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Asf1b, the necessary Asf1 isoform for proliferation, is predictive of outcome in breast cancer.

ABSTRACT: Mammalian cells possess two isoforms of the histone H3-H4 chaperone anti-silencing function 1 (Asf1), Asf1a and Asf1b. However to date, whether they have individual physiological roles has remained elusive. Here, we aim to elucidate the functional importance of Asf1 isoforms concerning both basic and applied aspects. First, we reveal a specific proliferation-dependent expression of human Asf1b unparalleled by Asf1a. Strikingly, in cultured cells, both mRNA and protein corresponding to Asf1b decrease upon cell cycle exit. Depletion of Asf1b severely compromises proliferation, leads to aberrant nuclear structures and a distinct transcriptional signature. Second, a major physiological implication is found in the applied context of tissue samples derived from early stage breast tumours in which we examined Asf1a/b levels. We reveal that overexpression of Asf1b mRNA correlate with clinical data and disease outcome. Together, our results highlight a distribution of tasks between the distinct Asf1 isoforms, which emphasizes a specialized function of Asf1b required for proliferation capacity. We discuss the implications of these results for breast cancer diagnosis and prognosis.

SUBMITTER: Corpet A

PROVIDER: S-EPMC3034011 | biostudies-literature | 2011 Feb

REPOSITORIES: biostudies-literature

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Asf1b, the necessary Asf1 isoform for proliferation, is predictive of outcome in breast cancer.

Corpet Armelle A De Koning Leanne L Toedling Joern J Savignoni Alexia A Berger Frédérique F Lemaître Charlène C O'Sullivan Roderick J RJ Karlseder Jan J Barillot Emmanuel E Asselain Bernard B Sastre-Garau Xavier X Almouzni Geneviève G

The EMBO journal 20101221 3

Mammalian cells possess two isoforms of the histone H3-H4 chaperone anti-silencing function 1 (Asf1), Asf1a and Asf1b. However to date, whether they have individual physiological roles has remained elusive. Here, we aim to elucidate the functional importance of Asf1 isoforms concerning both basic and applied aspects. First, we reveal a specific proliferation-dependent expression of human Asf1b unparalleled by Asf1a. Strikingly, in cultured cells, both mRNA and protein corresponding to Asf1b decr ...[more]

PMID: 21179005

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Project description:Compelling evidence shows that progestins regulate breast cancer growth. Using preclinical models, we demonstrated that antiprogestins are inhibitory when the level of progesterone receptor isoform A (PR-A) is higher than that of isoform B (PR-B) and that they might stimulate growth when PR-B is predominant. The aims of this study were to investigate ex vivo responses to mifepristone (MFP) in breast carcinomas with different PR isoform ratios and to examine their clinical and molecular characteristics. We performed human breast cancer tissue culture assays (n = 36) to evaluate the effect of MFP on cell proliferation. PR isoform expression was determined by immunoblotting (n = 282). Tumors were categorized as PRA-H (PR-A/PR-B ≥ 1.2) or PRB-H (PR-A/PR-B ≤ 0.83). RNA was extracted for Ribo-Zero-Seq sequencing to evaluate differentially expressed genes. Subtypes and risk scores were predicted using the PAM50 gene set, the data analyzed using The Cancer Genome Atlas RNA-seq gene analysis and other publicly available gene expression data. Tissue microarrays were performed using paraffin-embedded tissues (PRA-H n = 53, PRB-H n = 24), and protein expression analyzed by immunohistochemistry. All statistical tests were two-sided. One hundred sixteen out of 222 (52.3%) PR+ tumors were PRA-H, and 64 (28.8%) PRB-H. Cell proliferation was inhibited by MFP in 19 of 19 tissue cultures from PRA-H tumors. A total of 139 transcripts related to proliferative pathways were differentially expressed in nine PRA-H and seven PRB-H tumors. PRB-H and PRA-H tumors were either luminal B or A phenotypes, respectively ( P = .03). PRB-H cases were associated with shorter relapse-free survival (hazard ratio [HR] = 2.70, 95% confidence interval [CI] = 1.71 to 6.20, P = .02) and distant metastasis-free survival (HR = 4.17, 95% CI = 2.18 to 7.97, P < .001). PRB-H tumors showed increased tumor size ( P < .001), Ki-67 levels ( P < .001), human epidermal growth factor receptor 2 expression ( P = .04), high grades ( P = .03), and decreased total PR ( P = .004) compared with PRA-H tumors. MUC-2 ( P < .001) and KRT6A ( P = .02) were also overexpressed in PRB-H tumors. The PRA/PRB ratio is a prognostic and predictive factor for antiprogestin responsiveness in breast cancer.

Project description:Abstract: A subset of HER2 breast cancers with amplification of the TFAP2C gene locus becomes addicted to AP-2g. We sought to define AP-2g-regulated genes that control growth and invasiveness by comparing HER2 cell lines with differential response to TFAP2C knockdown. A set of 68 differentially expressed genes was identified, which included CDH5 and CDKN1A. Pathway analysis implicated the MAPK13/p38δ and retinoic acid regulatory nodes, which were confirmed to display divergent responses. The AP-2g gene signature was highly predictive of outcome in HER2-positive breast cancer patients. We conclude that AP-2g regulates a set of genes in HER2 breast cancer that drive cancer growth and invasiveness and that the AP-2g gene signature can predict outcome of patients with HER2 breast cancer. Results: Using an optimized data analysis workflow, we mapped about 50-75 million sequence reads per sample to the human genome Human Feb.2009 (GRCh37/hg19) (hg19). By RNA-seq analysis, knockdown of TFAP2C in HCC1954 with siRNA (compared to NT siRNA) identified 364 genes with significantly altered expression. To further create specificity for AP-2gamma-regulated genes, RNA-seq analysis was performed comparing expression in shHCC1954 with shTFAP2C cells vs. shNT; this analysis identified 8,986 genes with significantly altered expression. The two data sets were subsequently compared to identify a set of genes that were consistently altered with knockdown of TFAP2C by siRNA and shRNA. This comparison confirmed the identification of 152 AP-2gamma target genes in HCC1954 cells. Because HCC1954 demonstrated opposite growth regulation and invasiveness with knockdown of TFAP2C compared to SKBR3, we hypothesized that the AP-2gamma target genes responsible for growth and invasion would be differentially regulated with knockdown of TFAP2C in HCC1954 versus SKBR3. Hence, RNA-seq analysis was performed in SKBR3 after knockdown of TFAP2C with siRNA; in this analysis, a total of 3814 genes were significantly altered. The pattern of expression for the 152 AP-2gamma target genes identified in HCC1954 was subsequently compared to expression changes in SKBR3. Of note, only 79 of the 152 TFAP2C target genes in HCC1954 were found to change expression significantly in the RNA-seq data set from SKBR-3. Conclusions: Knockdown of TFAP2C with co-knockdown of CDH5 in SKBR-3 confirmed no significant effect on invasion, though there was a slight reduction in invasiveness with knockdown of CDH5 that failed to reach statistical significance (p=0.12). These findings support the conclusion that regulation of CDH5 and CDKN1A contribute to alterations of proliferation and invasiveness induced by knockdown of TFAP2C.

Dataset Information

Asf1b, the necessary Asf1 isoform for proliferation, is predictive of outcome in breast cancer.

Publications

Asf1b, the necessary Asf1 isoform for proliferation, is predictive of outcome in breast cancer.

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