Chronic exposure to cadmium (Cd) damages the kidney. Circulating Cd bound to the high-affinity metal-binding protein metallothionein (CdMT) is filtered by the kidney and taken up by proximal tubule cells (PTC) where toxicity develops. Receptor-mediated endocytosis (RME) is responsible for protein reabsorption by PTC. The receptor-complex megalin:cubilin is partly responsible for RME of CdMT by cultured PTC (WKPT-0293 Cl.2) causing apoptosis. A cell-surface receptor for lipocalin-2 (24p3, NGAL), a secreted protein binding to iron-containing siderophores, has been recently cloned. This receptor (Lip2R) modulates iron uptake and apoptosis in cancer cells. Lip2R is expressed in WKPT-0293.Cl.2 cells by RT-PCR, immunoblotting and immunofluorescence microscopy (IFM). In cultured PTC, lipocalin-2 reduced CdMT toxicity, hence we hypothesized that Lip2R contributes to RME of CdMT and other protein-metal complexes. We transiently transfected CHO cells that do not express megalin:cubilin with Lip2R which was mainly expressed in plasma membranes. Cells were incubated with the Alexa-coupled proteins MT, transferrin (Tf) or the plant Cd-detoxifying phytochelatin (PC) and uptake was studied by IFM. CdMT toxicity was investigated by MTT assay and apoptosis measured by Hoe33432 fluorescence staining. All three Alexa-coupled proteins were selectively taken up by Lip2R-overexpressing cells. CdMT induced apoptotic cell death in Lip2R-, but not in vector-transfected cells and saturated at 24 hours exposure and 1.4mM MT/10 mM Cd²⁺. At this MT concentration the kinetics of Alexa546-MT uptake mirrored the time course of CdMT toxicity. Hence, MT, Tf and PC are ligands of the Lip2R which, in addition to megalin:cubilin, mediates RME of CdMT and cell death. Funded by DFG TH345/11-1.