Cell-type specific trafficking of expressed mutant COMP in a cell culture model for PSACH.

Abstract

Pseudoachondroplasia (PSACH) is an autosomal dominant disease that mainly affects cartilage, resulting in skeletal dysplasias and early onset osteoarthritis. PSACH is caused by mutations in the cartilage oligomeric matrix protein (COMP) gene. PSACH chondrocytes accumulate unique COMP-containing lamellar structures in an expanded rough endoplasmic reticulum (rER). Although COMP is also present in tendon extracellular matrix (ECM), it does not accumulate in PSACH tendon cells, suggesting the disease involves a chondrocyte-specific trafficking problem. To investigate putative cell-specific trafficking differences, we generated a cell culture model utilizing expression of the common DeltaD469 COMP mutation. In rat chondrosarcoma (RCS) cells, we find delayed secretion and ER accumulation of DeltaD469 COMP, paralleling the altered trafficking defect in PSACH chondrocytes. Non-chondrocytic COS-1 cells, in contrast, efficiently trafficked and secreted both mutant and wild-type COMP. In chondrocytic cells, expression of DeltaD469 COMP led to ER accumulation of type IX collagen, but did not affect aggrecan trafficking. Endogenous rat COMP accumulated in the ER along with expressed DeltaD469 COMP in a stably expressing RCS clone, consistent with the dominant negative effect of PSACH. When these stably expressing cells were cultured to promote ECM deposition, the small amount of secreted mutant COMP disrupted assembly of the normal fibrillar meshwork and caused irregular aggregates of COMP and type IX collagen to form. Thus, in a new model that reflects the cellular pathology of PSACH, we establish trafficking differences for mutant COMP in chondrocytic and non-chondrocytic cells and demonstrate that mutant COMP interferes with assembly of a normal ECM.

• Authors: Tung-Ling L Chen, Jeff W Stevens, William G Cole, Jacqueline T Hecht, Barbara M Vertel
• Journal: Matrix biology : journal of the International Society for Matrix Biology (Matrix Biol) Vol. 23 Issue 7 Pg. 433-44 (Nov 2004) ISSN: 0945-053X [Print] Netherlands
• PMID: 15579310 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Acan protein, rat
• Aggrecans
• Cartilage Oligomeric Matrix Protein
• Extracellular Matrix Proteins
• Glycoproteins
• Lectins, C-Type
• Matrilin Proteins
• Proteoglycans
• TSP5 protein, human
• Collagen
• DNA

Topics

• Achondroplasia (genetics, metabolism)
• Aggrecans
• Animals
• Blotting, Western
• COS Cells
• Cartilage Oligomeric Matrix Protein
• Cell Culture Techniques
• Chondrocytes (metabolism)
• Chondrosarcoma (metabolism)
• Collagen (metabolism)
• DNA (metabolism)
• Endoplasmic Reticulum (metabolism)
• Extracellular Matrix Proteins (biosynthesis, genetics, metabolism)
• Glycoproteins (biosynthesis, genetics)
• Golgi Apparatus (metabolism)
• Humans
• Immunoprecipitation
• Lectins, C-Type
• Matrilin Proteins
• Microscopy, Fluorescence
• Mutation
• Proteoglycans (metabolism)
• Rats
• Time Factors