Multilineage differentiation of adult human bone marrow progenitor cells transduced with human papilloma virus type 16 E6/E7 genes

We have established a new adult human bone marrow-derived cell line hMPC 32F, stably transduced with human papilloma virus type 16 E6/E7 genes, that displays mesenchymal multilineage differentiation ability in vitro. The hMPC 32F cells exhibited a population doubling time of 22 h and have been maintained in culture for about 20 passages. When cultured in conditions promoting osteogenic, adipogenic, or chondrogenic differentiation, hMPC 32F cells expressed mature differentiated phenotypes. These include (1) osteoblastic phenotype characterized by upregulated alkaline phosphatase (ALP) expression and extracellular matrix mineralization, (2) adipocytic phenotype with the presence of intracellular lipid droplets, and (3) chondrocytic phenotype of round cells surrounded by a sulfated proteoglycan-rich matrix. In addition, the hMPC 32F cells expressed differentiation lineage-specific genes, as detected by RT-PCR. Furthermore, osteogenic and adipogenic cultures responded to regulatory factors such as transforming growth factor-beta1 (TGF-beta1) and 1alpha, 25-dihydroxyvitamin D3 (1,25(OH)2D3). Thus, continuous treatment of osteogenic cultures for 2 weeks with TGF-beta1 decreased ALP activity and mRNA expression and inhibited osteocalcin mRNA expression and matrix mineralization, whereas l,25(OH)2D3 had an additive, stimulatory effect. In adipogenic cultures, treatment with TGF-beta1 for 2 weeks markedly inhibited adipogenesis whereas 1,25(OH)2D3 had no obvious effect. Finally, clonal analysis of hMPC 32F cells revealed a high percentage of multipotent clones, although clones of more restricted differentiation potential were also present. These characteristics of the hMPC 32F cell line suggest their pluripotent, progenitor, and nontransformed nature and indicate their potential application for studying the mechanisms governing developmental potential of adult human bone marrow mesenchymal progenitor cells.

p38 MAP kinase regulation of AP-2 binding in TGF-beta1-stimulated chondrogenesis of human trabecular bone-derived cells

Collagenase-treated, explanted human trabecular-bone chips are an excellent source of osteoblast-like cells. We have recently shown the multiple differentiation potential of these cells; in addition to osteogenesis and adipogenesis, these cells also undergo chondrogenesis when maintained as high-density pellet cultures (250,000 cells/pellet) in a serum-free, chemically defined medium stimulated with TGF-beta1 (10 ng/mL). In this investigation, we have analyzed how transactivating nuclear transcription factors, specifically AP-2 and SP-1, may interact with common cis-acting elements found in the regulatory region of cartilage-specific genes as part of the signal transduction mechanism of TGF-beta1 and p38 during chondrogenesis of human trabecular bone-derived multipotential cells. Both TGF-beta1 stimulation and p38 MAP kinase activation affect the binding of AP-2 as well as SP-1 to oligonucleotides with sequence similarity to the overlapping AP-2/SP-1 sites found in the putative 52-bp immediate upstream regulatory region and the 5'-untranslated region of the human aggrecan gene. Electrophoretic mobility shift assays show that TGF-beta1 treatment of the bone-derived cells inhibits AP-2 DNA binding but enhances the DNA binding ability of SP-1. Additionally, treatment of these TGF-beta1-stimulated cells with p38 MAP kinase inhibitor, SB203580, rescued the AP-2 DNA binding but did not affect SP-1 DNA binding. These findings indicate that AP-2 DNA binding is the target of both TGF-beta1 and p38 MAP kinase signaling pathways and suggest a possible signal transduction cascade whereby TGF-beta1 induction of chondrogenesis involves the activation of p38 MAP kinase and the subsequent inhibition of DNA binding by AP-2, thereby preventing the transcriptional repression of the aggrecan gene.

Three-dimensional cartilage formation by bone marrow-derived cells seeded in polylactide/alginate amalgam

Bone marrow-derived cells are considered as candidate cells for cartilage tissue engineering by virtue of their ability to undergo chondrogenesis in vitro when cultured in high density or when embedded within a three-dimensional matrix in the presence of growth factors. This study evaluated the potential of human bone marrow-derived cells for cartilage tissue engineering by examining their chondrogenic properties within a three-dimensional amalgam scaffold consisting of the biodegradable polymer, poly-L-lactic acid (PLA) alone, and with the polysaccharide gel, alginate. Cells were suspended either in alginate or medium and loaded into porous PLA blocks. Alginate was used to improve cell loading and retention within the construct, whereas the PLA polymeric scaffold provided appropriate mechanical support and stability to the composite culture. Cells seeded in the PLA/alginate amalgams and the plain PLA constructs were treated with different concentrations of recombinant human transforming growth factor-beta1 (TGF-beta 1) either continuously (10 ng/mL) or only for the initial 3 days of culture (50 ng/mL). Chondrogenesis was assessed at weekly intervals with cultures maintained for up to 3 weeks. Histological and immunohistochemical analysis of the TGF-beta 1-treated PLA/alginate amalgam and PLA constructs showed development of a cartilaginous phenotype from day 7 to day 21 as demonstrated by colocalization of Alcian blue staining with collagen type II and cartilage proteoglycan link protein. Expression of cartilage specific genes, including collagen types II and IX, and aggrecan, was detected in TGF-beta 1-treated cultures by reverse transcription-polymerase chain reaction analysis. The initiation and progression of chondrogenic differentiation within the polymeric macrostructure occurred with both continuous and the initial 3-day TGF-beta 1 treatment regimens, suggesting that key regulatory events of chondrogenesis take place during the early period of cell growth and proliferation. Scanning electron microscopy revealed abundant cells with a rounded morphology in the PLA/alginate amalgam. These findings suggest that the three-dimensional PLA/alginate amalgam is a potential candidate bioactive scaffold for cartilage tissue engineering applications.

Transcriptional and posttranscriptional regulation of proteoglycan gene expression

Proteoglycans are among the most complex and sophisticated molecules of mammalian systems in terms of their protein and carbohydrate moieties. These macromolecules are in a continuous interplay with each other and the cell surface signal-transducing pathways, some of which are beginning to be elucidated. Because of their domain structure, catalytic potential, and diversity, these molecules appear to be designed for integrating numerous signaling events. For example, some proteoglycans interact with hyaluronan and lectins, thereby linking cell surfaces and distant matrix molecules. Some interact with collagen during the complex process of fibrillogenesis and regulate this biological process fundamental to animal life. Others interact with growth factors and serve as depot available during growth or tissue remodeling. In this review, we center on the most recent developments of proteoglycan biology, focusing primarily on genomic organization and transcriptional and posttranscriptional control. We discuss only those proteoglycans whose gene and promoter elements have been characterized and proved to be functional. When possible, we correlate the effects of growth factors and cytokines on proteoglycan gene expression with the topology of cis-acting elements in their genomic control regions. The analysis leads to a comprehensive critical appraisal of the principles that underlie the regulation of proteoglycan gene expression and to the delineation of common regulatory mechanisms.

Tumorigenic conversion of p53-deficient colon epithelial cells by an activated Ki-ras gene

Distinct genetic abnormalities (loss-of-function mutations of APC and p53 and oncogenic activation of Ki-ras) are associated with specific stages of the sporadic, most common types of colorectal tumors. However, the inability to maintain primary colon epithelial cells in culture has hindered the analysis of the pathogenetic role of these abnormalities in colorectal tumorigenesis. We have now established primary cultures of epithelial cells from the colon crypts of p53-deficient mice; these cells are nontumorigenic as indicated by their failure to form colonies in soft agar and to grow as tumors in immunodeficient SCID mice and in immunocompetent syngeneic hosts. Upon ectopic expression of an activated Ki-ras gene, p53-deficient colon epithelial cells form colonies in soft agar and highly invasive subcutaneous tumors in both immunodeficient and immunocompetent mice. Ectopic expression of wild-type p53, but not of a DNA-binding-deficient mutant, markedly suppressed the colony-forming ability of the Ki-ras-transformed p53-deficient epithelial cells. Together, these findings establish a functional synergism in colorectal tumorigenesis dependent on the effects of an oncogenic Ki-ras in a p53-deficient background. This model of tumorigenic conversion of colon epithelial cells might be useful to identify genetic changes associated with disease progression and to evaluate the therapeutic response to conventional and novel anticancer drugs.

Mice that lack thrombospondin 2 display connective tissue abnormalities that are associated with disordered collagen fibrillogenesis, an increased vascular density, and a bleeding diathesis

Thrombospondin (TSP) 2, and its close relative TSP1, are extracellular proteins whose functions are complex, poorly understood, and controversial. In an attempt to determine the function of TSP2, we disrupted the Thbs2 gene by homologous recombination in embryonic stem cells, and generated TSP2-null mice by blastocyst injection and appropriate breeding of mutant animals. Thbs2-/- mice were produced with the expected Mendelian frequency, appeared overtly normal, and were fertile. However, on closer examination, these mice displayed a wide variety of abnormalities. Collagen fiber patterns in skin were disordered, and abnormally large fibrils with irregular contours were observed by electron microscopy in both skin and tendon. As a functional correlate of these findings, the skin was fragile and had reduced tensile strength, and the tail was unusually flexible. Mutant skin fibroblasts were defective in attachment to a substratum. An increase in total density and in cortical thickness of long bones was documented by histology and quantitative computer tomography. Mutant mice also manifested an abnormal bleeding time, and histologic surveys of mouse tissues, stained with an antibody to von Willebrand factor, showed a significant increase in blood vessels. The basis for the unusual phenotype of the TSP2-null mouse could derive from the structural role that TSP2 might play in collagen fibrillogenesis in skin and tendon. However, it seems likely that some of the diverse manifestations of this genetic disorder result from the ability of TSP2 to modulate the cell surface properties of mesenchymal cells, and thus, to affect cell functions such as adhesion and migration.

Structural and functional characterization of the human perlecan gene promoter. Transcriptional activation by transforming growth factor-beta via a nuclear factor 1-binding element

Perlecan, a modular heparan sulfate proteoglycan of basement membranes and cell surfaces, plays a crucial role in regulating the assembly of extracellular matrices and the binding of nutrients and growth factors to target cells. To achieve a molecular understanding of perlecan gene regulation, we isolated the 5'-flanking region and investigated its functional promoter activity and its response to cytokines. Transient cell transfection assays, using plasmid constructs harboring the perlecan promoter linked to the chloramphenicol acetyltransferase reporter gene, demonstrated that the largest approximately 2.5-kilobase construct contained maximal promoter activity. This promoter region was functionally active in a variety of cells of diverse histogenetic origin, thus corroborating the widespread expression of this gene product. Stepwise 5' deletion analyses demonstrated that the -461-base pair (bp) proximal promoter retained approximately 90% of the total activity, and internal deletions confirmed that the most proximal sequence was essential for proper promoter activity. Nanomolar amounts of transforming growth factor-beta induced 2-3-fold perlecan mRNA and protein core levels in normal human skin fibroblasts, and this induction was transcriptionally regulated; in contrast, tumor necrosis factor-alpha had no effect and was incapable of counteracting the effects of TGF-beta. Using additional 5' deletions and DNase footprinting analyses, we mapped the TGF-beta responsive region to a sequence of 177 bp contained between -461 and -285. This region harbored a 14-bp element similar to a TGF-beta-responsive element present in the promoters of collagen alpha1(I), alpha2(I), elastin, and growth hormone. Electrophoretic mobility shift assays and mutational analyses demonstrated that the perlecan TGF-beta-responsive element bound specifically to TGF-beta-inducible nuclear proteins with high affinity for NF-1 member(s) of transcription factors.

Targeted disruption of decorin leads to abnormal collagen fibril morphology and skin fragility

Decorin is a member of the expanding group of widely distributed small leucine-rich proteoglycans that are expected to play important functions in tissue assembly. We report that mice harboring a targeted disruption of the decorin gene are viable but have fragile skin with markedly reduced tensile strength. Ultrastructural analysis revealed abnormal collagen morphology in skin and tendon, with coarser and irregular fiber outlines. Quantitative scanning transmission EM of individual collagen fibrils showed abrupt increases and decreases in mass along their axes. thereby accounting for the irregular outlines and size variability observed in cross-sections. The data indicate uncontrolled lateral fusion of collagen fibrils in the decorindeficient mice and provide an explanation for the reduced tensile strength of the skin. These findings demonstrate a fundamental role for decorin in regulating collagen fiber formation in vivo.

Characterization of the complete genomic structure of the human WNT-5A gene, functional analysis of its promoter, chromosomal mapping, and expression in early human embryogenesis

We report the complete genomic organization of the human WNT-5A gene, which encodes a cysteine-rich growth factor involved in cell-cell signaling during growth and differentiation. The gene comprises five exons with the terminal exon coding for a large 3'-untranslated region of approximately 6.5 kilobase pairs and utilizes multiple polyadenylation signals to generate at least four discrete transcripts. We discovered a new leader exon interrupted by a 411-base pair intron that was retained in our original cDNA cloning. The promoter region was located in a GpC-rich island and harbored numerous cis-acting elements including several GC boxes and Sp1, AP1, and AP2 binding motifs. It lacked TATA or CAAT boxes typical of housekeeping and growth factor genes. In support of this, primer extension revealed extension two transcription start sites. Transient cell transfection assays showed functional promoter activity for the 3.9-kilobase pair 5'-flanking region. Interestingly, internal and 5' deletions revealed tha the distal promoter was not required for full transcriptional activity and that the first 631 base pairs of WNT-5A harbored the strongest promoter activity. Using a panel of rodent-human hybrid DNAs carrying portions of chromosome 3p, we mapped the gene to 3p14.2-p21.1, between a constitutional and a familial renal cell carcinoma-associated translocation. In situ hybridization analyses of early human embryos at 28-42 days of gestation revealed that WNT-5A transcripts were not restricted to the developing brain and limbs but were also observed in the mesenchyme bordering the pharyngeal clefts and pouches and in the developing gonads and kidneys. The relatively high expression in the celomic epithelium and in the precursors of follicles and seminiferous tubules suggest a novel role for WNT-5A in germ-cell differentiation. This study provides the molecular basis for discerning the regulation of the WNT-5A gene and offers the opportunity to investigate genetic disorders linked to this important gene.

The murine biglycan: complete cDNA cloning, genomic organization, promoter function, and expression

Biglycan is a ubiquitous chondroitin/dermatan sulfate proteoglycan that belongs to a growing family of proteins harboring leucine-rich repeats. We have cloned and sequenced the cDNA containing the complete murine biglycan, elucidated its genomic organization, and demonstrated functional promoter activity of its 5' flanking region. The deduced biglycan protein core was highly conserved across species. However, the mouse biglycan (Bgn) gene was significantly larger than the human counterpart, primarily because of a large > 4.5-kb intron between exons 1 and 2. The mouse Bgn gene spanned over 9.5 kb of continuous DNA and comprised 8 exons, with a perfectly conserved intron/exon organization vis-á-vis the human counterpart. The promoter region was enriched in GC dinucleotide and contained numerous cis-acting elements including binding sites for SP-1, AP-1 and AP-2 factors. It lacked TATA and CAAT boxes typical of housekeeping genes. In support of this, primer extension analysis showed the existence of multiple transcription start sites. Transient cell transfection assays with a construct comprising the 548 bp upstream of the major transcription start site fused to the chloramphenicol acetyl transferase reporter gene showed functional promoter activity. Internal and 5' deletion constructs showed that the distal promoter of the Bgn gene was required for full transcriptional activity. In contrast to the homologous proteoglycan decorin, the highest expression of biglycan mRNA was observed in lung, liver, and spleen of adult mouse and the lowest in skin, heart, and kidney. These results will be useful for the study of biglycan gene regulation and for the generation of mice with targeted null mutation of the Bgn gene.

Aberrant expression of the growth factor Wnt-5A in human malignancy

The Wnt-5A gene codes for a secreted cysteine-rich growth factor that mediates cell to cell signaling via a paracrine mechanism during development and ontogeny. We have recently determine the genomic organization and chromosomal mapping of the human Wnt-5A, and observed distinct patterns of expression in developing human embryos. In this report, we have performed a detailed expression analysis of 100 adult human tissues and tumors and 10 human cell lines. Our data show a widespread expression of Wnt-5A in adult tissues and cells, and aberrant mRNA levels in lungs, breast, and prostate carcinomas and in melanomas. The up-regulation of Wnt-5A in human malignancy was not due to either gene rearrangement or amplification. These findings document an abnormal expression of this growth factor in malignancy and implicate Wnt-5A in the genesis of human cancer.

Structural and functional characterization of the human decorin gene promoter. A homopurine-homopyrimidine S1 nuclease-sensitive region is involved in transcriptional control

Decorin is a leucine-rich, chondroitin/dermatan sulfate proteoglycan which binds collagen and growth factors. We have recently completed the genomic organization of human decorin and discovered two alternatively spliced leader exons, designated exon Ia and Ib, in the 5'-untranslated region. Initial analysis of the sequences upstream to these two exons showed that promoter Ia contained only two GC boxes while promoter Ib contained a CAAT and two TATA boxes in close proximity to the transcription start site. To determine if these 5'-flanking sequences exhibited promoter activity, chimeric chloramphenicol acetyltransferase expression plasmids containing the promoter region of either exon Ia or Ib were transfected into HeLa and MG-63 osteosarcoma cells. The results showed that only the region flanking exon Ib was functional. In vitro transcription assay generated two transcripts of 92 and 82 base pairs (bp) indicating that both TATA boxes could be used. Using stepwise 5' deletion analysis we found that the minimum promoter region at -140 bp from the transcription start site, which contained only the CAAT and the two TATA boxes, exhibited strong promoter activity. When a larger construct containing an additional 800 bp of upstream region was tested, a significant increase in transcriptional activity was observed. Interestingly, this promoter region contained several putative binding sites for ubiquitous factors (AP1, AP5, and NF-kappa B) and for transforming growth factor-beta and a 150-bp homopurine/homopyrimidine element with several mirror repeats. When contained in a supercoiled plasmid, this sequence exhibited sensitivity to endonuclease S1, an enzyme that preferentially digests single-stranded DNA. Precise S1 mapping, obtained by direct sequencing of nine distinct S1-generated clones, revealed that in all cases the borders of the sensitive sequence resided within the pur/pyr segment. We propose that this region of the promoter could adopt an intramolecular hairpin triplex structure in vivo and may play a role in the chromatin organization at the decorin gene locus. In addition, this region was able to up-regulate a minimal heterologous promoter in transient transfection assays. The results show that the structure of the decorin gene promoter is different from that of any other proteoglycan promoter characterized so far and indicate that the pur/pyr segment plays a role in the regulation of gene transcription.

The human decorin gene: intron-exon organization, discovery of two alternatively spliced exons in the 5' untranslated region, and mapping of the gene to chromosome 12q23

Decorin is a chondroitin/dermatan sulfate proteoglycan expressed by most vascular and avascular connective tissues and, because of its ability to interact with collagen and growth factors, has been implicated in the control of matrix assembly and cellular growth. To understand the molecular mechanisms involved in regulating its tissue expression, we have isolated a number of genomic clones encoding the complete decorin gene. The human decorin gene spans over 38 kb of continuous DNA sequence and contains eight exons and very large introns, two of which are 5.4 and > 13.2 kb. We have discovered two alternatively spliced leader exons, exons Ia and Ib, in the 5' untranslated region. These exons were identified by cloning and sequencing cDNAs obtained by polymerase chain reaction amplification of a fibroblast cDNA library. Using Northern blotting or reverse transcriptase PCR, we detected the two leader exons in a variety of mRNAs isolated from human cell lines and tissues. Interestingly, sequences highly (74-87%) homologous to exons Ia and Ib are found in the 5' untranslated region of avian and bovine decorin, respectively. This high degree of conservation among species suggests regulatory functions for these leader exons. In the 3' untranslated region there are several polyadenylation sites, and at least two of these sites could give rise to the transcripts of approximately 1.6 and approximately 1.9 kb, typically detected in a variety of tissues and cells. Using a genomic clone as the labeled probe and in situ hybridization of human metaphase chromosomes, we have mapped the decorin gene to the discrete region of human chromosome 12q23. This study provides the molecular basis for discerning the transcriptional control of the decorin gene and offers the opportunity to investigate genetic disorders linked to this important human gene.

Establishment of a cell line from the EHS tumor: biosynthesis of basement membrane constituents and characterization of a hybrid proteoglycan containing heparan and chondroitin sulfate chains

We have established a continuous cell line from the Engelbreth-Holm-Swarm (EHS) tumor, a transplantable murine neoplasm that has been extensively utilized to investigate basement membrane constituents. The EHS-derived cells, designated BAM cells, have been subcultured for over 40 passages and have maintained phenotypic and biological properties of the parent EHS tumor cells. BAM cells have retained an epithelioid morphology and the ability to induce EHS-like tumors in mice. Biochemical and immunochemical studies demonstrated that BAM cells synthesize laminin A and B chains, collagen type IV, entactin and the basement membrane specific heparan sulfate proteoglycan. Interestingly, the proteoglycan synthesized by BAM cells was a hybrid molecule containing 2-3 heparan sulfate chains of 25-35 kDa and 1 chondroitin sulfate chain of approximately 17 kDa attached to a 400-kDa protein core. This cell line will be useful to investigations concerning biosynthesis of basement membrane constituents and will be a valuable source of extracellular matrix for testing cellular properties such as attachment, locomotion and differentiation.

Functional differentiation of mouse uterine epithelial cells grown on collagen gels or reconstituted basement membranes

Epithelial cells were isolated from mouse endometrium and cultured on two types of extracellular matrix, namely, rat-tail collagen (type I) gels and basement membrane extract (BME) derived from the Engelbreth-Holm-Swarm murine sarcoma. Cell attachment in serum-free medium during the initial 24 h after seeding was approximately twofold higher on BME compared with collagen type I. Addition of serum to the medium enhanced cell attachment on both matrices. On both collagen and BME, uterine cells grew as smooth-bordered colonies, and within a week of culture the cells became cuboidal to columnar in shape. Electron microscopy revealed the presence of apical microvilli associated with a glycocalyx, junctional complexes, tonofilaments, short strands of undilated endoplasmic reticulum, Golgi complex, and lipid droplets. However, cells on BME showed a higher degree of differentiation as assessed by occasional formation of small patches of basement membranelike structure subjacent to the flattened basal surface and formation of glandlike structures within the matrix. Proliferation of these cells as measured by radioactive thymidine incorporation into DNA was increased threefold by addition of epidermal growth factor (EGF) and insulin to the medium, but was not changed by 17 beta-estradiol. The expression of progesterone receptors by uterine epithelial cells grown on both matrices was doubled by addition of EGF and estradiol to the medium.

A 14-kilodalton selenium-binding protein in mouse liver is fatty acid-binding protein

In a previous study, we purified three selenium-binding proteins (molecular masses 56, 14, and 12 kDa) from mouse liver using column chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The aim of the present study was to determine the amino acid sequence of the 14-kDa protein thereby establishing any relationship with known proteins. Although the amino terminus of the 14-kDa protein was blocked, separate in situ digestions of the protein with endoproteinases Glu-c and Lys-c gave overlapping peptides that provided a continuous sequence of 93 amino acids. This sequence exhibited a 92.5% sequence homology with rat liver fatty acid-binding protein. In situ enzymatic digestion and partial sequencing of a 12-kDa selenium-binding protein revealed identical homology to the 14-kDa protein. The 14-kDa protein bound specifically to an oleate-affinity column from which the protein and 75Se coeluted. Delipidation or sodium dodecyl sulfate treatment failed to remove 75Se from the protein, indicating that the selenium moiety was tightly bound to the protein. These observations confirm that the mouse liver selenium-binding 14-kDa protein is a fatty acid-binding protein. The nature of the selenium linkage to the protein still needs to be explored.

Clonal populations of the mouse mammary cell line, COMMA-D, which retain capability of morphogenesis in vivo

Clonal populations were isolated from the mouse mammary cell line, COMMA-D, by transfection with a dominant-selectable gene, pSV2Neo, which confers resistance to the antibiotic, G418. Seven of twenty-four clones isolated retained the ability of the parental line to repopulate cleared mammary fat pads in vivo as ductal-alveolar hyperplasias. Two sublines designated CDNR2 and CDNR4 retained hyperplastic growth potential after multiple passages in vitro with low incidence of tumor formation. A third subpopulation, CDNR1, contained a single integration site for the pSV2Neo plasmid indicating a bonafide clonal origin for this subline. CDNR1 cells displayed heterogeneous growth phenotypes in vivo including hyperplasia, adenocarcinoma, and bone formation. Functional differentiation of CDNR1 cells organized as alveolarlike structures in vivo or on floating collagen gels in vitro was observed as determined by immunoperoxidase staining for the milk-specific protein, casein. Overall, the results indicate that a subset of cells from the COMMA-D cell line may be functionally analogous to stem cells existing in the mammary gland.

Evidence for two selenium-binding proteins distinct from glutathione peroxidase in mouse liver

Labeling studies with 75selenium (75Se) have suggested the existence of selenium-binding proteins in addition to glutathione peroxidase (GSH-Px) in rodent tissues. Three selenium-binding proteins of apparent mol. wt 56, 14 and 12K on SDS-PAGE were isolated from mouse liver using Sephadex G-150 and DEAE-Sephadex chromatography. The proteins were electroeluted from SDS-PAGE gels and injected into rabbits to elicit antibodies. Western immunoblot experiments indicated that the 56K protein was distinct from the 14 and 12K proteins. The latter two proteins appeared to be immunologically related, perhaps as differentially processed variants. The 56 and 14/12K proteins appeared to be distinct from GSH-Px and the 57K plasma selenium-binding proteins. These results indicate that the mouse liver contains at least two selenium-binding proteins distinct from GSH-Px. The existence of the antibodies should permit experiments which help to examine the role of these proteins in the biological function of selenium in mammals.

Distribution of selenoproteins in mouse mammary epithelial cells in vitro and in vivo

Resolution of selenium-containing proteins synthesized by mouse mammary gland cells was achieved using the technique of two-dimensional gel electrophoresis. Radioactive selenium as H2[75Se]O3 was incorporated into relatively few proteins within mammary gland cells maintained in vitro and cells of mammary gland tissue in vivo. The pattern of selenoproteins obtained was identical qualitatively between a nontumorigenic differentiated cell line, COMMA-D, and a tumorigenic cell line, MOD. Eleven selenoproteins ranging in molecular weight from 12,000-78,000 were detected and a total of 25 spots were visible indicating charge heterogeneity of some of the proteins. A major selenoprotein (Mr 26,000) migrated identically with the subunit form of glutathione peroxidase, a well-characterized protein containing four selenocysteine residues. Other major selenoproteins had molecular weights of 58,000, 22,000, 18,000, and 14,000. Analysis of the total cellular protein extract and of each of the five major proteins indicated that selenium was incorporated as selenocysteine in the proteins. Incorporation of selenium as selenomethionine into cellular proteins was detected only when selenomethionine was provided in the culture medium. Cleavage of 75Se-labeled proteins with N-chlorosuccinimide produced polypeptides of different molecular weights indicating that the Mr 58,000, 26,000, and 22,000 selenoproteins were dissimilar in the amino acid sequences containing the selenoamino acid. The pattern of selenoproteins of mammary gland cells in vivo was similar to that obtained for cells in culture and most other tissues in vivo. These results provide evidence for the presence of multiple selenium-containing proteins in mammary epithelial cells. The possible significance of these proteins in selenium-mediated inhibition of cell growth awaits future clarification.

Epithelial mouse mammary cell line exhibiting normal morphogenesis in vivo and functional differentiation in vitro

An epithelial cell line, designated COMMA-1D, was derived from mammary tissue of BALB/c mice in the middle of pregnancy. This line, in continuous cell culture for 12 months, exhibits several characteristics distinctive of normal mammary epithelial cells, including induction of casein synthesis in vitro and normal duct morphogenesis in the cleared mammary fat pads of syngeneic mice. The cells also form domes in high density culture and are positive for keratin intermediate filaments by indirect immunofluorescence. COMMA-1D cells have a near diploid number of chromosomes and do not grow in suspension culture or produce tumors in syngeneic hosts. This cell line should prove useful for studies examining the regulation of normal cellular differentiation of mammary cells as well as transformation of epithelial cells to the preneoplastic and neoplastic phenotypes.

Immunochemical localization of metallothionein in rat liver and kidney

An indirect immunoperoxidase staining technique was employed to localize the heavy metal binding protein, metallothionein, in rat liver and kidney. Immunostaining for metallothionein was observed in all hepatocytes and most renal tubular cells. This protein was not detectable, however, in cell types such as endothelial or connective tissue cells, indicating that metallothionein synthesis or accumulation is tissue- and cell-type specific. Hepatocytes from cadmium-exposed animals showed increased staining for metallothionein. The presence of metallothionein was also seen extracellularly within the liver sinusoids and renal tubules in both normal and cadmium-exposed animals, suggesting transport and excretion, respectively, of this protein.

Glycosaminoglycan synthesis by subpopulations of epithelial cells from a mammary adenocarcinoma

Glycosaminoglycan synthesis by two subpopulations of a mouse mammary tumor cell line was compared. The two sublines express distinctly different growth characteristics in vitro and in vivo which indicate differences in growth regulation. Newly made glycosaminoglycans were recovered from the culture media, the cell surfaces, and residual cellular material. The cell population which grows more aggressively in vivo (+SA subline, a subline that grows in soft agarose) incorporated about 8 times more [14C]glucosamine per cell into total glycosaminoglycans than did the slower-growing population (-SA subline, which does not grow in soft agarose). Appropriate control experiments indicated that the apparent difference in rates of synthesis was not due to discrepancies in glucosamine uptake. The main residual cellular molecule labeled was heparan sulfate, but the predominant molecule at the cell surface and in the culture fluid was hyaluronic acid. Overall, +SA cells synthesized more hyaluronic acid and -SA cells synthesized more heparan sulfate; in both cell populations, these two molecules accounted for about 90% of total glycosaminoglycans produced.

Immunochemical detection of metallothionein in specific epithelial cells of rat organs

The distribution of a heavy metal binding protein, metallothionein, was studied immunocytochemically by using antimetallothionein antibody and the immunoperoxidase staining technique on histological sections of liver, kidney, intestine, lung, and testis from cadmium-treated rats. These tissues either accumulate heavy metals (e.g., liver, kidney, and testis) or are exposed to metal by ingestion or inhalation (intestine and lung). Staining for metallothionein was observed intracellularly in epithelial parenchymal cells of the liver and kidney; all hepatocytes and most renal tubular cells stained for the protein. Accumulation of metallothionein was not seen in connective tissue cells surrounding either blood vessels or renal tubules. Extracellular localization of metallothionein was also observed in the liver sinusoids and within the lumina of the renal tubules, suggesting a metal transport or excretory function for this protein. Surface columnar epithelial cells of the intestinal villi indicated the presence of metallothionein but connective tissue cells of the lamina propria were negative for the protein. The granular secretory Paneth cells of the small intestine also stained strongly for metallothionein as did respiratory epithelial cells of the lung. In the testis, metallothionein was detected in the Sertoli cells and interstitial cells but not within the spermatogonia. Sertoli cells are closely associated with the developing spermatogonia and appear to serve a nutritive role in spermatogenesis. Because of the secretory, absorptive, or nutritive function of the metallothionein-localizing cells in the organs studied, we suggest that metallothionein may be involved in metal storage or transport in addition to its commonly proposed detoxification role.

Invasion of endothelial cell monolayers on collagen gels by cells from mammary tumor spheroids

Suspensions of multicellular mammary tumor spheroids (MTS) were allowed to interact with confluent monolayers of endothelial cells cultured on top of collagen gels. A number of early and late interactions between MTS and endothelial cell monolayers occurred. The early phase was characterized by the attachment of MTS to the culture and retraction of endothelial cells near the attached spheroid. Only these early interactions were observed up to 8 hr after addition of the MTS. Thereafter, cells from MTS migrated away from the spheroids. The late phase was characterized by cells of the MTS spreading on top of the collagen gel, moving underneath the edges of the endothelial cells, extending as cords of cells on top of the endothelium, and invading into the collagen matrix. During both the early and late phases, cells from the MTS were distinguished from the endothelial cells by the intense staining of tumor cells with Giemsa and the presence of microvilli found only on tumor cells. Attached MTS, which were noted at 2 hr after addition (the earliest time examined), increased in number for up to 12 hr. Polyionic compounds known to affect cell surface charge were found to reduce the numbers of attached MTS. The results demonstrate that the system described in this study can provide a useful model for analyzing the mechanisms of tumor embolus interaction with blood vessel walls.

New cell line. Epithelial cell line and subline established from premalignant mouse mammary tissue

A cell line and subline with epithelial characteristics were established from mouse mammary hyperplastic alveolar nodules (HAN). The cells do not grow in suspension cultures in vitro or form tumors in vivo. The cells do produce significant amounts of C-type and A-type virus and low amounts of plasminogen activator.