Scanning electron microscopic observations on cells grown in vitro. VII. HeLa cells can penetrate Wi38 fibroblasts

When HeLa cells are seeded on a preexisting monolayer of Wi38 fibroblasts, the HeLa cells "try" to get into direct contact with the glass substrate. Once on top of a flat fibroblast the HeLa cell can either migrate from the fibroblast to settle between two fibroblasts on glass or somehow stimulate the underlying cells to retract. In a few cases the HeLa cell directly penetrates the fibroblast, "melting" its way through the underlying cell. The mechanism of this phenomenon which has never been described before in this combination is discussed.     

Role of IIb-IIIa-like glycoproteins in cell-substratum adhesion of human melanoma cells

The platelet fibrinogen receptor, glycoprotein complex IIb-IIIa, was isolated from human platelets by lectin and monoclonal antibody affinity chromatography and a polyclonal antiserum (anti-IIb-IIIa) was generated and used to probe for the presence and function of IIb-IIIa-like molecules in two adherent human cell lines. Both C32 melanoma cells and WI38 fibroblasts expressed a IIb-IIIa-like complex on their surface as indicated by immunoprecipitation of detergent extracts of surface radiolabeled cells. When added to cells plated in medium containing 10% serum, the anti-IIb-IIIa antiserum perturbed the adhesion of C32 melanoma cells, but not of WI38 fibroblasts. In a serum-free system, anti-IIb-IIIa antibodies inhibited attachment and spreading of C32 cells to fibrinogen, vitronectin, and fibronectin adsorbed to glass. Anti-IIb-IIIa had no effect on the attachment and spreading of WI38 cells to the extracellular matrix proteins, however. Thus, the IIb-IIIa-like complex appears to play a predominant role in cell-substratum adhesion of C32 cells, but not WI38 cells, and may result from the fact that, on a protein basis, the C32 melanoma cells express approximately 3 times more complex on their surface than do WI38 fibroblasts. The results suggest that the relative abundance of a particular adhesion receptor on the cell surface may govern its importance to cell-substratum adhesion.     

Fibroblasts share mesenchymal phenotypes with stem cells, but lack their differentiation and colony-forming potential

Background information. Although MSCs (mesenchymal stem cells) and fibroblasts have been well studied, differences between these two cell types are not fully understood. We therefore comparatively analysed antigen and gene profiles, colony‐forming ability and differentiation potential of four human cell types in vitro: commercially available skin‐derived fibroblasts [hSDFs (human skin‐derived fibroblasts)], adipose tissue‐derived stem cells [hASCs (human adipose tissue‐derived stem cells)], embryonic lung fibroblasts (WI38) and dermal microvascular endothelial cells [hECs (human dermal microvascular endothelial cells)]. Results. hSDFs, hASCs and WI38 exhibited a similar spindle‐like morphology and expressed same antigen profiles: positive for MSC markers (CD44, CD73 and CD105) and fibroblastic markers [collagen I, HSP47 (heat shock protein 47), vimentin, FSP (fibroblast surface protein) and αSMA (α smooth muscle actin)], and negative for endothelial cell marker CD31 and haemopoietic lineage markers (CD14 and CD45). We further analysed 90 stem cell‐associated gene expressions by performing real‐time PCR and found a more similar gene expression pattern between hASCs and hSDFs than between hSDFs and WI38. The expression of embryonic stem cell markers [OCT4, KLF4, NANOG, LIN28, FGF4 (fibroblast growth factor 4) and REST] in hASCs and hSDFs was observed to differ more than 2.5‐fold as compared with WI38. In addition, hSDFs and hASCs were able to form colonies and differentiate into adipocytes, osteoblasts and chondrocytes in vitro, but not WI38. Moreover, single cell‐derived hSDFs and hASCs obtained by clonal expansion were able to differentiate into adipocytes and osteoblasts. However, CD31 positive hECs did not show differentiation potential. Conclusions. These findings suggest that (i) so‐called commercially available fibroblast preparations from skin (hSDFs) consist of a significant number of cells with differentiation potential apart from terminally differentiated fibroblasts; (ii) colony‐forming capacity and differentiation potential are specific important properties that discriminate MSCs from fibroblasts (WI38), while conventional stem cell properties such as plastic adherence and the expression of CD44, CD90 and CD105 are unspecific for stem cells.     

Laser effects on cellular adhesion and influence on the interrelation between HeLa S3 and human diploid cells

The interactions between HeLa S3 tumoral cells and human fibroblasts after nitrogen-laser irradiation (337.1 nm) have been studied by using an in vitro cell invasion model. For the quantitative and morphological evaluation of nitrogen-laser radiation action upon tumoral adhesion to the fibroblast monostrate, we used: a) 3H-thymidine labelling of HeLa S3 tumoral cells; b) morphological modifications studies by phase contrast and scanning electron microscopy. The results emphasized the following aspects: 1. In non-irradiated cell cultures we noticed three interaction stages: adhesion, tumoral spreading and displacement with fibroblasts destruction; on the other side, we found a reduced adhesion to non-irradiated human fibroblasts of laser irradiated tumoral cells. 2. Significant percent increasing of non-irradiated tumoral cells adhesion to fibroblast monostrate, irradiated with various laser fluences (e.g. 0.2 kJ/m2--48.1%; 0.8 kJ/m2--63.8% and for 1.6 kJ/m2--79.5%). This phenomenon evidenced the close interrelation between irradiation fluences and tumoral adhesion rates. 3. The importance of numerical ratio between tumoral cells and fibroblasts in tumoral adhesion and invasion processes (e.g. ratio 1:10 tumoral adhesion reached 8.1%; in 1:5--25.9%; in 1:1--59.4% and for 2:1--83.9%). 4. Marked cytotoxic effects for both cell types after exposure to high and very high laser fluences (1.6--6.4 kJ/m2). Our results emphasize near UV-laser irradiation effects upon some of tumoral adhesion and invasion mechanisms and demonstrate the interrelations between cell populations manifesting a different vital potential.     

Interactions between human fibroblasts and HeLa cells in vitro

Affinity toward each other was demonstrated in co-cultures between HeLa cells and fibroblasts originating from human tumor stromal or normal tissues. Both cell types in the mixed cultures (ratio 1:1, 1:2, 2:1) proliferated normally as shown by 3H-thymidine labeling index estimation for up to 48 hr of co-culture. At ratios of fibroblasts: HeLa lower than 1:10, fibroblasts were eventually eliminated after serial passaging. It was shown that 3H-nucleotides could be transferred between heterologous cells in either direction. Contact of cells was essential for this phenomenon. Transfer of the label from HeLa to fibroblasts required a longer interaction time and was evidently lower than the transfer from fibroblasts to HeLa. 3H-thymidine incorporated into the DNA of either cell type could not be transferred from one cell to another. The model provides a means for studying neoplastic X normal (or tumour stromal) cell interactions in vitro.     

Adhesion, orientation, and movement of cells cultured on ultrathin fibronectin fibers

Summary This study examined the behavior of rat tendon fibroblasts, baby hamster kidney fibroblasts, macrophage-like P388D1 cells, and neurons from rat dorsal root ganglia, cultured on fibronectin strands 0.2–5 μm in diameter. We investigated cell spreading, orientation, formation of focal contacts, the speed of cell movement, and the speed of neurite outgrowth in cells cultured on fibronectin strands, glass covered with fibronectin, and plain, nontreated glass. Fibronectin strands significantly promoted cell spreading and caused a marked alignment of all kinds of cells to the direction of the fiber. The fibers caused the alignment of actin filaments in fibroblasts and focal contacts in fibroblasts and macrophages and increased polymerization of F-actin in cells. Fibronectin fibers also increased the speed and persistence of cell movement and the rate of neurite outgrowth. Macrophages grown on fibronectin fibers produced numerous actin-rich microspikes and adopted a polarized, migratory phenotype. These findings indicate that fibronectin strands, resembling natural components of the extracellular matrix, are more effective in activating various types of cells than two-dimensional, fibronectin-covered substrata. The results also confirm the suitability of the three-dimensionally oriented fibronectin form for use in clinical practice.     

Down regulation and recovery of the epidermal growth factor receptor in serum supplemented versus defined medium

The down regulation of surface membrane receptors for(¹²⁵I) epidermal growth factor (EGF) has been evaluated in normal and SV40-transformed human fibroblasts (WI38) under conditions of serum-supplemented versus defined growth media. Both normal and transformed WI38 cells down regulate and recover the EGF receptor and these processes do not differ significantly in serum-supplemented versus defined media. These data are in contrast to a recent study that reported that the HeLa cell does not down regulate the EGF receptor in defined media, whereas it does in serum-supplemented media.     

Analysis of fibronectin receptor function with monoclonal antibodies: roles in cell adhesion, migration, matrix assembly, and cytoskeletal organization

We have developed two rat mAbs that recognize different subunits of the human fibroblast fibronectin receptor complex and have used them to probe the function of this cell surface heterodimer. mAb 13 recognizes the integrin class 1 beta polypeptide and mAb 16 recognizes the fibronectin receptor alpha polypeptide. We tested these mAbs for their inhibitory activities in cell adhesion, spreading, migration, and matrix assembly assays using WI38 human lung fibroblasts. mAb 13 inhibited the initial attachment as well as the spreading of WI38 cells on fibronectin and laminin substrates but not on vitronectin. Laminin-mediated adhesion was particularly sensitive to mAb 13. In contrast, mAb 16 inhibited initial cell attachment to fibronectin substrates but had no effect on attachment to either laminin or vitronectin substrates. When coated on plastic, both mAbs promoted WI38 cell spreading. However, mAb 13 (but not mAb 16) inhibited the radial outgrowth of cells from an explant on fibronectin substrates. mAb 16 also did not inhibit the motility of individual fibroblasts on fibronectin in low density culture and, in fact, substantially accelerated migration rates. In assays of the assembly of an extracellular fibronectin matrix by WI38 fibroblasts, both mAbs produced substantial inhibition in a concentration-dependent manner. The inhibition of matrix assembly resulted from impaired retention of fibronectin on the cell surface. Treatment of cells with mAb 16 also resulted in a striking redistribution of cell surface fibronectin receptors from a streak-like pattern to a relatively diffuse distribution. Concomitant morphological changes included decreases in thick microfilament bundle formation and reduced adhesive contacts of the streak-like and focal contact type. Our results indicate that the fibroblast fibronectin receptor (a) functions in initial fibroblast attachment and in certain types of adhesive contact, but not in the later steps of cell spreading; (b) is not required for fibroblast motility but instead retards migration; and (c) is critically involved in fibronectin retention and matrix assembly. These findings suggest a central role for the fibronectin receptor in regulating cell adhesion and migration.     

Differences in DNA-binding proteins isolated from normal and transformed human cells

When the DNA-binding proteins (DBPs) of WI38 normal human fibroblasts and their SV40-transformed counterpart were compared, two DBPs were present in greater amounts in the transformed cells. These two DBPs, P5a and P6b, were also present in greater amounts in HeLa cells versus WI38 cells and in chemically transformed human liver cells versus normal liver cells. Therefore, these DBP differences do not appear to be specific for transformation by SV40. Increased amounts of P5a were present in 7 of 9 transformed cell lines examined. The two tumor cell lines lacking the P5a change were sensitive to density-dependent inhibition of replication, whereas the other seven cell lines were not. This correlation suggests that the increase in P5a may play a role in the release from density-dependent inhibition of replication observed in most transformed cells.     

The differentiation of normal and transformed human fibroblasts in vitro is influenced by electromagnetic fields

We studied the effect of symmetric, biphasic sinusoidal electromagnetic fields (EMF) (20 Hz, 6 mT) on the differentiation of normal human skin fibroblasts (HH-8), normal human lung fibroblasts (WI38), and SV40-transformed human lung fibroblasts (WI38SV40) in in vitro cultures. Cells were exposed up to 21 days for 2 x 6 h per day to EMF. Normal mitotic human skin and lung fibroblasts could be induced to differentiate into postmitotic cells upon exposure to EMF. Concomitantly, the synthesis of total collagen as well as total cellular protein increased significantly by a factor of 5-13 in EMF-induced postmitotic cells. As analyzed by two-dimensional gel electrophoresis of [35S]methionine-labeled polypeptides, EMF-induced postmitotic cells express the same differentiation-dependent and cell type-specific marker proteins as their spontaneously arising counterparts. In SV40-transformed human lung fibroblasts (cell line WI38SV40) the exposure to EMF induced the differentiation of mitotic WI38SV40 cells into postmitotic and degenerating cells in subpopulations of WI38SV40 cell cultures. Other subpopulations of WI38SV40 cells did not show any effect of EMF on cell proliferation and differentiation. These results indicate that long-term EMF exposure of fibroblasts in vitro induces the differentiation of mitotic to postmitotic cells that are characterized by differentiation-specific proteins and differentiation-dependent enhanced metabolic activities.     

Mg2+ mediates the cell-substratum interaction of Arg-Gly-Asp-dependent HeLa cell collagen receptors

Three HeLa cell surface collagen receptors of apparent molecular mass 102/58, 87, and 38/33 kDa were eluted from gelatin-Sepharose with salt gradients or Arg-Gly-Asp-containing peptides. To understand how the collagen receptors are involved in HeLa cell spreading on collagen we investigated the effects of divalent cations and Arg-Gly-Asp-containing peptides on adhesion to gelatin, since HeLa cells behave similarly on both native type I collagen and gelatin substrata and also whether Arg-Gly-Asp-containing substrata would substitute for gelatin in facilitating cell spreading. Gly-Arg-Gly-Asp-Ser-containing peptides in solution inhibited HeLa cell spreading onto gelatin and promoted only partial HeLa cell spreading when bound to tissue culture plastic. Both partial spreading of HeLa cells on the Gly-Arg-Gly-Asp-Ser substratum and full spreading on gelatin was dependent on Mg2+, but not on Ca2+. Binding of the 102/58-, 87-, and 38/33-kDa collagen receptors to gelatin-Sepharose was increased fourfold in the presence of Mg2+, and subsequent elution of the collagen receptors and a 45-kDa collagen-binding protein not thought to be involved in HeLa cell spreading was achieved with EDTA. In contrast, affinity chromatography on Gly-Arg-Gly-Asp-Ser-Sepharose eluted predominantly the 45-kDa collagen-binding protein and the 38/33-kDa collagen receptor. In summary, the Mg2(+)-dependent interaction of the collagen receptors with the Arg-Gly-Asp sequence in collagen appears to be essential for the initial events in HeLa cell spreading but is not sufficient for full cell spreading.     

Levels of synthesis of primate-specific nuclear proteins differ between growth-arrested and proliferating cells

A monoclonal antibody that reacts specifically with the proliferation-sensitive nuclear proteins, isoelectric focusing (IEF) 8Z30 and 8Z31 (molecular weight (MW), 76,000 charge variants, HeLa protein catalogue number) has been characterized. As determined by indirect immunofluorescence, the antibody stains the nucleolus and nucleoplasm of interphase-cultured cells of primate origin, but does not react with cells of other species. Proteins having similar MWs and isoelectric points as the human or monkey (primates) proteins were not observed in cultured cells of the following species: aves, bat, dog, dolphin, goat, hamster, mink, mouse, pisces, potoroo, rabbit and rat. Quantitative two-dimensional (2D) gel electrophoretic analysis of [35S]methionine-labeled proteins synthesized by normal (quiescent, proliferating) and SV40-transformed human MRC-5 fibroblasts revealed significant differences in the levels of synthesis of both IEF 8Z30 and 8Z31. In quiescent cells the main labelled product corresponded to IEF 8Z31 (ratio IEF 8Z31/8Z30, 2.3), while in the transformed cells the major product was IEF 8Z30 (ratio, 0.62). Normal proliferating fibroblasts exhibited similar levels of both proteins (ratio, 1.21). Combined levels of synthesis of both proteins were 1.50 and 1.20 times as high in the transformed cells as in the quiescent and proliferating cells, respectively. Similar results were observed in other pairs of normal and transformed human cells, such as WI38/WI38 SV40 and amnion/AMA. Modulation of the levels of synthesis of these proteins may play a role in cell proliferation.     

gamma-Glutamyltransferase in human diploid fibroblasts and other mammalian cells.

gamma-Glutamyltransferase was determined in WI-38 human diploid fibroblasts and compared to enzyme levels determined in several other mammalian cell lines including: fibroblast-like cells from human skin, tibia and foreskin; epithelial-like cells from human, bovine and monkey kidney; and transformed cells (Chinese hamster ovary, HeLa S3 and SV-40 transformed WI-38). Transformed cells had the lowest activity found followed in increasing order by fibroblasts, human and bovine epithelial cells and monkey kidney epithelial cells. The enzyme isolated from the plasma membrane of WI-38 cells, like the enzyme from kidney and brain, was found to be irreversibly inhibited by iodoacetamide, reversibly by serine-borate, and had a strong specificity for certain amino acids. The possibility exists that gamma-glutamyltransferase could be involved in transport of amino acids into cells in culture; and glutamine, used in media, is an excellent substrate for the enzyme.     

The differentiation of normal and transformed human fibroblasts in vitro is influenced by electromagnetic fields

We studied the effect of symmetric, biphasic sinusoidal electromagnetic fields (EMF) (20 Hz, 6 mT) on the differentiation of normal human skin fibroblasts (HH-8), normal human lung fibroblasts (WI38), and SV40-transformed human lung fibroblasts (WI38SV40) in in vitro cultures. Cells were exposed up to 21 days for 2 × 6 h per day to EMF. Normal mitotic human skin and lung fibroblasts could be induced to differentiate into postmitotic cells upon exposure to EMF. Concomitantly, the synthesis of total collagen as well as total cellular protein increased significantly by a factor of 5–13 in EMF-induced postmitotic cells. As analyzed by two-dimensional gel electrophoresis of [³⁵S]methionine-labeled polypeptides, EMF-induced postmitotic cells express the same differentiation-dependent and cell type-specific marker proteins as their spontaneously arising counterparts. In SV40-transformed human lung fibroblasts (cell line WI38SV40) the exposure to EMF induced the differentiation of mitotic WI38SV40 cells into postmitotic and degenerating cells in subpopulations of WI38SV40 cell cultures. Other subpopulations of WI38SV40 cells did not show any effect of EMF on cell proliferation and differentiation. These results indicate that long-term EMF exposure of fibroblasts in vitro induces the differentiation of mitotic to postmitotic cells that are characterized by differentiation-specific proteins and differentiation-dependent enhanced metabolic activities.     

DNA fork displacement rates in synchronous aneuploid and diploid mammalian cells.

DNA fork displacement rates were measured in Chinese hamster ovary cells (CHO), human HeLa cells and human diploid fibroblasts. For CHO cells two independent techniques were used: one based on CsCl equilibrium density gradients and the other on 313 nm photolysis of incorporated bromodeoxyuridine (BrdUrd). Both methods indicated that there was no significant variation in fork displacement rates in CHO cells as they progressed through S phase. Asynchronous CHO cultures displayed the same average value (1.0 micron/min) and range of values as found in synchronous cells. In contrast, the rate of DNA fork displacement in HeLa cells, measured by the BrdUrd-313 nm method, increased continuously from 0.8 micron/min in early S to 2.5 micron/min in late S. For human diploid fibroblasts, in early S, the rate was approximately 0.7 micron/min and decreased to a minimum of 0.5 micron/min in mid S. The replication fork displacement rate then increased to a maximum of 0.9 micron/min in late S and declined again before the end of S phase. This pattern of DNA fork displacement rates roughly paralleled the overall thymidine incorporation rate and appears quite different from the patterns found for HeLa and CHO cells.     

Calcium-mediated cell surface changes in Chinese hamster cells.

Scanning electron microscopy (SEM) revealed quantitative differences in both surface characteristics and spreading behavior of young and senescent WI38 human diploid fibroblasts. Measurement of spreading behavior involved the determination of the rate of cell elongation beyond an axial ratio of 1.5 after time intervals of 1.5, 3, 6, 9, and 12 h following subculture. Early passage cells exhibited a 44–52% increased spreading rate compared with later passage cells, both obeying zero-order kinetics. Surface microvilli and blebs were also found to vary in number and size after those same time intervals following subculture. In young cells, microvilli density was found initially to be very low but then increased steadily with time. Later passage cells exhibited an initial high density of microvilli, followed by a gradual disappearance with time. The density of cellular blebs did not, however, vary significantly with time following subculture. After approx. 24 h, both early and late passage cells resembled each other. These studies do show that physical membrane characteristics of young and senescent cells differ under certain conditions, and suggest the importance of that structure in the phenomena of senescence.     

Differential ASF/SF2 activity in extracts from normal WI38 and transformed WI38VA13 cells.

The normal human fibroblast cell line WI38 and a transformed derivative, WI38VA13, differentially splice fibronectin pre-mRNA in vivo. As a first step to understand the molecular basis for this regulation of splicing, we examined the ability of WI38 and WI38VA13 nuclear extracts to splice model adenovirus and globin pre-mRNAs. Adenovirus RNA splicing was detected in WI38VA13 but not in WI38 extracts. Likewise, when supplemented with a HeLa post-nuclear supernatant (S100), human beta-globin RNA splicing was detected in WI38VA13 but not in WI38 extracts. The splicing defect in WI38 extracts was associated with a reduced ability to form splicing complexes and with a corresponding decrease in the interaction of U2 small nuclear ribonucleoprotein (snRNP) with the branchsite. These defects did not correlate with a decrease in 65 kD U2AF binding since equivalent U2AF level and activity were detected in WI38 and WI38VA13 extracts. Rather, WI38 extracts displayed reduced ASF/SF2 activity and contained a low level of 30 and 40 kD SR phosphoproteins. Moreover, addition of purified ASF/SF2 dramatically increased splicing complex formation in WI38 extracts. These results raise the possibility that variations in the level and activity of ASF/SF2 and other SR proteins play a role in the regulation of fibronectin splicing.     

Overexpression of ORC subunits and increased ORC-chromatin association in transformed mammalian cells

The origin recognition complex (ORC) is a conserved heterohexamer required for the formation of pre-replication (pre-RC) complexes at origins of DNA replication. Many studies of ORC subunits have been carried out in transformed human cell lines but the properties of ORC in primary cells have not been addressed. Here, we compare the expression levels and chromatin-association of ORC subunits in HeLa cells to the primary human cell line, WI38, and a virally transformed derivative of WI38, VA13. ORC subunits 2 and 4 were highly overexpressed in both HeLa and VA13, whereas ORC1 levels were elevated in VA13 but considerably higher in HeLa cells. Cellular extraction revealed that the proportion of ORC2 and ORC4 subunits bound to chromatin was similar in all three cell lines throughout the cell-cycle. In contrast, very little ORC1 was associated with chromatin after extraction of primary WI38 cells, whereas the majority of overexpressed ORC1 in both HeLa and VA13 co-fractionated with chromatin throughout the cell-cycle. Although none of the cell lines displayed significant changes in the levels or chromatin-association of ORC during the cell-cycle, the chromatin-associated fraction of ORC1 displayed an increase in apparent molecular weight during S-phase. Similar experiments comparing immortalized CHO cells to an isogenic virally transformed derivative revealed no changes in levels of ORC subunits but an increase in the proportion of all three ORC subunits associated with chromatin. These results demonstrate a complex influence of cellular immortalization and transformation properties on the expression and regulation of ORC subunits. These results extend the potential link between cancer and deregulation of pre-RC proteins, and underscore the importance of considering the transformation status of cell lines when working with these proteins.     

Effects of Staphylococcus aureus lysozyme on human fibroblasts.

The purified lysozyme excreted by Staphylococcus aureus strains promotes elongation and spreading on plastic surfaces and stimulates DNA synthesis of human fibroblasts (WI38). This enzyme also raises twofold the saturation density level of cultures of these cells. It is suggested that the primitive and main effect of lysozyme on fibroblasts is the triggering of morphogenesis.