Identification of a lipoprotein receptor-related protein in Giardia lamblia.

TOUZ MC; MIRAS S; ROPOLO AS; RIVERO MR

Orvieto. Italia.

Conferencia; III International Giardia and Cryptosporidium Conference.; 2009

The LDL receptor-related protein (LRP) is a large endocytic receptor that plays diverse roles such as in lipoprotein metabolism, degradation of proteases, and activation of lysosomal enzymes, among others. We identified a protein that shares a cysteine-rich N-terminal domain with LRP1 and LRP1b and named gLRP for Giardia Lipoprotein Receptor-related Protein. Using confocal microscopy, we determined that the HA-tagged gLRP colocalized with LDL at the plasma membrane and in the lysosome-like peripheral vacuoles (PVs). Surface localization of gLRP was confirmed using TIRFM. Interestingly, the cysteine-rich domain has been shown to be important for LDL binding and LDL internalization by endocytosis in other cells. In this sense, similar to LRP1 and LRP1b, gLRP contains a potential FXNPXY-type internalization signal (FNSPTY) within its cytoplasmic tail. By YTH and co-IPP assays, we found that gLRP directly bind to the medium subunit of Giardia adaptor protein 2 (gAP2). Furthermore, epifluorescence microscopy demonstrated that gLRP was also present in the nuclei. The nuclear localization of gLRP implies the participation of this receptor in cell signaling, as has been extensively described for the LRP family. These results suggest that gLRP is involved in the internalization of cholesterol from LDL via a regulated AP2-dependent pathway with a potential role in intracellular signalling.   Supported by R01 TW007245, NIH (USA), and PICT00698, FONCyT (Argentina).