GLUTAMINE INCREASES COLLAGEN GENE-TRANSCRIPTION IN CULTURED HUMAN FIBROBLASTS

We have previously shown that glutamine stimulates the synthesis of co llagen in human dermal confluent fibroblast cultures (Bellon, G. et al . [1987] Biochim. Biophys. Acta, 930, 39-47). In this paper, we examin e the effects of glutamine on collagen gene expression. A dose-depende nt effect of glutamine on collagen synthesis was demonstrated from 0 t o 0.25 mM followed by a plateau up to 10 mM glutamine. Depending on th e cell population, collagen synthesis was increased by 1.3-to 2.3-fold . The mean increase in collagen and non-collagen protein synthesis was 63% and 18% respectively. Steady-state levels of alpha 1(I) and alpha 1(III) mRNAs, were measured by hybridizing total RNA to specific cDNA probes at high stringency. Glutamine increased the steady-state level of collagen alpha 1(I) and alpha 1(III) mRNAs in a dose-dependent man ner. At 0.15 mM glutamine, collagen mRNAs were increased by 1.7-and 2. 3-fold respectively. Nuclear run-off experiments at this concentration of glutamine indicated that the transcriptional activity was increase d by 3.4-fold for the pro alpha 1(I) collagen gene. The effect of glut amine on gene transcription was also supported by the measurement of p ro alpha 1(I) collagen mRNA half-life since glutamine did not affect i ts stability. Protein synthesis seemed to be required for the glutamin e-dependent induction of collagen gene expression since cycloheximide suppressed the activation. The effect of glutamine appeared specific b ecause analogues and/or derivatives of glutamine, such as acivicin, 6- diazo-5-oxo-L-norleucine, homoglutamine, ammonium chloride and glutama te did not replace glutamine. The influence of amino acid transport sy stems through plasma membrane was assessed by the use of 2(methylamino )-isobutyric acid and beta 2-aminobicyclo-(2.2.1)-heptane-2-carboxylic acid. The glutamine-dependent induction of collagen gene expression w as found to be independent of transport system A but dependent on tran sport system L whose inhibition induced a decrease in pro alpha 1(I) c ollagen gene transcription by an unknown mechanism. Thus, glutamine, a t physiological concentrations, indirectly regulates collagen gene exp ression.