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ASMT Regulates Tumor Metastasis Through the Circadian Clock System in Triple-Negative Breast Cancer.

ABSTRACT: Objective:Triple-negative (PR-, ER-, HER-2-) breast cancer (TNBC) is regarded as more aggressive and more likely to recur after medical care. Emerging evidence has demonstrated that the circadian clock system regulates cell-signaling pathways critical to cancer cell proliferation, survival and metastasis, meaning that it could be a good candidate for TNBC treatment. As such, the aim of the current study was to examine the molecular mechanism by which the circadian clock system contributes to cancer progression in TNBC. Methods:Cancer cells and primary breast cancer tissues were immunostained for the measurement of circadian clock proteins (CLOCK, BMAL1 and PER1) and acetylserotonin methyltransferase (ASMT). The association between ASMT and clock proteins was assessed using siRNA and Western blot. Transwell assays were used to detect cancer cell migration and invasion while MTT assays were utilized to evaluate cell proliferation. Results:Circadian clock proteins (CLOCK, BMAL1, and PER1) and ASMT expression were higher in TNBC and triple positive breast cancer (TPBC) compared with para-carcinoma tissues (PCTs). Intriguingly, there was an obvious correlation between circadian clock proteins and ASMT expression in both TPBC and TNBC. Similarly, circadian clock proteins and ASMT were expressed to a greater extent in BT-474 (triple-positive) cells than in MDA-MB-231 (triple-negative) cells. The inhibition of ASMT reduced circadian clock protein levels in both breast cancer cell lines. Further analysis showed that the expression levels of ASMT and circadian clock proteins did not correlate with clinical parameters such as age, tumor size, histologic grade and CK5/6, but increased significantly with lymphatic invasion in TNBC. In agreement with this finding, knockdown of ASMT significantly leads to reductions in migration and invasion in MDA-MB-231 cells. However, over-expression of CLOCK reversed the decreases seen in ASMT inhibited cells. Conclusion:Our study suggests that ASMT regulates the circadian clock system in breast cancer and inhibition of ASMT reduces the invasiveness of triple-negative breast cancer cells by downregulating clock protein in a certain extent, indicating the potential value of ASMT as a drug target for TNBC treatment.

SUBMITTER: Xie F

PROVIDER: S-EPMC7609885 | biostudies-literature | 2020

REPOSITORIES: biostudies-literature

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ASMT Regulates Tumor Metastasis Through the Circadian Clock System in Triple-Negative Breast Cancer.

Xie FenFen F Wang LiLi L Liu YaJing Y Liu ZhenBang Z Zhang ZuoYang Z Pei Jing J Wu ZhengSheng Z Zhai MuXin M Cao YunXia Y

Frontiers in oncology 20201021

<h4>Objective</h4>Triple-negative (PR<sup>-</sup>, ER<sup>-</sup>, HER-2<sup>-</sup>) breast cancer (TNBC) is regarded as more aggressive and more likely to recur after medical care. Emerging evidence has demonstrated that the circadian clock system regulates cell-signaling pathways critical to cancer cell proliferation, survival and metastasis, meaning that it could be a good candidate for TNBC treatment. As such, the aim of the current study was to examine the molecular mechanism by which the ...[more]

PMID: 33194597

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Project description:Tumor-initiating cells with reprogramming plasticity and/or de-differentiation attributes have been thought to initiate primary tumor development as well as to regenerate secondary tumors in metastatic organs; however, the molecular mechanisms are not fully understood. We previously found that breast tumor-initiating cell marker, CD44, directs multicellular aggregation and cluster formation of circulating tumor cells (CTCs), which further enhance stemness and survival of such cells, enabling metastatic colonization to the lungs. To further elucidate the molecular network underlying CTC cluster formation, we performed global proteomic profiling and discovered that the tetraspanin protein CD81, which is normally enriched in exosomes (small extracellular vesicles), is a new driver of cancer initiation and metastasis as a facilitator and target of CD44. Loss of CD81 compromises tumorigenicity and mammosphere formation of triple negative breast cancer (TNBC) cells. Assisted by machine learning-based algorithms and mutagenesis approach, we found that CD81 interacts with CD44 on the cellular membrane through their extracellular regions. Notably, genetic knockout of CD44 or CD81 results in loss of both CD81 and CD44 in secreted exosomes, a state which abolishes exosome-induced self-renewal of recipient cells, such as mammosphere formation. In addition, RNA sequencing analysis showed that CD81 knockdown up-regulates expression of a cell differentiation marker, SEMA7a, whose down-regulation partially rescues mammosphere formation inhibition by CD81 depletion. Clinically, CD81 expression was observed in >80% of CTCs and specifically enriched and co-expressed along with CD44 in clustered CTCs of breast cancer patients. Mimicing the phenotypes of CD44 deficiency, loss of CD81 also inhibited tumor cell aggregation and lung metastasis of TNBC in both human and mouse tumor models, supporting the clinical significance of CD81 in association with patient outcomes. Our study highlights a new driving role of CD81 in cancer exosome-induced stemness, clustered CTCs, and metastasis initiation of TNBC, reported for the first time to our knowledge.

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ASMT Regulates Tumor Metastasis Through the Circadian Clock System in Triple-Negative Breast Cancer.

Publications

ASMT Regulates Tumor Metastasis Through the Circadian Clock System in Triple-Negative Breast Cancer.

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