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H Ponta

Publications and source records attributed to H Ponta.

At least 73 records · Page 4Linked to original sources
PubMed1993

The two major CD44 proteins expressed on a metastatic rat tumor cell line are derived from different splice variants: each one individually suffices to confer metastatic behavior.

The metastatic pancreas carcinoma cell line BSp73ASML produces a variety of different splice variants of the transmembrane glycoprotein CD44. The NH2-terminal portions are identical and heavily glycosylated. The variant sequences are inserted just outside the transmembrane region of the molecules. The two most abundant variants have 162 and 85 extra amino acids, respectively. When individually expressed, these suffice to establish metastatic properties in the nonmetastatic tumor cell line BSp73AS, as assayed by the spontaneous metastasis protocol.

Adenocarcinoma↗
PubMed1993

Splicing choice from ten variant exons establishes CD44 variability.

The enormous heterogeneity of the surface protein designated CD44 is in part due to posttranslational modification, and in part due to differential splicing. Alternative splicing occurs within one particular region encoding the extracellular portion of the protein. Comparison of various cDNA clones with different 'inserts' in this variable region with sequences of genomic clones from the mouse has revealed the existence of at least ten exons from which sequences are chosen by alternative splicing. Various combinations of these exons account for the tremendous heterogeneity of CD44 molecules expressed in different tissues, and in progressing tumor cells. The existence of different isoforms of CD44 suggests a broad spectrum of yet unknown physiologic functions.

Amino Acid Sequence↗
PubMed1993

Prevention of tumor metastasis formation by anti-variant CD44.

A splice variant of CD44 (CD44v) originally discovered on metastases of a rat pancreatic adenocarcinoma (BSp73ASML) has been shown by transfection to confer metastatic behavior to nonmetastatic tumor cells (Günthert U., M. Hofmann, W. Rudy, S. Reber, M. Zöller, I. Haussmann, S. Matzku, A. Wenzel, H. Ponta, and P. Herrlich. 1991. Cell. 65:13). A monoclonal antibody (mAb), 1.1ASML, to the metastasis-specific domain of the CD44v molecule retards growth of lymph node and lung metastases of the metastatic tumor line BSp73ASML, and can efficiently prevent formation of metastases by the transfected line. The antibody is only effective when given before lymph node colonization. Anti-CD44v does not downregulate the expression of CD44v, and prevention of metastatic growth by anti-CD44v is not due to activation of any kind of immune defense. We suggest that the mAb interferes with proliferation of metastasizing tumor cells in the draining lymph node, most probably by blocking a ligand interaction. The interference with metastatic spread will greatly facilitate the exploration of the function of CD44v and, in particular, may also open new strategies for the therapy of human metastases.

Animals↗
PubMed1993

CD44 splice variants: metastases meet lymphocytes.

Recent discoveries of surface proteins involved in tumor metastasis formation have revived an old hypothesis that tumor cells may acquire, and use for their metastatic spreading, properties which lymphoid cells had developed to defend the organism against foreign antigens. Splice variants of CD44 and integrins are expressed on metastasizing tumor cells and also on leukocytes at defined stages of their differentiation. Expression and function appear to be essential not only for the generation of an immune response but also for the establishment of metastatic tumor colonies.

Alternative Splicing↗
PubMed1993

A human homologue of the rat metastasis-associated variant of CD44 is expressed in colorectal carcinomas and adenomatous polyps.

A recently described splice variant of CD44 expressed in metastasizing cell lines of rat tumors has been shown to confer metastatic potential to a non-metastasizing rat pancreatic carcinoma cell line and to non-metastasizing sarcoma cells. Homologues of this variant as well as several other CD44 splice variants are also expressed at the RNA level in human carcinoma cell lines from lung, breast, and colon, and in immortalized keratinocytes. Using antibodies raised against a bacterial fusion protein encoded by variant CD44 sequences, we studied the expression of variant CD44 glycoproteins in normal human tissues and in colorectal neoplasia. Expression of CD44 variant proteins in normal human tissues was readily found on several epithelial tissues including the squamous epithelia of the epidermis, tonsils, and pharynx, and the glandular epithelium of the pancreatic ducts, but was largely absent from other epithelia and from most non-epithelial cells and tissues. In human colorectal neoplasia CD44 variant proteins, including homologues of those which confer metastatic ability to rat tumors, were found on all invasive carcinomas and carcinoma metastases. Interestingly, focal expression was also observed in adenomatous polyps, expression being related to areas of dysplasia. The distribution of the CD44 variants in human tissues suggests that they play a role in a few restricted differentiation pathways and that in colorectal tumors one of these pathways has been reactivated. The finding that metastasis-related variants are already expressed at a relatively early stage in colorectal carcinogenesis and tumor progression, i.e., in adenomatous polyps, suggests the existence of a yet unknown selective advantage linked to CD44 variant expression. The continued expression in metastases would be compatible with a role in the metastatic process.

Antibodies, Monoclonal↗
PubMed1993

CD44 splice variants: expression during lymphocyte activation and tumor progression.

A recently described splice variant of CD44 has been shown to confer metastatic potential to non-metastasizing rat pancreatic carcinoma and sarcoma cell lines. Using antibodies raised against a bacterial fusion protein encoded by variant CD44 sequences, we have explored the expression of variant CD44 glycoproteins in human lymphoid cells and tissues, in non-Hodgkin's lymphomas, and in colorectal neoplasia. Normal lymphohematopoietic cells express barely detectable low levels of variant CD44 glycoproteins, while T lymphocytes, upon activation by mitogen or antigen, transiently upregulate expression of specific CD44 variant glycoproteins. The reaction pattern of various antibodies indicates that these CD44 variants contain the domain encoded by exon v6, which is part of the variant that in the rat confers metastatic capability. Interestingly, overexpression of v6 was also found in several aggressive, but not in low-grade, non-Hodgkin's lymphomas (NHL). In human colorectal neoplasia we also observed strong overexpression of CD44 splice variants in all invasive carcinomas and carcinoma metastasis. Interestingly, focal expression was already observed in adenomatous polyps, expression being related to areas of dysplasia. The findings establish CD44 variants as tumor progression markers in colorectal cancer.

Alternative Splicing↗
PubMed1992

Participation in normal immune responses of a metastasis-inducing splice variant of CD44.

A variant of the glycoprotein CD44 (CD44v) that shares sequences with variants causally involved in metastasis formation is transiently expressed on B and T lymphocytes and macrophages after antigenic stimulation and in the postnatal period. Antibodies to the variant hinder in vivo activation of both B and T cells. The observation that a protein domain that is expressed on CD44 and required for the lymphatic spread of tumor cells can catalyze an essential step in the process of lymphocyte activation supports the idea that metastasizing tumor cells mimic lymphocyte behavior.

Animals↗
PubMed1992

Interference of pathway specific transcription factors.

A mechanism for reversibility of cellular decisions, e.g., proliferation or differentiation, is mediated by direct interference of pathway-specific transcription factors. Due to the relative activity of the transcription factors, genetic programs are reversibly switched on and off. In the case of the transcription factors AP-1 and the family of steroid hormone receptors (including retinoic acid receptor, thyroid hormone and vitamin D receptors) two different mechanisms account for negative interference. In one case overlapping DNA binding sites are suggestive of mutually exclusive binding of transcription factors to account for repression. In the other case, a DNA bound transcription factor is attacked by another one via protein-protein interaction, without the need of the latter factor binding to DNA. Although it is not excluded, that also in the case of overlapping DNA binding elements protein-protein interaction might in fact be responsible for repression instead of substitution, the two situations can be clearly distinguished by specific mutants in the glucocorticoid receptor and in Jun and Fos. For the interaction mechanism, we favor the interpretation that the binding of one transcription factor to another one interferes with transactivation directly without influence on DNA binding. The fact that at least two different mechanisms are established to guarantee effective interference, demonstrates how important this type of transcription factor crosstalk is.

Amino Acid Sequence↗
PubMed1992

Interference between pathway-specific transcription factors: glucocorticoids antagonize phorbol ester-induced AP-1 activity without altering AP-1 site occupation in vivo.

Phorbol esters stimulate and glucocorticoid hormones down-regulate a variety of promoters such as that of the collagenase gene through the transcription factor AP-1 (Fos/Jun). We now show by genomic footprinting of the collagenase promoter that phorbol ester treatment of cells results in the binding of AP-1 to its cognate DNA binding site in vivo. The DNA-protein contacts obtained in living cells are also found in vitro using cloned DNA and purified AP-1. Although in vitro synthesized glucocorticoid receptor can disturb the DNA binding of Jun homodimers, it does not interfere with the binding of Fos-Jun heterodimers or of purified AP-1 in vitro. Consistently, fully inhibitory doses of glucocorticoid hormone cause no change in apparent occupation of the AP-1 binding site in vivo. The hormone receptor acts without itself binding to DNA.

Base Sequence↗
PubMed1992

Steroids and growth promoting factors in the regulation of expression of genes and gene networks.

Steroid hormones and growth promoting factors regulate the expression of a number of genes involved in cellular growth and differentiation. In many cases, cellular proliferation and differentiation-specific pathways are mutually exclusive. As an example for the mechanism of mutual exclusion, transcription factors responsible for pathway-specific gene expression interact with each other. Steroid hormone receptors inhibit the action of the transcription factor AP-1 (Fos/Jun) and vice versa. This inhibitory interaction is predominantly effected at the level of protein-protein contact without the need for the interfering transcription factor to bind to DNA. In some cases the two pathways function additively or even synergistically resulting in cooperation of the transcription factors in regulation of gene expression. The examples to be discussed in this text document how elaborate and important cross-talks between signal transduction pathways are. This is particularly demonstrated by the fine tuning and reversibility of these processes.

Animals↗
PubMed1992

Ultraviolet-radiation induced c-jun gene transcription: two AP-1 like binding sites mediate the response.

In HeLa cells transcription of the c-jun gene is activated strongly and rapidly by ultraviolet (UV) irradiation and, to a somewhat lesser extent, by treatment with phorbol ester tumor promoters. In the same cells UV and phorbol esters only marginally enhance the abundance of RNA transcribed from the jun D gene and from the gene coding for the serum response factor (which in turn acts on the UV and phorbol ester response element of the c-fos gene). In contrast to c-jun, jun B transcription is induced more efficiently by phorbol ester than by UV irradiation, suggesting that the members of the jun family are differently regulated. The promoter of c-jun carries two enhancer elements resembling AP-1 binding sites: the jun1 UV response element (URE-71 TGACATCA -64) and the jun2 URE (-190 TTACCTCA-183). These elements act independently in the UV induced expression of c-jun. In the context of the complete c-jun promoter they seem not to be required for c-jun induction by phorbol esters. When fused to the Herpes simplex thymidine kinase promoter, however, the isolated elements mediate induction by both UV and phorbol esters. UV and phorbol ester treatment of cells increases the binding of transcription factors to both elements. Both elements bind factors different in modification or/and constitution from AP-1, the heterodimeric transcription factor composed of c-Fos and c-Jun that controls the activity of the UV and phorbol ester response element (-72 TGAGTCA-66) of the human collagenase gene.

Base Sequence↗
PubMed1992

Positive and negative regulation of collagenase gene expression.

Transcription of the human collagenase I gene is induced by phorbol esters and repressed by glucocorticoids. Both types of regulation are mediated by the major enhancer element of the gene, which is localized between positions -73 and -65. The enhancer suffices to transmit positive and negative signals to a heterologous promoter or to a minimal promoter carrying only the TATA-box, both detected by the appearance of chloramphenicol-acetyl-transferase transcribed from the reporter gene linked to the promoters. Sequences 5' of the enhancer modulate its activity. Up- and down-regulation of gene constructs which contain only the collagenase enhancer linked to a heterologous promoter, are independent of ongoing protein synthesis, suggesting posttranslational modification of the transcription factor binding to the enhancer. Repression by glucocorticoids depends on an activated glucocorticoid receptor; a tenfold lower glucocorticoid concentration is needed for repression of the collagenase gene as compared to the activation of the mouse mammary tumor virus long terminal repeat. Immunoprecipitates of the dexamethasone receptor contain AP-1, suggesting a direct interaction of both transcription factors; this interaction may lead to the inactivation of AP-1. The action mechanism of phorbol esters and dexamethasone confirms the central role of AP-1 in proliferation control and tumor promotion. It appears that the most effective tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA) and the most effective anti-tumor promoter dexamethasone exert their action through the modulation of the same transcription factor.

Base Sequence↗
PubMed1991

CD44 splice variants confer metastatic behavior in rats: homologous sequences are expressed in human tumor cell lines.

One of several splice variants of CD44 expressed in metastasizing cell lines of rat tumors has been shown to confer metastatic potential to the non-metastatic variant of a rat pancreatic carcinoma line (U. Günthert et al., Cell, 65: 13-24, 1991). The variant-specific rat CD44 sequences were used to detect RNA expression in human cell lines: in carcinoma lines from lung, breast and colon; and in keratinocyte lines. By polymerase chain reaction amplification, complementary DNAs encoding human homologues were isolated and sequenced. The largest splice variant has been found in a large cell lung carcinoma line and in keratinocyte cell lines. It carries at least 5 additional domains (exons) encoding a total of 338 amino acids in the membrane-proximal extracellular region of the standard CD44. Various alternative splice products have been detected in other human tumor cell lines. The distribution of CD44 splice variants is consistent with the speculation that they fulfill functions in only a few restricted differentiation pathways and that in tumor cells these pathways have been reactivated.

Amino Acid Sequence↗
PubMed1991

A new variant of glycoprotein CD44 confers metastatic potential to rat carcinoma cells.

Using a monoclonal antibody (MAb1.1ASML) raised against a surface glycoprotein of the metastasizing rat pancreatic carcinoma cell line BSp73ASML, cDNA clones have been isolated that encode glycoproteins with partial homology to CD44, a presumed adhesion molecule. In one of the clones, pMeta-1, the epitope marks an additional extracellular domain of 162 amino acids inserted into the rat CD44 protein between amino acid positions 223 and 247 (by analogy to human and murine CD44). The new variants are expressed only in the metastasizing cell lines of two rat tumors, the pancreatic carcinoma BSp73 and the mammary adenocarcinoma 13762NF; they are not expressed in the non-metastasizing tumor cell lines nor in most normal rat tissues. Overexpression of pMeta-1 in the nonmetastasizing BSp73AS cells suffices to establish full metastatic behavior.

Amino Acid Sequence↗
PubMed1991

Involvement of fos in spontaneous and ultraviolet light-induced genetic changes.

Transient overexpression of ras, mos, or fos transcribed from various inducible promoters in NIH 3T3 cells causes significant increases in the frequency of chromosomal aberrations and, as shown for fos, in gene mutations. Under the experimental conditions of exponential growth and full serum supply, overexpression of the oncogenes does not increase the proliferation rate of cells. The generation of ras- and mos-induced chromosomal aberrations was suppressed in cells that had been deprived of fos protein by antisense c-fos oligodeoxynucleotides. The induction of chromosomal aberrations by ultraviolet irradiation is also suppressed by antisense c-fos oligodeoxynucleotides. The data suggest that fos protein alone, or a transcription factor that contains fos protein as a subunit, activates or induces the synthesis of one or several mutator functions. Oncogene-driven mutagenesis could account for the accumulation of additional mutations after the activation of an oncogene, which may furnish a mechanistic basis for tumor promotion and tumor progression.

3T3 Cells↗
PubMed1990

Retardation of metastatic tumor growth after immunization with metastasis-specific monoclonal antibodies.

The influence of 4 murine monoclonal antibodies (MAbs) directed against surface determinants of a metastasizing rat adenocarcinoma (BSp73ASML) on metastatic spread was evaluated and compared to their in vivo binding as well as to the induction of a humoral anti-MAb response, especially with respect to the development of anti-idiotypic (ID) antibodies of the internal image type. In a protocol of explicit immunization, all 4 MAbs transiently inhibited metastatic growth. Survival was prolonged only with one MAb (4.4ASML). With another MAb (1.1ASML), directed against a new variant form of CD44, metastatic growth was accelerated after transient retardation. Retardation of metastatic growth correlated with the humoral anti-MAb response. This accounted for the isotype- as well as for the idiotype-specific response. An exception was noted after immunization with MAb 1.1ASML. Rats with high levels of anti-1.1ASML antibodies, which inhibited binding to the tumor cells (internal image-type antibodies) showed accelerated metastatic spread. Data are interpreted to mean that MAb-induced inhibition of metastatic spread may be based on 2 independent mechanisms: blockade of metastasis-associated epitopes (i.e., with MAb 1.1ASML) and induction of an anti-mouse Ig response. In the latter case it was irrelevant whether the response was isotype- or idiotype-specific.

Adenocarcinoma↗