Regulation of ASIC channels by a stomatin/STOML3 complex located in a mobile vesicle pool in sensory neurons

Abstract

A complex of stomatin-family proteins and acid-sensing (proton-gated) ion channel (ASIC) family members participate in sensory transduction in invertebrates and vertebrates. Here, we have examined the role of the stomatin-family protein stomatin-like protein-3 (STOML3) in this process. We demonstrate that STOML3 interacts with stomatin and ASIC subunits and that this occurs in a highly mobile vesicle pool in dorsal root ganglia (DRG) neurons and Chinese hamster ovary cells. We identify a hydrophobic region in the N-terminus of STOML3 that is required for vesicular localization of STOML3 and regulates physical and functional interaction with ASICs. We further characterize STOML3-containing vesicles in DRG neurons and show that they are Rab11-positive, but not part of the early-endosomal, lysosomal or Rab14-dependent biosynthetic compartment. Moreover, uncoupling of vesicles from microtubules leads to incorporation of STOML3 into the plasma membrane and increased acid-gated currents. Thus, STOML3 defines a vesicle pool in which it associates with molecules that have critical roles in sensory transduction. We suggest that the molecular features of this vesicular pool may be characteristic of a ‘transducosome’ in sensory neurons.

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“…Moreover, deletion of Atat1 was remarkably selective in that it impacted only on cutaneous mechanosensation and had no effect on thermal responses, or on electrical or other functional properties of sensory neurons such as their sensitivity to capsaicin and pH. We have previously reported that STOML3, another critical mediator of mechanotransduction, associates with microtubules in a specialized vesicle where it interacts with acid-sensing (proton-gated) ion channel (ASIC) subunits (Lapatsina et al, 2012). Uncoupling of vesicles from microtubules leads to incorporation of STOML3 into the plasma membrane and increased acid-gated currents.…”

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“…Since STOML3 is the only protein known to participate directly in fast mechanotransduction it was of interest to examine how this membrane protein is trafficked within sensory neurons. We found that STOML3 is localized to a highly mobile and molecularly distinct transport vesicle within cultured sensory neuron axons (Lapatsina et al, 2012b).…”

“…The STOML3 vesicle is obviously enriched in proteins are destined to function in transduction at the peripheral endings of sensory neurons and so we have proposed to name these vesicles "transducosomes". Indeed uncoupling of the "transducosome" from microtubules leads to rapid incorporation into the plasma membrane with an accompanying increase in acid-gated currents (Lapatsina et al, 2012b). Ex vivo recordings from sensory afferents innervating the skin have demonstrated that transduction of mechanical stimuli at the peripheral endings of sensory neurons is very stable for many hours in the absence of a connection to the cell body.…”

“…Rab11-positive vesicles have been characterized as composing a slowly recycling endocytic compartment and may be transported predominantly anterogradely in sensory neurons (Ascaño et al, 2009;Eva et al, 2010). Indeed gain or loss of function Rab11 mutants radically change vesicle behavior but these compartments still contain STOML3 (Lapatsina et al, 2012b). The STOML3 vesicle is obviously enriched in proteins are destined to function in transduction at the peripheral endings of sensory neurons and so we have proposed to name these vesicles "transducosomes".…”

“…Indeed a much larger proportion of thinly myelinated nociceptors innervating the hairy skin, lack mechanosensitivity in STOML3 mutant mice, a phenotype that is reminiscent of the mechanically insensitive nociceptors identified in normal human and pig skin (Weidner et al, 1999;Hirth et al, 2013). Stomatin-domain proteins like STOML3 and stomatin modulate the proton gating of ASIC2 and ASIC3 proteins and some of the structural motifs of the stomatin-domains required for this modulation were recently identified Brand et al, 2012;Lapatsina et al, 2012b). In this context, it is interesting that deletion of stomatin or stoml3 genes, together with the Asic3 or Asic2 genes, leads to a dramatic loss of mechanosensitivity in nociceptors, especially those with thinly myelinated Aδ axons (Moshourab et al, 2013).…”