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Sci. Signal., 19 May 2009
Vol. 2, Issue 71, p. ra22
[DOI: 10.1126/scisignal.2000054]


Deciphering Signaling Outcomes from a System of Complex Networks

Robert C. Hsueh1*{dagger}, Madhusudan Natarajan1*{ddagger}, Iain Fraser2, Blake Pond1, Jamie Liu2, Susanne Mumby1, Heping Han1, Lily I. Jiang1, Melvin I. Simon2, Ronald Taussig1, and Paul C. Sternweis1§

1 University of Texas Southwestern Medical Center, Dallas, TX 75390–9041, USA.
2 California Institute of Technology, Pasadena, CA 91125, USA.

* These authors contributed equally to this work.

{dagger} Present address: Cadent Medical Communications, Irving, TX 75063, USA.

{ddagger} Present address: Systems Biology Group, Pfizer Research Technology Centre, Cambridge, MA 02139, USA.

Abstract: Cellular signal transduction machinery integrates information from multiple inputs to actuate discrete cellular behaviors. Interaction complexity exists when an input modulates the output behavior that results from other inputs. To address whether this machinery is iteratively complex—that is, whether increasing numbers of inputs produce exponential increases in discrete cellular behaviors—we examined the modulated secretion of six cytokines from macrophages in response to up to five-way combinations of an agonist of Toll-like receptor 4, three cytokines, and conditions that activated the cyclic adenosine monophosphate pathway. Although all of the selected ligands showed synergy in paired combinations, few examples of nonadditive outputs were found in response to higher-order combinations. This suggests that most potential interactions are not realized and that unique cellular responses are limited to discrete subsets of ligands and pathways that enhance specific cellular functions.

§ To whom correspondence should be addressed. Department of Pharmacology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390–9041, USA. E-mail: Paul.Sternweis{at}

Citation: R. C. Hsueh, M. Natarajan, I. Fraser, B. Pond, J. Liu, S. Mumby, H. Han, L. I. Jiang, M. I. Simon, R. Taussig, P. C. Sternweis, Deciphering Signaling Outcomes from a System of Complex Networks. Sci. Signal. 2, ra22 (2009).

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