Characterization of Mayven, a Novel Actin-binding Protein Predominantly Expressed in Brain

Abstract

The cytoskeleton plays an important role in neuronal morphogenesis. We have identified and characterized a novel actin-binding protein, termed Mayven, predominantly expressed in brain. Mayven contains a BTB (broad complex, tramtrack, bric-a-brac)/POZ (poxvirus, zinc finger) domain-like structure in the predicted N terminus and "kelch repeats" in the predicted C-terminal domain. Mayven shares 63% identity (77% similarity) with the Drosophila ring canal ("kelch") protein. Somatic cell-hybrid analysis indicated that the human Mayven gene is located on chromosome 4q21.2, whereas the murine homolog gene is located on chromosome 8. The BTB/POZ domain of Mayven can self-dimerize in vitro, which might be important for its interaction with other BTB/POZcontaining proteins. Confocal microscopic studies of endogenous Mayven protein revealed a highly dynamic localization pattern of the protein. In U373-MG astrocytoma/ glioblastoma cells, Mayven colocalized with actin filaments in stress fibers and in patchy cortical actin-rich regions of the cell margins. In primary rat hippocampal neurons, Mayven is highly expressed in the cell body and in neurite processes. Binding assays and far Western blotting analysis demonstrated association of Mayven with actin. This association is mediated through the "kelch repeats" within the C terminus of Mayven. Depolarization of primary hippocampal neurons with KCl enhanced the association of Mayven with actin. This increased association resulted in dynamic changes in Mayven distribution from uniform to punctate localization along neuronal processes. These results suggest that Mayven functions as an actin-binding protein that may be translocated along axonal processes and might be involved in the dynamic organization of the actin cytoskeleton in brain cells.

Krp1, a novel kelch related protein that is involved in pseudopod elongation in transformed cells

“…It should also be noted that when Krp1-myc was expressed in 208F cells, and when we examined the low level of endogenous Krp1 that is present in FBR-TAM67 cells, no co-localization with F-actin containing stress ®bres was detected. This result contradicts work presented by Hernandez et al, (1997) and Soltysik-Espanola et al (1999), who reported that two other kelch family members, ENC1 and Mayven, interact with stress ®bres containing F-actin. Together these data suggest that Krp1 only co-localizes with F-actin when it is in the looped membrane ru e-like structure at the tips of pseudopodia.…”

“…Another protein, alpha-scruin of Limulus, which has kelch repeats present at both its amino and carboxyl termini but lacks a BTB/POZ domain, cross-links actin ®laments within the acrosomal processes of sperm (Way et al, 1995a). Further kelch proteins are also thought to interact with actin: murine and human ENC1 (Hernandez et al, 1997(Hernandez et al, , 1998; spe-26 of C. elegans (Varkey et al, 1995); and human Mayven (Soltysik-Espanola et al, 1999). Many other family members are thought not to interact with actin; beta-scruin of Limulus, for instance, is found in sperm acrosomal vesicles, which do not contain actin (Way et al, 1995b).…”

“…Examination of Krp1 expression in pseudopod tips at a higher magni®cation revealed that it was present in membrane ru e-like structures that appeared to be forming a looping conformation (Figure 3d). Because it is known that some kelch family proteins interact with actin (Xue and Cooley, 1993;Hernandez et al, 1997;Soltysik-Espanola et al, 1999), and that the yeast Tea1 kelch family member localizes at the ends of microtubules (Mata and Nurse, 1997), we performed two double immuno¯uorescence experiments on FBR cells: anti-Krp1 antiserum and phalloidin to detect Factin; anti-Krp1 and tubulin antisera (Figure 3b ± d). Both tubulin and Krp1 were present in the cytoplasm, but while Krp1 extended into the loop-like structures at the tips of pseudopodia, tubulin stopped just short of these structures (Figure 3b).…”

KRIP6: A novel BTB/kelch protein regulating function of kainate receptors

“…BTB/kelch proteins are highly conserved across species, yet their functional roles appear quite diverse, ranging from organization of cytoskeletal elements to control of protein trafficking/ ubiquitination and regulation of gene expression. Two brain-enriched BTB/kelch proteins closely related to KRIP6, Mayven and actinfilin, associate with the actin cytoskeleton (Chen et al, 2002;Soltysik-Espanola et al, 1999). However, unlike Mayven and actinfilin, KRIP6 does not colocalize with F-actin in COS-7 cells or in neurons, and thus probably does not bind actin.…”

“…The BTB/POZ domain is a zinc finger and protein-protein interaction domain (Li et al, 1997) known to dimerize (e.g. (Cullen et al, 2004;Soltysik-Espanola et al, 1999). The kelch repeats, each four antiparallel β strands of 44-56 aa, combine to generate a β-propeller structure (Adams et al, 2000).…”