SP6 Role of Arl6iP1 in adaptive neuronal stress response

Project Leader: Christian Hübner

Background and previous work
In the past we could show that FAM134B deficiency causes a degeneration of sensory neurons in a disorder entitled hereditary sensory autonomic neuropathy type. In the previous funding period we were able to show that the ER resident protein FAM134B via its LIR motif serves as a receptor for LC3 to direct ER membranes into autophagosomes. Moreover, FAM134B can curve membranes via its RETICULON domain. While depletion of FAM134B impedes autophagy-dependent degradation of the ER and thus increases the overall ER size, its overexpression causes the ER to shrink. Impaired ER homeostasis renders Fam134b knockout mouse embryonic fibroblasts more sensitive to ER stressors like tunicamycin. In a yeast-2-hybrid screen for proteins interacting with FAM134B we identified ARL6IP1 as a putative interaction partner. Previous studies have demonstrated that ARL6IP1 expression is down-regulated by apoptotic stimuli and overexpression of exogenous ARL6IP1 conversely inhibits the activity of caspase 9, leading to the protection of cells from apoptosis. Of note, this protein also harbours a putative LIR motif and a RETICULON domain and is associated with a neurodegenerative disorder.

Specific aims and working programme
In the follow-up project we want to characterise the biochemical and functional interaction between FAM134B and ARL6IP1 in detail. To this end, we will assess whether ARL6IP1 indeed interacts with LC3 and thereby contributes either directly or indirectly to the regulation of reticulophagy and ER homeostasis. We will further characterise the membrane topology of ARL6IP1 and how it modulates membrane shape. How ER morphology and function is affected will be studied in a quantitativ manner by inducible overexpression and knockdown of ARL6IP1. We will further address in a time and dose dependent manner whether ER stressors like thapsigargin and tunicamycin modulate ARL6IP1 expression. Finally we hope to resolve why loss of ARL6IP1 results in a neurodegenerative disorder.