Serum Dependency of t(8;21) AML Cell Line Is Associated with VEGF/VEGFR Pathway and Early Phosphorylation of Akt.

Most human leukemia cell lines are dependent on serum supplementation (usually fetal calf serum (FCS)), although the extent of serum dependency differs among each cell line. Kasumi-1, a t(8;21) AML cell line is one of the most serum-dependent cell lines. Since growth and survival of many leukemia cell lines are associated with phosphorylation of Akt, we examined the Akt phosphorylation by FCS treatment. In Kasumi-1, Akt was phosphorylated by culture with FCS in a dose-dependent manner, although no such Akt phosphorylation was observed in NB-4, a t(15;17) cell line. By FCS stimulation, Akt (Thr308, Ser473) was phosphorylated from 0.5 hr and the phosphorylation sustained until 48 hours in Kasumi-1. Then, we tested the effect of VEGF/VEGFR signaling in phosphorylation of Akt by FCS. The addition of VEGFR1/Fc and VEGFR2/Fc (which bind external VEGF and abrogate its function) inhibited the Akt phosphorylation from 2 hours until 10 hours, although the growth of Kasumi-1 was not inhibited. The addition of VEGFR2 kinase inhibitor (which inhibits internal VEGF signal) inhibited the Akt phosphorylation from 0.5 hr until 2 hours, and the growth of Kasumi-1 was greatly inhibited.

Taken together, it is suggested that serum dependency of Kasumi-1 is at least in part attributed to VEGF/VEGFR pathway. Then, both external and internal VEGF/VEGFR pathways work in Kasumi-1, which in turn phosphorylate Akt. However, blockade of only internal VEGF signal (by VEGFR2 kinase inhibitor) inhibit the early Akt phosphorylation (0.5 hr), which resulted in growth inhibition, indicating the importance of early Akt phosphorylation.