New method for determining the extent of proline hydroxylation by measuring changes in the ratio of [4-3H]:[14C]proline in collagenase digests

Collagen IV promotes repair of renal cell physiological functions after toxicant injury

Collagen IV is found in the renal proximal tubular cell (RPTC) basement membrane and is a mediator of renal development and function. Pharmacological concentrations of L-ascorbic acid phosphate (AscP) promote the repair of physiological functions in RPTC sublethally injured by S-(1,2-dichlorovinyl)-L-cysteine (DCVC). We hypothesized that AscP promotes RPTC repair by stimulating collagen IV synthesis and/or deposition. RPTC exhibited increased synthesis but decreased deposition of collagen IV after DCVC exposure. In contrast, RPTC cultured in pharmacological concentrations of AscP maintained collagen IV deposition. The activity of prolyl hydroxylase was decreased in RPTC after DCVC injury, an effect that was partially attenuated in injured RPTC cultured in pharmacological concentrations of AscP. The addition of exogenous collagen IV to the culture media of DCVC-injured RPTC promoted the repair of mitochondrial function and Na(+)-K(+)-ATPase activity. However, neither collagen I, laminin, nor fibronectin promoted cell repair. These data demonstrate an association between AscP-stimulated deposition of collagen IV and exogenous collagen IV and repair of physiological functions, suggesting that collagen IV plays a specific role in RPTC repair after sublethal injury.

Selective inhibition of hepatic collagen accumulation in experimental liver fibrosis in rats by a new prolyl 4-hydroxylase inhibitor

Fibrosis and cirrhosis of the liver are often the result of chronic liver damage by a variety of different agents. Pathological accumulation of collagen, disruption of the lobular structure, and impaired hepatocellular function frequently lead to systemic involvement and fatal complications. Drugs inhibiting collagen hydroxylation and accumulation are expected to improve this situation, making prolyl 4-hydroxylase (P4H), the key enzyme of intracellular collagen processing, a rational target for pharmacological intervention. S 4682, a novel inhibitor of purified P4H (Ki = 155 nmol/L), reduced hydroxyproline (Hyp) synthesis in chicken embryo calvaria (IC50 = 8.2 micromol/L) and in cultured hepatic stellate cells (HSC) (IC50 = 39 micromol/L). S 4682 inhibited hepatic collagen hydroxylation in vivo after metabolic labeling with [14C]proline. In the CCl4 model of chronic hepatic injury, characterized by histologically and biochemically evident fibrosis and highly elevated levels of serum procollagen type III N-peptide, S 4682 reduced hepatic collagen accumulation, decreased prevalence of ascites, and lowered serum procollagen type III N-peptide (PIIINP) levels. The hepatic Hyp content of drug-treated animals was closely correlated with serum levels of PIIINP S 4682 had no influence on Hyp content of heart, lung, and kidney.

d-alpha-tocopherol inhibits collagen alpha 1(I) gene expression in cultured human fibroblasts. Modulation of constitutive collagen gene expression by lipid peroxidation

Ascorbic acid stimulates collagen gene transcription in cultured fibroblasts, and this effect is mediated through the induction of lipid peroxidation by ascorbic acid. Quiescent cultured fibroblasts in the absence of ascorbic acid have a high constitutive level of collagen production, but the mechanisms of collagen gene regulation in this unstimulated state are not known. Because lipid peroxidation also occurs in normal cells, we wondered if lipid peroxidation plays a role in the regulation of basal collagen gene expression. Inhibition of lipid peroxidation in cultured human fibroblasts with d-alpha-tocopherol or methylene blue decreased the synthesis of collagen, the steady-state levels of procollagen alpha 1(I) mRNA and the transcription of the procollagen alpha 1(I) gene. This effect on collagen gene expression was selective and not associated with cellular toxicity. Thus, these experiments suggest a role for lipid peroxidation in the modulation of constitutive collagen gene expression.

Inhibition of prolyl hydroxylation and procollagen processing in chick-embryo calvaria by a derivative of pyridine-2,4-dicarboxylate. Characterization of the diethyl ester as a proinhibitor

The biochemical and morphological consequences of procollagen prolyl 4-hydroxylase inhibition by pyridine-2,4-dicarboxylic acid (2,4-PDCA) and its diethyl ester (diethyl-2,4-PDC) were studied in chick-embryo calvaria, which predominantly synthesize type I collagen. Half-maximal inhibition of tissue hydroxyproline formation required 650 microM-2,4-PDCA, whereas the Ki with respect to chicken prolyl 4-hydroxylase in vitro was 2 microM. In contrast, half-maximal inhibition was caused by 10 microM-diethyl-2,4-PDC in the intact calvaria, although chicken prolyl 4-hydroxylase in vitro was not inhibited even at 1 mM. The collagenous material produced in the presence of diethyl-2,4-PDC showed an altered 'melting' profile and a lowering of the transition temperature by 10 degrees C, indicating misalignment and thermal instability of its triple-helical structure. Amount and electrophoretic mobility of procollagen type I chains were increased in a dose-dependent manner. The amounts of partially processed species and alpha-chains were decreased, without change in mobility. This marked effect on procollagen-collagen conversion in the intact calvaria suggests that the underhydroxylated collagenous material generated in the presence of diethyl-2,4-PDC is resistant to or acts as endogenous secondary inhibitor of type I procollagen N-proteinase. Electron microscopy of treated calvaria cells showed dilated rough endoplasmic reticulum and numerous phagolysosomes, indicating intracellular retention and lysosomal degradation of the newly synthesized underhydroxylated collagenous material. In summary, these results identify 2,4-PDCA and diethyl-2,4-PDC as the first prolyl 4-hydroxylase-directed inhibitor/proinhibitor pair that affects intra- and extra-cellular events during collagen formation.

Inhibition of collagen hydroxylation by 2,7,8-trihydroxyanthraquinone in embryonic-chick tendon cells

Prolyl 4-hydroxylase (EC 1.14.11.2) is an essential enzyme in the post-translational modification of collagen. Inhibitors of this enzyme are of potential interest for the treatment of diseases involving excessive deposition of collagen. 2,7,8-Trihydroxyanthraquinone (THA) is an effective inhibitor of prolyl 4-hydroxylase by virtue of its ability to compete with the co-substrate 2-oxoglutarate (Ki = 40.3 microM). Using a simple and reproducible assay for collagen hydroxylation, we show that THA inhibits the hydroxylation of collagen in embryonic-chick tendon cells in short-term culture, with an IC50 value (concn. giving 50% inhibition) of 32 microM. In comparison, the ethyl ester of 3,4-dihydroxybenzoic acid has an IC50 value of 0.1 mM against collagen hydroxylation by chick tendon cells, whereas its Ki versus isolated prolyl 4-hydroxylase is 49 microM.

Different mechanisms decrease hepatic collagen and albumin production in fasted rats

Weight loss is correlated with a specific decrease in collagen synthesis in extrahepatic tissues, mainly through modulation of mRNA levels. Here, we investigated the response to weight loss in the rat liver. Male rats were either fed ad libitum or fasted for 92 hr; fasted animals lost approximately 20% of their initial body weight. Following i.p. injection of [5-3H]proline, hepatic collagen was extracted and de novo collagen production was measured. There was a decrease in the specific radioactivities of purified hepatic collagen (-75%) and albumin (-70%) relative to total hepatic protein, indicating that production of both of these proteins was specifically decreased. In fasted animals, the absolute hepatic collagen production was markedly decreased (-60%), while changes in absolute hepatic protein production were small (-15%). Using hybridization with specific DNA probes, we found that fasting causes about a 70% decrease in albumin mRNA, but the quantities of hepatic procollagen alpha 1(I) and alpha 2(I) mRNAs were unchanged. These results are consistent with regulation of albumin production during fasting by modulation of mRNA levels. The inhibition of hepatic collagen production in fasted animals, however, appears to be modulated at a posttranscriptional level or may result from increased degradation. This response differs from the pretranslational regulation of collagen synthesis in extrahepatic tissues during fasting. Furthermore, our results suggest that decreased body weight could be a potentially complicating variable in studies of collagen metabolism and fibrogenesis in the liver.

Regulation and organization of connective tissues

It is difficult to study the regulation and interactions of the connective tissue macromolecules in vivo. However, studies of genetically determined diseases of the connective tissues have yielded a large amount of new information in these areas. Specific molecular defects can then be correlated with the functional and pathological changes in the tissues. We have concentrated on this approach which takes advantage of the large number of families with genetic diseases who come to our Hospital from all parts of Australasia and also takes advantage of developments in molecular biology in our Unit which were initiated with a RACS John Mitchell Crouch Fellowship. In addition to these studies on naturally occurring mutations we are also studying specific mutations that we are able to produce in specific regions of the collagen molecule. Another approach takes advantage of a unique model culture system developed in our Unit. These studies will be supplemented by various collaborative projects such as current ones involving smooth muscle cells in atherosclerosis, bone cells metabolism and myelofibrosis in leukaemia.

Comprehensive analysis of collagen metabolism in vitro using [4(3H)]/[14C]proline dual-labeling and polyacrylamide gel electrophoresis

A method to simultaneously quantify the production, secretion, and prolyl hydroxylation of individual types of collagen in cell culture samples has been developed. Collagens were biosynthetically labeled with a mixture of [14C]proline and [4-3H]proline. The labeled collagens were isolated and their component alpha-chains were resolved by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. Migration of the collagen alpha-chains was determined by fluorography, and radioactivity in excised bands was quantified by scintillation counting. [14C]Proline labeling of collagen chains was used to determine the production and secretion of the different types of collagen. The ratios of the component alpha 1(I) and alpha 2(I) chains of type I collagen were also determined in this way. Prolyl hydroxylation of collagen alpha-chains was readily determined by measurement of their 3H:14C ratios. Following 4-hydroxylation, 3H was lost from the [4-3H]proline with alteration of this ratio. This dual-labeling method is suitable for the comprehensive analysis of collagen metabolism in multiple samples.

Quantitative study of tissue collagen metabolism

A procedure for the quantification of various parameters of metabolism of collagen in fibrotic mouse liver has been developed. The method involves derivatization of hydroxyproline, a marker of collagen, with dansyl chloride, high-performance liquid chromatography of the derivative on an octadecyl C-18 column, and its detection by fluorescence. This assay improves upon existing procedures in several respects: It extends the analysis so that not only the collagen content of the tissue but also the metabolism of collagen is determined at levels found intracellularly. It is sensitive enough to quantify 0.1-10 nmol of hydroxyproline, and it includes three major amino acids (hydroxyproline, glycine, and proline) of collagen and two assay controls; it generates information on both the purity and quantity of collagen in each assay. The determination of specific activity of intracellular free [14C]proline, which is the precursor of protein-bound hydroxyproline, defines the specific activity of [14C]hydroxyproline of collagen converted from precursor residues of [14C]proline by the action of prolyl hydroxylase. The specific activity of [14C]hydroxyproline can be used for the evaluation of collagen synthesis and secretion and intracellular and extracellular degradation of the newly synthesized and secreted collagen in the tissue. The determination of specific activities of [14C]hydroxyproline and [14C]proline and of the ratio of [14C]hydroxyproline to [14C]proline of newly secreted collagen provides information concerning the extent of hydroxylation of [14C]proline residues of newly synthesized collagen.

Introduction of the human pro alpha 1(I) collagen gene into pro alpha 1(I)-deficient Mov-13 mouse cells leads to formation of functional mouse-human hybrid type I collagen

The Mov-13 mouse strain carries a retroviral insertion in the pro alpha 1(I) collagen gene that prevents transcription of the gene. Cell lines derived from homozygous embryos do not express type I collagen although normal amounts of pro alpha 2 mRNA are synthesized. We have introduced genomic clones of either the human or mouse pro alpha 1(I) collagen gene into homozygous cell lines to assess whether the human or mouse pro alpha 1(I) chains can associate with the endogenous mouse pro alpha 2(I) chain to form stable type I collagen. The human gene under control of the simian virus 40 promoter was efficiently transcribed in the transfected cells. Protein analyses revealed that stable heterotrimers consisting of two human alpha 1 chains and one mouse alpha 2 chain were formed and that type I collagen was secreted by the transfected cells at normal rates. However, the electrophoretic migration of both alpha 1(I) and alpha 2(I) chains in the human-mouse hybrid molecules were retarded, compared to the alpha (I) chains in control mouse cells. Inhibition of the posttranslational hydroxylation of lysine and proline resulted in comigration of human and mouse alpha 1 and alpha 2 chains, suggesting that increased posttranslational modification caused the altered electrophoretic migration in the human-mouse hybrid molecules. Amino acid sequence differences between the mouse and human alpha chains may interfere with the normal rate of helix formation and increase the degree of posttranslational modifications similar to those observed in patients with lethal perinatal osteogenesis imperfecta. The Mov-13 mouse system should allow us to study the effect specific mutations introduced in transfected pro alpha 1(I) genes have on the synthesis, assembly, and function of collagen I.

A [4,5-3H]lysine:[14C]lysine dual-label method to measure lysine hydroxylation in collagen

A new method has been developed to determine the extent of lysine hydroxylation in newly synthesized collagen. This method relies on the measurement of changes in the ratio of [3H]lysine:[14C]lysine in collagenase digests, resulting from loss of tritium from the C-5 position of lysine during hydroxylation. Lysine hydroxylation can be measured in the presence of large amounts of noncollagen proteins, and simultaneous quantitation of the relative rates of collagen and non-collagen protein production is obtained. The dual-label lysine method is simple, rapid, and accurate. There was a very good correlation between this method and column chromatography procedures currently used for the measurement of lysine hydroxylation.

Hepatocyte collagen production in vivo in normal rats

Although hepatocytes produce collagen in vitro, their contribution to hepatic collagen synthesis in vivo is unknown. To answer this question, we injected rats intraperitoneally with [3H]proline and [14C]ornithine. [3H]Proline labeled prolyl-t-RNA in both hepatocytes and nonparenchymal cells. In contrast, [14C]ornithine was rapidly converted to [14C]arginine via the urea cycle only in hepatocytes, labeling arginyl-t-RNA. Approximately 60% of the 14C in albumin and transferrin was present as arginine while the remainder was found in proline and related amino acids. As expected for proteins that have the same proline/arginine ratio and that are produced solely by the hepatocyte, the [3H]proline/[14C]arginine ratio was very similar in albumin and transferrin. Conversely, in nonparenchymal cells a negligible percentage of 14C was present as arginine. A sizeable percentage of the 14C in hepatic collagen was present as arginine; given the greater proline(+hydroxyproline)/arginine ratio in hepatic collagen, our data indicate that in normal rats, hepatocytes contribute most of newly synthesized hepatic collagen.

Indirect assays for deoxyhypusine hydroxylase using dual-label ratio changes and oxidative release of radioactivity

Two procedures for rapid assay of deoxyhypusine hydroxylase activity are described. One of these assays measures changes in the 3H:14C ratio of dual-labeled protein that results from the release of tritium from a specific position in the side chain of the 3H,14C-labeled constituent amino acid deoxyhypusine upon its conversion to [3H,14C]hypusine. The other assay relies upon release of radioactivity from product protein by periodate oxidation of the radiolabeled side chain of component hypusine. The good correspondence of each of these assays with the ion exchange chromatographic method which measures hypusine and deoxyhypusine in acid hydrolysates of protein indicates that each provides a valid means of determining deoxyhypusine hydroxylase activity.

Coordinate regulation of collagen and proteoglycan synthesis in costal cartilage of scorbutic and acutely fasted, vitamin C-supplemented guinea pigs

The effects of ascorbic acid deficiency and acute fasting (with ascorbate supplementation) on the synthesis of collagen and proteoglycan in costal cartilages from young guinea pigs was determined by in vitro labeling of these components with radioactive proline and sulfate, respectively. Both parameters were coordinately decreased by the second week on a vitamin C-free diet, with a continued decline to 20-30% of control values by the fourth week. These effects were quite specific, since incorporation of proline into noncollagenous protein was reduced by only 30% after 4 weeks on the deficient diet. The time course of the decrease in collagen and proteoglycan synthesis paralleled the loss of body weight induced by ascorbate deficiency. Hydroxylation of proline in collagen synthesized by scorbutic costal cartilage was reduced to about 60% of normal relatively early, and remained at that level thereafter. Neither collagen nor proteoglycan synthesis was returned to normal by the addition of ascorbate (0.2 mM) to cartilage in vitro. Administration of a single dose of ascorbate to scorbutic guinea pigs increased liver ascorbate and restored proline hydroxylation to normal levels by 24 h, but failed to increase the synthesis of collagen or proteoglycan. Synthesis of both extracellular matrix components was restored to control levels after four daily doses of ascorbate. A 96-h total fast, with ascorbate supplementation, produced rates of weight loss and decreases in the synthesis of these two components similar to those produced by acute scurvy. There was a linear correlation between changes in collagen and proteoglycan synthesis and changes in body weight during acute fasting, scurvy, and its reversal. These results suggest that it is the fasting state induced by ascorbate deficiency, rather than a direct action of the vitamin in either of these two biosynthetic pathways, which is the primary regulatory factor.

Regulation of collagen synthesis and mRNA levels in articular cartilage of scorbutic guinea pigs

Previous studies suggested that decreased type I collagen synthesis in calvaria of ascorbate-deficient guinea pigs was correlated with weight loss rather than defective proline hydroxylation. The generality of this correlation was examined in articular cartilage, which synthesizes mainly type II collagen, by measuring collagen synthesis and proline hydroxylation in vitro in tissue from ascorbate-supplemented and scorbutic guinea pigs. Ascorbate concentrations in tissues were almost completely depleted after 1 week of deficiency, but proline hydroxylation remained normal until after approximately 3 weeks, when it had decreased only by 10%. At that point collagen synthesis had decreased to about 50% of the control value. There was little additional effect on proline hydroxylation but collagen synthesis decreased further to 20% of normal. Procollagen mRNA levels in cartilage, as measured by dot-blot hybridization with a type II-specific cDNA probe, were unchanged after 2 weeks of scurvy, which correlated with the lack of effect on collagen synthesis during that period. Thereafter, during the period when collagen synthesis decreased, procollagen mRNA levels decreased to 20% of control values. Refeeding ascorbate to acutely scorbutic animals led to reversal of defective proline hydroxylation within 24 h with a slower increase in collagen synthesis and mRNA levels. Collagen synthesis returned to the normal level after 4 days with no further increase, while mRNA levels continued to increase to 2.7 times the control values after 7 days. Thus the major mechanism for regulation of collagen synthesis in articular cartilage during scurvy and ascorbate repletion occurs independently of the effect on proline hydroxylation and is associated with changes in mRNA levels. The lack of precise coordination between collagen synthesis and mRNA levels during repletion, however, suggests that there may be additional regulation through post-transcriptional mechanisms.

[3H]tryptophan-[14C]proline dual label method for the simultaneous determination of collagen and noncollagen protein production

A new method for the simultaneous determination of newly synthesized collagen and noncollagen proteins has been developed. Because tryptophan is not found in collagen noncollagen proteins were specifically labeled with [3H]tryptophan. [14C]Proline was used to label both groups of proteins. To calculate the 14C-labeled noncollagen protein the 3H radioactivity of the protein mixture was divided by the ratio of 3H:14C in noncollagen protein of a representative sample. This value was obtained by collagenase digestion. The remaining 14C radioactivity in the protein mixture was attributed to [14C]collagen. There was a very good correlation between the dual label method and the widely used collagenase digestion method for the measurement of collagen and noncollagen protein production and for the calculation of the relative rate of collagen synthesis. This new method provides a simple and accurate analysis of collagen production, and it is suitable for rapid processing of a large number of biological samples.

Acetaldehyde stimulates collagen and noncollagen protein production by human fibroblasts

The mechanisms responsible for the increased hepatic collagen deposition in alcoholic cirrhosis remain unknown. The question of whether ethanol or acetaldehyde has a direct effect on collagen and noncollagen protein production was investigated in human fibroblasts with no detectable activity of alcohol dehydrogenase to distinguish the effects of these metabolites. To eliminate environmental factors, protein production by confluent human skin, fetal and hepatic fibroblasts was studied after three passages. Cells were labeled with [5-3H]proline for 4 hr in the presence of 0.2 mM ascorbate alone or with addition of either ethanol (50 mM) or acetaldehyde (0 to 300 microM). Rates of protein production were calculated from the radioactivities of collagenase-sensitive and collagenase-resistant proteins. Skin fibroblasts from alcoholic individual either with cirrhosis or without liver disease have comparable rates of collagen and noncollagen protein production. Acetaldehyde, in a concentration found in the liver during ethanol abuse, significantly increased collagen production by human skin fibroblasts (up to 140%), fetal fibroblasts (up to 240%) and hepatic fibroblasts (up to 70%) but the addition of ethanol had no significant effect on basal collagen production. The effect of acetaldehyde was dose-related and affected noncollagen protein production in a similar manner. Acetaldehyde did not cause changes in either proline transport or the specific activity of the proline precursor pool. This newly recognized stimulation of collagen production by acetaldehyde may be a possible mechanism of fibrogenesis in alcoholic individuals.

Abnormal type I collagen metabolism by cultured fibroblasts in lethal perinatal osteogenesis imperfecta

Cultured skin fibroblasts from seven consecutive cases of lethal perinatal osteogenesis imperfecta (OI) expressed defects of type I collagen metabolism. The secretion of [14C]proline-labelled collagen by the OI cells was specifically reduced (51-79% of control), and collagen degradation was increased to twice that of control cells in five cases and increased by approx. 30% in the other two cases. Sodium dodecyl sulphate/polyacrylamide-gel electrophoresis revealed that four of the OI cell lines produced two forms of type I collagen consisting of both normally and slowly migrating forms of the alpha 1(I)- and alpha 2(I)-chains. In the other three OI cell lines only the 'slow' alpha (I)'- and alpha 2(I)'-chains were detected. In both groups inhibition of the post-translational modifications of proline and lysine resulted in the production of a single species of type I collagen with normal electrophoretic migration. Proline hydroxylation was normal, but the hydroxylysine contents of alpha 1(I)'- and alpha 2(I)'-chains purified by h.p.l.c. were greater than in control alpha-chains. The glucosylgalactosylhydroxylysine content was increased approx. 3-fold while the galactosylhydroxylysine content was only slightly increased in the alpha 1(I)'-chains relative to control alpha 1(I)-chains. Peptide mapping of the CNBr-cleavage peptides provided evidence that the increased post-translational modifications were distributed throughout the alpha 1(I)'- and alpha 2(I)'-chains. It is postulated that the greater modification of these chains was due to structural defects of the alpha-chains leading to delayed helix formation. The abnormal charge heterogeneity observed in the alpha 1 CB8 peptide of one patient may reflect such a structural defect in the type I collagen molecule.

Specifically decreased collagen biosynthesis in scurvy dissociated from an effect on proline hydroxylation and correlated with body weight loss. In vitro studies in guinea pig calvarial bones

The question whether ascorbate regulates collagen production solely through its direct role in proline hydroxylation was investigated. Proteins in calvarial bones from control and scorbutic weanling guinea pigs were labeled in short-term cultures with radioactive proline. Proteins were digested with purified bacterial collagenase to distinguish between effects on collagen polypeptide production and hydroxyproline formation. There was a preferential decrease in the absolute rate of collagen biosynthesis beginning after 2 wk of ascorbate deficiency, and this effect was temporally dissociated from decreased proline hydroxylation. There were no significant changes in the absolute rates of collagen degradation or noncollagen protein production. In vitro inhibition of proline hydroxylation in normal bone with alpha, alpha'-dipyridyl did not affect the relative rate of collagen synthesis, further dissociating these functions. Ascorbate added to scorbutic bone cultures reversed defective proline hydroxylation but not defective collagen synthesis, suggesting that the latter was an indirect effect of scurvy. There was a linear correlation between the extent of body weight lost during the 3rd and 4th wk of scurvy and the rate of collagen synthesis in scorbutic bone. This correlation also applied to control animals receiving ascorbate, but with weight loss induced by food restriction. These studies establish for the first time that ascorbate deficiency in guinea pigs leads to a specific decrease in collagen polypeptide synthesis and suggest that this decrease results from the reduced food intake and/or weight-loss characteristic of scurvy.

Mechanisms of Kirsten murine sarcoma virus transformation-induced changes in the collagen phenotype and synthetic rate of BALB 3T3 cells

Specific viral transformation rather than cell selection can explain the previously observed increase in the proportion of type III procollagen compared to type I procollagen in BALB 3T3 cells transformed by Kirsten murine sarcoma virus (Ki-MSV). Two subclones of BALB 3T3 A31 were productively infected with with a temperature-sensitive Ki-MSV in the presence of helper murine leukemia virus (MLV), resulting in virtually complete transformation of cultures and eliminating selection of transformed foci. Analysis of radioactive collagen, derived from procollagen by pepsin treatment, showed that both of the tsKi-MSV/MLV-transformed subclones contained a 4-fold greater proportion of type III procollagen than did control MLV-infected cultures. A nonproducer derivative exhibited an even greater change (10-fold), indicating that viral replication was irrelevant. After 48 hr at a nonpermissive temperature, tsKi-MSV-transformed cells retained a high proportion of type III procollagen, suggesting that either this change is not induced by src protein or else there is a slowly reversible or irreversible step involved. Alternatively, type III procollagen mRNA may be long lived. In contrast, the relative rate of procollagen synthesis in transformed cells was clearly regulated by src protein. Translation of mRNA from cells preincubated at permissive or nonpermissive temperatures revealed that the decreased relative rate can be explained by a simultaneous small decrease in the level of procollagen mRNA and a large increase in mRNA for noncollagen proteins.