FIGURE 8.

Scube1 forms a complex with BMP ligands and receptors and augments BMP signal activity. The expression plasmid encoding the Myc-tagged BMP2/BMP4 or IL-8 (A), HA-tagged BMPR-IA/IB or TLR4 (B), or FLAG-tagged BMPR-II (C) was transfected alone or with the FLAG-tagged SCUBE1 or Myc-tagged SCUBE1 in HEK-293T cells. After 2 days, cell lysates underwent immunoprecipitation (IP) and then Western blot analysis (WB) of expression of the indicated proteins to determine protein-protein interactions. D, SCUBE1 enhances BMP signaling. HepG2 cells were transfected with BRE-Luc and pRL-TK alone or with the expression plasmid encoding SCUBE1. Transfected cells were then incubated for 24 h with or without 50 ng/ml BMP2, and luciferase activity was measured. Relative luciferase activity represents firefly luciferase values normalized to Renilla activity. Data are means ± S.E. (error bars). *, p < 0.05.