Apolipoprotein(a) stimulates nuclear translocation of β-catenin: a novel pathogenic mechanism for lipoprotein(a).

Lipoprotein(a) (Lp(a)) is associated with cardiovascular disease risk. This may be attributable to the ability of Lp(a) to elicit endothelial dysfunction. We previously reported that apolipoprotein(a) (apo(a); the distinguishing kringle-containing component of Lp(a)) elicits cytoskeletal rearrangements in vascular endothelial cells, resulting in increased cellular permeability. These effects require a strong lysine-binding site (LBS) in apo(a). We now report that apo(a) induces both nuclear β-catenin-mediated cyclooxygenase-2 (COX-2) expression and prostaglandin E2 secretion, indicating a proinflammatory role for Lp(a). Apo(a) caused the disruption of VE-cadherin/β-catenin complexes in a Src-dependent manner, decreased β-catenin phosphorylation, and increased phosphorylation of Akt and glycogen synthase kinase-3β, ultimately resulting in increased nuclear translocation of β-catenin; all of these effects are downstream of apo(a) attenuation of phosphatase and tensin homologue deleted on chromosome 10 activity. The β-catenin-mediated effects of apo(a) on COX-2 expression were absent using a mutant apo(a) lacking the strong LBS. Of interest, the normal and LBS mutant forms of apo(a) bound to human umbilical vein endothelial cells in a similar manner, and the binding of neither was affected by lysine analogues. Taken together, our findings suggest a novel mechanism by which apo(a) can induce proinflammatory and proatherosclerotic effects through modulation of vascular endothelial cell function.