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Globoside-dependent adhesion of human embryonal carcinoma cells, based on carbohydrate-carbohydrate interaction, initiates signal transduction and induces enhanced activity of transcription factors AP1 and CREB.
Undifferentiated human embryonal carcinoma cells are characterized by high expression of lactoneotetraosylceramide (nLc4), globoside (Gb4), and extended globo-series glycosphingolipids (GSLs) termed "stage-specific embryonic antigens 3 and 4" (SSEA-3 and -4). Expression of these GSLs declines in association with a decline of homotypic adhesion during the differentiation process. Therefore, these GSLs may play an essential role in adhesion among these cells. As an example, human embryonal carcinoma 2102 cells display strong adhesion to plates coated with Gb4 ("Gb4-dependent cell adhesion"). This adhesion, which simulates homotypic 2102 cell aggregation, is based on interaction between Gb4 and nLc4, or between Gb4 and GalGb4 (IV3GalGb4; the major SSEA-3 epitope), as indicated by the following observations: (i) adhesion of 2102 cells or GSL-liposomes to GSL-coated plates in various combinations; (ii) inhibition of Gb4-dependent 2102 cell adhesion by preincubation of cells with anti-SSEA-3 or anti-nLc4 antibodies, or by pretreatment of Gb4-coated plates with aqueous micellar solution of nLc4 or GalGb4; (iii) decline of the cell adhesion in association with retinoic acid-induced differentiation, whereby SSEA-3 and nLc4 levels are reduced. Since cell adhesion is an essential prerequisite for induction of differentiation, as observed at each step of embryogenesis, expression of seven transcription factors following adhesion of 2102 cells to Gb4-coated plates, and to detergent-insoluble substrate adhesion matrix prepared from 2102 cells, were studied. In both types of adhesion, a strong enhancement of AP1 and CREB site binding activity was observed during the early stage (15-60 min following initial adhesion). Although 2102 cells showed strong adhesion to Gg3-coated plates, based on interaction between Gg3 and Gb4, adhesion of the cells to Gg3 did not cause changes of AP1 and CREB activity. No other transcription factors showed changes induced by Gg3- or Gb4-dependent adhesion.
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