Dept . of Biomedical Sciences and Oncology , University of Torino , Italy .
Growth Factors 5 : 233-42 ( 1991)
Abstract
Incubation of Swiss 3T3 murine fibroblasts at low temperatures induces phosphorylation on tyrosine of a transmembrane protein of 175 kDa .
This phenomenon is time and temperature dependent and reaches a maximum after hr at 4 degrees C. The 175 kDa protein phosphorylated in vivo at low temperatures can be immunoprecipitated by phosphotyrosine antibodies and displays auto-kinase activity in vitro in the presence of radiolabelled ATP .
This molecule was found to react with anti-peptide antibodies directed against the product of the HER2/neu proto-oncogene only when immunoprecipitated with phosphotyrosine antibodies from cold-stimulated cells .
Activation of protein kinase-C by treatment of the cells with phorbol esters , bombesin or PDGF inhibits the effect of the exposure to low temperatures .
Phosphorylation of p175 is not induced by treatment of the cells with the phosphatases inhibitor sodium orthovanadate .
These results suggest that , at low temperatures , the tyrosine kinase associated with the putative receptor encoded by c-neu is activated by physico-chemical modifications of the plasma membrane .
Gene Symbols
Chemical Identifiers ( Names)
Sam and Rose Stein Institute for Research on Aging , Department of Medicine , University of California , San Diego , La Jolla 92093 .
EMBO J 11 : 135-43 ( 1992)
Abstract
This study shows that cultured human articular chondrocytes express high levels of 1.4 kb prepro-enkephalin mRNA .
Chondrocytes store met-enkephalin intracellularly and secrete this neuropeptide in mature as well as in precursor form .
Gene expression is inducible by serum factors .
High levels of prepro-enkephalin mRNA are detected in proliferating chondrocytes but not in confluent , contact-inhibited cells .
Phorbol myristate acetate and dibutyryl cyclic AMP , but not dexamethasone , increase levels of prepro-enkephalin mRNA .
Furthermore , transforming growth factor beta ( TGF beta ) and platelet derived growth factor ( PDGF ) upregulate gene expression , whereas retinoic acid , which inhibits chondrocyte proliferation , suppresses both basal and induced gene expression .
Using in situ hybridization it is shown that only 1-3% of primary chondrocytes express prepro-enkephalin mRNA , whereas 52 +/- % of subcultured cells are strongly positive .
Analysis of DNA synthesis , by autoradiography of incorporated [ 3H]thymidine , shows that these numbers correspond to the percentage of cells in S-phase of the cell cycle .
In cultures of primary chondrocytes TGF beta promotes the formation of cartilage nodules and stimulates proliferation of adherent cells .
This is associated with high levels of prepro-enkephalin mRNA in proliferating cells but not in contact-inhibited cells in cartilage nodules .
In contrast , formation of cartilage nodules , proliferation and the expression of enkephalin are suppressed by interleukin-1 beta .
In summary , expression of prepro-enkephalin in human articular chondrocytes is differentially controlled by cartilage regulatory factors and closely associated with cell proliferation .