TAF4 inactivation reveals the 3 dimensional growth promoting activities of collagen 6A3

• Published in: PloS one Vol. 9; no. 2; p. e87365
• Main Authors: Martianov, Igor, Cler, Emilie, Duluc, Isabelle, Vicaire, Serge, Philipps, Muriel, Freund, Jean-Noel, Davidson, Irwin
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 03.02.2014; Public Library of Science (PLoS)
• Subjects: Adaptor Proteins, Signal Transducing - genetics; Adaptor Proteins, Signal Transducing - metabolism; Analysis; Animals; Biology; Blotting, Western; Carrier Proteins - genetics; Carrier Proteins - metabolism; Cell Adhesion - drug effects; Cell Adhesion - genetics; Cell Cycle Proteins; Cell growth; Cell Proliferation; Cells, Cultured; Cellular Biology; Collagen; Collagen Type VI - genetics; Collagen Type VI - metabolism; Contact inhibition; Deactivation; Embryo fibroblasts; Embryo, Mammalian - cytology; Embryos; Extracellular matrix; Fibroblasts; Fibroblasts - cytology; Fibroblasts - metabolism; Gene Expression; Genes; Genomics; Growth; Inactivation; Intracellular Signaling Peptides and Proteins; Kinases; Life Sciences; Membrane Proteins - genetics; Membrane Proteins - metabolism; Mice; Mice, Knockout; Microscopy, Confocal; Phosphoproteins - genetics; Phosphoproteins - metabolism; Protein-Serine-Threonine Kinases - genetics; Protein-Serine-Threonine Kinases - metabolism; Retinoic acid; Reverse Transcriptase Polymerase Chain Reaction; RNA Interference; Rodents; Signal transduction; Signaling; Spheroids, Cellular - cytology; Spheroids, Cellular - drug effects; Spheroids, Cellular - metabolism; TFIID protein; Transcription Factor TFIID - genetics; Transcription Factor TFIID - metabolism; Tretinoin - pharmacology; Tumors; Wnt protein; Wnt Signaling Pathway - drug effects; Wnt Signaling Pathway - genetics; Yes-associated protein
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0087365

Collagen 6A3 (Col6a3), a component of extracellular matrix, is often up-regulated in tumours and is believed to play a pro-oncogenic role. However the mechanisms of its tumorigenic activity are poorly understood. We show here that Col6a3 is highly expressed in densely growing mouse embryonic fibroblasts (MEFs). In MEFs where the TAF4 subunit of general transcription factor IID (TFIID) has been inactivated, elevated Col6a3 expression prevents contact inhibition promoting their 3 dimensional growth as foci and fibrospheres. Analyses of gene expression in densely growing Taf4(-/-) MEFs revealed repression of the Hippo pathway and activation of Wnt signalling. The Hippo activator Kibra/Wwc1 is repressed under dense conditions in Taf4(-/-) MEFs, leading to nuclear accumulation of the proliferation factor YAP1 in the cells forming 3D foci. At the same time, Wnt9a is activated and the Sfrp2 antagonist of Wnt signalling is repressed. Surprisingly, treatment of Taf4(-/-) MEFs with all-trans retinoic acid (ATRA) restores contact inhibition suppressing 3D growth. ATRA represses Col6a3 expression independently of TAF4 expression and Col6a3 silencing is sufficient to restore contact inhibition in Taf4(-/-) MEFs and to suppress 3D growth by reactivating Kibra expression to induce Hippo signalling and by inducing Sfrp2 expression to antagonize Wnt signalling. All together, these results reveal a critical role for Col6a3 in regulating both Hippo and Wnt signalling to promote 3D growth, and show that the TFIID subunit TAF4 is essential to restrain the growth promoting properties of Col6a3. Our data provide new insight into the role of extra cellular matrix components in regulating cell growth.