Forskolin and IBMX, 2 cAMP inducers, are potent inducers of CXCR4 expression on HMECs. (A) HMECs were stimulated with forskolin (1 μM), IBMX (0.02 mM), or PGE₂(10^–9 M) for 24 hours. Thereafter, the cell surface expression of CXCR4 was analyzed. As depicted by the histograms, CXCR4 expression (thick histograms) was enhanced by IBMX, forskolin, or PGE₂ relative to the basal expression of CXCR4 on these cells. The background level of fluorescence in the presence of mouse IgG2a control is depicted by the thin histograms. A representative experiment of 3 is shown. (B) A comparison of MFI of PGE₂-, dorskolin-, and IBMX-stimulated HMECs indicated that IBMX and forskolin induce up to a 6-fold increment of CXCR4 in relation to the basal CXCR4 expression, and about a 1.5-fold increment in relation to PGE₂ stimulation. Statistical analysis was performed using ANOVA relative to the basal expression of CXCR4 on HMECs. The mean + SEM of 3 experiments is shown. *P < .01.