Peptidylarginine Deiminase IV Regulates Breast Cancer Stem Cells via a Novel Tumor Cell-Autonomous Suppressor Role.

Peptidylarginine deiminases (PADI) catalyze posttranslational modification of many target proteins and have been suggested to play a role in carcinogenesis. Citrullination of histones by PADI4 was recently implicated in regulating embryonic stem and hematopoietic progenitor cells. Here, we investigated a possible role for PADI4 in regulating breast cancer stem cells. PADI4 activity limited the number of cancer stem cells (CSC) in multiple breast cancer models in vitro and in vivo. Mechanistically, PADI4 inhibition resulted in a widespread redistribution of histone H3, with increased accumulation around transcriptional start sites. Interestingly, epigenetic effects of PADI4 on the bulk tumor cell population did not explain the CSC phenotype. However, in sorted tumor cell populations, PADI4 downregulated expression of master transcription factors of stemness, NANOG and OCT4, specifically in the cancer stem cell compartment, by reducing the transcriptionally activating H3R17me2a histone mark at those loci; this effect was not seen in the non-stem cells. A gene signature reflecting tumor cell-autonomous PADI4 inhibition was associated with poor outcome in human breast cancer datasets, consistent with a tumor-suppressive role for PADI4 in estrogen receptor-positive tumors. These results contrast with known tumor-promoting effects of PADI4 on the tumor stroma and suggest that the balance between opposing tumor cell-autonomous and stromal effects may determine net outcome. Our findings reveal a novel role for PADI4 as a tumor suppressor in regulating breast cancer stem cells and provide insight into context-specific effects of PADI4 in epigenetic modulation. SIGNIFICANCE: These findings demonstrate a novel activity of the citrullinating enzyme PADI4 in suppressing breast cancer stem cells through epigenetic repression of stemness master transcription factors NANOG and OCT4.

The Outcome of TGFß Antagonism in Metastatic Breast Cancer Models In Vivo Reflects a Complex Balance between Tumor-Suppressive and Proprogression Activities of TGFß.

PURPOSE: TGFßs are overexpressed in many advanced cancers and promote cancer progression through mechanisms that include suppression of immunosurveillance. Multiple strategies to antagonize the TGFß pathway are in early-phase oncology trials. However, TGFßs also have tumor-suppressive activities early in tumorigenesis, and the extent to which these might be retained in advanced disease has not been fully explored. EXPERIMENTAL DESIGN: A panel of 12 immunocompetent mouse allograft models of metastatic breast cancer was tested for the effect of neutralizing anti-TGFß antibodies on lung metastatic burden. Extensive correlative biology analyses were performed to assess potential predictive biomarkers and probe underlying mechanisms. RESULTS: Heterogeneous responses to anti-TGFß treatment were observed, with 5 of 12 models (42%) showing suppression of metastasis, 4 of 12 (33%) showing no response, and 3 of 12 (25%) showing an undesirable stimulation (up to 9-fold) of metastasis. Inhibition of metastasis was immune-dependent, whereas stimulation of metastasis was immune-independent and targeted the tumor cell compartment, potentially affecting the cancer stem cell. Thus, the integrated outcome of TGFß antagonism depends on a complex balance between enhancing effective antitumor immunity and disrupting persistent tumor-suppressive effects of TGFß on the tumor cell. Applying transcriptomic signatures derived from treatment-naïve mouse primary tumors to human breast cancer datasets suggested that patients with breast cancer with high-grade, estrogen receptor-negative disease are most likely to benefit from anti-TGFß therapy. CONCLUSIONS: Contrary to dogma, tumor-suppressive responses to TGFß are retained in some advanced metastatic tumors. Safe deployment of TGFß antagonists in the clinic will require good predictive biomarkers.

The transcription factor CBFB suppresses breast cancer through orchestrating translation and transcription.

Translation and transcription are frequently dysregulated in cancer. These two processes are generally regulated by distinct sets of factors. The CBFB gene, which encodes a transcription factor, has recently emerged as a highly mutated driver in a variety of human cancers including breast cancer. Here we report a noncanonical role of CBFB in translation regulation. RNA immunoprecipitation followed by deep sequencing (RIP-seq) reveals that cytoplasmic CBFB binds to hundreds of transcripts and regulates their translation. CBFB binds to mRNAs via hnRNPK and enhances translation through eIF4B, a general translation initiation factor. Interestingly, the RUNX1 mRNA, which encodes the transcriptional partner of CBFB, is bound and translationally regulated by CBFB. Furthermore, nuclear CBFB/RUNX1 complex transcriptionally represses the oncogenic NOTCH signaling pathway in breast cancer. Thus, our data reveal an unexpected function of CBFB in translation regulation and propose that breast cancer cells evade translation and transcription surveillance simultaneously through downregulating CBFB.