A growth factor signaling cascade confined to circular ruffles in macrophages
Summary The formation of macropinosomes requires large-scale movements of membranes and the actin cytoskeleton. Over several minutes, actin-rich surface ruffles transform into 1–5 µm diameter circular ruffles, which close at their distal margins, creating endocytic vesicles. Previous studies using f...
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doaj-10043ca2af1942b5bb30ccc62dec0b062021-06-02T18:02:20ZengThe Company of BiologistsBiology Open2046-63902012-06-011875476010.1242/bio.2012178420121784A growth factor signaling cascade confined to circular ruffles in macrophagesTimothy P. Welliver0Joel A. Swanson1 Program in Immunology, University of Michigan Medical School, Ann Arbor, MI 48109-5620, USA Program in Immunology, University of Michigan Medical School, Ann Arbor, MI 48109-5620, USA Summary The formation of macropinosomes requires large-scale movements of membranes and the actin cytoskeleton. Over several minutes, actin-rich surface ruffles transform into 1–5 µm diameter circular ruffles, which close at their distal margins, creating endocytic vesicles. Previous studies using fluorescent reporters of phosphoinositides and Rho-family GTPases showed that signals generated by macrophages in response to the growth factor Macrophage Colony-Stimulating Factor (M-CSF) appeared transiently in domains of plasma membrane circumscribed by circular ruffles. To address the question of how signaling molecules are coordinated in such large domains of plasma membrane, this study analyzed the relative timing of growth factor-dependent signals as ruffles transformed into macropinosomes. Fluorescent protein chimeras expressed in macrophages were imaged by microscopy and quantified relative to circular ruffle formation and cup closure. The large size of macropinocytic cups allowed temporal resolution of the transitions in phosphoinositides and associated enzyme activities that organize cup closure. Circular ruffles contained transient and sequential spikes of phosphatidylinositol (4,5)-bisphosphate (PI(4,5)P2), phosphatidylinositol (3,4,5)-trisphosphate (PIP3), diacylglycerol, PI(3,4)P2, PI(3)P and the activities of protein kinase C-α, Rac1, Ras and Rab5. The confinement of this signal cascade to circular ruffles indicated that diffusion barriers present in these transient structures focus feedback activation and deactivation of essential enzyme activities into restricted domains of plasma membrane.http://bio.biologists.org/content/1/8/754MacropinocytosisPhosphoinositidesSignal transition |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
Timothy P. Welliver Joel A. Swanson |
spellingShingle |
Timothy P. Welliver Joel A. Swanson A growth factor signaling cascade confined to circular ruffles in macrophages Biology Open Macropinocytosis Phosphoinositides Signal transition |
author_facet |
Timothy P. Welliver Joel A. Swanson |
author_sort |
Timothy P. Welliver |
title |
A growth factor signaling cascade confined to circular ruffles in macrophages |
title_short |
A growth factor signaling cascade confined to circular ruffles in macrophages |
title_full |
A growth factor signaling cascade confined to circular ruffles in macrophages |
title_fullStr |
A growth factor signaling cascade confined to circular ruffles in macrophages |
title_full_unstemmed |
A growth factor signaling cascade confined to circular ruffles in macrophages |
title_sort |
growth factor signaling cascade confined to circular ruffles in macrophages |
publisher |
The Company of Biologists |
series |
Biology Open |
issn |
2046-6390 |
publishDate |
2012-06-01 |
description |
Summary
The formation of macropinosomes requires large-scale movements of membranes and the actin cytoskeleton. Over several minutes, actin-rich surface ruffles transform into 1–5 µm diameter circular ruffles, which close at their distal margins, creating endocytic vesicles. Previous studies using fluorescent reporters of phosphoinositides and Rho-family GTPases showed that signals generated by macrophages in response to the growth factor Macrophage Colony-Stimulating Factor (M-CSF) appeared transiently in domains of plasma membrane circumscribed by circular ruffles. To address the question of how signaling molecules are coordinated in such large domains of plasma membrane, this study analyzed the relative timing of growth factor-dependent signals as ruffles transformed into macropinosomes. Fluorescent protein chimeras expressed in macrophages were imaged by microscopy and quantified relative to circular ruffle formation and cup closure. The large size of macropinocytic cups allowed temporal resolution of the transitions in phosphoinositides and associated enzyme activities that organize cup closure. Circular ruffles contained transient and sequential spikes of phosphatidylinositol (4,5)-bisphosphate (PI(4,5)P2), phosphatidylinositol (3,4,5)-trisphosphate (PIP3), diacylglycerol, PI(3,4)P2, PI(3)P and the activities of protein kinase C-α, Rac1, Ras and Rab5. The confinement of this signal cascade to circular ruffles indicated that diffusion barriers present in these transient structures focus feedback activation and deactivation of essential enzyme activities into restricted domains of plasma membrane. |
topic |
Macropinocytosis Phosphoinositides Signal transition |
url |
http://bio.biologists.org/content/1/8/754 |
work_keys_str_mv |
AT timothypwelliver agrowthfactorsignalingcascadeconfinedtocircularrufflesinmacrophages AT joelaswanson agrowthfactorsignalingcascadeconfinedtocircularrufflesinmacrophages AT timothypwelliver growthfactorsignalingcascadeconfinedtocircularrufflesinmacrophages AT joelaswanson growthfactorsignalingcascadeconfinedtocircularrufflesinmacrophages |
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