Abstract
Genetic screens in the fruit fly Drosophila melanogaster have identified a class of neoplastic tumor suppressor genes (endocytic nTSGs), which encode proteins that localize to endosomes and facilitate the trafficking of membrane-bound receptors and adhesion molecules into the degradative lysosome. Loss of endocytic nTSGs transforms imaginal disc epithelia into highly proliferative, invasive tissues that fail to differentiate and display defects in cellular apicobasal polarity, adhesion and tissue architecture. As vertebrate homologs of some Drosophila nTSGs are linked to tumor formation, identifying molecular changes in signaling associated with nTSG loss could inform understanding of neoplastic transformation in vertebrates. Here we show that mutations in genes that act at multiple steps of the endolysosomal pathway lead to autonomous activation of the Sav/Wts/Hpo (SWH) transcriptional effector Yki (YAP/TAZ in vertebrates) and the Jun N-terminal kinase (JNK), which is known to promote Yki activity in cells with disrupted polarity. Yki and JNK activity are elevated by mutations at multiple steps in the endolysosomal pathway including mutations in the AP-2σ gene, which encodes a component of the AP-2 adaptor complex that recruits cargoes into clathrin-coated pits for subsequent internalization. Moreover, reduction of JNK activity can decrease elevated Yki-signaling caused by altered endocytosis. These studies reveal a broad requirement for components of the endocytic pathway in regulating SWH and JNK outputs, and place Drosophila endocytic nTSGs into a network that involving two major signaling pathways implicated in oncogenesis.
Disclosure of Potential Conflicts of Interest
No potential conflicts of interest were disclosed.
Acknowledgments
We thank M. Gilbert, D. Bilder, G. Halder, M. Scott, R. Fehon, U. Tepass and E. Knust for gifts of fly stocks and antibodies. We also thank the Bloomington Drosophila Stock Center and the Developmental Studies Hybridoma Bank for fly stocks and antibodies. We are grateful to R. Jones and members of the Moberg laboratory for helpful discussions. This work was supported by NIH R01CA123368 to K.H.M. and the Emory BCDB and MTSP Training Grants (T32 GM008367 and T32 GM008169) to B.S.R.