Abstract P5-11-04: Post-translational modification of the cell-fate factor Dachshund determines p53 binding and signaling modules in breast cancer

Breast cancer is a leading form of cancer in the world. Initially cloned as a dominant inhibitor of the hyperactive EGFR, Ellipse, in Drosophila, the mammalian DACH1 regulates expression of target genes in part through interacting with DNA-binding transcription factors (c-Jun, Smads, Six, ERα), and in part through intrinsic DNA-sequence specific binding to Forkhead binding sites. The Drosophila dac gene is a key member of the retinal determination gene network (RDGN), which also includes eyes absent (eya), ey, twin of eyeless (toy), teashirt (tsh) and sin oculis (so), that specifies eye tissue identity.

Several lines of evidence suggest DACH1 may function as a tumor suppressor. Clinical studies have demonstrated a correlation between poor prognosis and reduced expression of the cell-fate determination factor DACH1 in breast cancer, and loss of DACH1 expression has been observed in prostate and endometrial cancer. DACH1 inhibits breast cancer tumor metastasis and reduces breast cancer stem cell expansion via Sox2/Nanog. Although these studies suggest DACH1 may function as a tumor suppressor, the molecular mechanisms remain poorly defined. Herein, endogenous DACH1 co-localized with p53 in a nuclear, extranucleolar compartment and bound to p53 in human breast cancer cell lines, p53 and DACH1 bound common genes in ChIP-Seq. Full inhibition of breast cancer contact-independent growth by DACH1 required p53. The p53 breast cancer mutants R248Q and R273H, evaded DACH1 binding. DACH1 phosphorylation at serine residue (S439) inhibited p53 binding and phosphorylation at p53 amino-terminal sites (S15, S20) enhanced DACH1 binding. DACH1 binding to p53 was inhibited by NAD-dependent deacetylation via DACH1 K628. DACH1 repressed p21CIP1 and induced RAD51, an association found in basal breast cancer. DACH1 inhibits breast cancer cellular growth in an NAD and p53 dependent manner through direct protein-protein association.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P5-11-04.

Low abundance protein enrichment for discovery of plasma protein biomarkers for early detection of breast cancer

77

Background: Protein biomarkers for breast cancer are desired for early diagnosis, disease prognosis and drug response monitoring. Biomarkers in bodily fluids, such as plasma, allow for non-invasive monitoring and have additional value compared to tissue-based markers. Plasma-based biomarker discovery faces a challenge in that the wide dynamic range of protein concentrations prevents the detection of lower abundance proteins. In this study, we have investigated the use of a novel protein enrichment strategy combined with isobaric label-based LC-MS/MS as well as two experimental designs for the identification of biomarkers of early stage breast cancer.

Methods: Plasma from 12 patients with benign breast lesions and 12 with stage I breast cancer were processed using ProteoMiner enrichment followed by on-bead digestion. Two types of standards were investigated: a pooled standard, consisting of equal portions from the 24 plasma digests and a universal standard. The samples were digested, labeled and analyzed using by HPLC-Chip/Q-TOF analysis. Proteins were identified and quantified using Spectrum Mill software.

Results: Use of ProteoMiner beads resulted in extraction of sufficient protein for at least 10 technical replicates and cut down preparation time by 80%, as compared to MARS-based immunodepletion. A total of 414 plasma proteins were identified, 89% of which are low abundance plasma proteins and 14 of which were differentially expressed. Expression values normalized using the pooled vs. universal standards were significantly correlated.

Conclusions: This study demonstrated use of the ProteoMiner technology for enrichment of low abundance proteins from plasma. Fourteen plasma-based biomarkers of stage I breast cancer were identified with statistical significance. A number of these proteins (e.g., protocadherin FAT2, flightless-1 homolog) have been linked to breast cancer relevant processes, such as cell migration, adhesion, estrogen receptor signaling and proliferation.

Protein expression comparison and physiological profiling of matched pairs DCIS/normal and invasive/normal primary epithelial cells

Abstract #6031

Background: Approximately 50% of patients who are diagnosed with Ductal Carcinoma In-Situ (DCIS) develop invasive breast cancer. The progression from DCIS to invasive cancer is not well understood. To better understand the range of biological processes involved in this progression, we have successfully isolated primary epithelial cell cultures from patient breast tissue and are using mass spectrometry-based methods to identify differentially expressed proteins in these different cell types. Bioinformatics analysis was used to identify differences in the underlying pathways.
 Methods: Primary Human Mammary epithelial cells from DCIS and Stage 3 Invasive tumors and normal tissue from the same patient were isolated immediately after surgery. Cells were maintained in defined CNT27 media for up to 2 passages and were characterized for epithelial and breast cancer markers by immunohistochemistry and western blot. Tamoxifen response was measured by cell proliferation assay. Protein lysates were labeled with the ITRAQ isobaric tags. Two-dimensional high-pressure liquid chromatography and mass spectrometry were used to identify differentially expressed proteins.
 Results: The proliferation rate of cells from DCIS tissue was 33% higher than the matched control cells and 50% higher from invasive tissue. Furthermore, Tamoxifen was more effective at inhibiting DCIS cell proliferation than the invasive cells in a dose- and time-dependent manner. We identified 50-100 proteins differentially expressed between the different tissue types. Validated tumor markers such as members of protein S100 family were significantly different between the tumor and normal samples. Thrombospondin, a known angiogenesis inhibitor, had similar concentrations in normal and DCIS tissues but was down-regulated (ratio=0.4) in the invasive tumor samples.
 Discussion: Using the analogous methods from gene expression studies, we found that pathways associated with processes such as differentiation, angiogenesis, and invasion are enriched in the proteome of the invasive tumors. Further comparisons of additional samples is continuing with the goals of better understanding the underlying biology that drives DCIS to invasive breast cancer and ultimately defining markers that could be used in better prognosis for DCIS patients.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 6031.