Coordinate transcriptional regulation of type I procollagen genes by Rous sarcoma virus

Generalized inhibition of cell-free translation by the amino-terminal propeptide of chick type I procollagen

Fragments of the amino-terminal propeptide of procollagen have been shown to inhibit the synthesis of procollagen in cultured cells and in a reticulocyte lysate cell-free system (for review see Timpl, R. and Glanville, R.W. (1981) Clin. Orth. Rel. Res. 158, 224-242). In this report, we show that the full-length amino-terminal propeptide of chick pro alpha1(I) chains inhibits the translation of chick tendon mRNA and rat brain mRNA in a reticulocyte lysate cell-free system. The synthesis of procollagen and non-collagenous proteins was equally affected. Inhibition was dose-dependent up to 10 microM. A similar pattern of inhibition was observed for the collagenase-resistant fragment, col 1(I).

Increased type I procollagen mRNA levels and in vitro protein synthesis in the baboon model of chronic alcoholic liver disease

We have investigated the molecular mechanisms responsible for the histologic changes induced by ethanol in the baboon model of alcoholic liver disease. Eleven ethanol-fed baboons and their pair-fed controls had histology evaluated and RNA extracted from percutaneous liver biopsy specimens. In 6 of the ethanol-fed animals, fatty liver developed, but no significant differences were found when the RNA from the control and ethanol-fed livers was translated in the reticulocyte lysate system or analyzed with specific cDNA probes. Five of the baboons given ethanol, however, developed significant fibrosis. Molecular evaluation revealed that the RNA from these livers was more active in in vitro protein synthesis, and the type I procollagen mRNA content was significantly higher per microgram of liver RNA as determined by hybridization analysis (183% +/- 23% SEM of control, p less than 0.02). In addition, there were higher levels of albumin mRNA content in the livers of ethanol-fed baboons that developed fibrosis (180% +/- 21% SEM of control, p less than 0.05). There was no change, however, in the levels of beta-actin mRNA, a representative constitutive protein. These findings in the baboon model of alcoholic fibrosis show that ethanol consumption increases type I procollagen mRNA, which may foster fibrogenesis; increases albumin mRNA content without causing an increase in serum albumin; and induces no change in levels of beta-actin mRNA. These studies also show that percutaneous needle biopsy can supply sufficient tissue to evaluate molecular changes in human liver disease.

Regulation of type I collagen synthesis. Total pro alpha 1(I) and pro alpha 2(I) mRNAs are maintained in a 2:1 ratio under varying rates of collagen synthesis

The type I collagen molecule contains two alpha 1(I) chains and one alpha 2(I) chain. Previous investigations, using embryonic chick calvaria, have indicated that the two chains are synthesized in a 2:1 ratio which is controlled at a pretranslational level, since the cells contain twice as much translatable pro alpha 1(I) mRNA as pro alpha 2(I) mRNA. The present report describes hybridization analyses of the cellular levels of total cellular RNAs coding for the pro alpha 1(I) and pro alpha 2(I) chains, using as probes two cloned cDNAs complementary to chick pro alpha 1(I) and pro alpha 2(I) mRNA, respectively. Total cellular RNA was extracted from embryonic chick calvaria, pro alpha 1(I) and pro alpha 2(I) RNA sequences were quantified by Northern hybridization using conditions ensuring that hybridization efficiency and specific radioactivity were the same for the two probes. Similar analyses were carried out on RNA extracted from calvaria with different levels of collagen synthesis after culture in the presence or absence of ascorbic acid. The results for all samples analyzed indicate that total cellular pro alpha 1(I) and pro alpha 2(I) mRNAs are present in a 2:1 ratio which is maintained even during variations in collagen synthesis rate. There is no evidence for regulation mediated by different rates of processing of mRNA precursors, although preferential degradation of the pro alpha 2(I) gene transcript cannot be excluded. Thus, the synthesis of type I procollagen chains is presumably coordinated by transcriptional control.

Pleiotropic mutants of NIH 3T3 cells with altered regulation in the expression of both type I collagen and fibronectin

Transformation of NIH 3T3 fibroblasts by v-mos causes a decrease in the levels of type I collagen RNA. In NIH 3T3 cells that have been made resistant to G418 by transfection with a plasmid in which the mouse alpha 2(I) collagen promoter is linked to the neo gene, subsequent v-mos transformation causes a loss of G418 resistance. After mutagenesis of these v-mos-transformed cells, G418-resistant colonies were selected. Two of these G418-resistant mutants showed an increased expression of the neo gene and of the endogenous type I collagen and fibronectin genes, without changes in their levels of v-mos RNA or in their ability to induce tumors. The mutations might alter cellular trans-acting factors that either directly or indirectly control the expression of the type I collagen and fibronectin genes in transformed cells.

Effect of avian osteopetrosis virus infection on cells and their collagen synthesis in vitro

Primary avian tendon fibroblasts and calvarial osteoblasts were infected with the avian osteopetrosis virus MAV.2-O, in vitro. The infected tendon cells could be cloned in soft agar and kept in culture for at least 25 passages, a number not reached by uncloned infected cells. In contrast to many other virus-transformed fibroblasts, these cells continued making collagen and fibronectin, and there were no gross morphological changes as observed in the light microscope. Changes were seen in their cytoskeletal structure, however, as observed by immunofluorescence. The cloned cells were not tumorigenic in nude mice, nor had they an altered pattern of protein phosphorylation. MAV.2-O-infected fibroblasts and the cloned cells synthesized 2-3 times more collagen type I, the main product of their biosynthetic machinery, than control cells. The proportion of the total cellular RNA consisting of specific mRNAs for the precursor of collagen, procollagen pro-alpha 1 and pro-alpha 2 chains, was higher in the infected cells than in normal fibroblasts. Southern blotting experiments indicated that there was no rearrangement of the collagen genes after infection with this virus. Furthermore, large viral DNA fragments were not integrated into the immediate vicinity of the 5' end of the alpha 2-collagen gene.

Regulation of a collagen gene promoter by the product of viral mos oncogene

Oncogenic transformation of cells produces important changes in the biosynthetic pattern of certain cellular proteins. For example, the synthesis of type I collagen in transformed fibroblasts is severely reduced as a result of changes in transcription. Here we report the results of DNA-mediated transfection experiments using recombinant plasmids in which the promoter region of the alpha 2(I) collagen gene is fused to an easily recognizable marker gene, and cell lines expressing the marker gene are isolated. Our data show that the expression of the marker gene fused to the cloned alpha 2(I) collagen promoter is strongly inhibited by v-mos transformation, suggesting that a common mechanism inhibits both the transfected and endogeneous alpha 2(I) collagen promoters.

Effect of src infection on long-term marrow cultures: increased self-renewal of hemopoietic progenitor cells without leukemia

Long-term marrow cultures prepared from mice have been infected with a molecular recombinant of Rous sarcoma virus and murine amphitropic leukemia virus. This resulted in introduction of the src gene into the cultured cells and expression of its protein kinase function. The infected cultures displayed an altered balance in the accumulation of cells in different compartments of granulocyte differentiation. There was a dramatic increase in the stem cell (CFU-S) compartment and the committed progenitor cell (GM-CFC) compartment and a decrease in mature granulocytes. The altered balance appears to be caused by intrinsic alterations in the CFU-S and GM-CFC themselves, which increase their "self-renewal" capacity at the expense of cell differentiation. Remarkably, unlike its effects in other systems, src did not produce a neoplastic transformation of the hemopoietic cells.

Cortisol decreases the cellular concentration of translatable procollagen mRNA species in cultured human skin fibroblasts

The effect of cortisol on the cellular concentration of translatable procollagen mRNAs was studied in cultured human skin fibroblasts. Cortisol selectively decreased the amount of procollagen mRNAs, in comparison to the total mRNA activity, when the cells were grown in enriched medium conditions, i.e., with 10% newborn calf serum. The selective decrease was first observed after 6 h exposure to 1 microM cortisol. In depleted medium conditions, i.e., with 2% newborn calf serum, the initial response was a stimulatory one, followed after about 12 h by a decrease in the procollagen mRNA activity. The results suggest that the selective inhibitory effect of cortisol on the cellular concentration of translatable procollagen mRNA species needs an optimal serum concentration. Furthermore, the results give support to the hypothesis that the decrease in the procollagen mRNA concentration after cortisol administration is a secondary response, preceded by the induction of some intracellular regulation system.

Control of type I collagen synthesis: evidence for pretranslational coordination of pro alpha 1 (I) and pro alpha 2 (I) chain synthesis in embryonic chick bone

The normal type I collagen molecule contains two alpha 1 (I) chains and one alpha 2 (I) chain. In embryonic chick calvaria, the two-chains are synthesized in a 2:1 ratio, and total polysomes from this tissue contain twice as much mRNA for pro alpha 1 (I) as for pro alpha 2 (I). To further investigate the mechanism by which synthesis may be coordinated, RNA isolated from various cell fractions of embryonic chick calvaria was translated in a rabbit reticulocyte lysate cell-free system. The procollagen chain products were separated by gel-electrophoresis and densitometrically quantitated from autoradiograms of the gels. Total cellular RNA, total cytoplasmic RNA, and polysomal RNA each directed the synthesis of pro alpha 1 (I) and pro alpha 2 (I) in a proportion of 2:1, whereas no procollagen mRNA activity was found in nonpolysomal cytoplasmic RNA. These results indicate that in the chick bone cells, all compartments contain twice as much pro alpha 1 (I) mRNA as pro alpha (I) mRNA, and that virtually all procollagen mRNA in the cytoplasm in polysome-bound. The coordination of procollagen chain synthesis thus presumably occurs at a pretranslational level, through differential rates of formation and/or degradation of the two mRNAs.

Propagation of globin DNAase I-hypersensitive sites in absence of factors required for induction: a possible mechanism for determination

We tested whether DNAase I-hypersensitive sites, once induced, can be propagated to daughter cells in the absence of the original inducer. Chicken embryo fibroblasts infected with a temperature-sensitive Rous sarcoma virus at 41 degrees C and then shifted to 36 degrees C become transformed and begin to transcribe globin RNA. DNAase I-hypersensitive sites appear in the alpha- and beta-globin chromatin domains. Neither transcription nor hypersensitive sites are detected in cells infected and maintained at 41 degrees C. Activation of the globin hypersensitive sites occurs within 30 min of a temperature shift to 36 degrees C and does not require new protein synthesis. To test for the self-propagation of these hypersensitive structures, we inactivated the v-src gene product by a shift back up to 41 degrees C, and allowed the cells to divide 20 times at 41 degrees C. Although transcription of the globin genes was minimal after this treatment, the DNAase I-hypersensitive sites remained. The same sites can be induced by NaCl shock of cells. After the cells are returned to normal medium and allowed to grow for 20 doublings, the hypersensitive sites remain. This suggests that once formed, DNAase I-hypersensitive sites have the capacity to template their own structure independent of the initial "inductive" event. The single-stranded character of these DNAase I-hypersensitive sites could explain these results.

Regulation of collagen synthesis

Collagen synthesis is a complex orchestration of intracellular and extracellular events. In addition to synthesis of the polypeptide chains more than a dozen modifications of the molecule occur; most of these are enzymatic and specific for collagen. Regulational control of collagen synthesis promises to be equally complex. Examples are described to 4 specific regulatory influences. Ascorbic acid markedly stimulates collagen synthesis without affecting synthesis of other proteins. This effect appears to be unrelated to its cofactor roles for hydroxylation of lysine and proline. Glucocorticoids at microM concentration specifically inhibit collagen synthesis. Tissues treated with glucocorticoids have diminished levels of mRNA for collagen. During collagen synthesis the aminoterminal propeptide of procollagen is cleaved by a specific protease. This peptide appears to be a feedback inhibitor of collagen synthesis. This effect can be demonstrated in cells and in cell-free synthesizing systems. A membrane receptor system may permit the peptide to be recognized and subsequently act as a translational control mechanism. Viral transformation of fibroblasts results in selectively decreased synthesis of collagen. Levels of cytoplasmic and nuclear mRNA are likewise selectively diminished consistent with transcriptional control.

Unusual methylation pattern of the alpha 2 (l) collagen gene

We studied the methylation pattern of the alpha 2 (type 1) collagen gene in DNA from five cell types with varying rates of type I collagen synthesis: chick embryo fibroblast (CEF), CEF transformed by Rous sarcoma virus, erythrocyte, brain and sperm. The methylation-sensitive restriction enzymes, Msp I, Hpa II, Ava I and Sma I were used to detect methylation in three regions of the alpha 2 (type I) collagen gene: a 5.7 kb region, which includes the start site of transcription and the first two exons of the collagen gene; a 5.2 kb region containing exons in the middle of the gene; and a 3.5 kb region containing exons in the 3' portion of the gene. The DNA around the start site of transcription is not methylated whether or not the cells synthesize collagen. In contrast, the DNA from the central and 3' region of the gene is methylated to about the same extent whether or not the cells make collagen. Our data indicate that a gene that is methylated can be actively transcribed and that the level of expression of the alpha 2 (type I) collagen gene seems to be independent of methylation.