It was recently demonstrated that a lack of p27(KIP1) degradation resulted in the suppression of cdc2 activity and consequent inhibition of entry into the M-phase. The aim of this study was to examine the distribution of phosphorylated p27(KIP1) on threonine 187 (T187-phospho-p27) and cdc2 in mitotic cells of human retinoblastoma, a malignant retinal neoplasm. Several T187-phospho-p27-immunopositive cells were observed in mitotic retinoblastoma cells, but not in the normal retina. Immunoreactivity for T187-phospho-p27 was located in the prophase and metaphase of mitotic tumor cells. In contrast, tumor cells in the anaphase showed no immunoreactivity for T187-phospho-p27. Nuclear expression of cdc2 was detected in many retinoblastoma cells, including mitotic cells. The immunoreactivity in mitotic cells was located in the prophase, as well as metaphase. In contrast, anaphase cells did not show immunoreactivity. Double staining demonstrated the same localization of T187-phospho-p27 and cdc2 in mitotic cells. These results suggest that p27(KIP1) interacts with cdc2 in the M-phase of human retinoblastoma cells.

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