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C H A P T E R
11
Intracellular signaling
Larry Ruben 1 , John M. Kelly 2 and
Debopam Chakrabarti 3
1 Department of Biological Sciences, Southern Methodist University,
Dallas, TX, USA;
2 Department of Infectious and Tropical Diseases, London School of Hygiene
and Tropical Medicine, London, UK; and
3 Department of Molecular Biology & Microbiology, University of Central Florida,
Orlando, FL, USA
OVERVIEW
Signal pathways are used by cells to elicit coordinated
changes in activity. Components of
motility, cell division, gene expression, energy
metabolism and secretion are potential targets
of regulatory control. Signal processes are
of interest because when they go awry, the result
is inappropriate cell behavior that can be lethal.
Consequently, some of the most heavily prescribed
pharmaceutical agents are directed
towards ablation or activation of signal
cascades.
A variety of molecules have been adopted
for use in signal production. These molecules
are typically allosteric regulators of specific
enzyme targets, and are neither substrates nor
products of the metabolic pathways they regulate.
Among the most widely studied signal
molecules are divalent cations, nucleotides,
phosphoryl transfer and phospholipid metabolites.
Phospholipids provide an especially
diverse source of signal molecules where polar
head groups (in the case of inositol phosphates),
fatty acyl chains (such as arachidonic
acid and its metabolites) and diacylglycerol
can function to regulate cell activity. The following
review focuses on intracellular signals
within protozoan parasites. Emphasis is placed
upon the ability of Ca 2 , cyclic nucleotides or
phosphoryl transfer to regulate cellular events.
Comparisons are made with metazoans, whose
broad range of interactions creates a rich
tapestry of signaling networks. By comparison,
the genomes of unicellular organisms reveal a
somewhat reduced signal capacity, with diminished
numbers of plasma membrane receptors,
hormone responsive transcription factors, and
Molecular Medical Parasitology
ISBN 0–12–473346–8
241
Copyright © 2003 Elsevier Science Ltd.
All rights of reproduction in any form reserved.