Editors' ChoiceCell Motility

Pseudopodial Proteome

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Science's STKE  22 May 2007:
Vol. 2007, Issue 387, pp. tw178
DOI: 10.1126/stke.3872007tw178

There is abundant evidence for polarity of moving cells. Certain signaling pathways are critical for cell movement, some key signaling molecules are inhomogeneously distributed in the cell, and dramatic reorganization of the cytoskeleton occurs primarily at the front of the cell. Wang et al. provide new insights into these phenomena through the global analysis of the proteome and phosphoproteome in the cell body versus the pseudopod at the front of a moving cell. Cos-7 cells were grown on microporous filters and then exposed to a chemotactic agent. The pseudopods were manually separated from the cell bodies, and the two fractions were subjected to liquid-chromatography-coupled tandem mass spectrometry (LC-MS/MS) or phosphoprotein analysis by immobilized metal affinity chromatography of isotopically labeled samples. About 3500 proteins were identified by LC-MS/MS; ~1300 were evenly distributed between the cell body and the pseudopod, and approximately equal numbers (~1100) were selectively enriched in either the cell body or the pseudopod. Not surprisingly, the cell body was enriched in proteins involved in nuclear receptor signaling, cell cycle regulation, and DNA and RNA metabolism, whereas the pseudopod was enriched in proteins that regulate the actin cytoskeleton, integrin signaling, and axon guidance. Phosphoproteome analysis identified 228 peptides, one-third of which were enriched in the pseudopod and ~40% of which were enriched in the cell body. The phosphorylated proteins fell into four categories: (i) Those for which high phosphorylation correlated with high abundance within a particular compartment, (ii) those for which abundance and phosphorylation were inversely correlated, (iii) those for which abundance was relatively uniform but phosphorylation was enriched in one compartment, and (iv) those for which the phosphorylated proteins were uniformly distributed but site-specific phosphorylation was enriched in one compartment. The proteins that activate or inhibit mitogen-activated protein kinase ERK, which is known to function in chemotaxis, were analyzed in greater detail, and the authors constructed three pathways by which ERK could be activated in chemotaxing cells: one from the G protein-coupled receptor activated by lysophosphatidic acid, one from transactivation of epidermal growth factor receptors, and one from integrins. Negative influences were also noted.

Y. Wang, S.-J. Ding, W. Wang, J. M. Jacobs, W.-J. Qian, R. J. Moore, F. Yang, D. G. Camp, II, R. D. Smith, R. L. Klemke, Profiling signaling polarity in chemotactic cells. Proc. Natl. Acad. Sci. U.S.A. 104, 8328-8333 (2007). [Abstract] [Full Text]

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