A novel miR-34a target, protein kinase D1, stimulates cancer stemness and drug resistance through GSK3/β-catenin signaling in breast cancer

// Do Yeon Kim 1, † , Eun Young Park 1, † , EunSun Chang 1 , Hyeok-Gu Kang 2, 3 , Yoonjin Koo 1 , Eun Ji Lee 1 , Je Yeong Ko 1 , Hyun Kyung Kong 1 , Kyung-Hee Chun 2, 3 , Jong Hoon Park 1 1 Department of Biological Science, Sookmyung Women’s University, Seoul, Republic of Korea 2 Department of Biochemistry and Molecular Biology, Yonsei University College of Medicine, Seoul, Republic of Korea 3 Brain Korea 21 PLUS Project for Medical Science, Yonsei University College of Medicine, Seoul, Republic of Korea † These authors contributed equally to this work Correspondence to: Jong Hoon Park, e-mail: parkjh@sookmyung.ac.kr Keywords: miR-34a, PRKD1, β-catenin signaling, cancer stemness, drug resistance Received: November 05, 2015      Accepted: January 31, 2016      Published: February 17, 2016 ABSTRACT One of the properties of human breast cancer cells is cancer stemness, which is characterized by self-renewal capability and drug resistance. Protein kinase D1 ( PRKD1 ) functions as a key regulator of many cellular processes and is downregulated in invasive breast cancer cells. In this study, we found that PRKD1 was upregulated in MCF-7-ADR human breast cancer cells characterized by drug resistance. Additionally, we discovered that PRKD1 expression was negatively regulated by miR-34a binding to the PRKD1 3′-UTR. PRKD1 expression increased following performance of a tumorsphere formation assay in MCF-7-ADR cells. We also found that reduction of PRKD1 by ectopic miR-34a expression or PRKD1 siRNA treatment resulted in suppressed self-renewal ability in breast cancer stem cells. Furthermore, we confirmed that the PRKD1 inhibitor CRT0066101 reduced phosphorylated PKD/PKCμ, leading to suppression of breast cancer stemness through GSK3/β-catenin signaling. PRKD1 inhibition also influenced apoptosis initiation in MCF-7-ADR cells. Tumors from nude mice treated with miR-34a or CRT0066101 showed suppressed tumor growth, proliferation, and induced apoptosis. These results provide evidence that regulation of PRKD1 , a novel miR-34a target, contributes to overcoming cancer stemness and drug resistance in human breast cancer.