YB-1, the E2F pathway, and regulation of tumor cell growth.
BACKGROUND
Y-box binding factor 1 (YB-1) has been associated with prognosis in many tumor types. Reduced YB-1 expression inhibits tumor cell growth, but the mechanism is unclear.


METHODS
YB-1 mRNA levels were compared with tumor grade and histology using microarray data from 771 breast cancer patients and with disease-free survival and distant metastasis-free survival using data from 375 of those patients who did not receive adjuvant therapy. Microarrays were further searched for genes that had correlated expression with YB-1 mRNA. Small interfering RNA (siRNA) was used to study the effects of reduced YB-1 expression on growth of three tumor cell lines (MCF-7 breast, HCT116 colon, and A549 lung cancer cells), on tumorigenesis by A549 cells in nude mice, and on global transcription in the three cancer cell lines. Reporter gene assays were used to determine whether YB-1 siRNAs affected the expression of E2F1, and chromatin immunoprecipitation was used to determine whether YB-1 bound to various E2F promoters as well as E2F1-regulated promoters. All P values were from two-sided tests.


RESULTS
YB-1 levels were elevated in more aggressive tumors and were strongly associated with poor disease-free survival and distant metastasis-free survival. YB-1 expression was often associated with the expression of genes with E2F sites in their promoters. Cells expressing YB-1 siRNA grew substantially more slowly than control cells and formed tumors less readily in nude mice. Transcripts that were altered in cancer cell lines with YB-1 siRNA included 32 genes that are components of prognostic gene expression signatures. YB-1 regulated expression of an E2F1 promoter-reporter construct in A549 cells (eg, relative E2F1 promoter activity with control siRNA = 4.04; with YB-1 siRNA = 1.40, difference= -2.64, 95% confidence interval = -3.57 to -1.71, P < .001) and bound to the promoters of several well-defined E2F1 target genes.


CONCLUSIONS
YB-1 expression is associated with the activity of E2F transcription factors and may control tumor cell growth by this mechanism.
Department of Molecular Medicine and Pathology, School of Medical Sciences, University of Auckland, Auckland, New Zealand. a.lasham@auckland.ac.nz
Annette
A
Lasham
Weini
W
Samuel
Helen
H
Cao
Rachna
R
Patel
Reena
R
Mehta
J Lewis
JL
Stern
Glen
G
Reid
Adele G
AG
Woolley
Lance D
LD
Miller
Michael A
MA
Black
Andrew N
AN
Shelling
Cristin G
CG
Print
Antony W
AW
Braithwaite
D000328:Adult; D000368:Aged; D000818:Animals; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000378:metabolism* / Q000401:mortality / Q000473:pathology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D047369:Chromatin Immunoprecipitation; D019295:Computational Biology; D050687:E2F1 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D017930:Genes, Reporter; D006801:Humans; D016014:Linear Models; D051379:Mice; D008819:Mice, Nude; D008875:Middle Aged; D011237:Predictive Value of Tests; D011379:Prognosis; D040081:Protein Array Analysis; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D015203:Reproducibility of Results; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016019:Survival Analysis; D014162:Transfection; D014183:Transplantation, Heterologous; D051840:Y-Box-Binding Protein 1 / Q000235:genetics / Q000378:metabolism*
D050687:E2F1 Transcription Factor; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D051840:Y-Box-Binding Protein 1; C070856:YBX1 protein, human