It has previously been implicated that nerve growth factor (NGF) with its high-affinity receptor tyrosine kinase A (TrkA) could play an important role in the growth modulation of human tumor cells, such as glioblastoma multiform cell lines and human breast cancer cell lines. However, the direct mitogenic effects of NGF and TrkA in these tumor cells still remain to be elucidated. Herein we show, by immunofluorescence staining, that NGF was colocalized with gamma-tubulin at the centrosomes or the spindle poles throughout the cell cycle and phosphorylated TrkA was colocalized with alpha-tubulin at mitotic spindle in the glioma cell line U251. The results suggest that NGF concentrated to centrosome can recruit its receptor TrkA there and cause phosphorylation of the latter. The phosphorylated TrkA with the tyrosine kinase activity may phosphorylate the tubulin and promote the mitotic spindle assembly. By these mechanisms, NGF can modulate the mitosis of human glioma cells. (c) 2005 Elsevier Inc. All rights reserved.