OBJECTIVE:Mechanical stress is an important regulator of chondrocyte function, but it is unknown how chondrocytes respond to mechanical stress. This study was performed to clarify the underlying mechanisms in human chondrocytes. DESIGN:Using a Flexercell strain unit (25% maximal elongation, 0.05 Hz-cyclic manner, and 48 h), mechanical stimulation was applied to confluent CS-OKB cells, human chondrocytic cells. To analyze transcriptional changes in response to mechanical stress, differential display reverse transcription-polymerase chain reaction (DDRT-PCR) and Northern blot analysis were performed. RESULTS:Among several differentially displayed fragments, one fragment (927 bp) tentatively named as SIC (Stress-Induced Chondrocytic) 1 was isolated from the human chondrocytic cell line and identified as one of the high molecular mass heat shock proteins. CONCLUSION:Mechanical stress induces the expression of a high molecular mass heat shock protein corresponding to SIC 1 in human chondrocytic cells. SIC 1 may play an important role in the mechanical stress-responded metabolism of human chondrocytes.