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. 2007 Dec 10;313(20):4091-106.
doi: 10.1016/j.yexcr.2007.08.012.

The phosphorylation of p25/TPPP by LIM kinase 1 inhibits its ability to assemble microtubules

Karla Acevedo  1 , Rong Li, Priscilla Soo, Randy Suryadinata, Boris Sarcevic, Valentina A Valova, Mark E Graham, Phillip J Robinson, Ora Bernard
Affiliations

The phosphorylation of p25/TPPP by LIM kinase 1 inhibits its ability to assemble microtubules

Karla Acevedo et al. Exp Cell Res. .

Abstract

LIM kinase 1 (LIMK1) is a key regulator of actin dynamics as it phosphorylates and inactivates cofilin, an actin-depolymerizing factor. LIMK1 activity is also required for microtubule disassembly in endothelial cells. A search for LIMK1-interacting proteins identified p25alpha, a phosphoprotein that promotes tubulin polymerization. We found that p25 is phosphorylated by LIMK1 on serine residues in vitro and in cells. Immunoblotting analysis revealed that p25 is not a brain specific protein as previously reported, but is expressed in all mouse tissues. Immunofluorescence analysis demonstrated that endogenous p25 is co-localized with microtubules and is also found in the nucleus. Down-regulation of p25 by siRNA decreased microtubule levels while its overexpression in stable NIH-3T3 cell lines increased cell size and levels of stable tubulin. Bacterially expressed unphosphorylated p25 promotes microtubule assembly in vitro; however, when phosphorylated in cells, p25 lost its ability to assemble microtubule. Our results represent a surprising connection between the tubulin and the actin cytoskeleton mediated by LIMK1. We propose that the LIMK1 phosphorylation of p25 blocks p25 activity, thus promoting microtubule disassembly.

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