Tissue-autonomous immune response regulates stress signalling during hypertrophy

Postmitotic tissues are incapable of replacing damaged cells through proliferation, but need to rely on buffering mechanisms to prevent tissue disintegration. By constitutively activating the Ras/MAPK-pathway via RasV12-overexpression in the postmitotic salivary glands of Drosophila larvae, we overrode the glands adaptability to growth signals, induced hypertrophy and stress accumulation. This allowed us to decipher a novel, spatio-temporally regulated interaction between the JNK-stress response and a genuine tissue-autonomous immune response. Central to this interaction is the direct inhibition of JNK-signalling by the antimicrobial peptide Drosomycin, which blocks programmed cell death and prevents recognition of the stressed tissue by the systemic immune response. While this mechanism might allow growing salivary glands to cope with temporary stress, continuous expression of Drosomycin favors survival of unrestricted, hypertrophic RasV12-glands. Our findings indicate the necessity for refined therapeutic approaches that fundamentally acknowledge detrimental effects that stimulated immune responses have on tissues coping with damage and stress.