Characterization of Palladin, a Novel Protein Localized to Stress Fibers and Cell Adhesions

Abstract

Here, we describe the identification of a novel phosphoprotein named palladin, which colocalizes with α-actinin in the stress fibers, focal adhesions, cell–cell junctions, and embryonic Z-lines. Palladin is expressed as a 90–92-kD doublet in fibroblasts and coimmunoprecipitates in a complex with α-actinin in fibroblast lysates. A cDNA encoding palladin was isolated by screening a mouse embryo library with mAbs. Palladin has a proline-rich region in the NH2-terminal half of the molecule and three tandem Ig C2 domains in the COOH-terminal half. In Northern and Western blots of chick and mouse tissues, multiple isoforms of palladin were detected. Palladin expression is ubiquitous in embryonic tissues, and is downregulated in certain adult tissues in the mouse. To probe the function of palladin in cultured cells, the Rcho-1 trophoblast model was used. Palladin expression was observed to increase in Rcho-1 cells when they began to assemble stress fibers. Antisense constructs were used to attenuate expression of palladin in Rcho-1 cells and fibroblasts, and disruption of the cytoskeleton was observed in both cell types. At longer times after antisense treatment, fibroblasts became fully rounded. These results suggest that palladin is required for the normal organization of the actin cytoskeleton and focal adhesions.

The N-terminus of the long MLCK induces a disruption in normal spindle morphology and metaphase arrest

“…The Ig-C2 motif was originally identified in the extracellular domain of adhesion molecules (Williams and Barclay, 1988) but this motif is now recognized in a number of intracellular cytoskeletal proteins including titin, MyBP-C, MyBP-M, MyBP-H, myotilin and palladin (Einheber and Fischman, 1990;Labeit et al, 1990;Noguchi et al, 1992;Parast and Otey, 2000;Salmikangas et al, 1999;Vaughan et al, 1993). It is notable that most of these molecules are specific to skeletal muscle, suggesting that the C2 motifs contribute to the maintenance of cytoskeletal architecture and organization.…”

α‐actinin revisited: A fresh look at an old player

“…Palladin is the most widely expressed member of the myotilin/palladin/myopalladin family, as it is virtually ubiquitous in developing mammalian tissues. Palladin directly binds to ␣-actinin and closely co-localizes with it in stress fiber-dense regions and focal adhesions, and it has been detected in cell-cell junctions and embryonic Z-discs [Parast and Otey, 2000]. The interaction is mediated by a unique sequence conserved in palladin and myotilin, and the C-terminal CaM domain of ␣-actinin.…”

“…The interaction is mediated by a unique sequence conserved in palladin and myotilin, and the C-terminal CaM domain of ␣-actinin. Palladin's function has been explored in a variety of cell types, and it has been implicated as having an important role in both the maintenance of cytoskeletal organization and in the establishment of cell morphology [Parast and Otey, 2000;Mykkänen et al, 2001;Boukhelifa et al, 2001Boukhelifa et al, , 2003]. Down-regulation of palladin in cultured fibroblasts results in a striking loss of stress fibers and focal adhesions [Parast and Otey, 2000].…”

“…Palladin's function has been explored in a variety of cell types, and it has been implicated as having an important role in both the maintenance of cytoskeletal organization and in the establishment of cell morphology [Parast and Otey, 2000;Mykkänen et al, 2001;Boukhelifa et al, 2001Boukhelifa et al, , 2003]. Down-regulation of palladin in cultured fibroblasts results in a striking loss of stress fibers and focal adhesions [Parast and Otey, 2000]. It is interesting to note that expression of truncated ␣-actinin, including a construct missing only the CaM-domain, also results in stress fiber collapse, suggesting that both proteins are critical for stress fiber maintenance [Pavalko and Burridge, 1991;Schultheiss et al, 1992].…”

A framework to identify physiological responses in microarray-based gene expression studies: selection and interpretation of biologically relevant genes

“…One of these six (palladin) was recognized to play a role in maintaining normal actin cytoskeleton architecture (32), indicating a possible role in the same biological process as the four annotated genes within this SOM profile.…”