Changes of G-actin localisation in the mitotic spindle region or nucleus during mitosis and after heat shock: a histochemical study of G-actin in various cell lines with fluorescent labelled vitamin D-binding protein

The presence and localisation of G-actin in various cell lines was studied using the highly G-actin specific, fluorescence-labelled vitamin D-binding protein. In various cell-types, pig kidney-derived cells (LLC-PK1), Chinese hamster ovary (CHO) cells, SV-40 transformed African green monkey kidney ( COS) cells and human hepatoma (HepG2) cells, G-actin was only visible in th e cytoplasm of interphase cells. However, in mitotic cells, depending on th e mitotic phase, intense G-actin staining was found associated with the mit otic spindle (early mitosis) or overlapping the DNA-staining pattern (late mitosis). Also after heat shock (60-180 min at 43 degrees C), an intense nu clear staining of G-actin was observed. In LLC-PK1 cells, the increase of n uclear G-actin staining disappeared again after 24 h at 37 degrees C, but i n COS, CHO and HepG2 cells, it was still present in the nucleus after 24 h at 37 degrees C, indicating that the process was not rapidly reversible in these cells; the increased nuclear C-actin was not associated with cell div ision. Comparison of the amount of G-actin present in the nucleus and in th e cytosol before and after heat shock using Western blotting demonstrated t hat the total amount of G-actin in both nucleus and cytosol was unchanged a fter heat shock. This indicates that the increased G-actin staining is not a result of import of G-actin into the nucleus. These observations suggests rearrangement of G-actin in the nucleus during both mitosis and heat shock , which may be due to changes in interaction of G-actin with chromosomes. ( C) 1999 Elsevier Science B.V. All rights reserved.