LDL induces intracellular signalling and cell migration via atypical LDL-binding protein T-cadherin

Cadherins are a superfamily of adhesion molecules that mediate Ca²⁺-dependent cell–cell adhesion. T-cadherin (T-cad), a unique glycosylphosphatidylinositol-anchored member of the cadherin superfamily, was initially identified by immunoblotting of vascular cell membranes as an atypical low affinity low density lipoprotein (LDL)-binding protein. It is not known whether this heterophilic interaction is physiologically relevant. Expression of T-cadherin is upregulated in vascular cells during atherosclerosis, restenosis and tumour angiogenesis, conditions characterized by enhanced cell migration and growth. Elevated levels of serum low density lipoproteins (LDL), which result in cholesterol accumulation in vascular wall, is a widely accepted risk factor in atherosclerosis development. Additionally to its metabolic effects, LDL can produce hormone-like effects in a number of cell types. This study has utilized HEK293 cells and L929 cells stably transfected with T-cadherin cDNA to investigate T-cad-dependent responses to LDL. Stable expression of T-cad in both HEK293 and L929 cells results in significantly (p < 0.05) elevated specific surface binding of I¹²⁵]-LDL. Compared with mock-transfectants, cells expressing T-cad exhibit significantly (p < 0.01) enhanced LDL-induced mobilization of intracellular Ca²⁺-stores and a significantly (p < 0.01) increased migration toward an LDL gradient (0.1% BSA + 60 g/ml LDL) in Boyden chamber migration assay. Thus LDL-binding to T-cad is capable of activating physiologically relevant intracellular signaling and functional responses.