Hormone-induced chromosomal instability in p53-null mammary epithelium.
The absence of p53 function increases risk for spontaneous tumorigenesis in the mammary gland. Hormonal stimulation enhances tumor risk in p53-null mammary epithelial cells as well as the incidence of aneuploidy. Aneuploidy appears in normal p53-null mammary epithelial cells within 5 weeks of hormone stimulation. Experiments reported herein assessed a possible mechanism of hormone-induced aneuploidy. Hormones increased DNA synthesis equally between wild-type (WT) and p53-null mammary epithelial cells. There were two distinct responses in p53-null cells to hormone exposure. First, Western blot analysis demonstrated that the levels of two proteins involved in regulating sister chromatid separation and the spindle checkpoint, Mad2 and separase (ESPL1) were increased in null compared with WT cells. In contrast, the levels of securin and Rad21 proteins were not increased in hormone-stimulated p53-null compared with WT cells. ESPL1 RNA was also increased in p53-null mouse mammary cells in vivo by 18 h of hormone stimulation and in human breast MCF7 cells in monolayer culture by 8 h of hormone stimulation. Furthermore, both promoters contained p53 and steroid hormone response elements. Mad2 protein was increased as a consequence of the absence of p53 function. The increase in Mad2 protein was observed also at the cellular level by immunohistochemistry. Second, hormones increased gene amplication in the distal arm of chromosome 2, as shown by comparative genomic hybridization. These results support the hypothesis that hormone stimulation acts to increase aneuploidy by several mechanisms. First, by increasing mitogenesis in the absence of the p53 checkpoint in G2, hormones allow the accumulation of cells that have experienced chromosome missegregation. Second, the absolute rate of chromosome missegregation may be increased by alterations in the levels of two proteins, separase and Mad2, which are important for maintaining chromosomal segregation and the normal spindle checkpoint during mitosis.
Department of Pediatrics, Hematology-Oncology, Texas Children's Cancer Center, Baylor College of Medicine, Houston, Texas 77030, USA.
Debananda
D
Pati
Bassem R
BR
Haddad
Albert
A
Haegele
Henry
H
Thompson
Frances S
FS
Kittrell
Anne
A
Shepard
Cristina
C
Montagna
Nenggang
N
Zhang
Gouqing
G
Ge
Subhendu Kumar
SK
Otta
Maureen
M
McCarthy
Robert L
RL
Ullrich
Daniel
D
Medina
D000782:Aneuploidy; D000818:Animals; D001483:Base Sequence; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D002135:Calcium-Binding Proteins / Q000096:biosynthesis / Q000235:genetics; D018797:Cell Cycle Proteins / Q000096:biosynthesis / Q000235:genetics; D045744:Cell Line, Tumor; D043171:Chromosomal Instability; D010450:Endopeptidases / Q000096:biosynthesis / Q000235:genetics; D004847:Epithelial Cells / Q000187:drug effects / Q000473:pathology / Q000502:physiology; D004967:Estrogens / Q000494:pharmacology*; D005260:Female; D064246:Mad2 Proteins; D008321:Mammary Glands, Animal / Q000187:drug effects / Q000473:pathology / Q000502:physiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D011374:Progesterone / Q000494:pharmacology*; D012097:Repressor Proteins; D064247:Separase; D016159:Tumor Suppressor Protein p53 / Q000172:deficiency* / Q000235:genetics / Q000502:physiology
D002135:Calcium-Binding Proteins; D018797:Cell Cycle Proteins; D004967:Estrogens; C577697:MAD2L1 protein, human; D064246:Mad2 Proteins; D012097:Repressor Proteins; D016159:Tumor Suppressor Protein p53; D011374:Progesterone; D010450:Endopeptidases; C577987:ESPL1 protein, human; D064247:Separase