IDENTIFICATION OF THE BIOSYNTHETIC LEUKOTRIENE C-4 EXPORT PUMP IN MURINE MASTOCYTOMA-CELLS AS A HOMOLOG OF THE MULTIDRUG-RESISTANCE PROTEIN

A membrane glycoprotein of 190 kDa has been identified previously by p hotoaffinity labeling as a candidate for the ATP-dependent export pump for leukotriene C-4 in mastocytoma cells [Leier, I., Jedlitschky, G., Buchholz, U. & Keppler, D. (1994) Eur. J. Biochem. 220, 599-606]. The present study indicates that this protein represents the murine homol og of the human multidrug resistance protein (MRP). In immunoblot anal yses several polyclonal anti-MRP antibodies and one monoclonal antibod y recognized the protein of 190-kDa in plasma membranes of mastocytoma cells. Immunoprecipitation after photoaffinity labeling with [H-3]leu kotriene C-4 precipitated the labeled 190-kDa glycoprotein. Deglycosyl ation by glycopeptide N-glycosidase F of mastocytoma membrane proteins was performed in comparison with membranes from MRP-overexpressing ce lls and resulted in a reduction of the molecular mass of 190 kDa by ab out 20 kDa in all membrane preparations. The expression of the murine mrp gene in the mastocytoma cells was analyzed by amplification and se quencing of two mrp cDNA fragments in the first nucleotide binding dom ain (182 bp) and in a domain proximal to the 3'-end (291 bp). The dedu ced amino acid sequences of these fragments were identical with murine Mrp and 86.7% and 89.7% identical with the corresponding sequences of human MRP. These results indicate that the ATP-dependent release of l eukotriene C-4 by murine mastocytoma cells is mediated by murine Mrp.