Cellular processes underlying maturation of P19 neurons: Changes in protein folding regimen and cytoskeleton organization

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Abstract
Embryonal carcinoma P19 cells provide an ideal model to study molecular programs along differentiation. Upon induction by retinoic acid (RA), the cells undergo a program of differentiation that generates functioning neurons within 60 h. RA induced cells that were plated as sparse (1000 cells/mm2) or dense (4000 cells/mm2) cultures showed a marked difference in the culture morphology with the dense cultures exhibiting rapid maturation and accelerated neurite outgrowth. The protein expression levels of the sparse and dense cultures were compared 48 h following RA. Cell extracts were separated by 1‐DE and 2‐DE and differential expression (>four‐fold) proteins were identified by MS. Here, we focus on 20 proteins associated with cytoskeletal regulation and stress‐dependent protein refolding. The first group includes drebrin, cofilin, α‐internexin, vimentin, and nestin. Among the proteins in the second group are subunits of the TCP‐1, and several chaperones of the Hsp70 and Hsp90 families. We show that coordinated remodeling of the cytoskeleton and modulations in chaperone activity underlie the change in neurite extension rate. Furthermore, a proteomics‐based analysis applied on P19 neurons demonstrated pathways underlying neuronal outgrowth, suggesting that a malfunction of such pathways leads to neuropathological conditions.