Expression of Soluble Syndecan-1 or Heparanase by Myeloma Cells Enhances Levels of Angiogenic Growth Factors Present in Endothelial Cells.

Multiple myeloma is a devastating cancer with a high rate of morbidity and mortality. Our previous in vivo studies demonstrate that both shed syndecan-1 and heparanase can promote myeloma tumor growth, metastasis and angiogenesis. To examine the mechanism underlying this enhanced angiogenesis, human umbilical vein endothelial cells (HUVEC) were cocultured with cells of the CAG myeloma cell line (vector-only controls, CAG^control) or CAG cells engineered to express high levels of either soluble syndecan-1 ectodomain (CAG^ssyn1 ) or heparanase ( CAG^HPSE ). After coculture for 48 hours, levels of angiogenic growth factors present in the endothelial cells were examined. The goal was to determine if expression of either soluble syndecan-1 or heparanase by CAG myeloma cells altered growth factor levels relative to those present when control CAG cells were used. Co-culture with CAG^ssyn1 or CAG^HPSE cells did not enhance endothelial levels of FGF-2, while levels of hepatoma-derived growth factor (HDGF) and hepatocyte growth factor (HGF) were elevated in endothelia growing in the presence of CAG^ssyn1 cells but not CAG^HPSE cells or CAG^control cells. However, VEGF levels present in endothelial cells were substantially enhanced by the presence of CAG^ssyn1 (1.9-fold increase) or CAG^HPSE cells (1.6-fold increase). Surprisingly, levels of VEGF in conditioned media of cocultures containing either CAG^ssyn1 or CAG^HPSE cells was low. In contrast, when cultured in the absence of HUVECs, VEGF levels were elevated in conditioned media of both CAG^ssyn1and CAG^HPSE cells. Addition of this conditioned media containing high levels of VEGF to HUVECs growing in the absence of CAG cells did not result in an elevation of VEGF levels in the endothelial cells. Together, these experiments suggest that VEGF expression is upregulated in CAG cells expressing high levels of shed syndecan-1 or heparanase and that VEGF becomes associated with the endothelial cells only when they are cultured in the presence of the myeloma cells. This cross-talk between myeloma and endothelial cells may lead to the enhanced angiogenesis that occurs in vivo in tumors formed by myeloma cells producing high levels of shed syndecan-1 and/or heparanase.