GADD45β enhances Col10a1 transcription via the MTK1/MKK3/6/p38 axis and activation of C/EBPβ-TAD4 in terminally differentiating chondrocytes

Abstract

GADD45β (growth arrest- and DNA damage-inducible) interacts with upstream regulators of the JNK and p38 stress response kinases. Previously, we reported that the hypertrophic zone of the Gadd45β+/- mouse embryonic growth plate is compressed, and expression of typeXcollagen (Col10a1) and matrix metalloproteinase 13 (Mmp13) genes is decreased. Herein, we report that GADD45β enhances activity of the proximal Col10a1 promoter, which contains evolutionarily conserved AP-1, cAMP-response element, and C/EBP half-sites, in synergism with C/EBP family members, whereas the MMP13 promoter responds to GADD45β together with AP-1, ATF, or C/EBP family members. C/EBPβ expression also predominantly co-localizes with GADD45β in the embryonic growth plate. Moreover, GADD45β enhances C/EBPβ activation via MTK1, MKK3, and MKK6, and dominant-negative p38αapf, but not JNKapf, disrupts the combined trans-activating effect of GADD45β and C/EBPβ on the Col10a1 promoter. Importantly, GADD45β knockdown prevents p38 phosphorylation while decreasing Col10a1 mRNA levels but does not affect C/EBPβ binding to the Col10a1 promoter in vivo, indicating that GADD45β influences the transactivation function of DNA-bound C/EBPβ. In support of this conclusion, we show that the evolutionarily conserved TAD4 domain of C/EBPβ is the target of the GADD45β-dependent signaling. Collectively, we have uncovered a novel molecular mechanism linking GADD45β via the MTK1/MKK3/6/p38 axis to C/EBPβ-TAD4 activation of Col10a1 transcription in terminally differentiating chondrocytes. © 2010 by The American Society for Biochemistry and Molecular Biology, Inc.