title: Coordinate down-regulation of cartilage matrix gene expression in Bcl-2 deficient chondrocytes is associated with decreased SOX9 expression and decreased mRNA stability.
abstract: The anti-apoptotic protein Bcl-2 has been shown to function in roles unrelated to apoptosis in a variety of cell types. We have previously reported that loss of Bcl-2 expression alters chondrocyte morphology and modulates aggrecan expression via an apoptosis-independent pathway. Here we show that Bcl-2 is required for chondrocytes to maintain expression of a variety of cartilage-specific matrix proteins. Using quantitative, real-time PCR, we demonstrate that Bcl-2-deficient chondrocytes coordinately down-regulate genes coding for hyaline cartilage matrix proteins including collagen II, collagen IX, aggrecan, and link protein. The decrease in steady-state level of these mRNA transcripts results, in part, from decreased mRNA stability in Bcl-2-deficient chondrocytes. Transcriptional regulation is also likely involved because chondrocytes with decreased Bcl-2 levels show decreased expression of SOX9, a transcription factor necessary for expressing the major cartilage matrix proteins. In contrast, chondrocytes constitutively expressing Bcl-2 have a stable phenotype when subjected to loss of serum factor signaling. These cells maintain high levels of SOX9, as well as the SOX9 targets collagen II and aggrecan. These results suggest that Bcl-2 is involved in a pathway important for maintaining a stable chondrocyte phenotype.
authors.affiliation: Department of Anatomy, Northeastern Ohio Universities College of Medicine, 4209 State Route 44, Rootstown, Ohio 44272, USA. mk2@neoucom.edu
authors.forename: Mary D
authors.initials: MD
authors.lastname: Kinkel
authors.forename: Walter E
authors.initials: WE
authors.lastname: Horton
mesh_terms: D053674:Aggrecans; D000818:Animals; D002460:Cell Line; D019902:Chondrocytes / Q000502:physiology*; D024043:Collagen Type II / Q000235:genetics / Q000378:metabolism; D003609:Dactinomycin; D015536:Down-Regulation; D016326:Extracellular Matrix Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D006023:Glycoproteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D006609:High Mobility Group Proteins / Q000235:genetics / Q000378:metabolism*; D037181:Lectins, C-Type; D064235:Matrilin Proteins; D016133:Polymerase Chain Reaction / Q000379:methods; D011509:Proteoglycans / Q000235:genetics / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D020871:RNA Stability; D012333:RNA, Messenger / Q000032:analysis / Q000096:biosynthesis; D051381:Rats; D055758:SOX9 Transcription Factor; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
chemical_list: C508321:Acan protein, rat; D053674:Aggrecans; D024043:Collagen Type II; D016326:Extracellular Matrix Proteins; D006023:Glycoproteins; D006609:High Mobility Group Proteins; D037181:Lectins, C-Type; D064235:Matrilin Proteins; D011509:Proteoglycans; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D055758:SOX9 Transcription Factor; D014157:Transcription Factors; D003609:Dactinomycin