IL-32 Promotes Angiogenesis

IL-32 is a multifaceted cytokine with a role in infections, autoimmune diseases, and cancer, and it exerts diverse functions, including aggravation of inflammation and inhibition of virus propagation. We previously identified IL-32 as a critical regulator of endothelial cell (EC) functions, and we now reveal that IL-32 also possesses angiogenic properties. The hyperproliferative ECs of human pulmonary arterial hypertension and glioblastoma multiforme exhibited a markedly increased abundance of IL-32, and, significantly, the cytokine colocalized with integrin alpha v beta(3). Vascular endothelial growth factor (VEGF) receptor blockade, which resulted in EC hyperproliferation, increased IL-32 three-fold. Small interfering RNA-mediated silencing of IL-32 negated the 58% proliferation of ECs that occurred within 24 h in scrambled-transfected controls. Reduction of IL-32 neither affected apoptosis (insignificant changes in Bak-1, Bcl-2, Bcl-x(L), lactate dehydrogenase, annexin V, and propidium iodide) nor VEGF or TGF-beta levels, but siIL-32-transfected adult and neonatal ECs produced up to 61% less NO, IL-8, and matrix metalloproteinase-9, and up to 3-fold more activin A and endostatin. In coculture-based angiogenesis assays, IL-32 gamma dose-dependently increased tube formation up to 3-fold; an alpha v beta(3) inhibitor prevented this activity and reduced IL-32 gamma-induced IL-8 by 85%. In matrigel plugs loaded with IL-32 gamma, VEGF, or vehicle and injected into live mice, we observed the anticipated VEGF-induced increase in neocapillarization (8-fold versus vehicle), but unexpectedly, IL-32 gamma was equally angiogenic. A second signal such as IFN-gamma was required to render cells responsive to exogenous IL-32 gamma; importantly, this was confirmed using a completely synthetic preparation of IL-32 gamma. In summary, we add angiogenic properties that are mediated by integrin alpha v beta(3) but VEGF-independent to the portfolio of IL-32, implicating a role for this versatile cytokine in pulmonary arterial hypertension and neoplastic diseases.