Stimulation of JNK/SAPK signaling is linked to the Wnt/β-catenin-induced squamous metaplasia in mice. Sections of the mammary tumors, adenocarcinoma (AC; A–H) and adenocarcinoma with squamous metaplasia (SM; I–P), induced by Wnt1 were analyzed by histology (A, I) and immunochemistry (B–H and J–P) for the expression of β-cat (B, J), cyclin D1 (cycD1; C, K), PJNK (D, L), Pp38 (E, M), and PErk1/2 (F, N), PJun73 (G, O), and high-molecule weight keratin (HMW-K; H, P). The immunochemistry (brown)-stained sections were counterstained with hematoxylin (blue). Wnt signaling is stimulated in both AC and SM because β-catenin is nuclearly localized and cyclin D1 is highly expressed in malignant cells (B–C and J–K). In contrast, JNK/SAPK signaling is exclusively elevated in SM (D–G and L–O). Scale bars, 100 µm (A–P).