Transforming Growth Factor-Beta Expression in Mouse Lung Carcinogenesis

Abstract

Transforming growth factor-beta (TGF-β) is a multifunctional growth modulator that inhibits the proliferation of many epithelial cells while stimulating the proliferation of most fibroblasts. To examine the role of TGF-β in mouse lung chemically induced tumorigenesis, expression of the TGF-β1, -β2, and -β3 proteins was examined in A/J mice treated with the carcinogen urethane to induce lung adenomas using immunohistochemical staining analysis. Immunostaining for the TGF-β ligands was detected in the epithelium of the bronchioles of untreated A/J mice with immunostaining being more intense for TGF-β1 than for TGF-β2 and TGF-β3; immunostaining for each TGF-β ligand was also detected in the bronchiolar epithelium of urethane-treated A/J mice at levels similar to untreated mice. Immunostaining for the TGF-β ligands was also detected in adenomas by 2 months; staining for TGF-β1, -β2, and -β3 in adenomas was detected at levels comparable with bronchioles. Following treatment with urethane for 8 months, immunostaining for TGF-βs 1, 2, and 3 in bronchioles persisted at levels comparable to that in normal bronchioles and also persisted in adenomas, with staining for the TGF-β ligands being very prominent on the edge of the tumor. Expression of TGF-β1 mRNA was examined in urethane-treated mouse lung tissue using Northern blot hybridization; here, expression of TGF-β1 mRNA increased 2-fold in 3-month urethane-treated lung tissue and an additional 2.5-fold by 8 months following urethane administration. Expression of TGF-β1 mRNA was also examined in nontumorigenic and tumorigenic mouse lung cells; in these cells, expression of TGF-β1 mRNA was higher in the tumorigenic cells than in the nontumorigenic cell line. These data show that there is an increase in expression of TGF-β1 during tumorigenesis and suggest that TGF-β may play an important role in mouse lung carcinogenesis induced by urethane.

Key Words:

• A/J mouse
• chemical carcinogenesis
• gene expression
• tumor progression