Preferential expression of NuMA in the nuclei of proliferating cells

Nuclear mitotic apparatus protein (NuMA) has an indispensable function in n ormal mitosis as an organizer of the mitotic spindle. NuMA is a prominent c omponent of interphase cell nuclear matrix but its role during interphase i s largely unknown. We examined the presence of NuMA in several human tissue s. The majority of cells were positive for NuMA but a few negative cell typ es were found, including spermatozoa, superficial keratinocytes, neutrophil granulocytes, syncytiotrophoblasts, and some neurons, fibro blasts, and sm ooth and skeletal muscle cells. We further investigated the presence of NuM A in a cultured estrogen-dependent human breast cancer cell Line and observ ed the disappearance of nuclear NuMA in the quiescent cells. The percentage of NuMA-positive cells diminished from an initial similar to 100 to 60% du ring 6 days of culture. The presence of NuMA correlated positively with the presence of proliferation marker Ki-67 antigen and negatively with the cul ture time, confluence, and size of the cell islets. These results show that some nonproliferating, highly differentiated cell types lack NuMA and that cells may lose their NuMA without dramatic effects on the nuclear shape. T his suggests that NuMA may be a nonessential component of the interphase nu cleus. (C) 2000 Academic Press.