Andorfer, CA

Abstract Epigenetic silencing of tumor suppressing genes by promoter-specific DNA methylation is common in many types of cancer. As an early event, this process has been well shown to promote tumor initiation and progression; however little is known how such epigenetic silencing can contribute to tumor metastasis. The PRKD1 gene encodes Protein Kinase D1 (PKD1), a serine/threonine kinase expressed in epithelial cells of the normal mammary gland that maintains the epithelial phenotype of normal breast cells and prevents epithelial-to-mesenchymal transition (EMT). PKD1 is also a critical suppressor of tumor cell invasion and is silenced in expression and activity during breast tumor progression. Here, we show that aberrant methylation of PRKD1 promoter region is not only correlated with the silencing of its expression but is also associated with invasiveness of breast cancer cell lines and with aggressiveness of breast tumors. Using the highly invasive MDA-MB-231 cells, we show that the inhibition of PRKD1 promoter methylation with the DNA methyltransferase inhibitor decitabine restores PKD1 expression and significantly decreases their invasive abilities in vitro. More importantly, in a tumor xenograft model it dramatically blocks tumor spread and metastasis to the lung in a PKD1-dependent fashion. Our data suggest that the status of epigenetic regulation of the PRKD1 promoter can provide valid information on the invasiveness of breast tumors, and therefore could serve as an early diagnostic marker. Moreover, targeted upregulation of PKD1 expression may be used as a therapeutic approach to reverse the invasive phenotype of breast cancer cells. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P1-05-24.

Abstract Background: The role of fusion genes and associated fusion transcripts has long been recognized in hematopoietic malignancies. Until quite recently it has been difficult to detect such events on a genomic scale in solid tumors. Consequently, little is known about the potential role of fusion genes, transcripts, and proteins as driver mutations, biomarkers, or therapeutic targets in breast cancer. Methods: We have developed a novel analytical pipeline, Snowshoes-FTD, for detection of fusion transcripts in breast cancer cell lines and tumor samples (Asmann, et al. NAR 2011; May 27 ePub ahead of print). Preliminary analyses have been carried out with a panel of 8 each ER+, HER2+, and triple negative (TN) primary breast tumors, 8 primary human mammary epithelial cell (HMEC) lines from biopsy samples, plus 16 normal tissues from the Illumina Body Map dataset. Results: We have identified 120 redundant, tumor-specific fusion transcripts, expressed in two or more tumors and in no non-transformed samples. Sixteen of these represent intrachromosomal fusions and 104 arise from fusion of transcripts that map to two different chromosomes. Every breast tumor expressed one or more fusion transcripts. Twenty-nine fusion transcripts appeared to be tumor subtype specific. Among these, we have identified 2 HER2+, 10 ER+, and 17 triple negative specific redundant transcripts. In general, HER2+ tumors expressed fewer fusion transcripts (range 4 to 28/tumor) compared to TN (range11 to 44/tumor). Chromosomal distribution patterns were also markedly different among the tumor subtypes. For example, ER+ tumors expressed a preponderance of redundant fusion transcripts that involve chr1 and 2, whereas TN tumors had no fusion transcripts that map to either chromosome. Conversely, the predominant locus for TN fusion transcripts was chr19, which contains only one HER2+ fusion and no ER+ fusion transcripts. Conclusions: Primary breast tumors express many chimaeric transcripts, which we presume to arise primarily from genomic rearrangements. The majority of these transcripts are redundant, and a subset are tumor subtype specific. These transcripts may mark regions of chromosomal instability. HER2+ tumors, in general, appear to evidence less chromosomal instability, as inferred from fusion transcripts; although some HER2+ tumors appear to be quite unstable. TN tumors contain many more redundant fusion transcripts, implying increased genomic instability, particularly in chr19. We conclude that these fusion transcripts represent a class of heretofore unrecognized biomarkers that may be used for sub-classification of breast tumors. Some of these transcripts appear to encode proteins that may function as tumor-subtype-specific driver mutations and may have potential as therapeutic targets in breast cancer. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P3-06-02.