Chondrocyte-derived ezrin-like domain containing protein (CDEP), a rho guanine nucleotide exchange factor, is inducible in chondrocytes by parathyroid hormone and cyclic AMP and has transforming activity in NIH3T3 Cells

Objective: The purpose of this study is to investigate stage- and hormone-d ependent expression of chondrocyte-derived ezrin-like domain containing pro tein (CDEP), a putative guanine nucleotide exchange factor (GEF) for Rho in chondrocytes, and demonstrate the guanine nucleotide exchange activity of this protein in vitro, as well as the transforming activity in NIH3T3 cells . Methods: The expression of CDEP mRNA in growth plate chondrocytes in vivo a nd in vitro was examined by RT-PCR Southern analysis. The guanine nucleotid e exchange activity was determined using a recombinant CDEP peptide contain ing the DH and PH domains in Sf9 cell lysates. The transforming activity wa s examined using NIH3T3 cells transiently transfected with a truncated CDEP cDNA. Results: CDEP mRNA was expressed at the highest level in the hypertrophic ( terminal) stage of chondrocytes in vivo and in vitro. Parathyroid hormone ( PTH) elicited a biphasic increase of CDEP mRNA in chondrocytes. The CDEP mR NA level increased within 1 h, then decreased nearly to the control level a t 3 h. Thereafter the mRNA level started to increase at 6 h, reaching a pla teau at 24 h, Dibutyryl cyclic AMP had a similar effect on CDEP expression in chondrocytes. The dissociation of [H-3]GDP from RhoA was stimulated dose -dependently by Sf9 cell lysates containing the CDEP peptide. Furthermore, transfection of a truncated CDEP cDNA induced focus formation in NIH3T3 cul tures. Conclusions: CDEP is a novel GEF for Rho family GTPases with the transformi ng activity. CDEP may play a role in mediating or modulating the action of cAMP-elevating hormones on maturing chondrocytes. (C) 2001 OsteoArthritis R esearch Society International.