INTERLEUKIN-1 REPRESSES COLIA1 PROMOTER ACTIVITY IN CALVARIAL BONES OF TRANSGENIC COLCAT MICE IN-VITRO AND IN-VIVO

Interleukin-1 (IL-1) inhibits collagen synthesis in osteoblastic cell lines and primary osteoblast-like cells. However, promoter elements re gulating type I collagen A1 (COLIA1) expression in vivo and in organ c ulture may differ from those regulating expression in cell culture. We have examined the effects of IL-1 on reporter gene activity in neonat al transgenic mouse calvariae bearing COLIA1 promoter-chloramphenicol acetyltransferase (ColCAT) fusion genes. The parent construct, ColCAT 3,6, contains 3.5 kb of 5' flanking sequence and 115 bp of 5' untransl ated region fused to the CAT reporter. In 48-h calvarial organ culture s, IL-1 repressed ColCAT 3.6 promoter activity and collagen synthesis in a dose-related manner, with a maximal inhibition of 40-65%. This re pression was retained in 5' deletion constructs truncated to -1719 bp, The inhibition of transgene mRNA was blocked by cycloheximide, indica ting a requirement for new protein synthesis. Pretreatment with indome thacin diminished the inhibitory effect of IL-1 on CAT activity and co llagen synthesis, suggesting partial mediation by prostaglandins. Loca l in vivo injection of IL-1 (500 ng) decreased calvarial transgene mRN A after 8 h, an effect that,was partially blocked by indomethacin. Col CAT transgenic mice represent a useful model for in vitro and in vivo assessment of COLIA1 promoter regulation by cytokines and other factor s.