High frequency of hypermethylation at the 14-3-3 sigma locus leads to gene silencing in breast cancer.
Expression of 14-3-3 final sigma (final sigma) is induced in response to DNA damage, and causes cells to arrest in G(2). By SAGE (serial analysis of gene expression) analysis, we identified final sigma as a gene whose expression is 7-fold lower in breast carcinoma cells than in normal breast epithelium. We verified this finding by Northern blot analysis. Remarkably, final sigma mRNA was undetectable in 45 of 48 primary breast carcinomas. Genetic alterations at final sigma such as loss of heterozygosity were rare (1/20 informative cases), and no mutations were detected (0/34). On the other hand, hypermethylation of CpG islands in the final sigma gene was detected in 91% (75/82) of breast tumors and was associated with lack of gene expression. Hypermethylation of final sigma is functionally important, because treatment of final sigma-non-expressing breast cancer cell lines with the drug 5-aza-2'-deoxycytidine resulted in demethylation of the gene and synthesis of final sigma mRNA. Breast cancer cells lacking final sigma expression showed increased number of chromosomal breaks and gaps when exposed to gamma-irradiation. Therefore, it is possible that loss of final sigma expression contributes to malignant transformation by impairing the G(2) cell cycle checkpoint function, thus allowing an accumulation of genetic defects. Hypermethylation and loss of final sigma expression are the most consistent molecular alterations in breast cancer identified so far.
Ferguson
A T
AT
Johns Hopkins Oncology Center, 410 BBCRB, 1650 Orleans Street, Baltimore, MD 21231-1000, USA.
Evron
E
E
Umbricht
C B
CB
Pandita
T K
TK
Chan
T A
TA
Hermeking
H
H
Marks
J R
JR
Lambers
A R
AR
Futreal
P A
PA
Stampfer
M R
MR
Sukumar
S
S
D048948:14-3-3 Proteins; D001374:Azacitidine / Q000031:analogs & derivatives / Q000494:pharmacology; D001940:Breast / Q000166:cytology; D001943:Breast Neoplasms / Q000235:genetics* / Q000473:pathology; D018797:Cell Cycle Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology; D002460:Cell Line / Q000187:drug effects; D002461:Cell Line, Transformed / Q000187:drug effects; D002471:Cell Transformation, Neoplastic / Q000235:genetics; D018899:CpG Islands; D019175:DNA Methylation / Q000187:drug effects; D004260:DNA Repair / Q000235:genetics; D000077209:Decitabine; D004847:Epithelial Cells / Q000378:metabolism; D005260:Female; D016195:G2 Phase / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D020868:Gene Silencing; D006801:Humans; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D014176:Protein Biosynthesis; D011506:Proteins / Q000235:genetics* / Q000502:physiology; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D012334:RNA, Neoplasm / Q000096:biosynthesis / Q000235:genetics; D011836:Radiation Tolerance / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000502:physiology; D014158:Transcription, Genetic; D014162:Transfection; D014407:Tumor Cells, Cultured / Q000378:metabolism; D014446:Tyrosine 3-Monooxygenase
D048948:14-3-3 Proteins; D018797:Cell Cycle Proteins; D009363:Neoplasm Proteins; D011506:Proteins; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D011993:Recombinant Fusion Proteins; D000077209:Decitabine; D014446:Tyrosine 3-Monooxygenase; D001374:Azacitidine