Specific single chain variable fragment (ScFv) antibodies to angiotensin II AT2 receptor: evaluation of the angiotensin II receptor expression in normal and tumor-bearing mouse lung

To gain insight into the mechanism by which angiotensin II type 2 receptor (AT(2)) regulates carcinogen-induced lung tumorigenesis, we have newly developed anti-AT(2) single chain variable fragment (ScFv) antibodies using a rodent phage-displayed recombinant antibody library with various peptide fragments of the receptor protein, and investigated the expression of the AT(2) receptor protein. The specificity of the antibodies was verified using AT(2) over-expressing COS-7 cells and AT(2) naturally expressing PC12W cells. In control wild type mouse lung, a stronger immunoreactivity was observed in bronchial epithelial cells. A moderate immunoreactivity was detected in pulmonary vascular walls and vascular endothelial cells. In the lungs possessing tobacco-specific nitrosamine (NNK)-induced tumors, significantly increased AT(2) and AT(1 )immunostaining was observed in adenomatous lesions. These data suggest that the increase in both receptors' expression in the alveolar epithelial cells may be accompanied with the onset of NNK-induced tumorigenesis and hence play important roles in lung tumorigenesis.