No abstract

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 α6β4 integrin.An antibody-defined molecule was identified by mass spectrometry and cloning as α6β4 integrin. Transfectioninduced expression of α6β4 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 α6β4 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 α6β4 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 α6β4/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, α6β4 changes from an adhesion-supporting towards a migrationsupporting molecule by its association with a tetraspanin. The findings provide a convincing experimental explanation for the repeatedly described involvement of α6β4 in tumor progression.Key words: α6β4 integrin, Tetraspanin, Metastasis, Adhesion, Motility SummaryThe association of the tetraspanin D6.1A with the α6β4 integrin supports cell motility and liver metastasis formation

We have described recently that anti-CD44s, anti-CD44v6 and anti-CD44v7 interfere with delayed-type hypersensitivity (DTH) reactions. Yet, TNBS-induced colitis can be cured only by anti-CD44v7. To clarify the mechanisms underlying the divergent functional activities of CD44v6 and CD44v7 we explored their contribution to lymphocyte activation in vivo and in vitro. CD44v6 and CD44v7 are distinctly expressed on subpopulations of activated lymphocytes. Expression of CD44v6 is mainly restricted to T cell blasts. CD44v7 has been detected on CD4(+) cells, B cells and monocytes. Mitogenic and antigenic stimulation of lymphocytes in vitro was impaired in the presence of anti-CD44v6 and anti-CD44v7. Accordingly, anti-CD44v6 and anti-CD44v7 mitigated the DTH reaction in 2,4-dinitro-1-fluorobenzene-sensitized and challenged mice. However, the seemingly similar effects of CD44v6- and CD44v7-specific antibodies resulted from different activities. Anti-CD44v6 treatment led to a down-regulation of IL-2 and IFN-gamma production predominantly by CD8(+) cells. In anti-CD44v7-treated mice expression of IL-12 was decreased. Elevated levels of IL-10 accompanied this reduction. The latter resulted from an anti-CD44v7-mediated blockade of interactions between CD4(+) cells and monocytes as well as an active triggering of B cells. Thus, anti-CD44v6 and anti-CD44v7 interfere with lymphocyte activation at very specific points. CD44v6 functions predominantly at the T cell level. CD44v7 influences production of proinflammatory cytokines by B cells as well as an interaction between CD4(+) cells and antigen-presenting cells. As CD44 isoforms do not differ in their intracytoplasmatic tail, the distinct activities must result from expression on different leukocyte subsets and interactions with distinct ligands.