Biomedical subjects

Dirk-Steffen Schmidt

Publications and source records attributed to Dirk-Steffen Schmidt.

4 recordsLinked to original sources

PubMed2005

The cell-cell adhesion molecule EpCAM interacts directly with the tight junction protein claudin-7.

We recently described that in the metastasizing rat pancreatic carcinoma line BSp73ASML the cell-cell adhesion molecule EpCAM, CD44 variant isoforms and the tetraspanins D6.1A and CD9 form a complex that is located in glycolipid-enriched membrane microdomains. This complex contains, in addition, an undefined 20 kDa protein. As such complex formation influenced cell-cell adhesion and apoptosis resistance, it became of interest to identify the 20 kDa polypeptide. This 20 kDa protein, which co-precipitated with EpCAM in BSp73ASML lysates, was identified as the tight junction protein claudin-7. Correspondingly, an association between EpCAM and claudin-7 was noted in rat and human tumors and in non-transformed tissues of the gastrointestinal tract. Co-localization of the two molecules was most pronounced at basolateral membranes, but was also observed in tight junctions. Evidence for direct protein-protein interactions between EpCAM and claudin-7 was obtained by co-immunoprecipitation after treatment of tumor cells with a membrane-permeable chemical cross-linker. The complex, which is located in glycolipid-enriched membrane microdomains, is not disrupted by partial cholesterol depletion, but claudin-7 phosphorylation is restricted to the localization in glycolipid-enriched membrane microdomains. This is the first report on an association between EpCAM and claudins in both non-transformed tissues and metastasizing tumor cell lines.

Animals↗

PubMed2004

CD44 variant isoforms associate with tetraspanins and EpCAM.

The metastasizing subline of the rat pancreatic adenocarcinoma BSp73 expresses a set of membrane molecules, the combination of which has not been detected on non-metastasizing tumor lines. Hence, it became of interest whether these molecules function independently or may associate and exert specialized functions as membrane complexes. Separation of CD44v4-v7 containing membrane complexes in mild detergent revealed an association with the alpha3 integrin, annexin I, EpCAM, and the tetraspanins D6.1A and CD9. EpCAM and the tetraspanins associate selectively with CD44 variant (CD44v), but not with the CD44 standard (CD44s) isoform. The complexes are found in glycolipid-enriched membrane (GEM) microdomains, which are dissolved by stringent detergents, but the complexes are not destroyed by methyl-beta-cyclodextrin (MbetaCD) treatment, which implies that complex formation does not depend on a lipid-rich microenvironment. However, a complex-associated impact on cell-matrix and cell-cell adhesion as well as on resistance towards apoptosis essentially depended on the location in GEMs. Thus, CD44v-specific functions may well be brought about by complex formation of CD44v with EpCAM, the tetraspanins, and the alpha3 integrin. Because CD44v4-v7-EpCAM complex-specific functions strictly depended on the GEM localization, linker or signal-transducing molecules associating with the complex are likely located in GEMs.

Adenocarcinoma↗

PubMed2003

The association of the tetraspanin D6.1A with the alpha6beta4 integrin supports cell motility and liver metastasis formation.

The metastatic subline of a rat pancreatic adenocarcinoma differs from the non-metastasizing subline by overexpression of 5 membrane molecules: CD44 variant isoforms, EpCAM, the tetraspanin D6.1A, an uPAR-related molecule and, as described here, the alpha6beta4 integrin. An antibody-defined molecule was identified by mass spectrometry and cloning as alpha6beta4 integrin. Transfection-induced expression of alpha6beta4 in the non-metastasizing subline did not support migration on laminin 5 or tumor progression. However, when the non-metastasizing subline was doubly transfected to express alpha6beta4 and the D6.1A tetraspanin, intraperitoneally injected tumor cells frequently formed liver metastasis. For the following reasons we assume that metastasis formation is supported by an interaction between alpha6beta4 and D6.1A. (i) The 2 molecules can associate and co-localize. (ii) Co-localization is strengthened by PKC stimulation. (iii) PKC stimulation, which induces a migratory phenotype, leads to a redistribution of alpha6beta4/D6.1A complexes. In resting cells, the molecules co-localize at the trail of the cell; during PKC stimulation they become transiently internalized and are (re-)expressed in the leading lamella. Thus, in the appropriate milieu, i.e. intraperitoneally, alpha6beta4 changes from an adhesion-supporting towards a migration-supporting molecule by its association with a tetraspanin. The findings provide a convincing experimental explanation for the repeatedly described involvement of alpha6beta4 in tumor progression.

Amino Acid Sequence↗

PubMed2002

Allogeneic reconstitution after nonmyeloablative conditioning: mitigation of graft-versus-host and host-versus-graft reactivity by anti-CD44v6.

T-cell maturation is accelerated in transgenic mice expressing rat CD44v4-v7 on T cells, the effect being blocked by anti-CD44v6. This finding suggested functional activity of CD44v6 in thymocyte development. We tested the hypothesis by antibody blocking and using mice with targeted deletion of CD44v6/v7 exon products (CD44v6/v7(-/-)). When lethally irradiated CD44v6/v7-competent (CD44v6/v7(+/+)) mice were reconstituted syngeneically, higher numbers of CD44v6/v7(-/-) than CD44v6/v7(+/+) BMC were required for survival, the period of reconstitution was prolonged, and regain of immunocompetence was delayed. Similar findings were observed in lethally irradiated, anti-CD44v6-treated syngeneic CD44v6/v7(+/+) hosts. Thus, CD44v6/v7 supports maturation and expansion of hematopoietic progenitor cells. Surprisingly, reconstitution with CD44v6/v7(-/-) BMC or anti-CD44v6 treatment of the nonlethally irradiated allogeneic CD44v6/v7(+/+) host had only a minor impact on survival rates. When nonlethally irradiated CD44v6/v7(-/-) hosts received an allogeneic graft, survival rates were improved. These phenomena have been a result of reduced GvH reactivities when the donor was CD44v6/v7(-/-) and reduced HvG reactivities in the CD44v6/v7(-/-) host. Thus, although a deficit or blockade of CD44v6/v7 has a negative impact on hematopoietic reconstitution, a transient blockade will be of benefit for the allogeneically reconstituted host because of a strong reduction in GvH and HvG reactivities.

Animals↗