Spatial Sensing in Fibroblasts Mediated by 3′ Phosphoinositides

Abstract

The directed movement of fibroblasts towards locally released platelet-derived growth factor (PDGF) is a critical event in wound healing. Although recent studies have implicated polarized activation of phosphoinositide (PI) 3-kinase in G protein-mediated chemotaxis, the role of 3′ PI lipids in tyrosine kinase-triggered chemotaxis is not well understood. Using evanescent wave microscopy and green fluorescent protein–tagged Akt pleckstrin homology domain (GFP–AktPH) as a molecular sensor, we show that application of a shallow PDGF gradient triggers a markedly steeper gradient in 3′ PI lipids in the adhesion zone of fibroblasts. Polar GFP–AktPH gradients, as well as a new type of radial gradient, were measured from front to rear and from the periphery to the center of the adhesion zone, respectively. A strong spatial correlation between polarized 3′ PI production and rapid membrane spreading implicates 3′ PI lipids as a direct mediator of polarized migration. Analysis of the temporal changes of 3′ PI gradients in the adhesion zone revealed a fast diffusion coefficient (0.5 μm2/s) and short lifetime of 3′ PIs of <1 min. Together, this study suggests that the tyrosine kinase-coupled directional movement of fibroblasts and their radial membrane activity are controlled by local generation and rapid degradation of 3′ PI second messengers.

A PtdInsP3- and Rho GTPase-mediated positive feedback loop regulates neutrophil polarity

“…In summary, PtdInsP 3 asymmetries are observed during chemotaxis of many cells, from neutrophils 3 to Dictyostelium 1,2 to fibroblasts 4 , and in response to very different stimuli, such as ligands for G-protein coupled receptors [1][2][3] and tyrosine kinase receptors 4 , as well as direct delivery of PtdInsP 3 , as we have shown. We propose that the emergent properties of positive and negative regulatory links between PtdInsP 3 and Rho GTPases constitute a broadly conserved module for establishing cell polarity during eukaryotic chemotaxis.…”

Polarization and Movement of Keratocytes: A Multiscale Modelling Approach

“…of a chemoattractant, processed and integrated internally in a motile cell and transduced to its cytoskeleton, eventually determines the direction of cell movement (Haugh et al, 2000;Funamoto et al, 2002). Signal transduction pathways transmit signals from membrane-bound receptors to 'central nodes', including the small G-proteins, Cdc42, Rac, and Rho (also called the "rho family proteins") (Meili and Firtel, 2003).…”

Signaling mechanisms for regulation of chemotaxis

“…1B). Among all these, the polarized distribution of a phospholipid, PIP 3 , which was initially observed in Dictyostelium [16] and later in neutrophils [17] and other cells [18], appears to occur prior to other polarization events. PIP3 is converted from PIP 2 by PI3K [19].…”