DOMAIN-SPECIFIC GENE ACTIVATION BY PARATHYROID-HORMONE IN OSTEOBLASTIC ROS17 2.8 CELLS/

Parathyroid hormone (PTH)-mediated gene activation was assessed in the osteoblast-like rat cell line ROS17/2.8 with two PTH fragments harbor ing distinct activating domains: PTH-(1-34) and PTH-(28-48). The PTH r esponse of genes expressed immediate early in the cell cycle or in the osteoblast developmental sequence was investigated, In addition, subt ractive cloning was used to identify genes in ROS17/2.8 cells that are activated by the two PTH domains, PTH-(1-34) immediately increased th e transcript levels of c-fos and C-jun at a considerably higher rate t han PTH-(28-48), A significant immediate PTH effect on osteoblastic ma rker genes could not be detected, with the exception of elevated ornit hine decarboxylase transcript levels. However, continuous application of PTH-(1-34) increased transcript levels of the osteoblast-specific o steocalcin gene and reduced those of other osteoblastic marker genes i ncluding alkaline phosphatase and the PTH/PTH-related peptide receptor , By subtractive cloning, nine cDNAs were isolated corresponding to mR NAs directly up-regulated by PTH-(1-34) or PTH-(28-48). Among these we re a cyclic phosphodiesterase, a (cytosine 5)-methyltransferase, an 80 -kDa protein kinase C substrate, junB, and a novel GC-binding protein, Three cDNAs are unknown at present, Interestingly, in all cases, the efficiency of gene activation by PTH-(28-48) was substantially lower i n comparison with PTH-(1-34), PTH-mediated protein kinase C signaling in ROS17/2.8 cells may therefore constitute a minor pathway in compari son with the dominant cAMP/protein kinase A cascade.