scholarly journals The origins and evolution of macropinocytosis

2018 ◽  
Vol 374 (1765) ◽  
pp. 20180158 ◽  
Author(s):  
Jason S. King ◽  
Robert R. Kay
Keyword(s):  
Growth Factor ◽  
Actin Polymerization ◽  
Common Ancestor ◽  
Growth Factor Receptor ◽  
Phosphatidylinositol 3 Kinase ◽  
Growth Factor Signalling ◽  
Core Components ◽  
The Common ◽  
Phagocytic Cups ◽  
Coupled Growth

In macropinocytosis, cells take up micrometre-sized droplets of medium into internal vesicles. These vesicles are acidified and fused to lysosomes, their contents digested and useful compounds extracted. Indigestible contents can be exocytosed. Macropinocytosis has been known for approaching 100 years and is described in both metazoa and amoebae, but not in plants or fungi. Its evolutionary origin goes back to at least the common ancestor of the amoebozoa and opisthokonts, with apparent secondary loss from fungi. The primary function of macropinocytosis in amoebae and some cancer cells is feeding, but the conserved processing pathway for macropinosomes, which involves shrinkage and the retrieval of membrane to the cell surface, has been adapted in immune cells for antigen presentation. Macropinocytic cups are large actin-driven processes, closely related to phagocytic cups and pseudopods and appear to be organized around a conserved signalling patch of PIP3, active Ras and active Rac that directs actin polymerization to its periphery. Patches can form spontaneously and must be sustained by excitable kinetics with strong cooperation from the actin cytoskeleton. Growth-factor signalling shares core components with macropinocytosis, based around phosphatidylinositol 3-kinase (PI3-kinase), and we suggest that it evolved to take control of ancient feeding structures through a coupled growth factor receptor. This article is part of the Theo Murphy meeting issue ‘Macropinocytosis’.

scholarly journals Macropinosomes as units of signal transduction

2018 ◽  
Vol 374 (1765) ◽  
pp. 20180157 ◽  
Author(s):  
Joel A. Swanson ◽  
Sei Yoshida
Keyword(s):  
Signal Transduction ◽  
Amino Acids ◽  
Growth Factor ◽  
Morphological Changes ◽  
Feedback Regulation ◽  
Phosphatidylinositol 3 Kinase ◽  
Cell Dimensions ◽  
Growth Factor Signalling ◽  
Dependent Growth ◽  
Biochemical Signals

Macropinosome formation occurs as a localized sequence of biochemical activities and associated morphological changes, which may be considered a form of signal transduction leading to the construction of an organelle. Macropinocytosis may also convey information about the availability of extracellular nutrients to intracellular regulators of metabolism. Consistent with this idea, activation of the metabolic regulator mechanistic target of rapamycin complex-1 (mTORC1) in response to acute stimulation by growth factors and extracellular amino acids requires internalization of amino acids by macropinocytosis. This suggests that macropinocytosis is necessary for mTORC1-dependent growth of metazoan cells, both as a route for delivery of amino acids to sensors associated with lysosomes and as a platform for growth factor-dependent signalling to mTORC1 via phosphatidylinositol 3-kinase (PI3K) and the Akt pathway. Because the biochemical signals required for the construction of macropinosomes are also required for cell growth, and inhibition of macropinocytosis inhibits growth factor signalling to mTORC1, we propose that signalling by growth factor receptors is organized into stochastic, structure-dependent cascades of chemical reactions that both build a macropinosome and stimulate mTORC1. More generally, as discrete units of signal transduction, macropinosomes may be subject to feedback regulation by metabolism and cell dimensions. This article is part of the Theo Murphy meeting issue ‘Macropinocytosis’.

scholarly journals Integration of the Extranuclear and Nuclear Actions of Estrogen

2005 ◽  
Vol 19 (8) ◽  
pp. 1951-1959 ◽  
Author(s):  
Ellis R. Levin
Keyword(s):  
Signal Transduction ◽  
Growth Factor ◽  
Tyrosine Kinases ◽  
Growth Factor Receptor ◽  
Sex Steroid ◽  
Phosphatidylinositol 3 Kinase ◽  
Epidermal Growth ◽  
Small Pool ◽  
Physiological Outcomes ◽  
Nuclear Effects

Abstract Estrogen receptors (ERs) are localized to many sites within the cell, potentially contributing to overall estrogen action. In the nucleus, estrogen mainly modulates gene transcription, and the resulting protein products determine the cell biological actions of the sex steroid. In addition, a small pool of ERs localize to the plasma membrane and signal mainly though coupling, directly or indirectly, to G proteins. In response to steroid, signal transduction modulates both nontranscriptional and transcriptional events and impacts both the rapid and more prolonged actions of estrogen. Cross-talk from membrane-localized ERs to nuclear ERs can be mediated through growth factor receptor tyrosine kinases, such as epidermal growth factor receptor and IGF-I receptor. Growth factor receptors enact signal transduction to kinases such as ERK and phosphatidylinositol 3-kinase that phosphorylate and activate nuclear ERs, and this can also occur in the absence of sex steroid. A complex relationship between the membrane and nuclear effects of estrogen also involves membrane-initiated phosphorylation of coactivators, recruiting these proteins to the nuclear transcriptosome. Finally, large pools of cytoplasmic ERs exist, and some are localized to mitochondria. The integration of sex steroid effects at distinct cellular locations of its receptor leads to important cellular physiological outcomes and are manifest in both reproductive and nonreproductive organs.

scholarly journals Endosomal receptor kinetics determine the stability of intracellular growth factor signalling complexes

2007 ◽  
Vol 402 (3) ◽  
pp. 537-549 ◽  
Author(s):  
A. Rami Tzafriri ◽  
Elazer R. Edelman
Keyword(s):  
Growth Factor ◽  
Cell Surface ◽  
Dissociation Constant ◽  
Specific Binding ◽  
Ph Dependence ◽  
Growth Factor Receptor ◽  
Factor Binding ◽  
Receptor Complexes ◽  
Growth Factor Signalling ◽  
The Stability

There is an emerging paradigm that growth factor signalling continues in the endosome and that cell response to a growth factor is defined by the integration of cell surface and endosomal events. As activated receptors in the endosome are exposed to a different set of binding partners, they probably elicit differential signals compared with when they are at the cell surface. As such, complete appreciation of growth factor signalling requires understanding of growth factor–receptor binding and trafficking kinetics both at the cell surface and in endosomes. Growth factor binding to surface receptors is well characterized, and endosomal binding is assumed to follow surface kinetics if one accounts for changes in pH. Yet, specific binding kinetics within the endosome has not been examined in detail. To parse the factors governing the binding state of endosomal receptors we analysed a whole-cell mathematical model of epidermal growth factor receptor trafficking and binding. We discovered that the stability of growth factor–receptor complexes within endosomes is governed by three primary independent factors: the endosomal dissociation constant, total endosomal volume and the number of endosomal receptors. These factors were combined into a single dimensionless parameter that determines the endosomal binding state of the growth factor–receptor complex and can distinguish different growth factors from each other and different cell states. Our findings indicate that growth factor binding within endosomal compartments cannot be appreciated solely on the basis of the pH-dependence of the dissociation constant and that the concentration of receptors in the endosomal compartment must also be considered.

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