HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Wabnitz, G. H. Articles by Samstag, Y. Search for Related Content PubMed PubMed Citation Articles by Wabnitz, G. H. Articles by Samstag, Y. Pubmed/NCBI databases Substance via MeSH

Phosphatidylinositol 3-Kinase Functions as a Ras Effector in the Signaling Cascade That Regulates Dephosphorylation of the Actin-Remodeling Protein Cofilin after Costimulation of Untransformed Human T Lymphocytes¹

Ruprecht Karls University, Institute of Immunology, Heidelberg, Germany

The activity of cofilin, an actin-remodeling protein, is required for T lymphocyte activation with regard to formation of the immunological synapse, cytokine production, and proliferation. In unstimulated T PBL (PB-T), cofilin is present in its Ser³-phosphorylated inactive form. Costimulation of TCR/CD3 and CD28 induces dephosphorylation and, thus, activation of cofilin. In this study we characterized the signaling cascades leading to cofilin activation in untransformed human PB-T. We show that a Ras-PI3K cascade regulates dephosphorylation of cofilin in PB-T. The GTPase Ras is a central mediator of this pathway; transient expression of an activated form of H-Ras in PB-T triggered the dephosphorylation of cofilin. Inhibition of either MAPK/ERK kinase or PI3K blocked both Ras-induced and costimulation-induced cofilin dephosphorylation in PB-T, showing that the combined activities of both signaling proteins are required to activate cofilin. That Ras functions as a central regulator of cofilin dephosphorylation after costimulation through CD3 x CD28 was finally proven by transient expression of a dominant negative form of H-Ras in primary human PB-T. It clearly inhibited costimulation-induced cofilin dephosphorylation, and likewise, activation of PI3K was diminished. Our data, in addition, demonstrate that regarding the downstream effectors of Ras, a clear difference exists between untransformed human PB-T and the T lymphoma line Jurkat. Thus, in PB-T the Ras signaling cascade is able to activate PI3K, whereas in Jurkat cells this is not the case. In addition to the insights into the regulation of cofilin, this finding discloses a to date unrecognized possibility of PI3K activation in T lymphocytes.

This article has been cited by other articles:

				M. Gutscher, M. C. Sobotta, G. H. Wabnitz, S. Ballikaya, A. J. Meyer, Y. Samstag, and T. P. Dick Proximity-based Protein Thiol Oxidation by H2O2-scavenging Peroxidases J. Biol. Chem., November 13, 2009; 284(46): 31532 - 31540. [Abstract] [Full Text] [PDF]

				F. Garcon, D. T. Patton, J. L. Emery, E. Hirsch, R. Rottapel, T. Sasaki, and K. Okkenhaug CD28 provides T-cell costimulation and enhances PI3K activity at the immune synapse independently of its capacity to interact with the p85/p110 heterodimer Blood, February 1, 2008; 111(3): 1464 - 1471. [Abstract] [Full Text] [PDF]

				Y. Huang and J. K. Burkhardt T-cell-receptor-dependent actin regulatory mechanisms J. Cell Sci., March 1, 2007; 120(5): 723 - 730. [Abstract] [Full Text] [PDF]