YAP/TAZ regulates the expression of proteoglycan 4 and tenascin C in superficial-zone chondrocytes
1 Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Canada
2 Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, Canada
3 Faculty of Science, University of Ontario Institute of Technology, Oshawa, Canada
4 Faculty of Kinesiology, University of Calgary, Calgary, Canada
5 Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA, USA
6 Biomedical Engineering Department, University of Connecticut Health Center, Farmington, CN, USA
7 Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Canada
8 Pathology and Laboratory Medicine, Mount Sinai Hospital, Toronto, Canada
Abstract
The roles of cell division control protein 42 homologue (CDC42) and actin polymerisation in regulating the phenotype of superficial-zone chondrocytes (SZCs) have been demonstrated in vitro; however, the signalling pathway(s) downstream have yet to be fully elucidated. The study hypothesis was that Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ) act downstream to regulate proteoglycan 4 (PRG4) and tenascin C (TNC). Bovine SZCs grown in monolayer were treated with ML141 (CDC42 inhibitor) or the actin depolymerising agents, latrunculin B and cytochalasin D, to determine the effect on YAP/TAZ. Verteporfin (YAP/TAZ inhibitor) and YAP/TAZ siRNA-mediated knockdown were used to determine their role in regulating PRG4 and TNC. ML141 treatment reduced total YAP/TAZ protein, nuclear TAZ levels and the YAP/TAZ target gene, connective tissue growth factor (CTGF) mRNA levels. Latrunculin B decreased nuclear TAZ, while cytochalasin D treatment trended towards increased nuclear TAZ (p = 0.06), correlating with decreased and increased CTGF mRNA levels, respectively. Verteporfin treatment decreased PRG4 and TNC expression, with no effect on actin polymerisation. siRNA-mediated knockdown of YAP/TAZ revealed that PRG4 was regulated by YAP/TAZ while TNC was regulated by TAZ only. As cytochalasin D can activate myocardin-related transcription factor-A (MRTF-A), siRNA-mediated knockdown was performed to determine the role of MRTF-A in regulating YAP/TAZ. Although nuclear TAZ decreased, no significant changes in total protein levels were observed. Findings suggested that CDC42 and actin polymerisation regulated SZCs through multiple actin-regulated pathways. Understanding the regulation of these chondroprotective molecules may have important implications for prevention/treatment of osteoarthritis.
Graphical Abstract
Keywords
- Cell division control protein 42 homologue
- actin polymerisation
- superficial-zone chondrocyte
- primary chondrocyte phenotype
- proteoglycan 4
- tenascin C
- Yes-associated protein
- transcriptional co-activator with PDZ-binding motif
- myocardin-related transcription factor-A
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