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Institute for Research in Biomedicine
Istituto di Ricerca in Biomedicina

Via Vincenzo Vela 6 - CH-6500 Bellinzona
Tel. +41 91 820 0300 - Fax +41 91 820 0302 - info [at] irb [dot] usi [dot] ch

The guanine nucleotide exchange factor for Rac P-Rex1

Research area: Signal Transduction

Group leaders: Marcus Thelen


Status: In progress

The small GTPases of the Rho family, Rac and Cdc42, are critical for rapid rearrangements of the actin cytoskeleton observed during filopodia and lamellipodia formation in migrating cells.  Activation of the GTPases is catalyzed by specific GTP exchange factors (GEF). The phosphatidylinositol 3,4,5-trisphosphate (PIP3)-dependent exchanger 1 (P-Rex1) is assumed to be involved in G-protein coupled receptor (GPCR)-mediated Rac activation. P-Rex1 activity is stimulated by the PI 3-kinase product PIP3 and by the βγ subunits of heterotrimeric G-proteins, which are released upon activation of GPCRs. Consistent with the activation by these cofactors and their cellular localization following stimulation of the cells, P-Rex1 is recruited to the plasma membrane. Overexpression of P-Rex1 or its suppression by siRNA markedly alters chemokine-stimulated migratory capacity of myeloid leukocytes, consistent with the assumption that GEF is required for efficient chemotaxis.

Investigations shall reveal the function of different P-Rex1 domains and their role in chemokine receptor-mediated signal transduction. In particular downstream of the chemokine receptor CCR2, a typical GPCR. To this end mouse bone-marrow derived hematopoietic precursor cells from animals lacking either the expression of P-Rex1 and/or P-rex2 or CCR2  are arrested by the conditional expression of HoxB8 and HoxA9. Various P-Rex1 mutants and variants of CCR2 tagged with epitopes suitable for fluorescent labeling are transduced into these cells and differentiated later into neutrophils and monocytes.  Assessment of the chemotactic responsiveness allows to delineate the function of different P-Rex domains and the localization of the chemokine receptor CCR2 during migration.