Activation of Src-family kinases orchestrate secretion of flaviviruses by targeting mature progeny virions to secretory autophagosomes

Among the various host cellular processes that are hijacked by flaviviruses, very few mechanisms have been described with regard to viral secretion. Here we investigated how flaviviruses exploit the Src family kinases (SFKs) for exit from infected cells. We isolated three members of the SFK family - Src, Fyn and Lyn - that were specifically activated during secretion of Dengue and Zika or their corresponding virus like particles (VLPs). Pharmacological inhibition or genetic depletion of the SFKs blocked virus secretion, most significantly upon Lyn-deficiency. Lyn-/- cells were severely impaired in virus release, and were rescued when reconstituted with wild-type Lyn, but not a kinase- or palmitoylation-deficient Lyn mutant. We further established that Lyn, via its palmitoylation-dependent membrane association, triggered post-Golgi virus transport in specialised Rab11 and Transferrin receptor positive organelles resembling secretory autophagosomes, and distinct from conventional exocytic vesicles. In the absence of Lyn activity or its aberrant membrane association, virions were sorted into the lysosomal pathway for degradation. This mode of export was specifically triggered by processed, and mature, but not by furin-resistant virus particles, and occurred with significantly faster kinetics than the conventional secretory pathway. Our study therefore charts a previously undiscovered Lyn-dependent exit strategy, triggered by flaviviruses in secretory autophagosomes that might enable them to evade circulating antibodies and dictate tissue tropism.