The Interaction of the Senescent and Adjacent Breast Cancer Cells Promotes the Metastasis of Heterogeneous Breast Cancer Cells through Notch Signaling.

Chemotherapy is one of the most common strategies for tumor treatment but often associated with post-therapy tumor recurrence. While chemotherapeutic drugs are known to induce tumor cell senescence, the roles and mechanisms of senescence in tumor recurrence remain unclear. In this study, we used doxorubicin to induce senescence in breast cancer cells, followed by culture of breast cancer cells with conditional media of senescent breast cancer cells (indirect co-culture) or directly with senescent breast cancer cells (direct co-culture). We showed that breast cancer cells underwent the epithelial-mesenchymal transition (EMT) to a greater extent and had stronger migration and invasion ability in the direct co-culture compared with that in the indirect co-culture model. Moreover, in the direct co-culture model, non-senescent breast cancer cells facilitated senescent breast cancer cells to escape and re-enter into the cell cycle. Meanwhile, senescent breast cancer cells regained tumor cell characteristics and underwent EMT after direct co-culture. We found that the Notch signaling was activated in both senescent and non-senescent breast cancer cells in the direct co-culture group. Notably, the EMT process of senescent and adjacent breast cancer cells was blocked upon inhibition of Notch signaling with N-[(3,5-difluorophenyl)acetyl]-l-alanyl-2-phenyl]glycine-1,1-dimethylethyl ester (DAPT) in the direct co-cultures. In addition, DAPT inhibited the lung metastasis of the co-cultured breast cancer cells in vivo. Collectively, data arising from this study suggest that both senescent and adjacent non-senescent breast cancer cells developed EMT through activating Notch signaling under conditions of intratumoral heterogeneity caused by chemotherapy, which infer the possibility that Notch inhibitors used in combination with chemotherapeutic agents may become an effective treatment strategy.

Arginine methylation-dependent LSD1 stability promotes invasion and metastasis of breast cancer.

Histone lysine demethylase 1 (LSD1), the first identified histone demethylase, is overexpressed in multiple tumor types, including breast cancer. However, the mechanisms that cause LSD1 dysregulation in breast cancer remain largely unclear. Here, we report that protein arginine methyltransferase 4 (PRMT4 or CARM1) dimethylates LSD1 at R838, which promotes the binding of the deubiquitinase USP7, resulting in the deubiquitination and stabilization of LSD1. Moreover, CARM1- and USP7-dependent LSD1 stabilization plays a key role in repressing E-cadherin and activating vimentin transcription through promoter H3K4me2 and H3K9me2 demethylation, respectively, which promotes invasion and metastasis of breast cancer cells. Consistently, LSD1 arginine methylation levels correlate with tumor grade in human malignant breast carcinoma samples. Our findings unveil a unique mechanism controlling LSD1 stability by arginine methylation, also highlighting the role of the CARM1-USP7-LSD1 axis in breast cancer progression.

Phosphorylation of LSD1 at Ser112 is crucial for its function in induction of EMT and metastasis in breast cancer.

PURPOSE: LSD1 is overexpressed in various cancers including breast cancer, but its functional roles in tumourigenesis are not fully understood. This study aims at revealing the role of LSD1 in breast cancer development. In addition, it has been reported that phosphorylation of the Serine 112 residue of LSD1 by PKCα is crucial for its function in gene regulation. We also explored whether this phosphorylation affects LSD1's role in breast cancer development. METHODS: This study includes LSD1 IHC data generated with tissue microarrays of 163 cases of breast cancer samples and 72 normal tissues. In vitro, role of LSD1, LSD1 S112D mutant (a phosphorylation simulation) and LSD1 S112A mutant (an unphosphorylation simulation) in induction of EMT is evaluated. Mechanismly, we checked the role of LSD1 and its mutant on E-cadherin promoter histone modifications. We also investigated the role of LSD1 and its mutants in metastasis with a nude mice model. RESULTS: We found LSD1 is expressed at a higher level in breast cancer tissues compared with that in normal tissues, and LSD1 expression is closely linked to breast cancer metastasis. LSD1 potentiates EMT in breast epithelia cells by repressing E-cadherin expression through demethylating H3K4me at gene's promoter, during which phosphorylation of LSD1 Ser112 is crucial for its binding and demethylation activity. In vivo, knockdown of LSD1 impairs the metastatic ability of MDA-MB-231 breast cancer cells in nude mice. Ectopic overexpression of either LSD1 or LSD1 S112D mutant (a phosphorylation simulation) facilitates metastasis, whereas the LSD1 S112A mutant (an unphosphorylation simulation) fails to affect the metastasis. CONCLUSIONS: Data presented in this report indicate that LSD1 is able to induce EMT and to promote metastasis in breast cancer, and phosphorylation at LSD1 Ser112 is crucial for these functions.