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BCL-2 associated athanogene-1 (BAG-1): A transcriptional regulator mediating chondrocyte survival and differentiation during endochondral ossification

BCL-2 associated athanogene-1 (BAG-1): A transcriptional regulator mediating chondrocyte survival and differentiation during endochondral ossification
BCL-2 associated athanogene-1 (BAG-1): A transcriptional regulator mediating chondrocyte survival and differentiation during endochondral ossification
BAG-1, an anti-apoptotic protein, was identified by its ability to bind to BCL-2, HSP70-family molecular chaperones and nuclear hormone receptor family members. Two BAG-1 isoforms, BAG-1L (50 kDa) and BAG-1S (32 kDa) were identified in mouse cells and BAG-1 expression was reported in murine growth plate and articular chondrocytes. The present study aimed to elucidate the role of BAG-1 in the regulation of molecular mechanisms governing chondrocyte differentiation and turnover during endochondral ossification.

In long bones of skeletally immature mice, we observed expression of BAG-1 in the perichondrium, osteoblasts, osteocytes in the bone shaft, bone marrow, growth plate and articular chondrocytes. Monolayer cultures of murine chondrocytic ATDC5 cells, which exhibited robust expression of both BAG-1 isoforms and the Bag-1 transcript, were utilized as an in vitro model to delineate the roles of BAG-1. Overexpression of BAG-1L in ATDC5 cells resulted in downregulation of Col2a1 expression, a gene characteristically downregulated at the onset of hypertrophy, and an increase in transcription of Runx-2 and Alkaline phosphatase, genes normally expressed at the onset of chondrocyte hypertrophy and cartilage mineralization in the process of endochondral ossification. We also demonstrated the anti-apoptotic role of BAG-1 in chondrocytes as overexpression of BAG-1 protected ATDC5 cells, which were subjected to heat-shock at 48 °C for 30 min, against heat-shock-induced apoptosis. Overexpression of the SOX-9 protein in ATDC5 cells resulted in increased Bag-1 gene expression. To further investigate the regulation of Bag-1 gene expression by SOX-9, CHO cells were co-transfected with the human Bag-1 gene promoter–Luciferase reporter construct and the human pSox-9 expression vector. Activity of the Bag-1 promoter was significantly enhanced by the SOX-9 protein.

In conclusion, a novel finding of this study is the role of BAG-1 as a transcriptional regulator of genes involved in chondrocyte hypertrophy and cartilage mineralization during the process of endochondral ossification. Additionally, we have demonstrated for the first time the regulation of Bag-1 gene expression by SOX-9 and the anti-apoptotic role of BAG-1 in chondrocytic cells. Modulation of Bag-1 expression can therefore mediate chondrocyte differentiation and turnover, and offer further insight into the molecular regulation of endochondral ossification.
atdc5, chondrocyte differentiation, endochondral ossification, runx-2, alkaline phosphatase
8756-3282
113-128
Tare, Rahul S.
587c9db4-e409-4e7c-a02a-677547ab724a
Townsend, Paul A.
a2680443-664e-46d0-b4dd-97456ba810db
Packham, Graham
fdabe56f-2c58-469c-aadf-38878f233394
Inglis, Stefanie
cb950bb9-8b89-41c0-b547-3206580d16b4
Oreffo, Richard O.C.
ff9fff72-6855-4d0f-bfb2-311d0e8f3778
Tare, Rahul S.
587c9db4-e409-4e7c-a02a-677547ab724a
Townsend, Paul A.
a2680443-664e-46d0-b4dd-97456ba810db
Packham, Graham
fdabe56f-2c58-469c-aadf-38878f233394
Inglis, Stefanie
cb950bb9-8b89-41c0-b547-3206580d16b4
Oreffo, Richard O.C.
ff9fff72-6855-4d0f-bfb2-311d0e8f3778

Tare, Rahul S., Townsend, Paul A., Packham, Graham, Inglis, Stefanie and Oreffo, Richard O.C. (2008) BCL-2 associated athanogene-1 (BAG-1): A transcriptional regulator mediating chondrocyte survival and differentiation during endochondral ossification. Bone, 42 (1), 113-128. (doi:10.1016/j.bone.2007.08.032). (PMID:17950682)

Record type: Article

Abstract

BAG-1, an anti-apoptotic protein, was identified by its ability to bind to BCL-2, HSP70-family molecular chaperones and nuclear hormone receptor family members. Two BAG-1 isoforms, BAG-1L (50 kDa) and BAG-1S (32 kDa) were identified in mouse cells and BAG-1 expression was reported in murine growth plate and articular chondrocytes. The present study aimed to elucidate the role of BAG-1 in the regulation of molecular mechanisms governing chondrocyte differentiation and turnover during endochondral ossification.

In long bones of skeletally immature mice, we observed expression of BAG-1 in the perichondrium, osteoblasts, osteocytes in the bone shaft, bone marrow, growth plate and articular chondrocytes. Monolayer cultures of murine chondrocytic ATDC5 cells, which exhibited robust expression of both BAG-1 isoforms and the Bag-1 transcript, were utilized as an in vitro model to delineate the roles of BAG-1. Overexpression of BAG-1L in ATDC5 cells resulted in downregulation of Col2a1 expression, a gene characteristically downregulated at the onset of hypertrophy, and an increase in transcription of Runx-2 and Alkaline phosphatase, genes normally expressed at the onset of chondrocyte hypertrophy and cartilage mineralization in the process of endochondral ossification. We also demonstrated the anti-apoptotic role of BAG-1 in chondrocytes as overexpression of BAG-1 protected ATDC5 cells, which were subjected to heat-shock at 48 °C for 30 min, against heat-shock-induced apoptosis. Overexpression of the SOX-9 protein in ATDC5 cells resulted in increased Bag-1 gene expression. To further investigate the regulation of Bag-1 gene expression by SOX-9, CHO cells were co-transfected with the human Bag-1 gene promoter–Luciferase reporter construct and the human pSox-9 expression vector. Activity of the Bag-1 promoter was significantly enhanced by the SOX-9 protein.

In conclusion, a novel finding of this study is the role of BAG-1 as a transcriptional regulator of genes involved in chondrocyte hypertrophy and cartilage mineralization during the process of endochondral ossification. Additionally, we have demonstrated for the first time the regulation of Bag-1 gene expression by SOX-9 and the anti-apoptotic role of BAG-1 in chondrocytic cells. Modulation of Bag-1 expression can therefore mediate chondrocyte differentiation and turnover, and offer further insight into the molecular regulation of endochondral ossification.

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More information

e-pub ahead of print date: 4 September 2007
Published date: January 2008
Keywords: atdc5, chondrocyte differentiation, endochondral ossification, runx-2, alkaline phosphatase
Organisations: Dev Origins of Health & Disease

Identifiers

Local EPrints ID: 151695
URI: http://eprints.soton.ac.uk/id/eprint/151695
ISSN: 8756-3282
PURE UUID: 8b666a59-5af2-4bf3-94da-edcfa49be42b
ORCID for Rahul S. Tare: ORCID iD orcid.org/0000-0001-8274-8837
ORCID for Graham Packham: ORCID iD orcid.org/0000-0002-9232-5691
ORCID for Richard O.C. Oreffo: ORCID iD orcid.org/0000-0001-5995-6726

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Date deposited: 12 May 2010 09:45
Last modified: 14 Mar 2024 02:49

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Contributors

Author: Rahul S. Tare ORCID iD
Author: Paul A. Townsend
Author: Graham Packham ORCID iD
Author: Stefanie Inglis

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