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Blood, 15 April 2001, Vol. 97, No. 8, pp. 2390-2400
IMMUNOBIOLOGY
Regulation of nuclear factor of activated T cells by
phosphotyrosyl-specific phosphatase activity: a positive effect on
HIV-1 long terminal repeat-driven transcription and a possible
implication of SHP-1
Jean-François Fortin,
Benoit Barbeau,
Gilles A. Robichaud,
Marie-Ève Paré,
Anne-Marie Lemieux, and
Michel J. Tremblay
From the Centre de Recherche en Infectiologie, Centre
Hospitalier Universitaire de Québec, Pavillon CHUL, and
Département de Biologie médicale, Faculté de
Médecine, Université Laval, Ste-Foy, QC, Canada.
Although protein tyrosine phosphatase (PTP) inhibitors used in
combination with other stimuli can induce interleukin 2 (IL-2) production in T cells, a direct implication of nuclear factor of
activated T cells (NFAT) has not yet been demonstrated. This study
reports that exposure of leukemic T cells and human peripheral blood
mononuclear cells to bis-peroxovanadium (bpV) PTP inhibitors markedly
induce activation and nuclear translocation of NFAT. NFAT activation by
bpV was inhibited by the immunosuppressive drugs FK506 and cyclosporin
A, as well as by a specific peptide inhibitor of NFAT activation.
Mobility shift assays showed specific induction of the NFAT1 member by
bpV molecules. The bpV-mediated NFAT activation was observed to be
important for the up-regulation of the human immunodeficiency virus 1 (HIV-1) long terminal repeat (LTR) and the IL-2 promoter; NFAT1 was
demonstrated to be particularly important in bpV-dependent positive
action on HIV-1 LTR transcription. The active participation of
p56lck, ZAP-70, p21ras,
and calcium in the bpV-mediated signaling cascade leading to NFAT
activation was confirmed, using deficient cell lines and dominant-negative mutants. Finally, overexpression of wild-type SHP-1
resulted in a greatly diminished activation of NFAT by bpV, suggesting
an involvement of SHP-1 in the regulation of NFAT activation. These
data were confirmed by constitutive NFAT translocation observed in
Jurkat cells stably expressing a dominant-negative version of SHP-1.
The study proposes that PTP activity attenuates constitutive kinase
activities that otherwise would lead to constant NFAT activation and
that this activation is participating in HIV-1 LTR stimulation by PTP inhibition.

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