Spatial and Temporal Regulation of 3-Phosphoinositides by PI 3-Kinase and PTEN Mediates Chemotaxis

Abstract

We have investigated the mechanisms of leading edge formation in chemotaxing Dictyostelium cells. We demonstrate that while phosphatidylinositol 3-kinase (PI3K) transiently translocates to the plasma membrane in response to chemoattractant stimulation and to the leading edge in chemotaxing cells, PTEN, a negative regulator of PI3K pathways, exhibits a reciprocal pattern of localization. By uniformly localizing PI3K along the plasma membrane, we show that chemotaxis pathways are activated along the lateral sides of cells and PI3K can initiate pseudopod formation, providing evidence for a direct instructional role of PI3K in leading edge formation. These findings provide evidence that differential subcellular localization and activation of PI3K and PTEN is required for proper chemotaxis.

Identification of PTEN at the ER and MAMs and its regulation of Ca2+ signaling and apoptosis in a protein phosphatase-dependent manner

“…Localized PTEN activity appears to establish PIP3 signal gradients that regulate cell polarity during motility. 10 In addition, nuclear PTEN has important tumor-suppressive functions, 11,12 and mitochondrially localized PTEN contributes to mitochondria-dependent apoptosis under certain circumstances. 13,14 Mitochondria and endoplasmic reticulum (ER) have emerged as cellular targets of oncogenes and tumor suppressors, as they are crucial nodes where significant remodeling of calcium (Ca 2 þ ) signaling occurs in tumor cells to sustain proliferation and avoid cell death.…”

Signaling mechanisms for regulation of chemotaxis

“…PTEN is a protein and phospholipid phosphatase that can dephosphorylate PIP 3 [19,[47][48][49][50][51]. In chemotaxing Dictyostelium cells, PTEN was found to be translocated to the posterior membranes of the cells [45,46]. In chemotaxing neutrophils, we found that PTEN was also localized at the posterior and that this localization was dependent on PIXα [10].…”

“…Although we do not have a definitive answer to the question, one hypothesis suggests that this may be a result of amplification of a small receptor activation gradient corresponding to the ligand gradient through a cascade of positive feedbacks and negative regulations [43,44]. Studies from Dictyostelium suggest that PTEN is one of the negative regulators that helps establishing and maintaining the PIP 3 gradient [45,46]. PTEN is a protein and phospholipid phosphatase that can dephosphorylate PIP 3 [19,[47][48][49][50][51].…”

Dynamic Localization of the Actin-Bundling Protein Cortexillin I during Cell Migration

“…Upon chemoattractant stimulation, there is a rapid release of cortexillin I from the cortex followed by a transient translocation to the cell cortex with a peak at ~5 s and a subsequent decrease to the basal level. An initial delocalization from the cell cortex upon stimulation is also found in the translocation kinetics of several proteins including myosin II, PTEN, and PakA (Chung and Firtel, 1999;Funamoto et al, 2002;Jeon et al, 2007b), but the subsequent transient translocation of cortexillin I to the cortex within 10 s is not observed with other proteins. The transient translocation kinetics of cortexillin I, except the initial delocalization of the proteins, is similar to that of the Arp2/3 complex, a nucleator of F-actin assembly.…”

“…To understand temporal translocation kinetics of cortexillin I in more detail, the cell cortex translocation kinetics of cortexillin I were compared with those of other F-actin binding proteins such as ArpD, a subunit of Arp2/3 complex (Rodal et al, 2005), and coronin and PhdA-GFP (Funamoto et al, 2002), a pleckstrin homology domain containing PIP3 reporter (Fig. 3C).…”