1. ¹Department of Biology, Sapporo Medical University School of Medicine, Chuo-ku, Sapporo, Japan
2. ²Department of Oral Pathobiological Science, Hokkaido University Graduate School of Dental Medicine, Kita-ku, Sapporo, Japan
3. ³Department of Immunology, Osaka City University Graduate School of Medicine, Abeno-ku, Osaka, Japan
4. ⁴First Department of Internal Medicine, Sapporo Medical University School of Medicine, Chuo-ku, Sapporo, Japan

Correspondence: Dr K Yoshida, Department of Biology, Sapporo Medical University School of Medicine, S1, W17, Chuo-ku, Sapporo 060-8556, Japan. E-mail: kyoshida@sapmed.ac.jp

Received 22 November 2004; Revised 24 August 2005; Accepted 26 August 2005; Published online 3 October 2005.

Abstract

Signal transducers and activators of transcription (STATs) are latent transcription factors that mediate cytokine- and growth factor-induced transcription. Constitutive activation of STAT3 has been shown in human cancers and transformed cell lines. We report that STAT3, but not STAT1 and STAT5, becomes phosphorylated in response to epidermal growth factor (EGF) and achieves maximal induction of collagenase-1 (MMP-1) transcription by interacting with c-JUN. Phosphorylation of STAT3 protein is biphasic: the first peak within 30 min and the second peak between 4 and 8 h. Association of STAT3 with c-JUN is detected and its constituting STAT3 is increasingly phosphorylated. The STAT and AP-1 elements are necessary for effective induction of MMP-1 promoter by EGF. Mutation of AP-1 element closely located at the STAT site abolishes the binding not only of c-JUN but also of STAT3 to MMP-1 promoter, resulting in the loss of the responsiveness to EGF. By blocking STAT3 activity with the dominant-negative form, we show the requirement of STAT3 for EGF induction of MMP-1 and MMP-10 (stromelysin-2). Furthermore, expression of the dominant-negative STAT3 is sufficient to inhibit the constitutive and EGF-inducible cell migration and invasion and the tumor formation in nude mice. These results demonstrate that STAT3 phosphorylation and its possible interaction with c-JUN are required for the strong responsiveness of MMP-1 to EGF, and STAT3 activation is crucial for exhibition of malignant characteristics in T24 bladder cancer cells.