Cellular senescence induced by aberrant MAD2 levels impacts on paclitaxel responsiveness in vitro.
BACKGROUND
The mitotic arrest deficiency protein 2 (MAD2) is a key component of the mitotic spindle assembly checkpoint, monitoring accurate chromosomal alignment at the metaphase plate before mitosis. MAD2 also has a function in cellular senescence and in a cell's response to microtubule inhibitory (MI) chemotherapy exemplified by paclitaxel.


METHODS
Using an siRNA approach, the impact of MAD2 down-regulation on cellular senescence and paclitaxel responsiveness was investigated. The endpoints of senescence, cell viability, migration, cytokine expression, cell cycle analysis and anaphase bridge scoring were carried out using standard approaches.


RESULTS
We show that MAD2 down-regulation induces premature senescence in the MCF7 breast epithelial cancer cell line. These MAD2-depleted (MAD2) cells are also significantly replicative incompetent but retain viability. Moreover, they show significantly higher levels of anaphase bridges and polyploidy compared to controls. In addition, these cells secrete higher levels of IL-6 and IL-8 representing key components of the senescence-associated secretory phenotype (SASP) with the ability to impact on neighbouring cells. In support of this, MAD2 cells show enhanced migratory ability. At 72 h after paclitaxel, MAD2 cells show a significant further induction of senescence compared with paclitaxel naive controls. In addition, there are significantly more viable cells in the MAD2 MCF7 cell line after paclitaxel reflecting the observed increase in senescence.


CONCLUSIONS
Considering that paclitaxel targets actively dividing cells, these senescent cells will evade cytotoxic kill. In conclusion, compromised MAD2 levels induce a population of senescent cells resistant to paclitaxel.
Prencipe
M
M
UCD School of Medicine and Medical Science (SMMS), University College Dublin, UCD, Belfield, Dublin 4, Ireland. maria.prencipe@ucd.ie
Fitzpatrick
P
P
Gorman
S
S
Tosetto
M
M
Mosetto
M
M
Klinger
R
R
Furlong
F
F
Harrison
M
M
O'Connor
D
D
Roninson
I B
IB
O'Sullivan
J
J
McCann
A
A
D015153:Blotting, Western; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D002135:Calcium-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000187:drug effects / Q000502:physiology; D016922:Cellular Senescence / Q000187:drug effects* / Q000235:genetics; D015536:Down-Regulation; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D064246:Mad2 Proteins; D017239:Paclitaxel / Q000494:pharmacology*; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D008941:Spindle Apparatus / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D014162:Transfection
D002135:Calcium-Binding Proteins; D018797:Cell Cycle Proteins; C577697:MAD2L1 protein, human; D064246:Mad2 Proteins; D034741:RNA, Small Interfering; D012097:Repressor Proteins; D017239:Paclitaxel