The Phosphoinositol 3,4-Bisphosphate-binding Protein TAPP1 Interacts with Syntrophins and Regulates Actin Cytoskeletal Organization

Abstract

Syntrophins are scaffold proteins of the dystrophin glycoprotein complex (DGC), which target ion channels, receptors, and signaling proteins to specialized subcellular domains. A yeast two-hybrid screen of a human brain cDNA library with the PSD-95, Discs-large, ZO-1 (PDZ) domain of ␥1-syntrophin yielded overlapping clones encoding the C terminus of TAPP1, a pleckstrin homology (PH) domain-containing adapter protein that interacts specifically with phosphatidylinositol 3,4-bisphosphate (PI(3,4)P 2 ). In biochemical assays, the C terminus of TAPP1 bound specifically to the PDZ domains of ␥1-, ␣1-, and ␤2-syntrophin and was required for syntrophin binding and for the correct subcellular localization of TAPP1. TAPP1 is recruited to the plasma membrane of cells stimulated with platelet-derived growth factor (PDGF), a motogen that produces PI(3,4)P 2 . Cell migration in response to PDGF stimulation is characterized by a rapid reorganization of the actin cytoskeleton, which gives rise to plasma membrane specializations including peripheral and dorsal circular ruffles. Both TAPP1 and syntrophins were localized to PDGF-induced circular membrane ruffles in NIH-3T3 cells. Ectopic expression of TAPP1 potently blocked PDGF-induced formation of dorsal circular ruffles, but did not affect peripheral ruffling. Interestingly, coexpression of ␣1-or ␥1-syntrophin with TAPP1 prevented the blockade of circular ruffling. In addition to syntrophins, several other proteins of the DGC were enriched in circular ruffles. Collectively, our results suggest syntrophins regulate the localization of TAPP1, which may be important for remodeling the actin cytoskeleton in response to growth factor stimulation.

Quantification and visualization of phosphoinositides by quantum dot-labeled specific binding-domain probes

“…These transient and dynamic changes in the actin cytoskeleton are initiated by the production of consistent with previous reports ( 24,25 ) ( Fig. 7B ).…”

PTPL1: a large phosphatase with a split personality

“…The FERM domain of PTPL1 binds PIP2 as an intermediate step in plasma membrane localization [24]. TAPP1/2 are cytoplasmic adaptor proteins that can shuttle to the cell membrane via PIP2 binding and remodel the actin cytoskeleton [61]. EphrinB1 is a member of a class of transmembrane proteins that modulate many physiological functions including, but not limited to, cell motility [62].…”

Phosphatidylinositol Bisphosphate Mediated Sorting of Secretory Granule Cargo

“…Recently, PtdIns(3,4)P 2 was found to be transiently synthesized at the plasmalemma as a second messenger of platelet-derived growth factor (PDGF) (Hogan et al 2004). Importantly, our understanding of the roles of PtdInsPs derives primarily from studies of yeast and a few mammalian cell lines.…”

“…However, PtdIns(3,4)P 2 has tended to be neglected in studies of PtdInsP distribution, so little information is available. Nonetheless, immunofluorescence of a transfected PtdIns(3,4)P 2 -binding protein (TAPP1) showed clear localization to a Golgi-like structure adjacent to the nucleus (Hogan et al 2004). We isolated parotid gland secretory granules, and methanolic extracts of purified granule membranes were spotted on PVDF and probed with antibodies to specific phosphoinositides.…”