GAP43 stimulates inositol trisphosphate-mediated calcium release in response to hypotonicity.
The identification of osmo/mechanosensory proteins in mammalian sensory neurons is still elusive. We have used an expression cloning approach to screen a human dorsal root ganglion cDNA library to look for proteins that respond to hypotonicity by raising the intracellular Ca(2+) concentration ([Ca(2+)](i)). We report the unexpected identification of GAP43 (also known as neuromodulin or B50), a membrane-anchored neuronal protein implicated in axonal growth and synaptic plasticity, as an osmosensory protein that augments [Ca(2+)](i) in response to hypotonicity. Palmitoylation of GAP43 plays an important role in the protein osmosensitivity. Depletion of intracellular stores or inhibition of phospholipase C (PLC) activity abrogates hypotonicity-evoked, GAP43-mediated [Ca(2+)](i) elevations. Notably, hypotonicity promoted the selective association of GAP43 with the PLC-delta(1) isoform, and a concomitant increase in inositol-1,4,5-trisphosphate (IP(3)) formation. Collectively, these findings indicate that hypo-osmotic activation of GAP43 induces Ca(2+) release from IP(3)-sensitive intracellular stores. The osmosensitivity of GAP43 furnishes a mechanistic framework that links axon elongation with phospho inositide metabolism, spontaneous triggering of cytosolic Ca(2+) transients and the regulation of actin dynamics and motility at the growth cone in response to temporal and local mechanical forces.
Caprini
Marco
M
Instituto de Biología Molecular y Celular, Universidad Miguel Hernández, 03202 Alicante, Spain.
Gomis
Ana
A
Cabedo
Hugo
H
Planells-Cases
Rosa
R
Belmonte
Carlos
C
Viana
Félix
F
Ferrer-Montiel
Antonio
A
D000199:Actins / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D048429:Cell Size; D003599:Cytoskeleton / Q000378:metabolism; D004789:Enzyme Activation; D005456:Fluorescent Dyes / Q000378:metabolism; D016257:Fura-2 / Q000031:analogs & derivatives* / Q000378:metabolism; D019922:GAP-43 Protein / Q000378:metabolism*; D005727:Ganglia, Spinal / Q000166:cytology / Q000502:physiology; D006801:Humans; D007038:Hypotonic Solutions; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism; D040542:Mechanotransduction, Cellular; D021962:Membrane Microdomains / Q000378:metabolism; D009994:Osmolar Concentration; D054803:Phospholipase C delta; D011493:Protein Kinase C / Q000378:metabolism; D011984:Sensory Receptor Cells / Q000378:metabolism; D015398:Signal Transduction; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism; D014882:Water-Electrolyte Balance / Q000502:physiology*
D000199:Actins; D005456:Fluorescent Dyes; D019922:GAP-43 Protein; D007038:Hypotonic Solutions; D007527:Isoenzymes; C049925:fura-2-am; D015544:Inositol 1,4,5-Trisphosphate; D011493:Protein Kinase C; D010738:Type C Phospholipases; D054803:Phospholipase C delta; D002118:Calcium; D016257:Fura-2