An autocrine/paracrine circuit of growth differentiation factor (GDF) 15 has a role for maintenance of breast cancer stem-like cells

// Asako Sasahara 1, 2 , Kana Tominaga 1 , Tatsunori Nishimura 3 , Masao Yano 4 , Etsuko Kiyokawa 5 , Miki Noguchi 6 , Masakuni Noguchi 6 , Hajime Kanauchi 7 , Toshihisa Ogawa 2 , Hiroshi Minato 8 , Keiichiro Tada 2 , Yasuyuki Seto 9 , Arinobu Tojo 1 , Noriko Gotoh 1, 3 1 Division of Molecular Therapy, Institute of Medical Science, University of Tokyo, Tokyo, Japan 2 Department of Breast and Endocrine Surgery, Graduate School of Medicine, University of Tokyo, Tokyo, Japan 3 Division of Cancer Cell Biology, Cancer Research Institute, Kanazawa University, Kanazawa, Japan 4 Department of Surgery, Minamimachida Hospital, Machida, Tokyo, Japan 5 Department of Oncologic Pathology, Kanazawa Medical University, Ishikawa, Japan 6 Department of General and Digestive Surgery, Kanazawa Medical University, Ishikawa, Japan 7 Department of Breast and Endocrine Surgery, Showa General Hospital, Kodaira, Tokyo, Japan 8 Department of Pathology and Laboratory Medicine, Kanazawa Medical University, Ishikawa, Japan 9 Department of Gastrointestinal Surgery, Graduate School of Medicine, University of Tokyo, Tokyo, Japan Correspondence to: Noriko Gotoh, email: ngotoh@ims.u-tokyo.ac.jp Keywords: tumor spheres, cancer stem cells, breast cancer, TGFbeta, ERK Received: August 26, 2016      Accepted: January 06, 2017      Published: February 11, 2017 ABSTRACT Cancer stem cells are thought to be responsible for tumor growth, recurrence, and resistance to conventional cancer therapy. However, it is still unclear how they are maintained in tumor tissues. Here, we show that the growth differentiation factor 15 (GDF15), a member of the TGFβ family, may maintain cancer stem-like cells in breast cancer tissues by inducing its own expression in an autocrine/paracrine manner. We found that GDF15, but not TGFβ, increased tumor sphere formation in several breast cancer cell lines and patient-derived primary breast cancer cells. As expected, TGFβ strongly stimulated the phosphorylation of Smad2. GDF15 also stimulated the phosphorylation of Smad2, but the GDF15-induced tumor sphere forming efficiency was not significantly affected by treatment with SB431542, an inhibitor of the TGFβ signaling. Although TGFβ transiently activated ERK1/2, GDF15 induced prolonged activation of ERK1/2. Treatment with U0126, an inhibitor of the MEK-ERK1/2 signaling, greatly inhibited the GDF15-induced tumor sphere formation. Moreover, cytokine array experiments revealed that GDF15, but not TGFβ, is able to induce its own expression; furthermore, it appears to form an autocrine/paracrine circuit to continuously produce GDF15. In addition, we found heterogeneous expression levels of GDF15 among cancer cells and in human breast cancer tissues using immunohistochemistry. This may reflect a heterogeneous cancer cell population, including cancer stem-like cells and other cancer cells. Our findings suggest that GDF15 induces tumor sphere formation through GDF15-ERK1/2-GDF15 circuits, leading to maintenance of GDF15 high cancer stem-like cells. Targeting GDF15 to break these circuits should contribute to the eradication of tumors.