrated a prominent role of iNOS in nitrite production. beta 3-AR blockade decreased cell proliferation and induced apoptosis, while beta 3-AR activation had the opposite effects. The effects of beta 3-AR blockade/activation were prevented by iNOS activation/inhibition, respectively. Taken together, these results demonstrate that iNOS-produced NO is a downstream effector of beta 3-ARs and that the beneficial effects of beta 3-AR blockade on melanoma B16F10 cell proliferation and apoptosis are functionally linked to reduced iNOS expression and NO production. Although it is difficult to extrapolate these data to the clinical setting, the targeted inhibition of the beta 3-AR-NO axis may offer a new therapeutic perspective to treat melanomas.