FIGURE 2.

Shed syndecan-1 down-regulates histone acetyltransferase activity and histone H3 acetylation. A, ST2 cells incubated for 6 h with conditioned medium containing sSDC1 diminished the level of acetylated histone H3. This effect was prevented by pretreatment of medium with bacterial heparinase III (Hep III). Cell lysates were analyzed by Western blot for acetylated histone H3 or total histone H3. B, in experiments similar to those in A, histone acetyltransferase activity was quantified by fluorimetric activity assay. RFU, relative fluorescence units. *, p < 0.05 versus untreated controls; #, not significant versus untreated control. C, sSDC1 was immunoprecipitated (IP) from nuclear extracts and probed by Western blot for syndecan-1 and p300 (middle lane). The p300 co-immunoprecipitated with sSDC1. Pretreatment of extracts with hep III followed by sSDC1 immunoprecipitation failed to co-immunoprecipitate p300 (right lane). Note that the size of syndecan-1 is diminished following hep III treatment (right lane) confirming that the enzyme is cleaving the heparan sulfate chains, although the chondroitin sulfate chains remain attached to the core protein.