CRP1, a Protein Localized in Filopodia of Growth Cones, Is Involved in Dendritic Growth

Abstract

The cysteine-rich protein (CRP) family is a subgroup of LIM domain proteins. CRP1, which cross-links actin filaments to make actin bundles, is the only CRP family member expressed in the CNS with little known about its function in nerve cells. Here, we report that CRP1 colocalizes with actin in the filopodia of growth cones in cultured rat hippocampal neurons. Knockdown of CRP1 expression by short hairpin RNA interference results in inhibition of filopodia formation and dendritic growth in neurons. Overexpression of CRP1 increases filopodia formation and neurite branching, which require its actin-bundling activity. Expression of CRP1 with a constitutively active form of Cdc42, a GTPase involved in filopodia formation, increases filopodia formation in COS-7 cells, suggesting cooperation between the two proteins. Moreover, we demonstrate that neuronal activity upregulates CRP1 expression in hippocampal neurons via Ca 2ϩ influx after depolarization. Ca 2ϩ /calmodulin-dependent protein kinase IV (CaMKIV) and cAMP response element binding protein mediate the Ca 2ϩ -induced upregulation of CRP1 expression. Furthermore, CRP1 is required for the dendritic growth induced by Ca 2ϩ influx or CaMKIV. Together, these data are the first to demonstrate a role for CRP1 in dendritic growth.

Live cell imaging approaches reveal actin cytoskeleton-induced self-association of the actin-bundling protein WLIM1

“…Noticeably, counterparts of plant LIM proteins are found in mammals, suggesting that this subset of LIM domain proteins triggers basic, evolutionarily conserved, functions (Weiskirchen and Günther, 2003). Like plant LIM proteins, the so-called cysteine-rich proteins (CRPs) promote actin bundle assembly in both reconstituted in vitro assays and live cells (Jang and Greenwood, 2009;Kihara et al, 2011;Ma et al, 2011;Tran et al, 2005). In addition, recent data support the idea that CRP-bundling activity is involved in the stabilization of stress fibers in smooth muscle cells and the formation of dendritic filopodia (Kihara et al, 2011;Ma et al, 2011).…”

Molecular mechanisms of dendrite morphogenesis

“…Knockdown of CRP1 leads to a decrease in dendritic growth during development, while overexpression does not alter the total neurite length. This functional ability is mediated in part by its actin bundling activity (Ma et al, 2011). …”

Human Muscle LIM Protein Dimerizes along the Actin Cytoskeleton and Cross-Links Actin Filaments

“…In addition, CRP1 was shown to promote actin bundle formation in both in vitro biochemical assays and live cell experiments (32,33). Ma and coworkers (34) recently established that CRP1 functions in filopodium formation and dendritic growth in neurons. Remarkably, a truncated version of CRP1 containing the actin-bundling domain was sufficient to increase the number of filopodia and neuritic branches as efficiently as the full-length protein, supporting that the bundling activity of CRP1 is biologically relevant.…”