Relationship of nuclear invaginations to perinuclear rings composed of intermediate filaments in MIA PaCa-2 and some other cells.

There have been few investigations of the cause of nuclear invagination and lobule formation. The human pancreatic cancer cells MIA PaCa-2 often show nuclear lobulation and well-developed juxtanuclear aggregates of intermediate filaments with thick bundles of intermediate filaments developed from them. Therefore MIA PaCa-2 cells were used as model cells to examine whether or not there is any relationship between the shape of the nucleus and intermediate filaments. Immunoblotting showed that the intermediate filament proteins in MIA PaCa-2 cells are vimentin, and keratins 8, 18, and 19. Fluorescence microscopy and confocal laser scanning fluorescence microscopy revealed perinuclear rings composed of intermediate filaments, that is, thick bundles of both vimentin and keratin filaments run along deep invaginations in the nucleus and, together with juxtanuclear intermediate filament aggregates, they form closed rings around nuclear invaginated and constricted sites. In other cells such as human bladder carcinoma T24 cells, human melanoma G-361 cells, and human cervix carcinoma HeLa/S3 cells, there were also thick bundles of intermediate filaments cutting into the nucleus at the nuclear invagination site. Thus, it seems that the formation of perinuclear intermediate filament rings may be involved in nuclear invagination and lobule formation in some mammalian cells.