Biology Reference
In-Depth Information
F i g u r e 5.6. Tat di¨erentially modulates cell proliferation of various B-cell subsets. Total, naive
memory and GC B cells were stimulated by anti-IgM Ab and IL-4 (medium shading), CD40 mAb
and IL-4 (dark shading), or CD40 mAb and IL-2 plus IL-10 (light shading) in the presence or ab-
sence of 0.5 mg/mL wild-type Tat. Results of [
3
H]-thymidine incorporation are expressed as mean
counts per minute (cpm) G SD of triplicates determinations. Values are representative of ®ve inde-
pendent experiments.
time-dependent because the maximal e¨ect of Tat required the presence of this
molecule during the ®rst hours of the B-cell stimulation; (iii) blocked by the
prior incubation of Tat with heparin, with an ID
50
(1 mg/ml heparin) similar to
that reported for Tat-induced HIV-1 transactivation ( Rusnati et al., 1997); (iv)
similar for wild-type recombinant and synthetic Tat proteins from various
strains (IIIb, BH10, Mal, Eli) and for two mutated synthetic Tat devoid of
transactivating activity ( Tat Oyi and CmC Tat Bru) ( Fig. 5.7) (Lefevre et al.,
1999). This shows that the cysteine-rich region of Tat, essential for trans-
activation of the HIV-1 LTR, does not control the e¨ects of Tat on B cells.
The Tat-induced inhibition of naive and memory B-cell proliferation is not
due to apoptosis but to the arrest of IgM-mediated B-cell activation before
the G1 to S phase transition. Indeed, Tat modulates [
3
H]-thymidine and [
3
H]-
uridine incorporation to the same extent. The addition of Tat does not change
the percentage of CD69
- and CD71
-activated B cells but increases that of
CD95
B cells (Fig. 5.8). Tat decreases the amounts of cyclin D3, cyclin E,
cdk4, and cdk6 in IgM-activated B cells but not in CD40-activated B cells
