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Infection and Immunity, November 2000, p. 6402-6410, Vol. 68, No. 11
Institute of Cell, Animal and Population
Biology, University of Edinburgh, Edinburgh EH9 3JT, United Kingdom
Received 7 March 2000/Returned for modification 8 May 2000/Accepted 9 August 2000
A novel member of the transforming growth factor
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Identification of tgh-2, a Filarial Nematode Homolog
of Caenorhabditis elegans daf-7 and Human Transforming
Growth Factor
, Expressed in Microfilarial and Adult Stages
of Brugia malayi
(TGF-
)
family has been identified in the filarial nematode parasite
Brugia malayi by searching the recently developed Expressed
Sequence Tag (EST) database produced by the Filarial Genome Project.
Designated tgh-2, this new gene shows most similarity to a
key product regulating dauer larva formation in Caenorhabditis
elegans (DAF-7) and to the human down-modulatory cytokine
TGF-
. Homology to DAF-7 extends throughout the length of the
349-amino-acid (aa) protein, which is divided into an N-terminal 237 aa, including a putative signal sequence, a 4-aa basic cleavage site,
and a 108-aa C-terminal active domain. Similarity to human TGF-
is
restricted to the C-terminal domain, over which there is a 32%
identity between TGH-2 and TGF-
1, including every cysteine residue.
Expression of tgh-2 mRNA has been measured over the
filarial life cycle. It is maximal in the microfilarial stage, with
lower levels of activity around the time of molting within the mammal,
but continues to be expressed by mature adult male and female
parasites. Expression in both the microfilaria, which is in a state of
arrested development, and the adult, which is terminally
differentiated, indicates that tgh-2 may play a role other
than purely developmental. This is consistent with our observation that
TGH-2 is secreted by adult worms in vitro. Recombinant TGH-2 expressed
in baculovirus shows a low level of binding to TGF-
-receptor bearing
mink lung epithelial cells (MELCs), which is partially inhibited (16 to
39%) with human TGF-
, and activates plasminogen activator
inhibitor-1 transcription in MELCs, a marker for TGF-
-mediated
transduction. Further tests will be required to establish whether the
major role of B. malayi TGH-2 (Bm-TGH-2) is to modulate the
host immune response via the TGF-
pathway.
*
Corresponding author. Mailing address: Institute of
Cell, Animal and Population Biology, University of Edinburgh, West
Mains Road, Edinburgh EH9 3JT, United Kingdom. Phone: (44) 131 650 5511. Fax: (44) 131 650 5450. E-mail:
rick.maizels{at}ed.ac.uk.
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