Adiponectin inhibits cell proliferation by interacting with several growth factors in an oligomerization-dependent manner

Adiponectin, an adipocyte-specific secretory protein, is present in serum as three oligomeric complexes. Apart from its roles as an anti-diabetic and anti-atherogenic hormone, adiponectin has been implicated as an important regulator of cell growth and tissue remodeling. Here we show that some of these functions might be mediated by the specific interactions of adiponectin with several important growth factors. Among six different growth factors examined, adiponectin was found to bind with platelet-derived growth factor BB (PDGF-BB), basic fibroblast growth factor (FGF), and heparin-binding epidermal growth factor-like growth factor (HB EGF) with distinct affinities. The bindings of adiponectin with these growth factors are oligomerization-dependent. PDGF-BB bound to the high molecular weight (HMW) and middle molecular weight (MMW) complexes, but not to the low molecular weight (LMW) complex of adiponectin. Basic FGF preferentially interacted with the HMW form, whereas HB EGF bound to all three forms with comparable affinities. These three growth factors did not compete with each other for their bindings to adiponectin, suggesting the involvement of distinct binding sites. The interactions of adiponectin with PDGF-BB, basic FGF, and HB EGF precluded the bindings to their respective membrane receptors and attenuated the DNA synthesis and cell proliferation induced by these growth factors. Small interfering RNA-mediated down-regulation of adiponectin receptors did not affect the suppressive effects of adiponectin on cell proliferation stimulated by these growth factors. These data collectively suggest that the oligomeric complexes of adiponectin can modulate the biological actions of several growth factors by controlling their bioavailability at a pre-receptor level and that this effect might partly account for the anti-atherogenic, anti-angiogenic, and anti-proliferative functions of adiponectin.