Phosphatidylinositol 3-kinase binds to α-actinin through the p85 subunit

Abstract

Phosphatidylinositol 3-kinase (PI 3-kinase) has been shown to play an important role in the signal transduction of cell growth. It is also suggested that it is involved in cytoskeletal reorganization. We have found that alpha-actinin copurifies with PI 3-kinase from bovine thymus. The antibody against PI 3-kinase 85 kDa subunit (p85) also co-immunoprecipitates alpha-actinin from lysates of NIH/3T3 cells. In addition, anti-alpha-actinin antibody coprecipitates PI 3-kinase activity. This coprecipitation was observed even after depolymerization of actin fibres, suggesting that PI 3-kinase binds directly to alpha-actinin. As alpha-actinin is a phosphatidylinositol 4,5-bisphosphate (PI4,5P2)-binding protein, binding experiments using various constructs of truncated p85 were carried out in the presence or absence of PI4,5P2. In the absence of PI4,5P2, chicken gizzard alpha-actinin binds only to the whole p85 construct, but it binds to the proline-rich region of p85 fragments in the presence of PI4,5P2. This binding is enhanced with increased concentrations of Pi4,5P2 up to 10 microM, whereas phosphatidylinositol and phosphatidylinositol 4-phosphate were not good activators of alpha-actinin binding. These results suggest that PI 3-kinase binds to alpha-actinin and regulates cytoskeletal reorganization.

Cadherins are regulated by Ep-CAM via phosphaditylinositol-3 kinase

“…The same findings have been described for Ep-CAM expression [13][14][15]. As previously described, both Ep-CAM and p85, the regulatory subunit of Pi3K, are capable to bind a-actinin, although under different conditions [11,16]. Our results demonstrating co-precipitation of Ep-CAM and p85 suggest for the first time that these molecules do interact.…”

“…Both Ep-CAM and p85, the regulatory subunit of Pi3K, can bind a-actinin, although under different experimental conditions [11,16]. Recently, p85 was found to bind to a specific domain in membrane-bound ezrin, a plasma membrane-microfilament linker.…”

Phosphorylation–dependent interaction of the N‐methyl‐ d‐aspartate receptor ε2 subunit with phosphatidylinositol 3‐kinase

“…To determine the region of p85 that was responsible for its binding to tyrosine-phosphorylated NMDAR«2, we used GST-fusion proteins containing various regions of p85 [Full,SH3,SH2 (N), and SH2 (C)] (Shibasaki et al 1994;Itoh et al 1996). The mouse brain lysate was incubated with these fusion proteins.…”

The Cytoskeletal/Non-muscle Isoform of α-Actinin Is Phosphorylated on Its Actin-binding Domain by the Focal Adhesion Kinase

“…A partial list of proteins includes vinculin (17), zyxin (18), and the newly described proteins palladin (19) and CLP-36 (20,21). A third group of proteins that interact with ␣-actinin includes signaling molecules such as extracellular signal-regulated kinase 1 (22), mitogen-activated protein kinase/extracellular signal-regulated kinase kinase kinase 1 (23), PKN, a fatty acid and Rho-activated serine/threonine protein kinase (24), and the p85 subunit of phosphatidylinositol 3-kinase (25). The broad spectrum of molecules with which ␣-actinin interacts strongly suggests that in addition to its role as an actin cross-linking protein, ␣-actinin also functions as a scaffold to promote protein-protein interactions.…”