Nuclear cathepsin D enhances TRPS1 transcriptional repressor function to regulate cell cycle progression and transformation in human breast cancer cells

// Anne-Sophie Bach 1, 2, 3, 4 , Danielle Derocq 1, 2, 3, 4 , Valerie Laurent-Matha 1, 2, 3, 4 , Philippe Montcourrier 1, 2, 3, 4 , Salwa Sebti 1, 2, 3, 4 , Beatrice Orsetti 1, 2, 3, 4 , Charles Theillet 1, 2, 3, 4 , Celine Gongora 1, 2, 3, 4 , Sophie Pattingre 1, 2, 3, 4 , Eva Ibing 5 , Pascal Roger 6 , Laetitia K. Linares 1, 2, 3, 4 , Thomas Reinheckel 7 , Guillaume Meurice 8 , Frank J. Kaiser 5 , Christian Gespach 9 , Emmanuelle Liaudet-Coopman 1, 2, 3, 4 1 IRCM, Institut de Recherche en Cancerologie de Montpellier, Montpellier, France 2 INSERM U1194, Montpellier, France 3 Universite de Montpellier, Montpellier, France 4 Institut Regional du Cancer de Montpellier, Montpellier, France 5 Universitat zu Lubeck, Lubeck, Germany 6 Department of Pathology, CHU Nimes, Nimes, France 7 Institute of Molecular Medicine and Cell Research, Albert-Ludwigs-University, Freiburg, Germany 8 Functional Genomic Plateform, Institut Gustave Roussy, Villejuif, France 9 INSERM U938, Molecular and Clinical Oncology, Paris 6 University Pierre et Marie Curie, Hopital Saint-Antoine, Paris, France Correspondence to: Emmanuelle Liaudet-Coopman, e-mail: emmanuelle.liaudet-coopman@inserm.fr Keywords: GATA-factor, BAT3, PTHrP promoter, yeast-two hybrid, confocal microscopy Received: April 22, 2015      Accepted: June 15, 2015      Published: June 27, 2015 ABSTRACT The lysosomal protease cathepsin D (Cath-D) is overproduced in breast cancer cells (BCC) and supports tumor growth and metastasis formation. Here, we describe the mechanism whereby Cath-D is accumulated in the nucleus of ERα-positive (ER + ) BCC. We identified TRPS1 (tricho-rhino-phalangeal-syndrome 1), a repressor of GATA-mediated transcription, and BAT3 (Scythe/BAG6), a nucleo-cytoplasmic shuttling chaperone protein, as new Cath-D-interacting nuclear proteins. Cath-D binds to BAT3 in ER + BCC and they partially co-localize at the surface of lysosomes and in the nucleus. BAT3 silencing inhibits Cath-D accumulation in the nucleus, indicating that Cath-D nuclear targeting is controlled by BAT3. Fully mature Cath-D also binds to full-length TRPS1 and they co-localize in the nucleus of ER + BCC where they are associated with chromatin. Using the LexA-VP16 fusion co-activator reporter assay, we then show that Cath-D acts as a transcriptional repressor, independently of its catalytic activity. Moreover, microarray analysis of BCC in which Cath-D and/or TRPS1 expression were silenced indicated that Cath-D enhances TRPS1-mediated repression of several TRPS1-regulated genes implicated in carcinogenesis, including PTHrP , a canonical TRPS1 gene target. In addition, co-silencing of TRPS1 and Cath-D in BCC affects the transcription of cell cycle, proliferation and transformation genes, and impairs cell cycle progression and soft agar colony formation. These findings indicate that Cath-D acts as a nuclear transcriptional cofactor of TRPS1 to regulate ER + BCC proliferation and transformation in a non-proteolytic manner.