Rapid neurite outgrowth in neurosecretory cells and neurons is sustained by the exocytosis of a cytoplasmic organelle, the enlargeosome

• DOI: 10.1242/jcs.059634
• Publication Date: 2009-12-22T02:49:18Z
• Authors: Gabriella Racchetti; Anna Lorusso; Carsten Schulte; Daniela Gavello; Valentina Carabelli; Rosalba D'Alessandro; Jacopo Meldolesi
• Keywords: Organelles; rac1 GTP-Binding Protein; 0301 basic medicine; Rac1; Nerve-cell differentiation; Neuronal primary cultures; PC12 cells; SH-SY5Y cells; Vamp4; Pyridines; Membrane Proteins; Endosomes; Amides; Microtubules; Neurosecretory Systems; Exocytosis; Cell Line; Neoplasm Proteins; Rats; 12. Responsible consumption; Nerve-cell differentiation; PC12 cells; Vamp4; Enzyme Activation; R-SNARE Proteins; 03 medical and health sciences; Neurites; Animals; Humans; trans-Golgi Network

Neurite outgrowth is known as a slow (days) process occurring in nerve cells and neurons during neurotrophin treatment and upon transfer to culture, respectively. Using Y27632, a drug that induces activation of Rac1, a downstream step of the neurotrophin signaling cascade, we have identified a new form of outgrowth, which is rapid (<1 hour) and extensive (>500 μm2 surface enlargement/single cell/first hour). However, this outgrowth takes place only in cells (PC12-27 and SH-SY5Y cells, and embryonic and neonatal neurons) rich in an exocytic organelle, the enlargeosome. Golgi vesicles, TGN vesicles and endosomes are not involved. The need for enlargeosomes for plasma-membrane expansion was confirmed by the appearance of their marker, Ahnak, at the cell surface and by the dependence of neurite outgrowth on VAMP4, the vSNARE of enlargeosome exocytosis. In enlargeosome-rich cells, VAMP4 downregulation also attenuated the slow outgrowth induced by nerve growth factor (NGF). Similar to NGF-induced neurite outgrowth in enlargeosome-lacking cells, the new, rapid, Y27632-induced process required microtubules. Other properties of neurite outgrowth in cells lacking enlargeosomes — such as dependence on VAMP7, on microfilaments, on gene transcription and on protein synthesis, and blockade of mitoses and accumulation of neuronal markers — were not evident. The enlargeosome-sustained process might be useful for the rapid neurite outgrowth at peculiar stages and/or conditions of nerve and neuronal cells. However, its properties and its physiological and pathological role remain to be investigated.