vps25mosaics display non-autonomous cell survival and overgrowth, and autonomous apoptosis

Abstract

Appropriate cell-cell signaling is crucial for proper tissue homeostasis. Protein sorting of cell surface receptors at the early endosome is important for both the delivery of the signal and the inactivation of the receptor, and its alteration can cause malignancies including cancer. In a genetic screen for suppressors of the pro-apoptotic gene hid in Drosophila, we identified two alleles of vps25, a component of the ESCRT machinery required for protein sorting at the early endosome. Paradoxically, although vps25 mosaics were identified as suppressors of hid-induced apoptosis, vps25 mutant cells die. However, we provide evidence that a non-autonomous increase of Diap1 protein levels, an inhibitor of apoptosis, accounts for the suppression of hid. Furthermore, before they die, vps25 mutant clones trigger non-autonomous proliferation through a failure to downregulate Notch signaling, which activates the mitogenic JAK/STAT pathway. Hid and JNK contribute to apoptosis of vps25 mutant cells. Inhibition of cell death in vps25 clones causes dramatic overgrowth phenotypes. In addition, Hippo signaling is increased in vps25 clones, and hippo mutants block apoptosis in vps25 clones. In summary, the phenotypic analysis of vps25 mutants highlights the importance of receptor downregulation by endosomal protein sorting for appropriate tissue homeostasis, and may serve as a model for human cancer.

A Mosaic Genetic Screen for Drosophila Neoplastic Tumor Suppressor Genes Based on Defective Pupation

“…However, as we and others have reported, in imaginal discs mosaic for strong alleles of the neoplastic TSGs scrib, lgl, dlg, avl, and Rab5, homozygous mutant cells are usually lost due to the process of cell competition (Brumby and Richardson 2003;Pagliarini and Xu 2003;Zeitler et al 2004;Uhlirova et al 2005). Tsg101 and vps25 cells survive competition but, like cells mutant for all neoplastic TSGs, fail to differentiate and do not contribute to the adult eye (Moberg et al 2005;Thompson et al 2005;Vaccari and Bilder 2005;Herz et al 2006). Thus, in a genetically mosaic imaginal disc, neoplastic mutant cells do not overgrow to form a tumor that can be easily detected in either larvae or adults.…”

“…Three of these-scrib, dlg, and lgl-encode cytoplasmic proteins with various protein-protein interaction domains ( Jacob et al 1987;Woods and Bryant 1991;. Four others-avl, Rab5, tsg101, and vps25-encode components of the endocytic machinery (Lu and Bilder 2005;Moberg et al 2005;Thompson et al 2005;Vaccari and Bilder 2005;Herz et al 2006). The relationship between the cytoplasmic scaffolds and the endocytic regulators, the mechanism of action of these proteins in cell polarity, and in particular how they each act to restrain cell proliferation remains mysterious.…”

Non-cell autonomous control of apoptosis by ligand-independent Hedgehog signaling in Drosophila

“…Fourth, clones of a different mutant, vps25, which is characterized by strong N activity, cause non-autonomous accumulation of Diap-1 protein. 26 Fifth, clones of cells expressing the active form of N (N intra ) cause non-cell autonomous accumulation of Diap-1 in neighboring cells (Figures 5g, g 0 and g 00 ). This observation demonstrates that N does not directly induce diap1 transcription, but generates another signal that promotes diap1 …”

“…The autonomy of GMR-hid suppression was examined with GMR-hid[w -], an insertion on the third chromosome. 26 hs-FLP was used to induce mosaic wing discs. Mosaics were also generated using the MARCM (mosaic analysis with a repressible cell marker) technique, which allows expression of transgenes such as UAS-CiR in mutant clones.…”

A matter of regeneration and repair: caspases as the key molecules

“…Notch and Janus kinases-signal transducers and activators of transcription (JAK-STAT) signal pathways were associated with proliferation, which can be induced by apoptosis (Moberg et al, 2005;Thompson et al, 2005;Vaccari and Bilder, 2005;Herz et al, 2006). Mutations in ubiquitin-like modifier activating enzyme 1, which catalyzes the activation stage in the ubiquitin conjugation pathway, induce apoptosis directly and tissue growth indirectly.…”