TY - JOUR
T1 - Analysis of a mutant strain of human fibroblasts with a defect in the internalization of receptor-bound low density lipoprotein
AU - Brown, Michael S.
AU - Goldstein, Joseph L.
N1 - Funding Information:
Gloria Y . Brunschede and Mary K . Sobhani provided excellent technical assistance . Marian Eastman and Jean Helgeson provided invaluable help with the cell culture . We thank Dr . Neil Stone for sending us a skin biopsy on J .D . and for providing us with clinical information on this patient . This work was supported by research grants from the NIH (National Heart and Lung Institute and National Institute of General Medical Sciences) and the American Heart Association . M .S .B . is an established investigator of the American Heart Association . J .L .G . is the recipient of a USPHS Research Career Development Award .
PY - 1976/12
Y1 - 1976/12
N2 - A new type of mutation that affects a discrete step in the process of adsorptive endocytosis has been identified in one of 22 strains of fibroblasts derived from subjects with the clinical phenotype of homozygous familial hypercholesterolemia (FH). In this unique mutant strain (derived from subject J.D.), the cell surface receptor for plasma low density lipoprotein (LDL) was able to bind 125I-labeled LDL normally, but internalization of the receptor-bound lipoprotein failed to occur. Thus the defect in this strain differed from the defects found in the fibroblasts from the other 21 FH homozygote strains in which the binding of 125I-LDL to the receptor was either absent (receptor-negative) or markedly reduced (receptor-defective). The LDL receptor in the J.D. cells exhibited first, normal kinetics of high affinity binding at 4°C and 37°C; second, normal specificity (affinity for LDL more than 200 fold greater than for HDL); third, normal susceptibility to feedback suppression by 25-hydroxycholesterol plus cholesterol; and fourth, a normal rate of turnover when the cells were treated with cycloheximide. Despite its normal ability to bind 125I-LDL, the LDL receptor in the J.D. cells failed to transport its LDL into the cell, and degradation of the lipoprotein in cellular lysosomes therefore did not occur. As a result, the lipoprotein did not suppress 3-hydroxy-3-methylglutaryl coenzyme A reductase activity; nor did it activate cholesteryl ester formation. A phenocopy of the internalization defect in the J.D. cells could be created by incubation of normal fibroblasts with N-ethyl maleimide, an agent that did not affect 125I-LDL binding to the receptor but blocked its subsequent internalization by the cell. The current data indicate that at least two gene products are necessary for the adsorptive endocytosis of LDL: one that is required for the binding of the lipoprotein, and one that promotes the internalization of the receptor-bound ligand.
AB - A new type of mutation that affects a discrete step in the process of adsorptive endocytosis has been identified in one of 22 strains of fibroblasts derived from subjects with the clinical phenotype of homozygous familial hypercholesterolemia (FH). In this unique mutant strain (derived from subject J.D.), the cell surface receptor for plasma low density lipoprotein (LDL) was able to bind 125I-labeled LDL normally, but internalization of the receptor-bound lipoprotein failed to occur. Thus the defect in this strain differed from the defects found in the fibroblasts from the other 21 FH homozygote strains in which the binding of 125I-LDL to the receptor was either absent (receptor-negative) or markedly reduced (receptor-defective). The LDL receptor in the J.D. cells exhibited first, normal kinetics of high affinity binding at 4°C and 37°C; second, normal specificity (affinity for LDL more than 200 fold greater than for HDL); third, normal susceptibility to feedback suppression by 25-hydroxycholesterol plus cholesterol; and fourth, a normal rate of turnover when the cells were treated with cycloheximide. Despite its normal ability to bind 125I-LDL, the LDL receptor in the J.D. cells failed to transport its LDL into the cell, and degradation of the lipoprotein in cellular lysosomes therefore did not occur. As a result, the lipoprotein did not suppress 3-hydroxy-3-methylglutaryl coenzyme A reductase activity; nor did it activate cholesteryl ester formation. A phenocopy of the internalization defect in the J.D. cells could be created by incubation of normal fibroblasts with N-ethyl maleimide, an agent that did not affect 125I-LDL binding to the receptor but blocked its subsequent internalization by the cell. The current data indicate that at least two gene products are necessary for the adsorptive endocytosis of LDL: one that is required for the binding of the lipoprotein, and one that promotes the internalization of the receptor-bound ligand.
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U2 - 10.1016/0092-8674(76)90130-6
DO - 10.1016/0092-8674(76)90130-6
M3 - Article
C2 - 189940
AN - SCOPUS:0017246512
SN - 0092-8674
VL - 9
SP - 663
EP - 674
JO - Cell
JF - Cell
IS - 4 PART 2
ER -