Regulation of Indian hedgehog mRNA levels in chondrocytic cells by ERK1/2 and p38 mitogen-activated protein kinases

Indian hedgehog (Ihh) is produced by growth plate pre-hypertrophic chondrocytes, and is an irnportant regulator of endochondral ossification. However, little is known about the regulation of lhh in chondrocytes. We have examined the role of integrins and mitogen-activated protein (MAP) kinases in lhh rnRNA regulation in CFK-2 chondrocytic cells. Cells incubated with the beta(1)-integrin blocking antibody had decreased Ihh rnRNA levels, which was accompanied by decreases of activated extracellular signal-regulated kinases (ERK1/2) and activated p38 MAPK.Ihh rnRNA levels were also inhibited by U0126, a specific MFK 1/2 inhibitor, or SB203580, a specific p38 MAPK inhibitor. Cells transfected With Constitutively active MFK1 or MKK3 had increased lhh mRNA levels, which were diminished by dominant-negative MEK1, p38alpha or p38beta. Stimulation of the PTH I R with 10(-8) M rPTH (1 -34) resulted in dephosphorylation of ERK1 /2 that was evident within 15 min and sustained for 1 h, as well as transient dephosphorylation of p38 MAPK that was maximal after 25 min. PTH stimulation decreased lhh rnRNA levels, and this effect was blocked by transfecting the cells with constitutively active MEK 1 but not by MKK3. These studies demonstrated that activation of ERK1/2 or p38 MAPK increased Ihh rnRNA levels. Stimulation of the PTH1 R or blocking of beta(1)-integrin resulted in inhibition of ERK1/2 and p38 MAPK and decreased levels of Ihh rnRNA. Our data demonstrate the central role of MAPK in the regulation of Ihh in CFK-2 cells. J. Cell. Physiol. 203: 177-185, 2005. (C) 2004 Wiley-Liss, Inc.