THYMOSIN-BETA-4 IS EXPRESSED IN ROS 17/2.8 OSTEOSARCOMA CELLS IN A REGULATED MANNER

The differential expression of mRNAs between the closely related rat osteosarcoma cell lines ROS 17/2.8 and ROS 25/1 was used to identify genes whose expression is associated with the osteoblast phenotype. Thymosin β4 cDNA was cloned from an ROS 17/2.8 complimentary DNA library on the basis of its differential hybridization with radiolabeled cDNA prepared from ROS 17/2.8 and ROS 25/1 cells. Northern blot analysis confirmed that thymosin β4, hitherto a putative immunodulatory hormone, was indeed differentially expressed. Steady state mRNA levels were severalfold higher in ROS 17/2.8 cells exhibiting an osteoblast-like phenotype, compared with the less osteoblast-like ROS 25/1. Thymosin β4 transcripts were also detected in rat UMR 106 osteosarcoma cells and in intact neonatal and fetal rat calvaria. Sequence analysis of the cDNA indicated that thymosin β4 transcripts may arise by processing at a more distal polyadenylation signal. Treatment of ROS 17/2.8 cells with dexamethasone increased, while addition of 1, 25-dihydroxyvitamin D3 decreased thymosin β4 mRNA. The phenotype-dependent expression in the ROS cells and the response to steroid hormone suggest that thymosin β4 expression contributes to the osteoblast phenotype. © 1990 by The Endocrine Society.