Expression of the nuclear membrane protein statin in cycling cells.

Statin is a 57 kD protein previously reported to be expressed by cells in G0. We have studied the detailed distribution of statin immunoreactivity in normal human and rat tissues, and correlated this with investigation of in vitro model systems. By laser confocal microscopy, statin immunoreactivity is localized to the nuclear membrane. In contrast to previous reports, using in vitro model systems we found that statin was also expressed by replicating cells as judged by both co-localization with [3H]thymidine-labelled and Ki67-labelled cells. Furthermore, in a nude mouse xenograft model the number of statin-labelled cells exceeded the number of quiescent cells as assessed by both fraction of labelled mitosis methods and labelling with [3H]thymidine and Ki67. We conclude that although there is an association between expression of the 57 kD nuclear membrane protein statin and growth arrest, this is not absolute and it is expressed in a sub-population of cycling cells. The properties of statin closely resemble those of nuclear lamins, members of the intermediate filament family.