The human cation-independent mannose 6-phosphate receptor. Cloning and sequence of the full-length cDNA and expression of functional receptor in COS cells.

Abstract

We have cloned and sequenced the full-length cDNA for the human cation-independent mannose 6-phosphate receptor from four overlapping clones. The 9104-nucleotide sequence contains 7473 nucleotides which encode a protein of 2491 amino acids. The amino acid sequence includes a putative signal sequence of 40 amino acids, an extracytoplasmic domain consisting of 15 homologous repeat sequences of 134-167 amino acids, a transmembrane region of 23 amino acids, and a cytoplasmic domain of 164 amino acids. The predicted molecular size is greater than 270 kDa. Repeats 7-15 of the extracytoplasmic domain of the human receptor are highly homologous with the sequence recently reported for the partial cDNA for the bovine receptor (Lobel, P., Dahms, N. M., Breitmeyer, J., Chirgwin, J. M., and Kornfeld, S. (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 2233-2237). The nucleotide sequence for the full-length cDNA and the deduced amino acid sequence for the cation-independent mannose 6-phosphate receptor, which are reported here, are strikingly similar (99.8% identical at the nucleotide level and 99.4% identical at the amino acid level) to those recently reported for the human insulin-like growth factor II receptor from HepG2 hepatoma cells (Morgan, D. O., Edman, J.D., Standring, D. N., Fried, V. A., Smith, M. C., Roth, R. A., and Rutter, W. J. (1987) Nature 329, 301-307). These findings support the suggestion that the cation-independent mannose 6-phosphate receptor for lysosomal enzymes is a multifunctional binding protein which is identical with the insulin-like growth factor II receptor. A cDNA construct containing the full coding sequence for the cation-independent mannose 6-phosphate receptor in the expression vector pSVL was used to transfect COS cells. Expression of the cDNA in transfected COS cells produced a cell-surface protein which co-migrated on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with authentic human receptor, bound to an affinity column and was specifically eluted with mannose 6-phosphate, mediated cell-surface binding and endocytosis of beta-glucuronidase, and targeted the endocytosed enzyme to lysosomes.