Unconventional autophagic mechanisms involved in intracellular trafficking control and cell signalling.
Inmaculada Serramito Gómez
Centro de Investigación del Cáncer, CIC-IBMCC
Autophagy is an intracellular degradation pathway that helps maintain the metabolic homeostasis of the cell. Beside being a common response to nutritional stress, selective forms of this process are involved in the specific removal of potentially harmful components. Consequently, their disfunction plays an important role in the pathogenesis of several human diseases. ATG16L1 mediates autophagy by assembling the molecular complex that lipidates LC3, the main marker of autophagic vesicles. Recently, a risk polymorphic form of this critical autophagic effector (ATG16L1-T300A) has been reported to increase the risk of Crohn disease. This effect might be related to the various alternative activities recently linked to the WD domain (WDD) of ATG16L1, like inflammatory control, trafficking of secretory vesicles in Paneth cells or some forms of xenophagy.
Recent work from our laboratory showed that the WDD is specifically recognized by a novel 19-amino acid element found in the intracellular domain of the transmembrane protein TMEM59, as well as other molecules. The interaction between the WDD of ATG16L1 and TMEM59 triggers an unconventional autophagic process that cause LC3 labelling of the same single-membrane endosomes where TMEM59 is located, thus promoting a more efficient lysosomal targeting of these vesicles. Additionally, we found that T300A alters the ability of the WDD of ATG16L1 to interact with the amino acid motif that recognizes this region. Such alteration impairs the unconventional autophagic activity of TMEM59 and disrupts its normal intracellular trafficking and its ability to engage ATG16L1 in response to Staphylococcus aureus infection.
Therefore, identification of additional motif-containing WDD-binding proteins will likely unravel the signalling pathways whose dysfunction is required to trigger the onset of Crohn disease. To this end, we designed custom-made peptide microarrays with the aim of searching for motif-containing proteins. Notably, 23 cytokine receptors are represented between the collection of identified molecules. We selected a subgroup of these candidates based on their diverse pro- and anti-inflammatory activities. Then, we conducted several molecular and functional assays, which will be shown in this talk.