The DNA methyl-transferase protein DNMT1 enhances tumor-promoting properties of breast stromal fibroblasts

// Layla A. Al-Kharashi 1, 2 , Falah H. Al-Mohanna 3 , Asma Tulbah 4 and Abdelilah Aboussekhra 1 1 Department of Molecular Oncology, King Faisal Specialist Hospital and Research Center, Riyadh 11211, KSA 2 Department of Pharmacology and Toxicology, Faculty of Pharmacy, King Saud University, Riyadh 11451, KSA 3 Department of Comparative Medicine, King Faisal Specialist Hospital and Research Center, Riyadh 11211, KSA 4 Department of Pathology, King Faisal Specialist Hospital and Research Center, Riyadh 11211, KSA Correspondence to: Abdelilah Aboussekhra, email: aboussekhra@kfshrc.edu.sa Keywords: breast cancer; DNMT1; IL-6; mRNA decay; cancer-associated fibroblasts Received: September 13, 2017 Accepted: December 04, 2017 Published: December 18, 2017 ABSTRACT The activation of breast stromal fibroblasts is a crucial step toward tumor growth and spread. Therefore, it is extremely important to understand the molecular basis of this activation and determine the molecules and the mechanisms responsible for its sustainability. In the present report we have shown that the DNA methyl-transferase protein DNMT1 is critical for the activation of breast stromal fibroblasts as well as the persistence of their active status. Indeed, we have first revealed DNMT1 up-regulation in most cancer-associated fibroblasts relative to their corresponding adjacent normal fibroblasts. This effect resulted from HuR-dependent stabilization of the DNMT1 mRNA. Furthermore, ectopic expression of DNMT1 activated primary normal breast fibroblasts and promoted their pro-carcinogenic effects, both in vitro and in orthotopic tumor xenografts. By contrast, specific DNMT1 knockdown normalized breast myofibroblasts and repressed their cancer-promoting properties. These effects were sustained through inhibition of the IL-6/STAT3/NF-κB epigenetic cancer/inflammation positive feedback loop. Furthermore, we have shown that DNMT1-related activation of breast fibroblasts is mediated through upregulation of the RNA binding protein AUF1, which is also part of the loop. The present data demonstrate the critical function of DNMT1 in breast cancer-related sustained activation of breast stromal fibroblasts.