Immunohistochemical analysis of CYP2A13 in various types of human lung cancers

Abstract

Human CYP2A13, which is expressed in the respiratory tract, is the most efficient enzyme for the metabolic activation of tobacco-specific nitrosamines such as 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). The relevance of CYP2A13 in carcinogenicity and toxicity in the respiratory tract has been suggested, but the expression of CYP2A13 protein in lung cancer tissues remains to be determined. We first prepared a mouse monoclonal antibody against human CYP2A13. The antibody showed no cross reactivity with the other CYP isoforms including CYP2A6. Using the specific antibody, we performed immunohistochemical analysis for human lung carcinomas. In adenocarcinomas (n = 15), all specimens were positive for the staining and five samples showed strong staining. In squamous cell carcinomas (n = 15) and large cell carcinomas (n = 15), each 14 samples were positive for the staining and two and three samples showed strong staining, respectively. In small cell carcinoma samples (n = 15), eight samples were negative for the staining and five samples showed weak or moderate staining. In conclusion, we first found that the expression of CYP2A13 was markedly increased in non-small cell lung carcinomas. The high expression might be associated with the tumor development and progression in non-small cell lung carcinomas.

Figure 1

Immunoblot analysis using the mouse monoclonal antibody against human CYP2A13 prepared in this study. One pmol each of recombinant P450 isoforms, CYP1A1, CYP1B1, CYP2B6, CYP2D6, CYP2E1, and CYP3A4 expressed in baculovirus‐infected insect cells and CYP2A6, CYP2A13, and CYP2S1 expressed in E. coli, were separated on 10% SDS‐PAGE.

Figure 2

Immunohistochemical analysis of CYP2A13 in human lung cancer tissues. Adjacent noncancerous (a) bronchus and (b) peripheral lung tissues; (c) adenocarcinoma; (d) squamous cell carcinoma; (e) large cell carcinoma; (f) small cell carcinoma. Strong immunostaining was observed in the epithelial cells in bronchus, but not in peripheral lung tissues. In lung carcinomas, immunostaining was positive in most of non‐small cell carcinomas. In contrast, the staining was mostly negative in small cell carcinoma. Original mag‐nification, ×200.