Bombesin Receptor Subtype-3 Regulates Tumor Growth by HER2 Tyrosine Phosphorylation in a Reactive Oxygen Species-Dependent Manner in Lung Cancer Cells.

Bombesin receptor subtype-3 (BRS-3) is a type 1 G-protein-coupled receptor. BRS-3 is an orphan GPCR which is structurally related to the neuromedin B and gastrin-releasing peptide receptors. When activated, BRS-3 causes phosphatidylinositol turnover in lung cancer cells. BRS-3 stimulates tyrosine phosphorylation of the epidermal growth-factor receptor (ErbB1), however it is unknown if it transactivates ErbB2/HER2. Adding the nonpeptide BRS-3 allosteric-agonist, MK-5046 or the peptide agonist, BA1 to the lung cancer cell line, NCI-H727 or BRS-3-transfected NCI-H1299 lung cancer cells, increased tyrosine phosphorylation of HER2/ERK2. This increase was antagonized by the BRS-3 peptide antagonist, Bantag-1 and the small molecule BRS-3 antagonist, ML-18. The increase in HER2/ERK phosphorylation caused by MK-5046 was inhibited by ROS inhibitors, N-acetylcysteine and Tiron (superoxide-scavenger). Adding MK-5046 to lung cancer cells increased reactive-oxygen species which was inhibited by NAC or Tiron. MK-5024 and BA1 increased NSCLC colony formation whereas, Bantag-1/ML-18 inhibited proliferation. These results indicate that in lung cancer cells activation of BRS-3 regulates HER2-transactivation in ROS-dependent manner which can mediate tumor growth. These results raise the possibility that the use of HER2-inhibiting compounds alone or in combination with other agents, could be a novel approach in the treatment of these tumors.