Cytoskeletal influences on nuclear shape in granulocytic HL-60 cells.
BACKGROUND
During granulopoiesis in the bone marrow, the nucleus differentiates from ovoid to lobulated shape. Addition of retinoic acid (RA) to leukemic HL-60 cells induces development of lobulated nuclei, furnishing a convenient model system for nuclear differentiation during granulopoiesis. Previous studies from our laboratory have implicated nuclear envelope composition as playing important roles in nuclear shape changes. Specifically noted were: 1) a paucity of lamins A/C and B1 in the undifferentiated and RA treated cell forms; 2) an elevation of lamin B receptor (LBR) during induced granulopoiesis.


RESULTS
The present study demonstrates that perturbation of cytoskeletal elements influences nuclear differentiation of HL-60 cells. Because of cytotoxicity from prolonged exposure to cytoskeleton-modifying drugs, most studies were performed with a Bcl-2 overexpressing HL-60 subline. We have found that: 1) nocodazole prevents RA induction of lobulation; 2) taxol induces lobulation and micronuclear formation, even in the absence of RA; 3) cytochalasin D does not inhibit RA induced nuclear lobulation, and prolonged exposure induces nuclear shape changes in the absence of RA.


CONCLUSIONS
The present results, in the context of earlier data and models, suggest a mechanism for granulocytic nuclear lobulation. Our current hypothesis is that the nuclear shape change involves factors that increase the flexibility of the nuclear envelope (reduced lamin content), augment connections to the underlying heterochromatin (increased levels of LBR) and promote distortions imposed by the cytoskeleton (microtubule motors creating tension in the nuclear envelope).
Olins
Ada L
AL
Department of Biology, Bowdoin College, Brunswick, Maine 04011, USA. aolins@bowdoin.edu
Olins
Donald E
DE
D002454:Cell Differentiation / Q000187:drug effects; D002467:Cell Nucleus / Q000648:ultrastructure*; D048430:Cell Shape / Q000187:drug effects; D015638:Cytochalasin D / Q000494:pharmacology; D003599:Cytoskeleton / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D018922:HL-60 Cells / Q000737:chemistry / Q000187:drug effects / Q000648:ultrastructure*; D006410:Hematopoiesis; D006801:Humans; D034904:Lamin Type A / Q000032:analysis; D034921:Lamin Type B / Q000032:analysis; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D015739:Nocodazole / Q000494:pharmacology; D017239:Paclitaxel / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000502:physiology; D018160:Receptors, Cytoplasmic and Nuclear / Q000032:analysis; D014212:Tretinoin / Q000494:pharmacology; D000097682:Lamin B Receptor
D015638:Cytochalasin D; D034904:Lamin Type A; D034921:Lamin Type B; D015739:Nocodazole; D017239:Paclitaxel; D019253:Proto-Oncogene Proteins c-bcl-2; D018160:Receptors, Cytoplasmic and Nuclear; D014212:Tretinoin; D000097682:Lamin B Receptor; C440308:lamin C