The development of polysomes in the seed of Pisum arvense

1. Ribosomal preparations from dormant seed, cotyledon and growing tissue from Pisum arvense were examined. 2. Polysomes were obtained from growing tissues under all conditions used. 3. Such particles were obtained from seed immediately after imbibition only when 5mm-zinc sulphate was included in the medium used for extraction. 4. No polysomes were obtained from dry seed. 5. Extracts of dry seed showed limited incorporation of phenylalanine into protein. 6. Extracts of seed after imbibition showed enhanced activity in incorporation of phenylalanine amounting to 72% of the activity found in extracts of growing tissue. 7. A nuclear fraction from dry seed was able to incorporate ATP into acid-precipitable material. 8. It is concluded that the protein-synthesizing system of the dry seed is limited by the low concentration of functional polysomes.

p53-Independent induction of apoptosis in human melanoma cells by a bcl-2/bcl-xL bispecific antisense oligonucleotide

Mutations in the p53 tumor suppressor gene are implicated in defective apoptotic response of tumors to genotoxic damage and, thus, are major determinants of resistance to a variety of anticancer agents. Because even melanomas harboring wild-type (wt) p53 show an abnormal response to radiation and p53 mutations occur late during melanoma progression, we investigated whether the effect of the bcl-2/bcl-xL bispecific antisense oligonucleotide 4625 is dependent on the p53 status in human C8161 melanoma cells. Upon treatment with oligonucleotide 4625, p53-mut C8161 cells showed earlier DNA damage, which occurred concomitantly with the reduction of bcl-2 and bcl-xL expression and the increase in the expression of proapoptotic bax. Loss of cell viability, bcl-2 down-regulation, and poly(ADP-ribose) polymerase cleavage, indicative of apoptosis, also occurred in wt p53 C8161 cells on treatment with oligonucleotide 4625. These effects, however, were mediated by strong induction of p53 without changes in p21 WAF1 expression in wt p53 cells, whereas a 70% decrease in p21 WAF1 expression was observed in mut p53 cells. In contrast to many other anticancer agents to which the apoptotic response is decreased because of p53 mutations, our data suggest that the bcl-2/bcl-xL bispecific antisense oligonucleotide 4625 effectively induces p53-independent apoptosis in human C8161 melanoma cells.

Suppression of C8161 melanoma metastatic ability by chromosome 6 induces differentiation-associated tyrosinase and decreases proliferation on adhesion-restrictive substrates mediated by overexpression of p21WAF1 and down-regulation of bcl-2 and cyclin D3

Metastatic tumors grow under conditions that restrict proliferation of non-metastatic, more differentiated cells. To investigate this prediction, we developed a simple adhesion-restrictive assay which allows proliferation of human metastatic C8161 melanoma, but prevents growth of neo 6.3/C8161 cells in which metastasis is suppressed by introduction of neo-tagged chromosome 6. We show that tyrosinase, a key enzyme in melanocytic cell differentiation, and expression of chromosome 6-encoded cell cycle modulators like p21WAF1 and cyclin D3 is selectively increased in C8161 tumors in which metastasisis is suppressed by chromosome 6. In the latter cells, growth arrest evidenced only under adhesion-restrictive conditions correlated with down-regulation of cyclin D3 and anti-apoptotic bcl-2. No comparable growth arrest or down-regulation was detected under comparable conditions in metastatic cells, which showed activation of invasion-associated MMP-9 92 kDa gelatinase B. Our data suggests that the metastasis-suppressing effects of chromosome 6 involving increased differentiation-associated tyrosinase and growth arrest on adhesion-restrictive substrates; are partly mediated by modulation of growth regulators, like p21WAF1 and cyclin D3.

Lower cyclin H and cyclin-dependent kinase-activating kinase activity in cell cycle arrest induced by lack of adhesion to substratum

Knowledge about adhesion checkpoints is important to counteract dissemination of cells from solid tumors. Lack of anchorage in adherent cells is associated with growth arrest and inhibition of cyclin-dependent kinases (cdks) required to drive cell cycle progression. Because cyclin-cdk complex activation requires CDK-activating kinase comprising cdk7 and cyclin H, we now investigated their relationship to decreased proliferation by lack of cell spreading. This report shows that either UV irradiation on an adhesive substrate or culture on a nonadhesive substrate produced K1735 melanoma growth arrest. Inhibition of proliferation by UV primarily induced the cdk inhibitor p21WAF1 without a significant effect on cyclin H and cdk7. In contrast, lack of adhesion to substratum decreased cyclin H but not cdk7 with accumulation of a slower migrating, presumably unphosphorylated cdk4 isoform. These results were paralleled by decreased cdk7-mediated phosphorylation of GST-cdk2 and lower activation of a baculovirus-derived cdc2-cyclin B kinase complex. This is the first report showing that cyclin H-mediated down-regulation of cdk-activating kinase activity is involved in growth arrest induced by lack of anchorage.

Apoptosis-inducing levels of UV radiation and proteasome inhibitors produce opposite effects on p21(WAF1) in human melanoma cells

The stability of p21(WAF1) and p53 is increased by UV radiation or proteasome inhibitors in normal and some tumor cells. However, p21(WAF1) can either stimulate in vitro assembly of active cyclin-kinase complexes at low concentrations or inhibit this activity at high concentrations. Also, ectopic p21(WAF1) over-expression has been reported to promote or suppress apoptosis, depending on the target cells. We have investigated changes in p21(WAF1) expression as a result of exposure to either 25 J/m(2) UV or 10 microM MG-115 proteasome inhibitor, both of which cause apoptosis in human C8161 melanoma cells. p21(WAF1) mRNA increased in response to UV irradiation but failed to accumulate at the protein level because of its early UV-activated degradation counteracted by proteasome inhibition. UV-mediated loss of p21(WAF1) protein preceding induction of p53 and cell death was greater in non-metastatic than in metastatic C8161 melanoma cells. No loss in p21(WAF1) occurred with apoptosis induced by 10 microM proteasome inhibitors MG-115 or lactacystin, mediated by over-expression of p21(WAF1). Our results suggest that conditions causing prolonged or permanent changes in basal levels of p21(WAF1) may impair its reversible cell-cycle checkpoint function, leading to irreversible growth arrest or cell death.

Transfection of constitutively active mitogen-activated protein/extracellular signal-regulated kinase kinase confers tumorigenic and metastatic potentials to NIH3T3 cells

Cellular growth and differentiation are controlled by multiple extracellular signals, many of which activate extracellular signal-regulated kinase (ERK)/mitogen-activated protein (MAP) kinases. Components of the MAP kinase pathways also cause oncogenic transformation in their constitutively active forms. Moreover, expression of activated ras can confer metastatic potential upon some cells. Activation of MAP kinases requires phosphorylation of both Thr and Tyr in the catalytic domain by a family of dual-specificity kinases, called MEKs (MAP kinase/ERK kinase). MEK1 is activated by phosphorylation at Ser218 and Ser222 by Raf. Mutation of these two sites to acidic residues, specifically [Asp218], [Asp218, Asp222], and [Glu218, Glu222], results in constitutively active MEK1. Using these mutant variants of MEK1, we showed previously that transfection of NIH/3T3 or Swiss 3T3 cells causes morphological transformation and increases growth on soft agar, independent of ERK activity. The transformed cell lines show increased expression of matrix metalloproteinases 2 and 9 and cathepsin L, proteinases that have been implicated in the metastatic process. We tested NIH3T3 cells transfected with the [Asp218] or [Asp218, Asp222] for metastatic potential after i.v. injection into athymic mice. Parental 3T3 cells formed no tumors grossly or histologically. However, all MEK1 mutant transformants formed macroscopic metastases. Thus, like activated Ras, MEK1 can confer both tumorigenic and metastatic potential upon NIH3T3 cells. These results refine the mechanism through which ras could confer tumorigenic and metastatic potential (ie., the critical determinants of tumorigenic and metastatic potential are downstream of MEK1).

Tumor suppression without differentiation or apoptosis by antisense cyclin D1 gene transfer in K1735 melanoma involves induction of p53, p21WAF1 and superoxide dismutases

In mammalian cells, terminal differentiation is mutually exclusive with proliferation. However, resistance to differentiation-inducing therapy requires alternative strategies to control poorly responsive tumors. We now show that retroviral transfer of the antisense cyclin D1 gene to differentiation-refractory K1735 melanoma leads to loss of in vivo tumorigenicity, shortened replicative ability, induction of the tumor suppressor p53 protein and of the cdk-inhibitor p21WAF1, increased beta-galactosidase pH 6.0 activity, and elevation in the ratio of superoxide dismutases to peroxidases, all properties associated with replicative senescence. However, pigmentation and tyrosinase expression, characteristic of differentiated melanocytic cells or apoptosis-associated PARP cleavage, were not increased by antisense cyclin D1 transduction. Our data suggests that targetting cyclin D1 inhibition suppresses melanoma tumorigenicity by promoting a cytostatic differentiation-independent pathway, mediated by activation of p53 and anti-oxidant functions.

Unequal nuclear Sp1/GC box DNA binding activity distinguishes proliferating from differentiated senescent or apoptotic cells

Terminal differentiation can result in either viable, non-proliferating or apoptotic cells. In B16 melanoma, millimolar L-tyrosine induces tyrosinase, a key enzyme for terminal pigmentation concurrent with either irreversible growth arrest at low cell density, or apoptosis at high cell density. Since the promoter for melanocyte-specific tyrosinase expression contains sites for the Sp1 transcription factor, we have investigated the relationship of Sp1-mediated GC-box DNA binding activity to growth control in undifferentiated and in terminally differentiated viable or apoptotic cells. Nuclear extracts from viable, differentiated cells showed increased retardation of GC box DNA sequence compared with that seen in proliferating cells or those reversibly arrested in early G(1) or late G(1) / S. In contrast, nuclear proteins from dying, differentiated cells showed loss of nuclear GC box DNA binding activity without decrease in binding to TTTGCGCG sequences recognized by the E2F transcription factor, which is known to interact with Sp1. However, cyto-plasmic fractions from apoptotic cells revealed phos-phatase-activated retardation of GC box DNA, which was not evident in similarly treated fractions from undifferentiated cells or sparse differentiated cells. Terminal differentiation also correlated with increase in a slow-migrating phosphorylated Sp1 isoform. Our data suggests that lack of nuclear Sp1/GC box DNA binding activity, may promote apoptosis by diminishing expression of survival-associated genes regulated by GC box DNA promoter sequences in dense terminally differentiated melanoma cells.

Chromosome-6-mediated suppression of metastatic ability increases basal expression of UV-inducible superoxide dismutase and induction of p53

Since response to radiation and markers capable of distinguishing metastatic from non-metastatic cells are important, we now use high-stringency mRNA differential display with immune blotting and protein-activity assays, to identify genes induced after exposure to UV in human metastatic C8161 melanoma and its counterpart neo 6.3, in which metastatic ability is suppressed by introduction of neo-tagged chromosome-6 fragments. We cloned and sequenced a 600-bp cDNA 99% homologous to Cu/Zn superoxide dismutase, which was up-regulated after UV irradiation in both metastatic variants, and showed increased basal expression at the mRNA, protein and activity levels in non-metastatic cells. The latter cells also showed greater basal activity of chromosome-6-associated MnSOD, slower proliferation and greater UV-mediated inducibility of the p53 tumor-suppressor protein than did its metastatic counterpart. Our data suggest that suppression of metastatic ability by introduction of neo-tagged chromosome-6 fragments promotes basal expression of superoxide dismutases and increases inducibility of p53 in response to DNA damage.

Induction of p53 and melanoma cell death is reciprocal with down-regulation of E2F, cyclin D1 and pRB

Tumor-suppressor-gene products such as p53 and retinoblastoma (Rb) play an important role as negative regulators of cell-cycle progression, which is reciprocally favored by the availability of cyclin D1 and the E2F transcription factor. We now show that UV irradiation of B16 melanoma after prior exposure to the radiation sensitizer, bromodeoxyuridine (BUdR) leads to induction of p53 and DNA fragmentation, and concomitant decreases in Rb, E2F, cyclin D1, and cell viability, with no comparable effects on irradiated unsensitized cells. Our data suggest that over-expression of p53 correlates with down-regulation of E2F, cyclin D1 in inducing apoptosis.

Induction of p53 without increase in p21WAF1 in betulinic acid-mediated cell death is preferential for human metastatic melanoma

Because betulinic acid was recently described as a melanoma-specific inducer of apoptosis, we investigated whether this agent was comparably effective against metastatic tumors and those in which metastatic ability and 92-kD gelatinase activity had been decreased by introduction of a normal chromosome 6. Human metastatic C8161 melanoma cells showed greater DNA fragmentation and growth arrest and earlier loss of viability in response to betulinic acid than their non-metastatic C8161/neo 6.3 counterpart. These effects involved induction of p53 without activation of p21WAF1 and were synergized by bromodeoxyuridine in metastatic Mel Juso, with no comparable responses in non-metastatic Mel Juso/neo 6 cells. Our data suggest that betulinic acid exerts its inhibitory effect partly by increasing p53 without a comparable effect on p21WAF1.

Sensitization to DNA damage by okadaic acid or bromodeoxyuridine involves unequal effects on melanoma cell adhesion and differentiation

Because melanoma tumors originate partly from excessive UV exposure but become relatively resistant to radiation, we have now compared the effects of okadaic acid, a phosphatase inhibitor, with that of the thymidine analog bromodeoxyuridine as sensitizers of DNA damage in B16 melanoma. We now show that 25 nM okadaic acid promotes DNA fragmentation in B16 melanoma, increasing cell detachment as well as pigmentation, a characteristic of melanocytic cell differentiation. At lower levels, okadaic acid synergizes with UV exposure to increase DNA fragmentation. Although bromodeoxyuridine also caused DNA damage, it did not increase pigmentation and it suppressed cell detachment. Okadaic acid was also more effective in promoting DNA laddering in growing versus quiescent melanocytes. Because DNA damaging effects of okadaic acid are mediated by different pathways from those used by nucleoside analogs, like bromodeoxyuridine, we propose their concurrent effect with radiation as sensitizers to DNA damage.

PCR-mediated differential display and cloning of a melanocyte gene decreased in malignant melanoma and up-regulated with sensitization to DNA damage

Characterization of genes expressed in normal cells and decreased in their malignant counterparts is important for detecting candidate tumor suppressor genes. We have now used comparative differential display of MRNAs from B16 melanoma and matched syngeneic normal melanocytes to detect a G0A gene expressed preferentially in resting G0 melanocytes compared to proliferating cells. Cloning and sequencing revealed no homology of G0A in the GenBank Database, suggesting that this is a new gene. Northern blot analysis with the cloned probe, confirmed about a five-fold higher expression in normal melanocytes compared to melanoma. Up-regulation of this gene was not detected by L-tyrosine induction of B16 melanoma terminal differentiation, but was seen in these cells, when exposed to the radiation sensitizer bromodeoxyuridine and subsequent UV radiation. Our differential expression data suggest that the G0A gene is important for melanocytic growth control and for the response of melanoma cells to radiation sensitizers.

p53-independent increase in p21WAF1 and reciprocal down-regulation of cyclin A and proliferating cell nuclear antigen in bromodeoxyuridine-mediated growth arrest of human melanoma cells

Differentially regulated expression of activators and inhibitors of cyclin-dependent kinases (cdks) modulate cell cycle progression. In normal fibroblasts, these complexes consist of the cdk inhibitor p21WAF1/PCNA/G1 cyclin/cdk. We now show that bromodeoxyuridine (BrdUrd), a thymidine analogue and radiation sensitizer, inhibits growth and activity of cyclin A-cdk2 kinase in metastatic C8161 and nonmetastatic neo 6.3/C8161 human melanoma cells. Inhibition is not due to altered levels of cyclin D or catalytic cdk2 but involves a decrease in cyclin A and proliferating cell nuclear antigen, paralleled by higher levels of p21WAF1 without increases in p53. In contrast to serum starvation, which prevents accumulation of cyclins A and D in normal fibroblasts, such treatment did not down-regulate either cyclin in these melanoma cells, implying an aberrant control for G1 cyclins in these tumor cells. However, cyclin A was decreased by BrdUrd, suggesting that this pyrimidine analogue arrests melanoma cells at a G1 transition point, unlike that of serum starvation. This is the first report indicating that the antitumor therapeutic action of BrdUrd may be mediated by a p53-independent reciprocal effect on activators and inhibitors of cdk kinases.

Decrease in actin gene expression in melanoma cells compared to melanocytes is partly counteracted by BrdU-induced cell adhesion and antagonized by L-tyrosine induction of terminal differentiation

Malignant transformation is frequently accompanied by changes in the cytoarchitecture of adherent cells, which may be influenced by fluctuations in actin gene expression. We now show that normal melanocytes express a 5 fold higher level of actin mRNA than their melanoma counterparts. Induction of terminal melanogenesis did not increase actin in melanoma cells. However, culture with the thymidine analog, Bromodeoxyuridine, increased actin expression in undifferentiated but not in differentiating melanoma. Cell detachment assays and cell shape comparisons revealed a direct correlation of actin mRNA with increased melanoma cell adhesion rather than with differentiation-mediated suppression of tumor growth.

Suppression of cyclin D1 but not cdk4 or cyclin A with induction of melanoma terminal differentiation

To identify cyclins specifically associated with control of melanoma cell proliferation, we now compared expression of cyclin A, reported to be a marker for hematological malignancies, with that of cyclin D and its cdk4 kinase partner. All these proteins were expressed in proliferating B16 melanoma. However, L-tyrosine which induces melanoma terminal differentiation, selectively decreased cyclin D with no comparable effect on cdk4 or cyclin A. A 2-hour exposure of the cells to the tyrosine phosphatase inhibitor, sodium vanadate, further decreased cyclin D from differentiated cells, suggesting that tyrosine phosphorylation regulates cyclin D turnover. Addition of serum to starved cells also revealed that tyrosine did not block the early cyclin D increase associated with serum stimulation, but accelerated its subsequent loss. Our data suggest that cyclin D decrease with melanoma terminal differentiation could be an alternative mode of growth arrest even in cells harbouring a mutant or transcriptionally silent cdk4 inhibitor tumor suppressor p16ink4 gene. These results also imply that cyclin D may be useful as a target and as a prognostic marker in melanoma therapy.

Cyclin-dependent kinase 2 and cyclin A interaction with E2F are targets for tyrosine induction of B16 melanoma terminal differentiation

L-Tyrosine promotes a dramatic increase in melanogenesis and an apparent replicative senescence in B16 melanoma (M. Strasberg-Rieber and M. Rieber, Cancer Res., 53:2469-2471, 1993). Since cyclins are implicated in controlling cell proliferation and differentiation, we have now investigated their relationship to melanocytic growth arrest and pigmentation. In B16 melanoma cells enriched in G1 by serum starvation or synchronized in late G1/early S phase by exposure to hydroxyurea, L-tyrosine overrides mitogenic signals and induces terminal differentiation without cytotoxicity. This correlates with a decrease in cyclin A and cyclin E-dependent kinase 2 activity and with an altered interaction of cyclin A with the transcription factor E2F. This activity involves a lower level of the catalytic cdK2 kinase protein without a concomitant decrease in cyclin A or cyclin E. Upon addition of serum or removal of hydroxyurea, cells resume cell cycle progression and the ability to form tumors in vivo, but these properties are irreversibly inhibited in tyrosine-treated cells. Our data suggest that targeted inactivation of cdK2 with specific inducers of differentiation favors reacquisition of tumor growth control.

UV radiation induces DNA fragmentation and cell death in B16 melanoma sensitized by bromodeoxyuridine: impaired c-jun induction and defective tyrosine phosphorylation signalling

The relevance of tyrosine phosphorylation and c-jun protooncogene expression to radiation sensitization was investigated in B16 melanoma. These cells are sensitized by bromodeoxyuridine (BrdU), a thymidine analog, showing extensive DNA fragmentation reminiscent of apoptosis, after UV radiation. UV-irradiated unsensitized cells did not reveal DNA fragmentation but showed increased expression of c-jun and greater protein tyrosine phosphorylation in response to sodium vanadate, an inhibitor of tyrosine phosphatases. However, these responses were inhibited in UV-irradiated BrdU-treated cells. Our data suggest that the bromodeoxyuridine-induced sensitization to radiation can lead to DNA fragmentation and cell death, partly because of a defective tyrosine kinase signalling and an impaired c-jun expression, both of which appear important for cell survival in response to UV radiation.

Specific tyrosinases associated with melanoma replicative senescence and melanogenesis

Replicative senescence occurs in normal cells, in contrast to their malignant counterparts which are generally immortal in vitro. We now show that induction of melanogenesis in subconfluent B16 melanoma cells deprived of growth factors can lead to irreversible growth arrest but continued cell viability, concurrent with the expression of specific glycosylated high molecular weight tyrosinases. These tyrosinase activities identify withdrawal from the cell cycle since they were not detected in reversibly arrested quiescent melanocytes, serum-deprived melanoma, or apoptotic melanoma. Our data suggest that different tyrosinases can distinguish cycling and noncycling cells of melanocytic origin and also imply that replicative senescence can be restored in some tumor cells when induced to terminal differentiation in the absence of growth-promoting agents.

Early inhibition of protein phosphatases preferentially blocks phorbol ester-stimulated mitogenic signalling in melanocytes: increase in specific tyrosine phosphoproteins

Inhibition of protein phosphatases has been suggested as an alternative mechanism of tumor promotion (H. Fujiki, Mol. Carcinog. 5:91, 1992). We have now used early melanocyte passages dependent on phorbol esters and serum for growth and later passages with partial phorbol ester independence, to investigate the role of protein phosphatases on melanocyte DNA synthesis. Neither okadaic acid, an inhibitor of ser/thr protein phosphatases, nor vanadate, an inhibitor of tyrosine phosphatases, can stimulate basal or serum-stimulated mitogenesis in contrast to phorbol esters. Moreover, both phosphatase inhibitors are able to suppress serum and phorbol ester-stimulated mitogenesis, if added within 4 hours of growth activation. Inhibition of mitogenesis by either inhibitor correlated with an early increase in a common set of tyrosine phosphoproteins, which included a major 33 Kd species. Our data suggest that protein phosphatase inhibitors are growth suppressors and antagonize phorbol ester effects in cells of melanocytic origin, implying an early requirement for protein phosphatase activity during mitogenic signalling in these cells.

Accessibility to DNA in carcinoma chromatin is promoted by nanomolar okadaic acid: effect on AT-rich DNA binding proteins

Differential accessibility to DNA in tumor cell chromatin is important to growth, differentiation apoptosis, and the targeting of DNA modifying drugs. We now show that endonuclease accessibility to DNA in the nuclei of A431 human carcinoma cells is increased within 90 min by nontoxic nanomolar levels of okadaic acid, known to inhibit protein phosphatase 2A. This genomic hypersensitivity was partly enhanced by joint treatment with epidermal growth factor and okadaic acid but did not appear without the latter. Nuclei with greater DNA susceptibility showed a decrease in M(r) 80,000 DNA binding protein doublet specific for dAT-rich sequences concurrent with the "apparent" hyperphosphorylation of a M(r) 70,000 nuclear matrix protein. We propose that some of the tumor-promoting effects of okadaic acid may be partly associated with its ability to promote genomic susceptibility.

Extracellular RGD-binding proteins modulate cell adhesion

Cell/fibronectin adhesion in extracellular matrices is partly mediated by integrin receptor recognition of RGD domains in fibronectin. Since blood contains significant levels of soluble fibronectin we have now investigated the occurrence of extracellular RGD-binding proteins. Attachment assays indicate that extracellular RGD-binding proteins prevent cell adhesion, suggesting their potential as novel secreted modulators of blood-borne cell adhesive interactions. These extracellular RGD-binding proteins also showed electrophoretic changes with reducing agents, suggestive of intrachain disulphide bonds, like those found in RGD-binding integrins. However, they differed from the latter in their electrophoretic profile, which was greatly dependent on the presence of protease inhibitors. Plasma from tumor-bearing mice showed a greater proportion of fast-migrating RGD-binding species under reducing condition compared to similarly treated normal plasma, suggesting that tumor development is associated with a partial degradation of extracellular RGD-binding proteins.

Differential genomic susceptibility in malignancy correlates with changes in ATATAT DNA-binding proteins

Accesibility to DNA in the nucleus is important for the regulation of gene expression and for the effect of DNA-modifying drugs. We have now studied differential genome susceptibility in normal melanocytes and the corresponding malignant melanoma. DNA hypersensitivity assays revealed a markedly lesser degradation in melanoma nuclei compared to that in melanocytes. Cross-linking of DNA to nuclear proteins by ultraviolet light showed a cell-type dependent inverse correlation of genomic susceptibility with binding of (dA.dT) (dA.dT) sequences, compared to that shown with (dG.dC) (dG.dC), regardless of methylation in cytosines. Exposure to cholera toxin partly reversed genomic susceptibility and increased DNA/protein cross-linking in melanocytes. In contrast, melanoma cells showed decreased DNA/protein interactions and greater genome susceptibility after exposure to cholera toxin or okadaic acid. Our data suggest that a molecular mechanism for differential genome exposure in cancer cells involves a modified expression of sequence-specific DNA-binding proteins.

Cell adhesion regulates melanoma specific differentiation and interactions with the 3' region of the tyrosinase gene

Decreased attachment to substratum has now been found to increase melanosome formation and cell-cell interaction in B16 melanoma. Since melanosome formation involves tyrosinase gene expression, we assayed for differential RNA expression by hybridization with probes from the distal ends of this gene, detecting unequal reactivity only with the 3' end probe. The same DNA showed binding of 2 nuclear proteins of 50 and 60 kd in unanchored cells, in contrast with a decreased binding of the 60 kd species, in nuclear extracts from attached cells. No comparable differences were detected with a gamma-actin DNA of identical length, suggesting that the changes observed are sequence-specific. Our studies suggest that the adhesion-mediated modulation of pigmentation in B16 melanoma correlates with differential macromolecular interactions with the 3' end of the tyrosinase gene.

Tumor hypersensitive DNA is enriched in c-myc sequences and reacts differentially with normal and malignant genomic DNA

We now show that exposure of B16 melanoma cells to bromodeoxyuridine increases cell-substratum interactions concurrent with an increase in genome susceptibility to nucleases. Hypersensitive DNA was isolated after mild nicking of nuclei with DNase I followed by repair with DNA polymerase I in the presence of biotin-19-SS-dUTP and affinity chromatography on streptavidin-agarose. Dot blot studies showed that the hypersensitive DNA is enriched in c-myc sequences compared to total tumor genomic DNA, and hybridizes preferentially to the latter, compared to normal genomic DNA, particularly when prepared from BrdU-treated cells. Since hypersensitive DNA can hybridize with multiple Alu sequences in the genome, we postulate that one of the mechanisms for its differential reactivity may be by recognition of an unequal number of Alu repeats in normal and tumor genomic DNA.

A Hoechst H33258 agarose plate assay for the estimation of nanogram DNA levels without RNA interference: applications in PCR and in estimations of plasmid and cytoplasmic DNA

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Changes in cytoskeleton-associated molecules in cells with different degrees of proliferation and metastatic ability

An antiserum prepared against the Triton-insoluble cytoskeleton of in vivo grown B16 melanoma tumor has been used to analyze the differential expression of cytoskeleton-associated molecules in cells with different degrees of proliferation and metastatic ability. This antiserum identified a major 97 kd molecule associated with the cytoskeletal fraction in B16 melanoma tumors, mouse embryo and in proliferating lymphocytes, with no reactivity with the 97 kd species in non proliferating lymphocytes. The antiserum revealed immune reactivity with a 180 kd Triton-insoluble species in normal adult mouse liver and kidney. A comparison of tumor cells with differing metastatic ability also showed a minor 180 kd component in poorly metastatic cells which appeared decreased and partly degraded in its more invasive counterpart. The differential recognition of a 97 kd species in resting and proliferating lymphocytes, as well as the different cleavage of a 180 kd species in tumor cells of differing metastatic ability, implies a role for these molecules in cell proliferation. The fact that these differences can be detected with an antiserum to tumor cell cytoskeleton suggests that this Triton-insoluble fraction may be a good source of molecules involved in growth control.

Differential response of adherent and unanchored melanoma cells to bromodeoxyuridine evidenced by specific lectin-binding protein changes

The possible differential response of adherent and nonadherent cells of the same tumor type to pyrimidine analogues has been investigated. We show that bromodeoxyuridine (BUdR) increases interactions of attached cells with their substrate without markedly affecting the cell adhesion properties of the same cells when these are not anchored. However, evidence for an adhesion-independent response of both cell types to BUdR has been obtained with lectin binding assays using 125I-labelled Lens culinaris agglutinin (LCA). This revealed a greatly increased binding of LCA to a large glycoconjugate in all cultures exposed to the halogenated pyrimidine. Attachment-dependent effects of BUdR were manifested in flattened cells by a greater LCA-binding to a 240-kDa protein and by increased interaction of 125I-labelled wheat-germ agglutinin (WGA) with a 200-kDa protein and a large glycoconjugate sharply defined in electrophoresis. Although both tumor cell aggregates and anchored cells exhibit detectable responses to pyrimidine analogues such as BUdR, the corresponding effects are thus manifested unequally in cells with different adhesion properties.

DNA on membrane receptors: a target for monoclonal anti-DNA antibody induced by a nucleoprotein shed in systemic lupus erythematosus

Antibodies to double stranded (ds) DNA correlate with clinical evolution in systemic lupus erythematosus (SLE) although little is known about the immunogen and target for these antibodies, since ds DNA is poorly immunogenic. We now show that monoclonal anti DNA antibodies similar to those detected in human SLE can be produced by immunization of genetically non-autoimmune mice with a human circulating DNA-protein complex increased in the circulation of SLE patients. One such monoclonal antibody showed antinuclear reactivity, interacting with a 74 kd DNA-binding membrane protein, in reactions prevented by absorption with ds DNA cellulose. Our data suggests that anti ds DNA antibody reactions in SLE may be triggered by circulating nucleoproteins and directed toward membrane receptors capable of interacting with extracellular DNA.

Decrease in tumor-cell attachment and in a 140-kDa fibronectin receptor correlate with greater expression of multiple 34-kDa surface proteins and cytoplasmic 54-kDa components

B16 melanoma cells attach to matrix-bound fibronectin but fail to adhere to albumin-coated surfaces supplemented with soluble fibronectin. Attachment to substratum is also decreased in the presence of an adhesion-disrupting antibody, or when cells are seeded on substrates poorly adhesive for these cells, such as collagen gels. We have now investigated some of the more general adhesion-related alterations that occur between flattened and poorly attached cells. Immune blots of octylglucoside extracts with the adhesion-disrupting IgG revealed a 140-kDa component in flattened cells, in contrast to the increased detection of a 54-kDa species in a comparable assay with rounded cells. Surface iodination also showed a decreased external exposure of a 140-kDa fibronectin binding species and an increased labelling in multiple 34-kDa protein species, in cells with decreased attachment to substratum. Analysis of 35S-methionine-labelled cell aggregates cultured on collagen gels also revealed a decrease in the 140-kDa region and a greater labelling of multiple 54-kDa components, compared to the same cells flattened on fibronectin. A change in 54- and 34-kDa species was also seen in matrix-associated components of rounded cells that failed to attach with soluble fibronectin. Since the 34-kDa species increase in poorly adherent cells is mainly detected by iodination, and the 54-kDa species increase in the same cells is partly associated with the corresponding detergent-insoluble matrices, we propose that these 2 novel proteins may relate to cell rounding, through a transmembrane modulation involving both surface membrane and cytoskeletal structures.

Human repetitive and unique sequences coexist in a large circulating DNA species found in cryoprecipitates from SLE patients

Cryoprecipitates from systemic lupus erythematosus (SLE) patients with high levels of anti DNA antibodies show a sharply migrating large circulating DNA species of about 17-20 kb (M. Rieber et al., Clin. exp. Immunol. (1986) 66, 61). We have now used Southern blot analysis of circulating DNA from different individuals to analyse the relative cross-hybridization of circulating DNA from different individuals, as well as their homology with genomic DNA from different species. Molecular hybridization showed significant homology of the various circulating DNA examined, only with human genomic DNA, but limited cross-reactivity among circulating DNA from different individuals. This suggests that the circulating DNA is composed of sequences repeated in human genomic DNA and by specific sequences unique to circulating DNA from some individuals. Our data suggests the possibility of using probes derived from the specific sequences now reported in the circulating DNA, in gene typing and in the analysis of susceptibility to disease.

Antibodies to basement membrane proteins nidogen and laminin in sera from streptococcal-related diseases and juvenile rheumatoid arthritis patients

Using the ELISA technique, antibodies against two different basement proteins, laminin and nidogen (ALNA), were determined in 226 children suffering from one of 37 different inflammatory or infectious diseases. These included 80 patients with streptococcal infection and 40 with juvenile rheumatoid arthritis. Forty-eight percent of the streptococcus-infected patients (or 75% of those in the acute phase) and 60% of juvenile rheumatoid arthritis patients had significantly elevated ALNA levels compared with healthy controls. Interestingly 10 adult rheumatoid arthritis patients displayed normal ALNA levels, suggesting a particular immune process occurring in children affected by juvenile rheumatoid arthritis. By means of periodate oxidation and glycosidase treatments we have shown that ALNA positive sera recognized terminal alpha-galactose as the reactive epitope.

Relationship of a Mr 140 fibronectin receptor and other adhesion-related glycoproteins to tumor cell-cell interaction

Primary melanocytes attach poorly to collagen type IV and laminin, in contrast to their firm attachment to collagen type I/III and fibronectin [Gilchrest et al., In vitro (Rockville), 21: 114-120, 1985]. We have now found that metastatic B16 melanoma cells attach well to collagen type IV, laminin, vitronectin, and fibronectin but show a selective defect in attachment and cell aggregation on native collagen type I. Both flattened and aggregated melanoma cells revealed the presence of a Mr 120,000 surface-iodinated species with affinity for a matrix containing the hexapeptide (glycylarginylglycylaspartylserylproline) which includes the fibronectin cell attachment sequence, but only flattened cells showed significant exposure of a Mr 140,000 iodinated component with affinity for a large cell attachment-promoting fibronectin polypeptide. Decrease of the Mr 140,000 fibronectin-binding external protein in the collagen-cultured melanoma cells was also associated with an inability to respond to the cell attachment activity of fibronectin, laminin, or vitronectin added to the collagen gels. Metabolic labeling with [3H]glucosamine and electrophoretic analysis showed that lack of attachment and cell aggregation was associated with an increase in high molecular weight wheat germ agglutinin-binding glycoconjugates and an increase in Mr 55,000 concanavalin A-binding glycoprotein species. Our data suggest that: (a) melanoma cell attachment requires the expression of the Mr 140,000 fibronectin receptor which appears to be down regulated in cells exposed to poorly adhesive substrates; (b) expression of the Mr 120,000 iodinated species with affinity for the fibronectin attachment sequence (arginylglycylaspartic acid) may be necessary but not sufficient for firm cell-substratum interactions; (c) increased tumor cell-cell interaction may involve a decreased attachment to substrate and the expression of different glycoproteins which may modulate cell-cell association.

120 and 80 kd detergent-insoluble glycoproteins as markers of differentiation and adhesion in B16 melanoma

Surface glycoproteins correlating with cell adhesion and differentiation have now been studied in pigmented and amelanotic B16 melanoma cell monolayers and aggregates, labelled with 3H-glucosamine. Solubilization with the non-ionic detergent octyl glucoside revealed mostly adhesion-related changes, which involved a decrease in 140 and 110 kd glycoproteins in both pigmented and amelanotic cell aggregates. Nevertheless, differentiation-regulated changes were preferentially evident in the remaining detergent-insoluble glycoproteins. Pigmented cell monolayers showed a preferential increase in glycoprotein species of about 120 kd and 80 kd, which were not detected in amelanotic monolayers or in pigmented or amelanotic cell aggregates. Our findings suggest the relevance of these cytoskeleton associated glycoproteins as markers of differentiation and adhesion in melanoma cells.

Novel DNA-protein complex and a large DNA in SLE cryoprecipitates

Agarose gel electrophoresis of cryoprecipitates from systemic lupus erythematosus (SLE) patients revealed the presence of a slowly migrating DNAse I-sensitive DNA species at the top of the gel. Upon deproteinization, electrophoretic migration was modified favouring the migration of a 17.5 kb DNA fragment. Mixing experiments adding human serum or plasma to a lambda phage DNA digest revealed a DNA-protein interaction shown by an accumulation of high mol. wt polynucleotide at the top of the gels, and a slowed migration of the DNA bands. No comparable effect was observed when serum albumin was added to the lambda DNA digest. Dot hybridization analysis showed preferential reactivity of the 17.5 kb DNA to human DNA, implying its human origin. Our data suggests that most of this high molecular weight DNA exists as a DNA-2 protein complex. Our mixing experiments also suggest the occurrence of an excess of free DNA antibodies. We propose that the DNA-protein association may play a role in the stabilization and immunogenicity of the nucleoprotein complex.

Substrate-dependent effect of epidermal growth factor on intercellular adhesion and synthesis of triton-insoluble proteins in human carcinoma A431 cells

Human epidermoid carcinoma A431 cells attach more rapidly to collagen type-I and -IV substrates than to surfaces coated with laminin or fibronectin. The diminished intercellular interaction and rounding up manifested when these cells are exposed to epidermal growth factor (EGF) in tissue culture plastic or collagen films is not shown when the assay is performed on 3-dimensional collagen. In the latter substrate, cells exposed to EGF reveal greater cell cohesion with interdigitations and desmosomal junctions, compared to the limited intercellular interaction detected in similarly treated cells assayed in tissue culture substrate. Although the protein synthesis inhibitor, cycloheximide, did not prevent these EGF-mediated changes, metabolic labelling indicated a substrate-dependent effect of EGF on the synthesis of proteins associated with the Triton-insoluble cytoskeletal matrix. The involvement of cytoskeleton components in the EGF effects on intercellular adhesion was shown by its susceptibility to cytochalasin B, known to disorganize actin-containing microfilaments. Some of the mechanisms of epithelial morphogenesis and the influence of extracellular matrix components on cell-receptor/growth-factor interactions may now be suitably analyzed by examining the EGF effects on A431 cells grown on different substrata.

Improved detection of labile cell-surface components with zinc chloride-aprotinin: demonstration of glycoprotein differences in K-1735 metastatic melanoma variants

Metabolic labelling of K-1735 melanoma variants with 3H-glucosamine and cell harvesting with the commonly used protease inhibitor phenylmethylsulfonylfluoride revealed a Triton-insoluble fibronection-like 230 kd component in poorly metastatic cells. This component was not evident in highly metastatic cells. Significantly improved surface labelling and detection of the 230 kd glycoprotein in the highly metastatic variant was achieved by zinc chloride-aprotinin treatment of cells prior to harvesting. This procedure also revealed an increase in a trypsin-sensitive glycoprotein of higher molecular weight in the Triton-insoluble fraction of the highly metastatic cell variant. Glycoprotein labelling in this fraction showed an electrophoretic pattern strongly resembling that reported by others for the high-molecular-weight human melanoma-associated glycoprotein complex. The differential detection of the high-molecular-weight glycoprotein species in melanoma variants with differing metastatic abilities in an animal model provides a means of studying their possible relevance to metastatic melanoma. Our data also suggest that zinc chloride-aprotinin can be used to improve the detection of labile cell-surface components.

Serum mediated changes in cell attachment and cytoplasmic organization of B16 melanoma correlates with selective alterations in secreted proteins

B16 melanoma cells exhibited decreased adhesion to substration and the presence of cytoplasmic granules, resembling lipid inclusions, when cultured in vitro in the presence of syngenic serum from C57/BL6 mice. This constrasted with the rapid cell attachment and absence of cytoplasmic granules in cultures seeded in medium supplemented with an identical concentration of fetal bovine serum. Electrophoretic comparison of intracellular proteins revealed similar patterns in detergent-soluble and matrix-associated proteins from cells grown with bovine or mouse serum. However, a similar analysis of the conditioned media showed clear differences in methionine-rich species which migrated in the 100 kd region in cells grown with bovine serum, and as 110 kd component in cells grown with mouse serum. Our data indicate that the poor attachment to substratum and changes in cytoplasmic organization of B16 melanoma cells, is primarily associated with specific changes in secreted proteins.

Relationship of a novel extracellular matrix glycoprotein to cell detachment in highly metastatic B16 melanoma: modulating effect of bromodeoxyuridine

Growth of highly invasive B16 melanoma BL6 cells with bromodeoxyuridine (BUdR) decreases in vitro cell detachment and modulates extrapulmonary growth in vivo. We now show: (1) The presence of an 80 kd glycoprotein in the Triton-insoluble matrix of control BL6 cells but not in the corresponding fractions from BUdR-treated BL6 cells and poorly metastatic F1r cells. (2) The matrix fractions from the two last mentioned cells reveal Triton-insoluble glycoproteins of about 55-58 kd. (3) Mild trypsin treatment of intact cells before matrix preparation leads to the preferential disappearance of the 80 kd component from control BL6 matrix, suggesting its extracellular localization. (4) Prevention of Triton-mediated BL6 matrix detachment by zinc chloride pretreatment, and analysis of different BL6 clones with significant metastatic behavior, also revealed the presence of 80-90 kd matrix-associated glycoproteins in control but not in corresponding BUdR-grown cultures. Since BUdR decreases cell detachment, extrapulmonary metastasis and the levels of the 80-90 kd Triton-insoluble glycoprotein species in metastatic B16 melanoma, and this matrix component is also decreased in poorly metastatic F1r cells, we propose an involvement of this glycoconjugate in tumor cell detachment and metastatic behavior.

Unequal forms of 140-110 kD glycoproteins in B16 melanoma cells with differing detachment properties and metastatic behavior: influence of bromodeoxyuridine

Growth of B16 melanoma metastatic variants with 2.5 micrograms/ml of bromodeoxyuridine (BrdU) decreases cell detachment from the substratum, as measured by resistance to release by trypsin-EDTA treatment. Using an antiserum to intact melanoma cells and metabolic labelling of melanoma metastatic variants with 3H-glucosamine and subsequent electrophoretic analysis, we are now able to show that: (1) differential solubilization and immune precipitation permit the identification of hydrophilic glycoproteins of about 140 kD and 110 kD in melanoma cells with low colonizing ability; (2) the effects of BrdU on B16 melanoma appear to be exerted differentially on cells with differing metastatic behavior, since only poorly invasive melanoma cells show a stimulating effect of BrdU on the expression of the hydrophilic 140 kD glycoproteins; (3) cells with increased lung colonizing ability reveal hydrophobic 140 and 110 kD glycoprotein species with increased susceptibility to mild protease treatment, as compared with the corresponding components from poorly invasive cells. The possible relationship of the 140-110 kD glycoproteins to B16 melanoma biological behavior and cell-substratum interactions is suggested by the fact that such components undergo significant changes in cells with differing invasive behavior and detachment properties.

Antibodies to laminin in American cutaneous leishmaniasis

We found that serum samples from patients with different clinical forms of American cutaneous leishmaniasis (ACL) contained immunoglobulin G and immunoglobulin M antibodies which reacted with laminin but not with various other purified connective tissue components, such as collagen types I, III, IV, and V and fibronectin. Eighty-one percent of ACL patients had high antilaminin antibody levels, with a relationship existing between ACL ulcers and antibody levels. This was not, however, the case with patients having treated and healed ACL ulcers; only 34% of these patients had elevated antilaminin antibodies. Eighty-four percent of chronic Chagas' disease patients were also found to contain antilaminin antibodies that were limited to the immunoglobulin G class, but these were not detected in patients suffering from any of 11 other infectious diseases.

Tumor-associated changes in plasma samples revealed by two-dimensional macromolecular mapping and selective lectin binding

Two-dimensional electrophoretic analysis of plasma samples from EL-4 lymphoma-bearing C57 black mice revealed five 75 kd protein species in contrast with the presence of only two comparable components of similar migration in plasma from control animals. In contrast, no comparable alterations were observed in a comparison of plasma samples from L1210 tumor-bearing DBA mice and the corresponding plasma from animals immune-suppressed with antilymphocytic serum or in control plasma from DBA control plasma from DBA control animals. Analysis of selective binding using iodinated lectins revealed significant binding of I125 Lens culinaris in the more cathodic 75 kd component present in the plasma from control C57 black mice and a decreased Lens culinaris binding in the corresponding plasma components from EL-4 tumor-bearing C57 black animals. An identical assay with the same samples using I125 Ricinus communis did not show significant interaction with any 75 kd protein species, revealing instead lectin binding in components with molecular weights of about 70 and 50 kd. Our results suggest the use of combined two-dimensional electrophoretic separation and relative lectin binding in the analysis of tumor-specific and tumor-associated changes in plasma samples from tumor-bearing individuals.

Epidermal growth factor promoted changes in the triton-insoluble cytoskeletal matrix from human epidermal carcinoma cells: effect of bromodeoxyuridine

We have used monolayers of bromodeoxyuridine (BrdU)-grown and control human epidermoid carcinoma (A431) cells to investigate the polypeptide changes resulting when cells are rounded by epidermal growth factor (EGF). Whereas no significant change was detected in Triton-soluble components, the urea-solubilized matrix fraction revealed greater levels of a 20 kd species in cells exposed to EGF, compared with the same cells not exposed to the growth factor. The corresponding urea fraction from BrdU-grown cells showed decreased levels of the 20 kd species as a result of exposure to EGF. Further evidence for a differential effect of EGF resulting from growth of the cells with the pyrimidine analog was observed in the matrix fraction soluble in SDS, which revealed a decrease in a 20 kd species resulting from exposure of control cells to EGF, with no comparable effect in BrdU-grown cells. Our results suggest that EGF induces a change in the properties of matrix-associated components of low molecular weight in an effect which appears to be modified by prior growth of cells with BrdU.