Purification and characterization of a transformation-dependent protein secreted by cultured murine fibroblasts

Characterization and expression of AmphiCL encoding cathepsin l proteinase from amphioxus Branchiostoma belcheri tsingtauense

An amphioxus complementary DNA, AmphiCL, encoding cathepsin L proteinase was isolated from the gut cDNA library of Branchiostoma belcheri tsingtauense. It is 1480 bp long, and its longest open reading frame codes for a precursor protein, which consists of 327 amino acid residues including a signal peptide (preregion), a propeptide, and a mature proteinase. Northern blot showed that AmphiCL was expressed in the gill, testis, hepatic cecum, and hind-gut with a molecular size of about 1480 bp. AmphiCL was also expressed at low level in the muscle, notochord, and ovary as revealed by the more sensitive reverse transcriptase polymerase chain reaction techniques. Semiquantitative RT-PCR also showed that although AmphiCL expression in the gut was significantly downregulated by feeding Arthrospira platensis powder, a protein-rich food, its expression in the same tissue was upregulated by exposure to lipopolysaccharide, an integral component of the outer membrane of gram-negative bacteria. This suggests that although the involvement of AmphiCL in food digestion remains to be confirmed, AmphiCL may play a role in inflammatory reaction in amphioxus.

Shrimp cathepsin L encoded by an intronless gene has predominant expression in hepatopancreas, and occurs in the nucleus of oocyte

We have cloned the cDNA and genomic DNA of an active intronless cathepsin L from Metapenaeus ensis. The encoded enzyme has the shortest prosequence among cathepsin L subgroup. It was predominantly expressed in hepatopancreas with an expression level of at least 10 times higher than in any other tissues. It also has expression in stomach, intestine, eye, testis, ovary and muscle. Western blots visualized the mature enzyme in hepatopancreas and a procathepsin L in ovary, intestine and stomach. Metapenaeus cathepsin L (MeCatL) is localized in the large digestive vacuole of the digestive B cell of hepatopancreas. MeCatL has a role in food digestion. An interesting finding is that it exists in the nucleus of oocyte. MeCatL might have a specified physiological role in the nucleus of oocyte. MeCatL might also have a house-keeping function as is suggested for mammalian cathepsin L.

Glucose regulates protein catabolism in ras-transformed fibroblasts through a lysosomal-dependent proteolytic pathway

Transformed cells are exposed to heterogeneous microenvironments, including low D-glucose (Glc) concentrations inside tumours. The regulation of protein turnover is commonly impaired in many types of transformed cells, but the role of Glc in this regulation is unknown. In the present study we demonstrate that Glc controls protein turnover in ras-transformed fibroblasts (KBALB). The regulation by Glc of protein breakdown was correlated with modifications in the levels of lysosomal cathepsins B, L and D, while autophagic sequestration and non-lysosomal proteolytic systems (m- and mu-calpains and the zeta-subunit of the proteasome) remained unaffected. Lactacystin, a selective inhibitor of the proteasome, depressed proteolysis, but did not prevent its regulation by Glc. The sole inhibition of the cysteine endopeptidases (cathepsins B and L, and calpains) by E-64d [(2S,3S)-trans-epoxysuccinyl-L-leucylamido-3-methylbutane ethyl ester] was also not sufficient to alter the effect of Glc on proteolysis. The Glc-dependent increase in proteolysis was, however, prevented after optimal inhibition of lysosomal cysteine and aspartic endopeptidases by methylamine. We conclude that, in transformed cells, Glc plays a critical role in the regulation of protein turnover and that the lysosomal proteolytic capacity is mainly responsible for the control of intracellular proteolysis by Glc.

Metalloprotease activity in a small heat shock protein of the human malaria parasite Plasmodium vivax

The malaria parasite affects millions of people each year, lives and multiplies in two different hosts, and synthesizes a large number of proteases and heat shock proteins (HSPs) for its survival. We describe here the characterization of a metalloprotease activity which resides in the small HSP (PVHSP28) of the common but noncultivable human malaria parasite Plasmodium vivax. The protein is expressed by erythrocytic stages of the parasite. It is expressed as a approximately 55-kDa polypeptide which is then processed to the 28-kDa mature protein. The latter was found to be an active protease in gelatin zymography. This protease showed its optimal activity at 37 degrees C (pH 7.6). It also retained its proteolytic activity at higher temperatures of up to 55 degrees C. The enzyme belongs to the metalloprotease class, as its proteolytic activity was most effectively blocked by 1,10-phenanthroline and was restored to a maximal level by the addition of zinc metal ions. Inhibitors for the cysteine, serine, and aspartate classes of proteases were ineffective against this enzyme. A homology search indicates that PVHSP28 probably belongs to a new class of HSPs which possess the metalloprotease signature sequence.

Glucose controls cathepsin expression in Ras-transformed fibroblasts

Overexpression and altered trafficking of cathepsins have been associated with the malignant properties of tumors and transformed cells. A characteristic phenotype of transformed cells is also a profound deviation in their metabolism (aerobic glycolysis, glutaminolysis) which enables them to adapt to extreme nutritional conditions. However, whether the altered metabolism may change the expression of proteinases involved in malignancy has not been determined. Herein we present evidences in Kirsten-virus-transformed 3T3 fibroblasts (KBALB) that D-glucose selectively increases active forms of cathepsins L, B, and D, without altering other lysosomal nonproteolytic hydrolases (beta-D-glucosaminidase, acid phosphatase, beta-D-glucuronidase, and beta-D-galactosidase). D-Glucose did not modify mRNA levels for cathepsin B or L and did not affect secretion of pro-cathepsin L. However, D-glucose enhanced strongly the amount of the mature forms of cathepsins B and L, without altering their preferential distribution to light endosomal fractions. Induction by d-glucose of intracellular mature cathepsins B and L required a high growth density of KBALB cells and was reproduced in BALB/3T3 fibroblasts stably transfected with a constitutively activated form of Ras. d-Glucose induction of active cathepsins however was not observed in nontransformed BALB/3T3. D-Mannose, in contrast to nonmetabolized sugars (D-galactose, or L-glucose), caused a similar increase in lysosomal cathepsin activities in dense KBALB cells. The D-glucose analogue, 3-O-methyl-D-glucose, which is transported but not further metabolized, did not reproduce the d-glucose effects. Our findings indicate that, dependent on the nutrient supply and as a consequence of their altered metabolism, transformed cells may modulate the production of active proteinases implicated in malignant progression.

Effect of carbohydrate position on lysosomal transport of procathepsin L

To study the role of carbohydrate in lysosomal protein transport, we engineered two novel glycosylation signals (Asn-X-Ser/Thr) into the cDNA of human procathepsin L, a lysosomal acid protease. We constructed six mutant cDNAs encoding glycosylation signals at mutant sites Asn-138, Asn-175, or both sites together, in the presence or absence of the wild-type Asn-204 site. We stably transfected wild-type and mutant cDNAs into NIH3T3 mouse fibroblasts and then used species-specific antibodies to determine the glycosylation status, phosphorylation, localization, and transport kinetics of recombinant human procathepsin L containing one, two, or three glycosylation sites. Both novel glycosylation sites were capable of being glycosylated, although Asn-175 was utilized only 30-50% of the time. Like the wild-type glycosylation at Asn-204, carbohydrates at Asn-138 and Asn-175 were completely sensitive to endoglycosidase H, and they were phosphorylated. Mutant proteins containing two carbohydrates were capable of being delivered to lysosomes, but there was not a consistent relationship between the efficiency of lysosomal delivery and carbohydrate content of the protein. Pulse-chase labeling revealed a unique biosynthetic pattern for proteins carrying the Asn-175 glycosylation sequence. Whereas wild-type procathepsin L and mutants bearing carbohydrate at Asn-138 appeared in lysosomes by about 60 min, proteins with carbohydrate at Asn-175 were processed to a lysosome-like polypeptide within 15 min. Temperature shift, brefeldin A, and NH4Cl experiments suggested that the rapid processing did not occur in the endoplasmic reticulum and that Asn-175 mutants could interact with the mannose 6-phosphate receptor. Taken together, our results are consistent with the interpretation that Asn-175 carbohydrate confers rapid transport to lysosomes. We may have identified a recognition domain in procathepsin L that is important for its interactions with the cellular transport machinery.

Drug-selected coexpression of human glucocerebrosidase and P-glycoprotein using a bicistronic vector

Bicistronic cassettes under control of a single promoter have recently been suggested as useful tools for coordinate expression of two different foreign proteins in mammalian cells. Using the long 5' untranslated region of encephalomyocarditis virus as translational enhancer of the second gene, a bicistronic unit composed of cDNA for human P-glycoprotein [the product of the multidrug resistance gene, MDR1 (also called PGY1)] as selectable marker and cDNA for human glucocerebrosidase (GC; EC 3.2.1.45) (a membrane-associated lysosomal hydrolase) was constructed. NIH 3T3 cells transfected with a Harvey murine sarcoma virus retroviral vector carrying this bicistronic cassette (pHaMCG) express active P-glycoprotein and GC and expression of both proteins augments coordinately with selection for increased colchicine resistance. Percoll gradient analysis of homogenates showed that GC was targeted to the lysosomal fraction. The ability to select for expression of GC with natural product drugs after introduction of the pHaMCG retroviral vector may be useful in gene therapy strategies for Gaucher disease.

A difference in the enzyme contents of resorption lacunae and secondary lysosomes of osteoclasts

The distributions of tartrate sensitive lysosomal acid phosphatase (LAP) and cathepsin L in osteoclasts and the effect of parathyroid hormone (PTH) stimulation on them were investigated by using the protein A-gold method on ultracryosections of rat trabecular bone. LAP was located in association with the ruffled border membrane, in the resorption lacuna, on the mineral phase surrounding the lacuna, and in some primary lysosomes. After PTH treatment, the extracellular and ruffled border membrane associated LAP apparently increased. Heavy gold labelling for cathepsin L was confined exclusively to secondary lysosomes. No labelling was seen in the extracellular resorption lacuna or at the ruffled border. Acceleration of bone resorption by PTH-treatment did not change detectably the distribution or intensity of labelling. This study shows that the enzyme contents of secondary lysosomes and resorption lacunae are different and suggests that LAP is directly involved in extracellular bone degradation whereas the role of cathepsin L is restricted to lysosomes.

Collagenolytic cysteine proteinases of bone tissue. Cathepsin B, (pro)cathepsin L and a cathepsin L-like 70 kDa proteinase

The aim of the work was to identify and characterize the cysteine proteinases of bone tissue, as these enzymes appear necessary for bone resorption. Three cysteine-dependent proteolytic activities were separated from a homogenate of mouse calvaria by a fractionation procedure involving (NH4)2SO4 precipitation, gel filtration and ion-exchange chromatography. The first two are typical cathepsins B and L with respect to (1) their reactivity with anti-(cathepsin B) and anti-(cathepsin L) antibodies respectively, (2) their relative rate constants for inhibition by benzyloxycarbonyl-Phe-Phe-CHN2 and L-3-carboxy-trans-2,3-epoxypropionyl-L-leucylamido-(4-guanid ino)butane and (3) their enzymic properties, such as the higher activities of cathepsin L against collagen and gelatin as compared with cathepsin B, and the fact that benzyloxycarbonyl-Arg-Arg 4-methoxy-2-naphthylamide is hydrolysed only by cathepsin B. Cathepsin L was mainly recovered in its precursor form, as indicated by its apparent 40 kDa molecular mass and its relative stability at pH 7.2. The third enzyme is a cathepsin L-like proteinase with an apparent molecular mass of 70 kDa. It is immunoprecipitated by anti-(cathepsin L) antibodies, and appears as the 25 kDa band of mature cathepsin L in Western blots. It further resembles (pro)cathepsin L with regard to its activities against synthetic substrates and proteins such as collagen, and with regard to its response to various inhibitors. However, unlike (pro)cathepsin L, it is eluted as a 70 kDa protein on gel filtration (even in the presence of 1% Brij or 1 M-NaCl), it is stable at pH values as high as 9, and it exhibits stronger affinity for phenyl-Sepharose. It might thus result from a strong complex between mature cathepsin L and another entity that confers stability at alkaline pH and favours hydrophobic interactions. This 70 kDa activity was also detected in mouse muscle and long bones of Ca(2+)-deficient chicks but not in mouse liver, spleen or kidney.

Isolation of a mutant of Chinese hamster ovary cells with defective secretion of a subset of secretory proteins

The secretory pathway of mammalian cells involves a complex sequence of steps beginning with the translation and translocation of proteins across the rough endoplasmic reticulum membrane followed by their transport through a variety of intracellular compartments. Understanding the cellular mechanisms involved in protein transport would be facilitated by the application of somatic cell genetics techniques. Therefore, we have developed a procedure for the isolation of Chinese hamster ovary cell lines that are deficient in this pathway. Mutant (sec) clones that secrete into the medium a lesser amount of newly synthesized protein relative to wild type are detected in the screen. One of the sec cell lines, LEH6, has similar growth and protein synthetic rates as do wild-type cells. The extent of total protein secretion is 60-70% of wild-type with some proteins more reduced than others. Immunoprecipitation studies indicate that for LEH6 cells there is impaired secretion of fibronectin (three- to fourfold) and major excreted protein (two- to sixfold).

Comparison of cathepsin L synthesized by normal and transformed cells at the gene, message, protein, and oligosaccharide levels

The major excreted protein of transformed mouse fibroblasts (MEP) has recently been identified as the lysosomal cysteine protease, cathepsin L. The synthesis and intracellular trafficking of this protein in mouse fibroblasts are regulated by growth factors and malignant transformation. To further define the basis for this regulation, a cDNA encoding MEP/cathepsin L was isolated from a mouse liver cDNA library and used to compare cathepsin L of normal and Kirsten sarcoma virus-transformed NIH 3T3 fibroblasts. Although cathepsin L message levels were elevated 20-fold in the transformed fibroblasts, normal and transformed cells displayed similar cathepsin L genomic DNA digest patterns and gene copy numbers, and cathepsin L mRNA sequences appeared identical by RNase protection analysis. These findings indicate that (i) cathepsin L is synthesized from the same gene in normal and transformed cells and (ii) cathepsin L polypeptides made by these cells are translated with the same primary sequence. Cathepsin L polypeptides synthesized by quiescent, growing, and transformed cells displayed similar isoelectric focusing patterns, suggesting similar post-translational modification. Site-directed mutagenesis of the mouse liver cDNA and expression in COS monkey cells was used to examine the glycosylation of mouse cathepsin L. The results indicated that only one of the two potential N-linked glycosylation sites (the one at Asn221) is glycosylated. Analysis by ion exchange chromatography on QAE-Sephadex, and affinity chromatography on mannose 6-phosphate receptor-Affi-Gel 10, indicated that the cathepsin L oligosaccharide was phosphorylated similarly in normal and transformed cells. Although several phosphorylated oligosaccharide species were observed, the major species contained two phosphomonoester moieties and bound efficiently to the receptor. These findings suggest that cathepsin L made by normal and transformed mouse fibroblasts are identical and substantiate the hypothesis that trafficking of cathepsin L in these cells is regulated by growth-induced changes in the lysosomal protein transport system.

Glycosylation of procathepsin L does not account for species molecular-mass differences and is not required for proteolytic activity

Cathepsin L is a major lysosomal cysteine proteinase in mouse and human cells. Despite similar predicted molecular masses, procathepsin L in these two species migrates on SDS/polyacrylamide gels with apparent molecular masses of 39 kDa and 42 kDa respectively. To determine if glycosylation differences account for this discrepancy, and to ascertain whether glycosylation is essential for enzymic activity, mouse and human procathepsins L were expressed at high concentrations in mouse NIH 3T3 cells or in human A431 cells after DNA-mediated transfection of cloned DNAs for these enzymes. In pulse-chase studies, human procathepsin L transfectants synthesized and secreted large amounts of enzymically active 42 kDa proenzyme and processed it into 34 kDa and 26 kDa intracellular peptides, a pattern of secretion and processing similar to that seen with endogenous or transfected mouse procathepsin L. Both translation of cloned procathepsin L cDNAs in vitro and Endoglycosidase H treatment of 39 kDa mouse and 42 kDa human procathepsin L resulted in non-glycosylated proteins 2 kDa lower in molecular mass than the untreated proteins for both species. This suggests that glycosylation differences are not responsible for the molecular-mass disparity between the two species. Moreover, Endoglycosidase H-treated mouse enzyme retained full proteolytic activity, indicating that glycosylation of cathepsin L is not essential for enzymic function.

Serum factors alter the extent of dephosphorylation of ligands endocytosed via the mannose 6-phosphate/insulin-like growth factor II receptor

Mouse L-cells that contain the cation-independent (CI) mannose 6-phosphate (Man 6-P)/insulin-like growth factor (IGF) II receptor endocytose acid hydrolases and deliver these enzymes to lysosomes. The postendocytic loss of the Man 6-P recognition marker from the cell-associated acid hydrolases was assessed by CI-Man 6-P receptor affinity chromatography. 125I-labeled acid hydrolases internalized by L-cells grown at high density were delivered to lysosomes but were not dephosphorylated. In contrast, the same 125I-labeled hydrolases internalized by L-cells maintained at low density were delivered to lysosomes and were extensively dephosphorylated. The dephosphorylation at low density required 5 h for completion suggesting that the phosphatase responsible for the dephosphorylation is located within the lysosomal compartment. Transition from the high to low density state was rapid and was not inhibited by cycloheximide. Medium substitution experiments indicated that serum factors were necessary to maintain the L-cells in the dephosphorylation-competent (low density) state, and that serum-free conditions led to a dephosphorylation-incompetent (high density) state. Addition of IGF II to cells in serum-free medium allowed acid hydrolases subsequently introduced by endocytosis to be dephosphorylated. The results indicate that the removal of the Man 6-P recognition marker from endocytosed acid hydrolases is regulated by serum factors in the growth medium, including IGF II.

Use of a cloned multidrug resistance gene for coamplification and overproduction of major excreted protein, a transformation-regulated secreted acid protease

Malignantly transformed mouse fibroblasts synthesize and secrete large amounts of major excreted protein (MEP), a 39,000-dalton precursor to an acid protease (cathepsin L). To evaluate the possible role of this protease in the transformed phenotype, we transfected cloned genes for mouse or human MEP into mouse NIH 3T3 cells with an expression vector for the dominant, selectable human multidrug resistance (MDR1) gene. The cotransfected MEP sequences were efficiently coamplified and transcribed during stepwise selection for multidrug resistance in colchicine. The transfected NIH 3T3 cell lines containing amplified MEP sequences synthesized as much MEP as did Kirsten sarcoma virus-transformed NIH 3T3 cells. The MEP synthesized by cells transfected with the cloned mouse and human MEP genes was also secreted. Elevated synthesis and secretion of MEP by NIH 3T3 cells did not change the nontransformed phenotype of these cells.

Heparin modulates the secretion of a major excreted protein-like molecule by vascular smooth muscle cells

Previous work from our laboratory has shown that heparin specifically induces the release of a pair of proteins of approximately 35,000 and 37,000 Da into the culture medium of vascular smooth muscle cells (SMC). In this report, we demonstrate that the previously identified 37,000-Da smooth muscle protein is composed of two protein species with very similar molecular weights based on migration patterns in SDS-polyacrylamide gels. The larger molecular weight species in this doublet has a similar molecular weight and shares antigenic determinants with major excreted protein (MEP), a lysosomal proteinase previously shown to be secreted by normal and transformed fibroblasts and epidermal cells. Antisera to MEP precipitated the higher molecular weight band from the doublet; preimmune serum was not reactive with the smooth muscle protein. Exposure of smooth muscle cells to heparin resulted in decreased amounts of immunoprecipitable protein released into the medium. Thus, it now appears that three proteins in the 35,000-38,000 molecular weight range are modulated by heparin, and that the largest of the heparin-modulated vascular SMC proteins has a similar molecular weight and is immunologically related to MEP. The release of MEP-like protein from SMC is decreased by heparin, while the remaining two heparin-modulated proteins are increased in the presence of heparin.

Use of a cloned multidrug resistance gene for coamplification and overproduction of major excreted protein, a transformation-regulated secreted acid protease

Malignantly transformed mouse fibroblasts synthesize and secrete large amounts of major excreted protein (MEP), a 39,000-dalton precursor to an acid protease (cathepsin L). To evaluate the possible role of this protease in the transformed phenotype, we transfected cloned genes for mouse or human MEP into mouse NIH 3T3 cells with an expression vector for the dominant, selectable human multidrug resistance (MDR1) gene. The cotransfected MEP sequences were efficiently coamplified and transcribed during stepwise selection for multidrug resistance in colchicine. The transfected NIH 3T3 cell lines containing amplified MEP sequences synthesized as much MEP as did Kirsten sarcoma virus-transformed NIH 3T3 cells. The MEP synthesized by cells transfected with the cloned mouse and human MEP genes was also secreted. Elevated synthesis and secretion of MEP by NIH 3T3 cells did not change the nontransformed phenotype of these cells.

An acid protease secreted by transformed cells interferes with antigen processing

The major excreted protein of malignantly transformed mouse fibroblasts (MEP), which is the precursor to lysosomal cathepsin L, was used to study the effect of exogenous acid proteases on antigen processing. When MEP and native pigeon cytochrome c were added to Chinese hamster ovary (CHO) cells expressing transfected major histocompatability complex class II gene products, the antigen-specific T-cell hybridoma 2B4 did not respond to the antigen. MEP appears to destroy the antigen in an acid compartment of the presenting cell because: (a) MEP is only active as a protease under acid conditions; (b) mannose 6-phosphate inhibited the internalization of MEP and blocked its effect on antigen processing; (c) the destruction required the simultaneous entry of the antigen and MEP into the cells; and (d) cytochrome c fragment 66-104 which does not need to be processed stimulated 2B4 in the presence of MEP. These results support the hypothesis that antigen processing requires internalization of the antigen into an acidic compartment, and they provide a new model for the investigation of the contribution of acid proteases to the reduced immunocompetence of tumor-bearing animals.

Biosyntheses and processing of lysosomal cysteine proteinases in rat macrophages

The intracellular processing and release of three lysosomal cysteine proteinases, cathepsin B, H and L, by rat peritoneal macrophages were investigated by pulse-chase experiments. Newly synthesized procathepsins B (39 kDa), H(41 kDa) and L (39 kDa) after 15 min labeling were processed to the mature, single-chain enzymes within 1 h. The single-chain forms of cathepsin B, H and L were further processed to two-chain forms at different rates: conversion of cathepsin L to the two-chain form was rapid, whereas the conversions cathepsin B and H took at least 6 h. Macrophages released 30% of the procathepsins B and L, and 10% of the procathepsin H.

The improved efficient method for introducing macromolecules into cells using HVJ (Sendai virus) liposomes with gangliosides

Macromolecules such as DNA and RNA can be entrapped within liposomes associated with gangliosides by reverse-phase evaporation. When these liposomes are incubated with HVJ2 (Sendai virus), they deliver their contents into cultured cells efficiently. More than 95% cells of a Ltk- cell line (thymidine kinase-deficient cells) transiently expressed thymidine kinase activity by thymidine kinase gene transfer using HVJ liposomes with gangliosides. Stable transformants could be obtained efficiently from various cell lines by use of HVJ liposomes containing the neoR gene. The neo+ transformants were obtained at frequencies of about 0.2-1.0, 0.06-0.25, and 0.06-0.1% in monolayers of L, CHO-Kl, and HeLa-S3 cells, respectively. Moreover, in Ehrlich ascites tumor cells which grow in suspension, the frequency was more than 0.01%. On introduction of plasmid pTK4 into Ltk- cells, about 0.5-1.0% TK+ transformants were obtained. Cosmid DNA containing the neoR gene (about 45 kbp) was also introduced into L cells by this method and neo+ transformants were obtained at a frequency of 0.1%. When rat liver mRNA was introduced into L cells by HVJ liposomes with gangliosides, immunoprecipitation studies showed that the L cells secreted rat albumin and some other proteins into the cultured medium. Moreover, using erythrocyte membrane vesicles containing IgM that had been incubated with HVJ empty liposomes with gangliosides, the IgM could be introduced into all the L cells.

Sequence and expression of the cDNA for MEP (major excreted protein), a transformation-regulated secreted cathepsin

The major excreted protein (MEP) of malignantly transformed mouse fibroblasts is a secreted thiol proteinase. Sequencing of the MEP cDNA shows the coding region for the protein to be identical with the sequence for a mouse cysteine proteinase isolated from macrophages, but the MEP cDNA is polyadenylated at a different site in the 3' non-coding region. Strong homology of MEP with human cathepsin L suggests that MEP is the mouse analogue of cathepsin L. Amino acid sequencing of the N-terminus of the secreted form of MEP indicates that, during secretion, the polypeptide is cleaved between amino acids 17 and 18. We have placed the MEP cDNA in a eukaryotic expression vector and demonstrated the production of the 39 kDa polypeptide form of mouse MEP in monkey CV-1 cells.

Regulation of the transcript for a lysosomal protein: evidence for a gene program modified by platelet-derived growth factor

Platelet-derived growth factor (PDGF) stimulates density-arrested BALB/c-3T3 cells to synthesize MEP, a lysosomal protein. This enhanced synthesis appears to be largely regulated by the PDGF-modulated accumulation of MEP mRNA, a 1.8-kilobase species. The increase in the MEP transcript, which is dependent on the PDGF concentration, begins 3 to 4 h after PDGF addition and is maximal at 12 h. The accumulation of the MEP transcript is growth-factor specific: PDGF and the tumor promoter 12-O-tetradecanoylphorbol-13-acetate, an agent which acts like PDGF, induce MEP RNA accumulation, whereas epidermal growth factor, somatomedin C, insulin, and whole plasma do not. A spontaneously transformed BALB/c-3T3 cell line (ST2-3T3), which does not require PDGF for growth, optimally expresses MEP RNA in the absence of PDGF. The PDGF-modulated increase in MEP RNA is unlike PDGF-modulated c-myc and c-fos RNA accumulation because it is blocked by cycloheximide, suggesting a requirement for de novo protein synthesis. It appears that PDGF modulates a program of gene expression with the accumulation of some transcripts, typified by MEP, being dependent upon the translation of others.

Expression of simian virus 40 early and late genes in mouse oocytes and embryos

Simian virus 40 (SV40) large- and small-tumor antigens (T-Ag, t-Ag) are normally synthesized early after infection of either permissive (monkey) or nonpermissive (mouse) fibroblasts, whereas an equivalent amount of viral coat protein (V-Ag) is observed late after infection of permissive cells and only after viral DNA replication has occurred. To determine whether or not expression of these genes is regulated in the same manner during early mammalian development, SV40 DNA was injected into the nuclei of mouse oocytes and one- and two-cell embryos. In oocytes, about three times more V-Ag was produced than T-Ag, and both were synthesized concomitantly in the same cells. Viral mRNA and proteins synthesized in oocytes comigrated during gel electrophoresis with the same products synthesized in SV40-infected monkey cells. Viral gene expression required circular DNA molecules injected into the nuclei of transcriptionally and translationally active cells. Injected DNA was stable and underwent conformational changes consistent with chromatin assembly. Oocytes did not replicate either polyomavirus or SV40 DNA. Thus, the temporal order of viral gene expression is circumvented in mouse germ cells, allowing these proteins to be expressed concurrently and in equivalent amounts with no requirement for DNA replication. However, in preimplantation embryos, neither T-Ag nor V-Ag was detected by immunoprecipitation although T-Ag synthesis was demonstrated as a specific requirement for SV40 DNA replication. Thus, viral gene expression in mouse embryos as early as the one-cell stage was reduced at least 500-fold relative to that in oocytes. Similarities between SV40 gene expression in mouse oocytes and that in Xenopus oocytes suggest that germ cells in higher animals share common regulatory mechanisms.

Dissociation of cellular transformation from platelet-derived growth factor independence

ST2-3T3, a spontaneously transformed BALB/c-3T3 cell line which does not require platelet-derived growth factor (PDGF) for growth, was fused to THO2, a PDGF-responsive non-transformed BALB/c-3T3 cell line, in order to learn whether transformation is expressed coordinately with PDGF independence. Hybrid cells were selected and grown in medium containing both HAT (hypoxanthine-aminopterin-thymidine) and ouabain; unfused cells of each parental type were killed in HAT-ouabain medium. Five independently isolated ST2-3T3xTHO2 hybrid cell lines were established and characterized for both transformation and PDGF responsiveness. All five were transformed, having a disorganized growth pattern and achieving a final cell density similar to that of ST2-3T3 cells. Two of these lines did not respond to a brief treatment with PDGF: the mitogen neither induced the synthesis of a PDGF-modulated lysosomal protein (termed MEP), nor stimulated the cells to enter the S phase; one line responded to PDGF by synthesizing both MEP and DNA, whereas two others synthesized MEP but not DNA. In contrast, four independently isolated cell lines obtained by fusing PDGF-responsive non-transformed BALB/c-3TC cells to the THO2 line were all PDGF-responsive for both MEP and DNA synthesis and were not transformed. It appears that PDGF independence is not required for the transformation of BALB/c-3T3 cells.

Regulation of the transcript for a lysosomal protein: evidence for a gene program modified by platelet-derived growth factor

Platelet-derived growth factor (PDGF) stimulates density-arrested BALB/c-3T3 cells to synthesize MEP, a lysosomal protein. This enhanced synthesis appears to be largely regulated by the PDGF-modulated accumulation of MEP mRNA, a 1.8-kilobase species. The increase in the MEP transcript, which is dependent on the PDGF concentration, begins 3 to 4 h after PDGF addition and is maximal at 12 h. The accumulation of the MEP transcript is growth-factor specific: PDGF and the tumor promoter 12-O-tetradecanoylphorbol-13-acetate, an agent which acts like PDGF, induce MEP RNA accumulation, whereas epidermal growth factor, somatomedin C, insulin, and whole plasma do not. A spontaneously transformed BALB/c-3T3 cell line (ST2-3T3), which does not require PDGF for growth, optimally expresses MEP RNA in the absence of PDGF. The PDGF-modulated increase in MEP RNA is unlike PDGF-modulated c-myc and c-fos RNA accumulation because it is blocked by cycloheximide, suggesting a requirement for de novo protein synthesis. It appears that PDGF modulates a program of gene expression with the accumulation of some transcripts, typified by MEP, being dependent upon the translation of others.

Malignant transformation and tumor promoter treatment increase levels of a transcript for a secreted glycoprotein

The major excreted protein of transformed mouse fibroblasts, a secreted, mannose 6-phosphate-containing glycoprotein, is induced in nontransformed cells by a variety of transforming agents, by phorbol esters, and by platelet-derived growth factor. We report here the molecular cloning of the cDNA encoding this protein and demonstrate that its induction is a consequence of enhanced mRNA levels for major excreted protein in both tetradecanoyl phorbol acetate-treated 3T3 cells and 3T3 cells transformed by a variety of retroviruses or retroviral oncogenes. These results indicate that tumor promoters and retroviral transformation might share a common pathway of action in cultured cells and that major excreted protein is a molecular marker for the growth response of cells to these agents.

Modulation of the platelet-derived growth factor induced replicative response

Quiescent cultures of density arrested BALB/c-3T3 cells have been sensitized to the growth stimulatory action of the platelet-derived growth factor (PDGF). Sensitization was achieved by depriving the cultures of PDGF prior to growth stimulation and was noted after transfer of cultures from medium supplemented with 10% serum to medium containing either an equivalent concentration of platelet-poor plasma or a low concentration (0.5%) of serum. Sensitized cultures required less pure PDGF for growth stimulation than nonsensitized ones. In addition such cultures required less mitogen to synthesize a PDGF modulated major excreted protein (MEP). The mechanism of sensitization was investigated. Sensitized cultures did not bind more PDGF than non-sensitized ones. Rather, sensitization appeared to result from the loss of cells that occurred when cultures were deprived of PDGF. Such a loss increased the amount of PDGF available per cell, causing a higher percentage of cells to enter the S phase. Similarly, the amount of PDGF per cell regulated MEP synthesis. Furthermore, in non-sensitized cultures (containing the same number of cells), the absolute quantity rather than the concentration of PDGF regulated DNA synthesis. It appears that the amount of PDGF per cell modulates mitogenesis.

Malignant transformation and tumor promoter treatment increase levels of a transcript for a secreted glycoprotein

The major excreted protein of transformed mouse fibroblasts, a secreted, mannose 6-phosphate-containing glycoprotein, is induced in nontransformed cells by a variety of transforming agents, by phorbol esters, and by platelet-derived growth factor. We report here the molecular cloning of the cDNA encoding this protein and demonstrate that its induction is a consequence of enhanced mRNA levels for major excreted protein in both tetradecanoyl phorbol acetate-treated 3T3 cells and 3T3 cells transformed by a variety of retroviruses or retroviral oncogenes. These results indicate that tumor promoters and retroviral transformation might share a common pathway of action in cultured cells and that major excreted protein is a molecular marker for the growth response of cells to these agents.

Processing and lysosomal localization of a glycoprotein whose secretion is transformation stimulated

The major excreted protein (MEP) of transformed mouse fibroblasts is a mannose 6-phosphate-containing glycoprotein whose synthesis and secretion are increased in malignantly transformed 3T3 cells and whose synthesis is increased by treatment of 3T3 cells with tumor promoters or growth factors. When pulse-labeled extracts from Kirsten virus-transformed NIH 3T3 (KNIH) cells were immunoprecipitated using an antibody against secreted MEP, one cellular protein was immunoprecipitated that had the same molecular weight and tryptic peptide map as the secreted protein. Pulse-chase labeling experiments showed that 50-60% of this 39,000-mol-wt form was secreted in transformed cells. Of the 40-50% remaining, approximately 5% was processed into two lower molecular weight forms (29,000 and 20,000) which are sequestered within the cell. Similar processing of these proteins was observed in the nontransformed parent NIH 3T3 (NIH) cells. However, in NIH cells, much less of the synthesized MEP was secreted. Measurements of steady-state levels of these three forms of cellular MEP by Western blot immunolocalization revealed approximately fourfold more MEP in KNIH cells than in NIH cells as well as differences in the relative distribution of MEP forms in transformed and nontransformed cells. Subcellular fractionation of KNIH cells on a Percoll gradient demonstrated a distribution of total MEP similar to that of several lysosomal enzymes. The light lysosomal/Golgi peak from these gradients contained both the precursor 39,000-mol-wt form of MEP and the 20,000-mol-wt form, whereas the heavy lysosomal peak was enriched in the 20,000-mol-wt form. The distribution of MEP forms was found to be similar in NIH cells except that the 29,000-mol-wt form was also seen to be enriched in the heavy lysosomal peak. This biochemical localization of MEP was confirmed by immunolocalization with light and electron microscopy. These data support the hypothesis that MEP is a lysosomal protein that is secreted by transformed cells.

Cell adhesiveness is related to tumorigenicity in malignant lymphoid cells

Mouse lymphoma cells (S49) that grow in suspension culture were selected for increased tumorigenicity through continuous passages in syngeneic BALB/c mice. Developing tumors were classified as high grade malignant lymphoma, small noncleaved type. Variants were selected from these tumorigenic cells that were able to grow as a monolayer attached to their substrate, resembling, in this respect, fibroblastoid cells. Whereas the tumorigenic suspension-growing parental cells were able to induce progressive tumors with an inoculum as low as 100 cells per mouse, the adherent cells were unable to develop as tumors even at an inoculum of 1 X 10(8) cells per mouse. In addition, mice inoculated once with live adherent cells were immunized against 1 X 10(7) suspension-growing cells. Involvement of an immune response in the rejection of tumorigenic S49 cells was suggested by (a) adoptive transfer experiments in which spleen cells from immunized mice protected naive mice and (b) the appearance of antibodies in the sera of immunized syngeneic mice that specifically recognized both adherent and suspension-growing S49 cells and detected differences in [35S]methionine-labeled antigens from these cells. Antibodies raised in rabbits against adherent cells recognized three proteins of 34,000, 61,000, and 72,000 apparent molecular weight in radiolabeled adherent cell extracts that are either absent or present in small amounts in extracts of suspension-growing tumorigenic S49 cells. These findings, taken together with our previous report (Hochman, J., A. Katz, E. Levy, and S. Eshel, 1981, Nature (Lond.), 290:248-249), suggest the S49 system as a novel system for studying growth control in malignant lymphoid cells.

Uteroferrin has N-asparagine-linked high-mannose-type oligosaccharides that contain mannose 6-phosphate

Uteroferrin is an iron-containing, progesterone-induced, acid phosphatase that is secreted in large amounts by the uterine endometrium of pigs. During pregnancy, it transports iron across the chorioallantois (placenta) for use in fetal hematopoiesis. In this paper, it is reported that uteroferrin synthesized by cultured endometrial explants possesses N-linked, high-mannose, oligosaccharide chains that contain 6- phosphomannose units. The latter is regarded as a possible recognition marker whereby acid hydrolases are targeted to the lysosome. On uteroferrin, however, the majority of the phosphate is in single diester linkages between the mannose and a covering N-acetylglucosamine. It is suggested that uteroferrin is a lysosomal enzyme that has assumed a role in iron transport and metabolism and is secreted because the covering N-acetylglucosamine is not removed.

Platelet-derived growth factor-modulated translatable mRNAs

The treatment of density-arrested BALB/c 3T3 cells with electrophoretically homogeneous or highly purified preparations of the platelet-derived growth factor (PDGF) stimulated the rapid and selective accumulation of several species of abundant mRNA identified by cell-free translation. These translatable mRNAs appeared long before entry into the S phase. Less PDGF was required for selective mRNA accumulation than for PDGF-modulated DNA synthesis. The translatable mRNAs also accumulated after addition of the epidermal growth factor but not after addition of insulin or platelet-poor plasma. Their selective accumulation was blocked by addition of actinomycin D. Three classes of PDGF-modulated mRNAs were defined. An early (primary) RNA appeared within 30 to 60 min of PDGF addition; its accumulation was not blocked by cycloheximide. Another early mRNA also appeared within 60 min, but treatment with both PDGF and cycloheximide was required for optimal accumulation. A third class, secondary RNAs, began to accumulate later at 90 to 120 min; the appearance of this class was inhibited by cycloheximide. One- and two-dimensional gel electrophoresis of translation products demonstrated that a spontaneously transformed BALB/c 3T3 (ST2-3T3) cell line, which does not require PDGF or epidermal growth factor for growth, constitutively accumulated the secondary growth factor-regulated mRNAs. The accumulation of these translatable mRNAs may be required for PDGF-modulated DNA synthesis.

Nicotinamide and its derivatives increase growth hormone and prolactin synthesis in cultured GH3 cells: role for ADP-ribosylation in modulating specific gene expression

To determine if changes in ADP-ribosylation of the chromosomal proteins can influence the expression of specific genes, the effects of compounds that influence this modification were investigated on the expression of the growth hormone (GH) and prolactin (Prl) genes in cultured rat pituitary (GH3) cells. The drugs tested, nicotinamide, N'-methylnicotinamide, 5-methylnicotinamide, 3-acetylpyridine, and 3-aminobenzamide, decrease ADP-ribosylation either by inhibiting (ADP-ribose)n synthetase and/or by decreaseing cellular levels of NAD+, the substrate for the enzyme. These drugs increased the synthesis of both GH and Prl and were synergistic in stimulating an increase in GH synthesis in response to triiodothyronine, a physiological regulator of GH synthesis. N'-methylnicotinamide, the most effective agent, was analyzed in detail; it increased the synthesis of both GH and Prl (maximally after 2 days) and increased their mRNAs in parallel; furthermore, this effect was reversible after drug removal. The effects of N'-methylnicotinamide were relatively specific for GH and Prl, since the synthesis of only a few other proteins was affected. These data suggest that changes in ADP-ribosylation can modulate the expression of specific genes.

Platelet-derived growth factor-modulated translatable mRNAs

The treatment of density-arrested BALB/c 3T3 cells with electrophoretically homogeneous or highly purified preparations of the platelet-derived growth factor (PDGF) stimulated the rapid and selective accumulation of several species of abundant mRNA identified by cell-free translation. These translatable mRNAs appeared long before entry into the S phase. Less PDGF was required for selective mRNA accumulation than for PDGF-modulated DNA synthesis. The translatable mRNAs also accumulated after addition of the epidermal growth factor but not after addition of insulin or platelet-poor plasma. Their selective accumulation was blocked by addition of actinomycin D. Three classes of PDGF-modulated mRNAs were defined. An early (primary) RNA appeared within 30 to 60 min of PDGF addition; its accumulation was not blocked by cycloheximide. Another early mRNA also appeared within 60 min, but treatment with both PDGF and cycloheximide was required for optimal accumulation. A third class, secondary RNAs, began to accumulate later at 90 to 120 min; the appearance of this class was inhibited by cycloheximide. One- and two-dimensional gel electrophoresis of translation products demonstrated that a spontaneously transformed BALB/c 3T3 (ST2-3T3) cell line, which does not require PDGF or epidermal growth factor for growth, constitutively accumulated the secondary growth factor-regulated mRNAs. The accumulation of these translatable mRNAs may be required for PDGF-modulated DNA synthesis.

Tumor promoters increase the synthesis of a 32,000-dalton protein in BALB/c 3T3 cells

The effect of 12-O-tetradecanoylphorbol 13-acetate (TPA), a potent tumor promoter, on the synthesis of proteins in BALB/c 3T3 mouse fibroblasts has been studied. When [35S]methionine-labeled proteins synthesized after the addition of TPA were analyzed by one- or two-dimensional polyacrylamide gel electrophoresis, the increased synthesis of a 32,000-dalton protein (designated p32) was noted as one of the earliest changes. The synthesis of p32 increased approximately 2-fold within 2 hr at a promoter concentration of 20 ng/ml. Phorbol 12,13-didecanoate, another potent tumor promoter, showed the same effect as TPA, whereas 4-O-methyl-TPA, which has little promoting activity, did not enhance the synthesis of p32 at the same concentration but did effect a slight increase at 1 microgram/ml. p32 differed immunologically from a major excreted protein discovered by Gottesman [Gottesman, M. M. (1978) Proc. Natl. Acad. Sci. USA 75, 2767-2771]. The increased rate of the synthesis of p32 was considered to be regulated at the transcriptional level, because the increase in synthesis of p32 was inhibited by actinomycin D, and TPA-treated cells were shown to contain a higher level of translatable mRNA coding for p32 than do control cells. A possible relationship between the increase in p32 synthesis and transformation is discussed.