Exosomal miR-940 maintains SRC-mediated oncogenic activity in cancer cells: A possible role for exosomal disposal of tumor suppressor miRNAs

// Mohammed H. Rashed 1, 4 , Pinar Kanlikilicer 1, 2 , Cristian Rodriguez-Aguayo 1, 2 , Martin Pichler 7 , Recep Bayraktar 1 , Emine Bayraktar 1 , Cristina Ivan 1, 2 , Justyna Filant 3 , Andreia Silva 5, 6 , Burcu Aslan 1, 2 , Merve Denizli 1 , Rahul Mitra 2 , Bulent Ozpolat 1, 2 , George A. Calin 1, 2 , Anil K. Sood 2, 3 , Mohamed F. Abd-Ellah 4 , Gouda K. Helal 4 , Gabriel Lopez Berestein 1, 2 1 Department of Experimental Therapeutics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA 2 Department of Center for RNAi and Non-Coding RNA, The University of Texas MD Anderson Cancer Center, Houston, TX, USA 3 Department of Gynecologic Oncology and Reproductive Medicine, The University of Texas MD Anderson Cancer Center, Houston, TX, USA 4 Department of Pharmacology and Toxicology, Faculty of Pharmacy, Al-Azhar University, Cairo, Egypt 5 Instituto de Investigacao em Saude, Universidade do Porto, Porto, Portugal 6 INEB-Institute of Biomedical Engineering, Universidade do Porto, Porto, Portugal 7 Division of Clinical Oncology, Department of Medicine, Medical University of Graz, Graz, Austria Correspondence to: Gabriel Lopez Berestein, email: glopez@mdanderson.org Keywords: exosomes, ovarian cancer, miR-940, SRC, tumor suppressive Received: May 10, 2016      Accepted: January 03, 2017      Published: February 20, 2017 ABSTRACT Exosomes have emerged as important mediators of diverse biological functions including tumor suppression, tumor progression, invasion, immune escape and cell-to-cell communication, through the release of molecules such as mRNAs, miRNAs, and proteins. Here, we identified differentially expressed exosomal miRNAs between normal epithelial ovarian cell line and both resistant and sensitive ovarian cancer (OC) cell lines. We found miR-940 as abundant in exosomes from SKOV3-IP1, HeyA8, and HeyA8-MDR cells. The high expression of miR-940 is associated with better survival in patients with ovarian serous cystadenocarcinoma. Ectopic expression of miR-940 inhibited proliferation, colony formation, invasion, and migration and triggered G0/G1 cell cycle arrest and apoptosis in OC cells. Overexpression of miR-940 also inhibited tumor cell growth in vivo . We showed that proto-oncogene tyrosine-protein kinase (SRC) is directly targeted by miR-940 and that miR-940 inhibited SRC expression at mRNA and protein levels. Following this inhibition, the expression of proteins downstream of SRC, such as FAK, paxillin and Akt was also reduced. Collectively, our results suggest that OC cells secrete the tumor-suppressive miR-940 into the extracellular environment via exosomes, to maintain their invasiveness and tumorigenic phenotype.