The complex allergen house dust mite (HDM) dramatically increases the abundance of the autophagy cargo adapter SQSTM1/p62 in macrophages and suppresses Torin 1-induced degradative autophagy

Abstract

Abstract Autophagy is an essential homeostatic process involving degradation of intracellular components, including soluble proteins, aggregated proteins, organelles, macromolecular complexes and foreign bodies. Several components of the autophagy pathway have been linked to allergic asthma and macrophage phenotypes, however the contribution of autophagy to these processes is unclear. We previously showed that house dust mite (HDM) increased the number of fluorescent foci (autophagosomes) in bone-marrow derived macrophages (BMM) in a manner similar to the autophagy inducer Torin 1. Further, electron microscopy revealed an increase in double membraned vesicles in response to HDM and Torin 1. While Torin induced a specific increase in lipidated LC3, treatment with HDM caused equal increases in both non-lipidated and lipidated LC3. Torin 1 stimulated autophagic degradation as measured by reduction of SQSTM1/p62. In contrast, SQSTM1/p62 levels increased dramatically in response to HDM. The increase was blocked by actinomycin D and cycloheximide indicating that new gene transcription and protein synthesis is required for the HDM-induced effect. HDM-stimulated increase in SQSTM1/p62 was also observed in alveolar macrophages treated in vitro. An increase in SQSTM1/p62 is often interpreted as a block in autophagic degradation. Indeed, we observed that in the presence of HDM, Torin 1 treatment did not lead to the loss of SQSTM1/p62 below baseline; however, the protein did not accumulate to the high level observed in the HDM-alone treatment group. Our results suggest that HDM engages autophagy machinery at multiple points, both inducing expression of SQSTM1/p62 and suppressing its degradation.