PICT-1 triggers a pro-death autophagy through inhibiting rRNA transcription and AKT/mTOR/p70S6K signaling pathway.

// Hongbo Chen 1, 2, * , Yanhong Duo 3, * , Bo Hu 4 , Zhiwei Wang 5 , Fang Zhang 1 , Hsiangi Tsai 1, 2 , Jianping Zhang 6 , Lanzhen Zhou 6 , Lijun Wang 1 , Xinyu Wang 3 , Laiqiang Huang 1, 2 1 The Shenzhen Key Lab of Gene and Antibody Therapy, Center for Biotechnology & Biomedicine, Division of Life and Health Sciences, Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, China 2 School of Life Sciences, Tsinghua University, Beijing 100084, China 3 Key Laboratory of Plant Cell Activities and Stress Adaptation, Ministry of Education, School of Life Sciences, Lanzhou University, Lanzhou 730000, China 4 Department of Laboratory Medicine, The Third Affiliated Hospital of Sun Yat-sen University, Guangzhou 510630, China 5 Department of Laboratory Medicine, The Fourth Affiliated Hospital of Guangzhou Medical University, Guangzhou 511447, China 6 Department of Quality Inspection, Shenzhen Weiguang Biological Products Co., Ltd, Shenzhen 518107, China * These authors have contributed equally to this work Correspondence to: Hongbo Chen, email: chen.hongbo@sz.tsinghua.edu.cn Xinyu Wang, email: wangxy@lzu.edu.cn Laiqiang Huang, email: huanglq@tsinghua.edu.cn Keywords: PICT-1, nucleolus, autophagy, rRNA transcription, p53 Received: May 26, 2016     Accepted: September 16, 2016     Published: September 27, 2016 ABSTRACT PICT-1 was originally identified as a tumor suppressor. Here, we found that PICT-1 overexpression triggered pro-death autophagy without nucleolar disruption or p53 accumulation in U251 and MCF7 cells. Truncated PICT-1 fragments 181-346 and 1-346, which partly or totally lack nucleolar localization, showed weaker autophagy-inducing effects than full-length PICT-1 and a well-defined nucleolar mutant (181-479). Furthermore, PICT-1 partly localizes to the nucleolar fibrillar center (FC) and directly binds to ribosomal DNA (rDNA) gene loci, where it interacts with upstream binding factor (UBF). Overexpression of PICT-1 or the 181-479 mutant, but not the 1-346 or 181-346 mutants, markedly inhibited the phosphorylation of UBF and the recruitment of rRNA polymerase I (Pol I) to the rDNA promoter in response to serum stimulation, thereby suppressing rRNA transcription, suggesting that rRNA transcription inhibition might be an important contributor to PICT-1-induced autophagy. This is supported by the finding that CX-5461, a specific Pol I inhibitor, also induced autophagy. In addition, both CX-5461 and PICT-1, but not the 1-346 or 181-346 mutants, significantly suppressed the activation of the Akt/mTOR/p70S6K signaling pathway. Our data show that PICT-1 triggers pro-death autophagy through inhibition of rRNA transcription and the inactivation of AKT/mTOR/p70S6K pathway, independent of nucleolar disruption and p53 activation.