A Tumor-Specific Molecular Network Promotes Tumor Growth in <i>Drosophila</i> by Enforcing a Jun N-Terminal Kinase–Yorkie Feedforward Loop

Abstract

Cancer cells expand rapidly in response to altered intercellular and signaling interactions to achieve the hallmarks of cancer. Impaired cell polarity combined with activated oncogenes is known to promote several hallmarks of cancer, e.g., activating invasion by increased activity of Jun N-terminal kinase (JNK) and sustained proliferative signaling by increased activity of Hippo effector Yorkie (Yki). Thus, JNK, Yki, and their downstream transcription factors have emerged as synergistic drivers of tumor growth through pro-tumor signaling and intercellular interactions like cell competition. However, little is known about the signals that converge onto JNK and Yki in tumor cells and enable tumor cells to achieve the hallmarks of cancer. Here, using mosaic models of cooperative oncogenesis (RasV12,scrib−) in Drosophila, we show that RasV12,scrib− tumor cells grow through the activation of a previously unidentified network comprising Wingless (Wg), Dronc, JNK, and Yki. We show that RasV12,scrib− cells show increased Wg, Dronc, JNK, and Yki signaling, and all these signals are required for the growth of RasV12,scrib− tumors. We report that Wg and Dronc converge onto a JNK–Yki self-reinforcing positive feedback signal-amplification loop that promotes tumor growth. We found that the Wg–Dronc–Yki–JNK molecular network is specifically activated in polarity-impaired tumor cells and not in normal cells, in which apical-basal polarity remains intact. Our findings suggest that the identification of molecular networks may provide significant insights into the key biologically meaningful changes in signaling pathways and paradoxical signals that promote tumorigenesis.

Keywords

• apical basal polarity
• cancer
• <i>Drosophila</i>
• imaginal discs
• Wingless
• Hippo