Mammalian Scribble Forms a Tight Complex with the βPIX Exchange Factor

Abstract

Drosophila Scribble is implicated in the development of normal synapse structure and epithelial tissues, but it remains unclear how it plays a role and which process it controls. The mammalian homolog of Scribble, hScrib, has a primary structure and subcellular localization similar to that of its fly homolog, but its function remains unknown. Here we have used tandem mass spectrometry to identify major components of the hScrib network. We show that it includes betaPIX (also called Cool-1), a guanine nucleotide exchange factor (GEF), and its partner GIT1 (also called p95-APP1), a GTPase activating protein (GAP). betaPIX directly binds to the hScrib PDZ domains, and the hScrib/betaPIX complex is efficiently recovered in epithelial and neuronal cells and tissues. In cerebellar granule cell cultures, hScrib and betaPIX are both partially localized at neuronal presynaptic compartments. Furthermore, we show that hScrib is required to anchor betaPIX at the cell cortex and that dominant-negative betaPIX or hScrib proteins can each inhibit Ca2+-dependent exocytosis in neuroendocrine PC12 cells, demonstrating a functional relationship between these proteins. These data reveal the existence of a tight hScrib/betaPIX interaction and suggest that this complex potentially plays a role in neuronal transmission.

The tumour-suppressor Scribble dictates cell polarity during directed epithelial migration: regulation of Rho GTPase recruitment to the leading edge

“…While Scribble knockdown did not affect Rac activation per se, it was required for Rac1 localization at the leading edge following scratchinduced migration, indicating that Scribble is essential for the appropriate polarized membrane localization of activated Rac1. In support of a direct role for Scribble in mediating Rac function, others have shown that Scribble can physically associate in a complex with Rac1 following stimulation of PC12 cells (Audebert et al, 2004). In addition, Scribble constitutively associates with the RacGEF bPix and the Arf-GAP protein GIT1 that was recently shown to be required for the restricted activation of Rac1 at the leading edge of migrating epithelial cells (Audebert et al, 2004;Nishiya et al, 2005).…”

“…In support of a direct role for Scribble in mediating Rac function, others have shown that Scribble can physically associate in a complex with Rac1 following stimulation of PC12 cells (Audebert et al, 2004). In addition, Scribble constitutively associates with the RacGEF bPix and the Arf-GAP protein GIT1 that was recently shown to be required for the restricted activation of Rac1 at the leading edge of migrating epithelial cells (Audebert et al, 2004;Nishiya et al, 2005). This presents the intriguing possibility that Scribble and GIT1 associate in a complex with bPix to coordinately regulate the spatially restricted activation of Rac1.…”

hScrib interacts with ZO‐2 at the cell–cell junctions of epithelial cells

“…We recently characterized a bPIX-GIT1 complex bound to the PDZ domains of hScrib [31]. hScrib has four PDZ domains that interact with multiple partners [32].…”

Scrib, un gène suppresseur de tumeurs impliqué dans la polarité cellulaire

“…De même les domaines PDZ semblent absolument nécessaires à la fonction de Scrib car leur suppression ou leur surexpression bloque totalement la polarisation des astrocytes en migration [14]. Les domaines PDZ permettent la liaison de nombreux partenaires parmi lesquels la protéine βPIX [26]. Dans les astrocytes, Scrib interagit de manière constitutive avec βPIX et cette interaction augmente au cours de la polarisation des cellules.…”