The constitutive photomorphogenesis 9 signalosome directs vascular endothelial growth factor production in tumor cells

Angiogenesis is a prerequisite for solid tumor growth and metastasis. Eluci dation of the signaling pathways that control tumor angiogenesis constitute s the basis for a rational antiangiogenic tumor therapy. Here we show that the production of vascular endothelial growth factor (VEGF) in HeLa and HL- 60 cells is directed by the constitutive photomorphogenesis 9 signalosome ( CSN). The CSN is a kinase complex that cooperates with the ubiquitin/26S pr oteasome system in regulating the stability of proteins involved in signal transduction. VEGF expression is controlled by the transcription factors ac tivator protein (AP)-1, AP-2, SP-1, and hypoxia-inducible factor 1. Inhibit ion of CSN kinase activity by 50 muM curcumin for 2 h decreases the cellula r c-Jun concentration, resulting in a reduction of the VEGF production by a pproximately 75%. The removal of the inhibitor from the cells led to a time -dependent recovery of endogenous c-Jun that is paralleled by increasing VE GF production. Elevated cellular CSN activity induced by CSN subunit 2 over expression causes increased VEGF production in HeLa cells. A competitor of CSN-dependent c-Jun phosphorylation, the NH2-terminal c-Jun fragment Deltac -jun(1-226), inhibits VEGF production in HeLa cells. The transcription fact ors AP-2 and SP-1 act independently of the CSN. They contribute less than a quarter to basal VEGF production. Under our experimental conditions, hypox ia-inducible factor la protein was not detected. Overexpression of the tumo r suppressor p53 reduces VEGF production in HeLa cells. p53 competes with c -Jun for CSN-specific phosphorylation with the consequence of c-Jun destabi lization. We conclude that CSN-directed c-Jun signaling mediates high VEGF production in HeLa and HL-60 cells. The data provide an explanation for the known antiangiogenic and antitumorigenic activities of curcumin. Because t he CSN regulates the major part of VEGF production in the tested tumor cell s, it constitutes a potentially important target for tumor therapy.