Altered regulation of BRCA1 exon 11 splicing is associated with breast cancer risk in carriers of BRCA1 pathogenic variants.

Germline pathogenic variants in BRCA1 confer a high risk of developing breast and ovarian cancer. The BRCA1 exon 11 (formally exon 10) is one of the largest exons and codes for the nuclear localization signals of the corresponding gene product. This exon can be partially or entirely skipped during pre-mRNA splicing, leading to three major in-frame isoforms that are detectable in most cell types and tissue, and in normal and cancer settings. However, it is unclear whether the splicing imbalance of this exon is associated with cancer risk. Here we identify a common genetic variant in intron 10, rs5820483 (NC_000017.11:g.43095106_43095108dup), which is associated with exon 11 isoform expression and alternative splicing, and with the risk of breast cancer, but not ovarian cancer, in BRCA1 pathogenic variant carriers. The identification of this genetic effect was confirmed by analogous observations in mouse cells and tissue in which a loxP sequence was inserted in the syntenic intronic region. The prediction that the rs5820483 minor allele variant would create a binding site for the splicing silencer hnRNP A1 was confirmed by pull-down assays. Our data suggest that perturbation of BRCA1 exon 11 splicing modifies the breast cancer risk conferred by pathogenic variants of this gene.

Subjugation of TGFß Signaling by Human Papilloma Virus in Head and Neck Squamous Cell Carcinoma Shifts DNA Repair from Homologous Recombination to Alternative End Joining.

PURPOSE: Following cytotoxic therapy, 70% of patients with human papillomavirus (HPV)-positive oropharyngeal head and neck squamous cell carcinoma (HNSCC) are alive at 5 years compared with 30% of those with similar HPV-negative cancer. Loss of TGFß signaling is a poorly studied consequence of HPV that could contribute to patient outcome by compromising DNA repair. EXPERIMENTAL DESIGN: Human HNSCC cell lines (n = 9), patient-derived xenografts (n = 9), tissue microarray (n = 194), TCGA expression data (n = 279), and primary tumor specimens (n = 10) were used to define the relationship between TGFß competency, response to DNA damage, and type of DNA repair. RESULTS: Analysis of HNSCC specimens in situ and in vitro showed that HPV associated with loss of TGFß signaling that increased response to radiation or cisplatin. TGFß suppressed miR-182, which inhibited both BRCA1, necessary for homologous recombination repair (HRR), and FOXO3, required for ATM kinase activity. TGFß signaling blockade by either HPV or inhibitors released miR182 control, compromised HRR and increased response to PARP inhibition. Antagonizing miR-182 rescued the HRR deficit in HPV-positive cells. Loss of TGFß signaling unexpectedly increased repair by error prone, alternative end-joining (alt-EJ). CONCLUSIONS: HPV-positive HNSCC cells are unresponsive to TGFß. Abrogated TGFß signaling compromises repair by HRR and increases reliance on alt-EJ, which provides a mechanistic basis for sensitivity to PARP inhibitors. The effect of HPV in HNSCC provides critical validation of TGFß's role in DNA repair proficiency and further raises the translational potential of TGFß inhibitors in cancer therapy.

A TGFß-miR-182-BRCA1 axis controls the mammary differentiation hierarchy.

Maintenance of mammary functional capacity during cycles of proliferation and regression depends on appropriate cell fate decisions of mammary progenitor cells to populate an epithelium consisting of secretory luminal cells and contractile myoepithelial cells. It is well established that transforming growth factor-ß (TGFß) restricts mammary epithelial cell proliferation and that sensitivity to TGFß is decreased in breast cancer. We show that TGFß also exerts control of mammary progenitor self-renewal and lineage commitment decisions by stringent regulation of breast cancer associated 1 (BRCA1), which controls stem cell self-renewal and lineage commitment. Either genetic depletion of Tgfb1 or transient blockade of TGFß increased self-renewal of mammary progenitor cells in mice, cultured primary mammary epithelial cells, and also skewed lineage commitment toward the myoepithelial fate. TGFß stabilized the abundance of BRCA1 by reducing the abundance of microRNA-182 (miR-182). Ectopic expression of BRCA1 or antagonism of miR-182 in cultured TGFß-deficient mammary epithelial cells restored luminal lineage commitment. These findings reveal that TGFß modulation of BRCA1 directs mammary epithelial cell fate and, because stem or progenitor cells are thought to be the cell of origin for aggressive breast cancer subtypes, suggest that TGFß dysregulation during tumorigenesis may promote distinct breast cancer subtypes.

Consequences of epithelial or stromal TGFß1 depletion in the mammary gland.

Transforming growth factor ß1 (TGFß) affects stroma and epithelial composition and interactions that mediate mammary development and determine the course of cancer. The reduction of TGFß in Tgfß1 heterozygote mice, which are healthy and long-lived, provides an important model to dissect the contribution of TGFß in mammary gland biology and cancer. We used both intact mice and mammary chimeras in conjunction with Tgfß1 genetic depletion and TGFß neutralizing antibodies to evaluate how stromal or epithelial TGFß depletion affect mammary development and response to physiological stimuli. Our studies of radiation carcinogenesis have revealed new aspects of TGFß biology and suggest that the paradoxical TGFß switch from tumor suppressor to tumor promoter can be resolved by assessing distinct stromal versus epithelial actions.