Tat antagonizes signaling by CXCR4, but not CCR5, agonists. (Panel 1)
Tat wild-type (wt) (residues 11–50), but not Tat-mCXC (cysteines at
residues 25 and 27 changed to alanines), peptide-desensitized
SDF-1-induced calcium mobilization. Tat peptides were added 50–100 s
before SDF-1; measurements of calcium flux followed. Tat wt peptide did
not affect RANTES signaling in PBMCs (panel 2) and monocytes (panel
3); nor MIP1α (panel 4) or MIP1β (panel 5) signaling
in PBMCs. In each panel, the top tracing is the addition of chemokine
alone (100 nM) whereas the bottom tracing(s) is pretreatment with Tat
peptide(s) (200 nM), followed by addition of indicated chemokine (100
nM).