Cantharidin-induced mitotic arrest is associated with the formation of aberrant mitotic spindles and lagging chromosomes resulting, in part, from the suppression of PP2Aalpha.
Cantharidin, a natural vesicant, inhibits the activity of several PPP family phosphatases, displays antitumor activity, and induces apoptosis in many types of tumor cells. However, the molecular mechanisms underlying the antitumor activity of cantharidin are not clear. Here, dose-response studies confirm a strong correlation between the suppression of phosphatase activity and cell death. Flow cytometry analysis indicates that before apoptosis, cantharidin delays cell cycle progression following DNA replication with no apparent effect on G(1)-S or S-G(2) phase progression. In contrast, studies with double thymidine-synchronized populations of cells indicate that cantharidin can rapidly arrest growth when added during G(2) or early M phase. Immunostaining indicates that cell cycle arrest occurs before the completion of mitosis and is associated with the appearance of aberrant mitotic spindles. Live cell imaging with time-lapse microscopy shows that cantharidin disrupts the metaphase alignment of chromosomes and produces a prolonged mitotic arrest, with the onset of apoptosis occurring before the onset of anaphase. To explore the contribution of individual phosphatases, antisense oligonucleotides and small interfering RNA were developed to suppress the expression of cantharidin-sensitive phosphatases. The suppression of PP2Aalpha, but not PP2Abeta, is sufficient to induce metaphase arrest, during which time lagging chromosomes are observed moving between the spindle poles and the metaphase plate. Immunostaining revealed slightly abnormal, yet predominately bipolar, mitotic spindles. Nonetheless, after a 10- to 15-hour delay, the cells enter anaphase, suggesting that an additional cantharidin-sensitive phosphatase is involved in the progression from metaphase into anaphase or to prevent the onset of apoptosis in cells arrested during mitosis.
Bonness
Kathy
K
Department of Biochemistry and Molecular Biology, University of South Alabama, MSB 2362, Mobile, AL 36688, USA.
Aragon
Ileana V
IV
Rutland
Beth
B
Ofori-Acquah
Solomon
S
Dean
Nicholas M
NM
Honkanen
Richard E
RE
D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D002193:Cantharidin / Q000494:pharmacology* / Q000633:toxicity; D002453:Cell Cycle; D002877:Chromosomes, Human / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005455:Fluorescent Antibody Technique; D006367:HeLa Cells; D006801:Humans; D008938:Mitosis / Q000187:drug effects*; D020319:Oligodeoxyribonucleotides, Antisense / Q000378:metabolism; D009841:Oligonucleotides / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D054648:Protein Phosphatase 2; D034741:RNA, Small Interfering / Q000378:metabolism; D008941:Spindle Apparatus / Q000187:drug effects*; D013997:Time Factors; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; C517051:ISIS 110159; D020319:Oligodeoxyribonucleotides, Antisense; D009841:Oligonucleotides; D034741:RNA, Small Interfering; C517189:PPP2CA protein, human; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D002193:Cantharidin