A novel biological function of soluble biglycan: Induction of erythropoietin production and polycythemia.

Secondary polycythemia, a disease characterized by a selective increase in circulating mature erythrocytes, is caused by enhanced erythropoietin (Epo) concentrations triggered by hypoxia-inducible factor-2α (HIF-2α). While mechanisms of hypoxia-dependent stabilization of HIF-2α protein are well established, data regarding oxygen-independent regulation of HIF-2α are sparse. In this study, we generated a novel transgenic mouse model, in which biglycan was constitutively overexpressed and secreted by hepatocytes (BGN (Tg)), thereby providing a constant source of biglycan released into the blood stream. We discovered that although the mice were apparently normal, they harbored an increase in mature circulating erythrocytes. In addition to erythrocytosis, the BGN (Tg) mice showed elevated hemoglobin concentrations, hematocrit values and enhanced total iron binding capacity, revealing a clinical picture of polycythemia. In BGN (Tg) mice markedly enhanced Epo mRNA expression was observed in the liver and kidney, while elevated Epo protein levels were found in liver, kidney and blood. Mechanistically, we showed that the transgenic animals had an abundance of HIF-2α protein in the liver and kidney. Finally, by transiently overexpressing circulating biglycan in mice deficient in various Toll-like receptors (TLRs), we determined that this novel function of biglycan to promote Epo synthesis was specifically mediated by a selective interaction with TLR2. Thus, we discovered a novel biological pathway of soluble biglycan inducing HIF-2α protein stabilization and Epo production presumably in an oxygen-independent manner, ultimately giving rise to secondary polycythemia

Androgen receptor expression induces FGF2, FGF-binding protein production, and FGF2 release in prostate carcinoma cells: Role of FGF2 in growth, survival, and androgen receptor down-modulation

BACKGROUND. Alterations in fibroblast growth factors (FGFs) production and/or FGF receptors expression have been described to play key roles in prostate tumor progression, particularly in androgen-independent tumors. However, the role of androgen receptor (AR) in altering FGF-mediated growth and survival of prostatic neoplastic cells has not been completely defined. In this study, we investigated the alterations in FGF2 production and utilization by the PC3 cell line, after transfection with a full-length AR. METHODS. FGF1,2,7, FGF-binding protein (FGF-BP) production and FGF receptor (FGFR) 1-4 expression were investigated by polymerase chain reaction (PCR) and Western blot analysis. RESULTS. De novo AR expression by PC3 cells restores FGFR2 IIIb isoform expression and sensitivity to FGF7 and FGF2. Androgen stimulation induces AR+ PC3 clones to secrete FGF-BP, likely responsible for activation and mobilization from the extracellular matrix of the high amounts of FGF2 produced by the same cells. In addition to the effects on cell proliferation, FGF2 maintains the survival of AR+ PC3 clones through a positive modulation of the Bcl-2 protein and down-modulates AR protein expression, allowing the escape of selected clones from androgen regulation. CONCLUSION. In the presence of an active AR, the combined production of FGF2 and FGF-BP may play an important role in the progression of prostate cancer through the selection of AR+ clones expressing high levels of Bcl-2. © 2002 Wiley-Liss, Inc