M25 inhibits HIV expression in PMA-stimulated U1 cells both in the absence and presence of uPA. (A) U1 cells were incubated with different concentrations (5-80 μM) of the M25 peptide or its scrambled form (M25scr) in the presence or absence of uPA (10 nM) and were then stimulated with PMA. A concentration-dependent inhibition of HIV expression was observed in the presence of M25, but not of its control peptide, both in the presence and absence of uPA. (B) Cell disruption rescued HIV expression from the inhibitory effect of M25 (40 μM) or uPA (10 nM) after 5 days of culture (*P < .001; **P < .001). The results shown were derived from one experiment representative of 6 (A) and 3 (B) independently performed experiments. cpm indicates counts per minute.