P38 activation in C6 glioma cells by R5- or X4-tropic HIV-1 gp120.

Cell surface expression of CCR5 (A) and CXCR4 (B) on CD4⁻C6 glioma cells was analyzed by flow cytometry after staining of the cells with an isotype-matched control MAb (i) or the appropriate antichemokine receptor MAb (ii). CD4⁻/CCR5⁺/CXCR4⁺ C6 glioma cells were incubated in the presence of gp120 JRFL (10 μg/mL), MIP-1β (100 nM) (C), or gp120 HXB2 (10 μg/mL) and SDF-1α (100 nM) (D). Controls were done by using medium alone, anisomycin (500 ng/mL), or PMA (1 μM) for the indicated time period at 37°C. In some experiments, cells were pretreated for 16 hours at 37°C with pertussis toxin (100 ng/mL) before stimulation with gp120s. P38 kinase tyrosine phosphorylation was assessed as described in the legend to Figure 2.