A Drosophila Tumor Suppressor Gene Prevents Tonic TNF Signaling through Receptor N-Glycosylation

Drosophila tumor suppressor genes have revealed molecular pathways that control tissue growth, but mechanisms that regulate mitogenic signaling are far from understood. Here we report that the Drosophila TSG tumorous imaginal discs (tid), whose phenotypes were previously attributed to mutations in a DnaJ-like chaperone, are in fact driven by the loss of the N-linked glycosylation pathway component ALG3. tid/alg3 imaginal discs display tissue growth and architecture defects that share characteristics of both neoplastic and hyperplastic mutants. Tumorous growth is driven by inhibited Hippo signaling, induced by excess Jun N-terminal kinase (JNK) activity. We show that ectopic JNK activation is caused by aberrant glycosylation of a single protein, the fly tumor necrosis factor (TNF) receptor homolog, which results in increased binding to the continually circulating TNF. Our results suggest that N-linked glycosylation sets the threshold of TNF receptor signaling by modifying ligand-receptor interactions and that cells may alter this modification to respond appropriately to physiological cues. [Display omitted] •Drosophila tumor suppressor gene tid encodes a regulator of N-glycosylation•N-glycosylation of the fly TNF receptor homolog limits TNF-α binding•Excess JNK signaling upon TNFR glycosylation loss inhibits Hippo to drive overgrowth de Vreede et al. correct cloning of a classic Drosophila tumor suppressor gene, showing that it encodes a regulator of N-glycosylation rather than a DnaJ-like chaperone. Appropriate N-glycosylation of the fly TNF receptor limits binding of circulating TNF-α ligand, thus preventing excess JNK-driven signaling that inhibits Hippo signaling and causes tissue overgrowth.