In epithelial tissues, cells are linked to their neighbors through specialized cell-cell adhesion proteins. E-cadherin is one of the most important membrane proteins for the establishment of intimate cell-cell contacts, but the molecular mechanism by which it is recruited to contact sites is largely unknown. We report here that the cytoplasmic domain of E-cadherin interacts with C3G, a guanine nucleotide exchange factor for Rap1. In epithelial cell cultures, ligation of the extracellular domain of E-cadherin enhances Rap1 activity, which in turn is necessary for the proper targeting of E-cadherin molecules to maturing cell-cell contacts. Furthermore, our data suggest that Cdc42 functions downstream of Rap1 in this process. We conclude that Rap1 plays a vital role in the establishment of E-cadherin-based cell-cell adhesion.
A naturally occurring antisense RNA, transcribed in the opposite direction and complementary to the envelope transcript, was identified in various cell lines chronically infected with HIV-1. In T cells, the antisense transcript is constitutively expressed and enhanced by activation with phorbol myristate acetate. The open reading frame corresponding to the antisense transcript, when expressed in vitro, encodes a protein with an apparent molecular mass of 19 kDa. Antibodies against this protein have been detected in several sera of HIV+ individuals and not in any of the noninfected control sera. These results indicate, for the first time, that expression of an antisense open reading frame most likely accompanies the HIV infection cycle in humans.
We have shown previously that trophoblast cells from human placenta can be infected with HIV-1 and a productive infection established. Recently, (1991, J. Virol. 65, 2102-2107) Zachar et al. and D. M. Phillips and X. Tan (1992, AIDS Res. Hum. Retroviruses 8, 1697-1705) have described in vitro infection of choriocarcinoma cell lines. Using choriocarcinoma cell lines (JAR, BeWo, and FD25, a trophoblast-derived cell line) we have infected these cells with several laboratory strains of virus and have shown that this can be prevented either by sCD4 or by antibodies to CD4. This provides strong evidence that the infection may be through CD4. In addition, we have found that infection of JAR and FD25 cells by HIV-1/Lai was enhanced in the presence of human antisera to HIV-1. This supports an additional role for immunoglobulin receptors (Fc-R) in the entry of virus into the cell. We report here evidence that CD4 and Fc-R on the cell surface play crucial roles in the entry of HIV into such placenta-derived cell lines.
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