Calpain II involvement in mitosis.

Mitotic spindle disassembly requires major structural alterations in the associated cytoskeletal proteins and mitosis is known to be associated with Ca2+-sequestering phenomena and calcium transients. To examine the possible involvement of a ubiquitous Ca2+-activated protease, calpain II, in the mitotic process, synchronized PtK1 cells were monitored by immunofluorescence for the relocation of calpain II. The plasma membrane was the predominant location of calpain II in interphase. However, as mitosis progressed, calpain II relocated to (i) an association with mitotic chromosomes, (ii) a perinuclear location in anaphase, and (iii) a mid-body location in telophase. Microinjection of calpain II near the nucleus of a PtK1 cell promoted the onset of metaphase. Injection of calpain II at late metaphase promoted a precocious disassembly of the mitotic spindle and the onset of anaphase. These data suggest that calpain II is involved in mitosis.