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Molecular and Cellular Biology, June 2005, p. 5226-5241, Vol. 25, No. 12
0270-7306/05/$08.00+0 doi:10.1128/MCB.25.12.5226-5241.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Sohail Ahmed,1,2,
Jing-Ming Dong,1,2
Christine Hall,1 and
Louis Lim1,2*
Department of Molecular Neuroscience, Institute of Neurology, University College London, 1 Wakefield St., London WC1N 1PJ, United Kingdom,1 GSK-IMCB Group, Institute of Molecular & Cell Biology, Proteos, 61 Biopolis Dr., Singapore 138673, Singapore2
Received 25 August 2004/ Returned for modification 21 October 2004/ Accepted 17 March 2005
In the central nervous system (CNS), damaged axons are inhibited from regeneration by glial scars, where secreted chondroitin sulfate proteoglycan (CSPG) and tenascin repulse outgrowth of neurites, the forerunners of axons and dendrites. During differentiation, these molecules are thought to form boundaries for guiding neurons to their correct targets. In neuroblastoma NIE-115 cells, outgrowth of neurites on laminin could be induced by serum starvation or inhibition of RhoA by Clostridium botulinum C3 toxin. The outgrowing neurites avoided crossing onto the repulsive substrate CSPG or tenascin. This avoidance response was partially overcome on expression of membrane-targeted and kinase-inactive forms of PAK. In these cells, the endogenous PAK isoforms colocalized with actin in distinctive sites,
PAK in the cell center as small clusters and along the neurite shaft and ßPAK and
PAK in areas with membrane ruffles and filopodia, respectively. When isoform-specific N-terminal PAK sequences were introduced to interfere with PAK function, substantially more neurites crossed onto CSPG when cells contained a
PAK-derived peptide but not the corresponding
PAK- or ßPAK-derived peptide. Thus, while neurite outgrowth can be promoted by RhoA inhibition, overcoming the accompanying repulsive guidance response will require modulation of PAK activity. These results have therapeutic implications for CNS repair processes.
Present address: Genome Institute of Singapore, 60 Biopolis St., Singapore 138672.
Present address: Institute of Molecular & Cell Biology, 61 Biopolis Dr., Singapore 138673.
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