Cancer cells induce a set of adaptive response pathways to survive in the face of stressors due to inadequate vascularization1. One such adaptive pathway is the unfolded protein (UPR) or endoplasmic reticulum (ER) stress response mediated in part by the ER-localized transmembrane sensor IRE12 and its substrate XBP13. Previous studies report UPR activation in various human tumors4-6, but XBP1's role in cancer progression in mammary epithelial cells is largely unknown. Triple negative breast cancer (TNBC), a form of breast cancer in which tumor cells do not express the genes for estrogen receptor, progesterone receptor, and Her2/neu, is a highly aggressive malignancy with limited treatment options7, 8. Here, we report that XBP1 is activated in TNBC and plays a pivotal role in the tumorigenicity and progression of this human breast cancer subtype. In breast cancer cell line models, depletion of XBP1 inhibited tumor growth and tumor relapse and reduced the CD44high/CD24low population. Hypoxia-inducing factor (HIF)1α is known to be hyperactivated in TNBCs 9, 10. Genome-wide mapping of the XBP1 transcriptional regulatory network revealed that XBP1 drives TNBC tumorigenicity by assembling a transcriptional complex with HIF1α that regulates the expression of HIF1α targets via the recruitment of RNA polymerase II. Analysis of independent cohorts of patients with TNBC revealed a specific XBP1 gene expression signature that was highly correlated with HIF1α and hypoxia-driven signatures and that strongly associated with poor prognosis. Our findings reveal a key function for the XBP1 branch of the UPR in TNBC and imply that targeting this pathway may offer alternative treatment strategies for this aggressive subtype of breast cancer.

AUTHOR CONTRIBUTIONS G.R. designed the experimental approach, performed the experimental work, analyzed the data, coordinated the project and wrote the manuscript. A.H. performed primary tumour growth and exosome education in vivo studies, cancer cell proliferation in vitro studies, cancer cell culture and exosome isolation, coordinated the project and wrote the manuscript. C.M.K. generated CEMIP overexpression, performed molecular cloning work and genetic manipulation of cancer cells, cancer cell culture and exosome isolation, coordinated the project and wrote the manuscript. I.R.M. performed brain slice ex vivo FACS analysis and exosome education in vivo studies, cancer cell culture and exosome isolation, coordinated the project, wrote and reviewed the manuscript. L.S. performed brain slice ex vivo experimental work, tissue processing and immunostaining, ex vivo and in vivo ImageJ data analysis and quantification, cancer cell invasion in vitro studies, western blot analysis, cancer cell culture and exosome isolation, and contributed to figure panel assembly. D.F. performed density gradient exosome isolation, characterization and analysis, western blot analysis, and cancer cell culture. H.S.K. and P.R.O. performed RNA sequencing data analysis. I.S. performed tissue processing and immunostaining, ex vivo and in vivo ImageJ data analysis and quantification, cancer cell culture and exosome isolation. I.C.S. performed western blot analysis and assisted in analysis of human data.

Adenoid cystic carcinoma of the breast is a rare neoplasm that represents <1% of breast carcinomas. The tumors are histologically indistinguishable from examples in other sites, and they have a generally favorable prognosis. Several studies have investigated the possible correlation between histologic grade in adenoid cystic carcinoma (largely determined by cytology and growth pattern) and prognosis. Some earlier reports concluded that a solid variant of mammary adenoid cystic carcinoma had a more aggressive clinical course, but others did not confirm this impression. This report describes nine patients with a solid variant of mammary adenoid cystic carcinoma that has a striking basaloid appearance. All were women ranging in age from 37 to 83 years. A solitary mass was evident in all patients. Tumor size was 1.1-15 cm (mean 3.7 cm). The tumors exhibited a predominantly solid architecture comprised of basaloid appearing cells with moderate to marked nuclear atypia. Five tumors had >5 mitotic figures per 10 high power microscopic fields. Intercalated ducts were found in all tumors, being well formed in six and poorly formed in three. Immunohistochemical stains for cytokeratins, basement membranes, and vimentin were consistently positive. Surgery was performed in all cases consisting of excision in seven and mastectomy in two. Axillary lymph node metastases were found in two of six axillary dissections and four had negative lymph nodes. The lymph nodes were not examined in three patients. Follow-up information was available for seven patients. Six women had no evidence of disease after follow-up of 2-88 months (mean 32 months), one patient died of unknown causes, and one patient was lost to follow-up. It is concluded that the solid variant of mammary carcinoma with basaloid features is a histologically distinct tumor that is capable of axillary metastases. Long-term follow-up of a larger series of cases will be needed to determine whether the prognosis of these patients differs significantly from that of women with conventional adenoid cystic carcinoma. Presently, these patients are candidates for axillary staging by sentinel lymph node mapping or low axillary dissection if there is no clinical evidence of axillary metastases. Systemic adjuvant treatment would be prudent when axillary nodal metastases are present. Breast-conserving surgery with radiation is an option if negative margins can be achieved because this appears to be a unicentric form of carcinoma.

The three EglN prolyl hydroxylases (EglN1, EglN2, and EglN3) regulate the stability of the HIF transcription factor. We recently showed that loss of EglN2, however, also leads to down-regulation of Cyclin D1 and decreased cell proliferation in a HIF-independent manner. Here we report that EglN2 can hydroxylate FOXO3a on two specific prolyl residues in vitro and in vivo. Hydroxylation of these sites prevents the binding of USP9x deubiquitinase, thereby promoting the proteasomal degradation of FOXO3a. FOXO transcription factors can repress Cyclin D1 transcription. Failure to hydroxylate FOXO3a promotes its accumulation in cells, which in turn suppresses Cyclin D1 expression. These findings provide new insights into post-transcriptional control of FOXO3a and provide a new avenue for pharmacologically altering Cyclin D1 activity.

Pleomorphic lobular carcinomas (PLC) of the breast display histological features associated with classic invasive lobular carcinoma (ILC), yet they also exhibit more conspicuous nuclear atypia and pleomorphism, and an aggressive clinical behaviour. From a breast cancer progression perspective, it is unclear whether PLC is a variant of ILC or is a high-grade invasive ductal carcinoma (IDC) that has lost E-cadherin. The molecular features of 26 PLC were studied using immunohistochemistry [oestrogen receptor (ER), progesterone receptor (PR), HER2, p53 and E-cadherin], 0.9 Mb resolution, microarray-based comparative genomic hybridization (aCGH), fluorescent (FISH) and chromogenic (CISH) in situ hybridization and loss of heterozygosity. Comparative analysis was performed with aCGH data from PLC with classic ILC (16 cases) and high grade IDC (35 cases). PLCs were frequently ER- and PR-positive, E-cadherin-negative and occasionally HER2- and p53-positive. Recurrent copy number changes identified by aCGH included gains on 1q, 8q, 11q, 12q, 16p and 17q and losses on 8p, 11q, 13q, 16q and Xq. Highly recurrent 1q+ (100% of cases), 16p+ (93%), 11q- (53%) and 16q- (93%) and evidence of the der(1;16)/der(16)t(1;16) rearrangement, as detected by FISH, suggested that PLC had a 'lobular genotype'. Focal amplifications were evident at 8p12-p11, 8q24, 11q13.1-q14.1, 12q14, 17q12 and 20q13. Loss of BRCA2 was detected in 40% of PLC by LOH. Comparative analysis of aCGH data suggested the molecular features of PLC (ER/PR-positive, E-cadherin-negative, 1q+, 11q(-), 16p+ and 16q(-)) were more closely related to those of ILC than IDC, implicating an overlapping developmental pathway for these lobular tumour types. Molecular alterations found in PLC that are more typical of high-grade IDC than ILC (p53 and HER2 positivity, 8q+, 17q24-q25+, 13q(-) and amplification of 8q24, 12q14, 17q12 and 20q13) are likely to drive the high-grade and more aggressive biology of PLC.

Cancer/testis (CT) genes are predominantly expressed in human germ line cells, but not somatic tissues, and frequently become activated in different cancer types. Several CT antigens have already proved to be useful biomarkers and are promising targets for therapeutic cancer vaccines. The aim of the present study was to investigate the expression of CT antigens in breast cancer. Using previously generated massively parallel signature sequencing (MPSS) data, together with 9 publicly available gene expression datasets, the expression pattern of CT antigens located on the X chromosome (CT-X) was interrogated. Whereas a minority of unselected breast cancers was found to contain CT-X transcripts, a significantly higher expression frequency was detected in estrogen and progesterone receptor (ER) negative breast cancer cell lines and primary breast carcinomas. A coordinated pattern of CT-X antigen expression was observed, with MAGEA and NY-ESO-1/ CTAG1B being the most prevalent antigens. Immunohistochemical staining confirmed the correlation of CT-X antigen expression and ER negativity in breast tumors and demonstrated a trend for their coexpression with basal cell markers. Because of the limited therapeutic options for ER-negative breast cancers, vaccines based on CT-X antigens might prove to be useful.cancer/testis antigens ͉ estrogen receptor ͉ therapy

Prostate-specific membrane antigen (PSMA) has been found to be expressed in the tumor-associated neovasculature of multiple solid tumor types including breast cancers. However, thus far, the number of cases studied from some tumor types has been limited. In this study, we set out to assess PSMA expression in the tumor-associated vasculature associated with invasive breast carcinomas in a sizable cohort of patients. One hundred and six patients with AJCC stage 0-IV breast cancer were identified. Ninety-two of these patients had primary breast cancer [invasive breast carcinoma with or without co-existing ductal carcinoma in situ (DCIS) (74) or DCIS alone (18)]. In addition, 14 patients with breast cancer metastases to the brain were identified. Immunohistochemical staining for PSMA and CD31 was performed on parallel representative tumor sections in each case. Tumor-associated vascular endothelial cell PSMA immunoreactivity was semi-quantitatively assessed based on two parameters: overall percent of endothelial positivity and staining intensity. PSMA expression for tumor-associated vascular endothelial cells was scored 0 if there was no detectable PSMA expression, 1 if PSMA staining was detectable in 5-50%, and 2 if PSMA expression was positive in >50% of microvessels. CD 31 staining was concurrently reviewed to confirm the presence of vasculature in each case. Tumor-associated vasculature was PSMA-positive in 68/92 (74%) of primary breast cancers and in 14/14 (100%) of breast cancers metastatic to brain. PSMA was not detected in normal breast tissue or carcinoma cells. All but 2 cases (98%) showed absence of PSMA expression in normal breast tissue-associated vasculature. The 10-year overall survival was 88.7% (95% CI = 80.0%, 93.8%) in patients without brain metastases. When overall survival (OS) was stratified based on PSMA score group, patients with PSMA scores of 0, 1, and 2 had 10-year OS of 95.8%, 96.0%, and 79.7%, respectively (p = 0.12). When PSMA scores of 0 and 1 were compared with 2, there was a statistically significant difference in OS (96.0% vs 79.7%, respectively, p = 0.05). Patients with a PSMA score of 2 had a significantly higher median tumor size compared with patients in the lower PSMA score groups (p = 0.04). Patients with higher nuclear grade were more likely to have a PSMA score of 2 compared with patients with lower nuclear grade (p < 0.0001). Patients with a PSMA score of 2 had a significantly higher median Ki-67 proliferation index compared with patients in the lower PSMA score groups (p < 0.0001). Patients with estrogen receptor (ER)-negative tumors were more likely to have a PSMA score of 2 compared with patients with ER-positive tumors (p < 0.0001). Patients with progesterone receptor (PR)-negative tumors were more likely to have a PSMA score of 2 compared with patients with PR-positive tumors (p = 0.03). No significant association was observed between PSMA score group status and lymph node involvement (p = 0.95). Too little variability was present in Human epidermal growth factor recept...

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