PubMed · 8187253
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
J E Cannon. 1994. Precurarization.. https://doi.org/10.1007/bf03009828
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
Insulin-like growth factor-1, IGF-1, is believed to be an important anabolic modulator of cartilage metabolism whose action is mediated by high affinity cell surface receptors and bioactivity and bioavailability regulated, in part, by IGF-1 binding proteins (IGFBPs). Prostaglandin E2 (PGE2) stimulates collagen and proteoglycan synthesis in cartilage via an autocrine feedback loop involving IGF-1. We determined whether the eicosanoid could regulate IGFBP-4, a major form expressed by chondrocytes and, as such, act as a modifier of IGF-1 action at another level. Using human articular chondrocytes in high-density primary culture, Western and Western ligand blotting to measure secreted IGFBP-4 protein, and Northern analysis to monitor IGFBP-4 mRNA levels, we demonstrated that PGE2 provoked a 2.7 +/- 0.3- and 3.8 +/- 0.5- (n = 3) fold increase in IGFBP-4 mRNA and protein, respectively. This effect was reversed by the Ca(++) channel blocker, verapamil, and the Ca(++)/calmodulin inhibitor, W-7. The Ca(++)ionophore, ionomycin, mimicked the effects of PGE2. The phorbol ester, PMA, which activated phospholipid-dependent protein kinase C (PKC) in chondrocytes, had no effect on IGFBP-4 production. Cyclic AMP mimetics and PKA activators, IBMX, and Sp-cAMP, inhibited the expression of the binding protein as did the PGE2 secretagogue, interleukin-1 beta (IL-beta). The inhibitory effect of the latter cytokine was mediated by a erbstatin/genistein (tyrosine) sensitive kinase. Dexamethasone, an inhibitor of cyclooxygenase (COX-2) expression and PGE2 synthesis, down-regulated control, constitutive levels of IGFBP-4 mRNA and protein, eliminating the previously demonstrated possibility of cross-talk between glucocorticoid receptor (GR) and PGE2-receptor signalling pathways. The results suggest that extracellular signals control IGFBP-4 production by a number of different transducing networks with changes in Ca(++) and calmodulin activity exerting a strong positive influence, possibly maintaining the constitutivity of IGFBP-4 synthesis under basal conditions. PGE2 activation of the IGF-1/IGFBP axis may play a pivotal role in the metabolism of cartilage and possibly connective tissues in general. Eicosanoid biosynthesis may be a rate-limiting step in cartilage repair processes.
The heme environment of lignin peroxidase (LiP) has been investigated by electronic absorption and electron paramagnetic resonance (EPR) spectroscopy. Native LiP was a pentacoordinate, high-spin ferric iron with a high-spin absorption band at 634 nm and g values at 5.86 and 2.07 in the EPR spectrum. Upon thermal inactivation, calcium ions were released from the enzyme and the Soret absorption decreased and red-shifted about 2 nm, the high-spin absorption band at 634 nm disappeared, and a low-spin absorption band appeared at 532 nm. The EPR spectrum and the temperature dependence of electronic absorption spectra revealed that the heme iron of the thermally inactivated enzyme was a mixture of high- and low-spin states, which was further supported by the changes in the electronic absorption and EPR spectra when cyanide was added to the thermally inactivated enzyme. Addition of various imidazoles or CN- to thermally inactivated enzyme demonstrated that the low-spin heme iron of inactivated enzyme was hexacoordinate with a distal histidine as its sixth ligand, in contrast to the active enzyme, which was pentacoordinate and high-spin. Upon addition of calcium to recover the thermally inactivated LiP, the reactivated enzyme had absorptions at 408, 502, and 634 nm and g values at 5.86 and 2.07 in the EPR spectrum, which demonstrated that the heme iron of the reactivated enzyme was again high-spin and pentacoordinated.
Ras-GRF is a guanine nucleotide exchange factor that activates Ras proteins. Its activity on Ras in cells is enhanced upon calcium influx. Activation follows calcium-induced binding of calmodulin to an IQ motif near the N-terminus of Ras-GRF. Ras-GRF also contains a Dbl homology (DH) domain C-terminal to the IQ motif. In many proteins, DH domains act as exchange factors for Rho-GTPase family members. However, we failed to detect exchange activity of this domain on well characterized Rho family members. Instead, we found that mutations analogous to those that block exchange activity of Dbl prevented Ras-GRF activation by calcium/ calmodulin in vivo. All DH domains are followed immediately by a pleckstrin homology (PH) domain. We found that a mutation at a conserved site within the PH domain following the DH domain also prevented Ras-GRF activation by calcium in vivo. These results suggest that in addition to playing a role as activators of Rho proteins, DH domains can also contribute to the coupling of cellular signals to Ras activation.