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A new class mutation of low density lipoprotein receptor with altered carbohydrate chains
Abstract:
In a monensin-resistant mutant (Monr-31) of Chinese hamster ovary cells, the O-linked sugar chains of the low density lipoprotein (LDL) receptor are altered, suggesting a mutation at a Golgi apparatus gene. In a compactin-resistant mutant (MF-2) of Chinese hamster V79 cells, the mature LDL receptor is apparently 5000 daltons smaller; the difference is due to altered glycosylation of O-linked sugar chains. Hybrids between MF-2 and Monr-31 still produced LDL receptor molecules with aberrant sugar chains; thus both mutants are in the same complementation group. Krieger and his colleagues (Krieger, M., Kingsley, D., Sege, R., Hobbie, L., and Kozarsky, K. (1985) Trends. Biochem. Sci. 10, 447-452) have classified Chinese hamster ovary cell mutants with altered LDL receptor structure into four groups: ldlA, ldlB, ldlC, and ldlD. Cell-cell hybrids between their ldl mutants and Monr-31 produced wild type mature LDL receptors with normal molecular sizes, suggesting that these compactin- and monensin-resistant mutants define a new class of LDL receptor mutant. Since both of our mutants are defective in internalization of LDL, we assign them as int mutants. This may imply a further etiology for hypercholesterolemia, and cases can now be examined for such a class.
Insights
Mutant Chinese hamster cells resistant to monensin and compactin show altered low-density lipoprotein (LDL) receptor glycosylation, indicating a new class of LDL receptor defect potentially linked to hypercholesterolemia.
Area of Science:
- Biochemistry
- Cell Biology
- Genetics
Background:
- Mutations affecting the low-density lipoprotein (LDL) receptor can lead to hypercholesterolemia.
- Previous studies classified LDL receptor mutants into four groups (ldlA-D) based on altered receptor structure.
Purpose of the Study:
- To characterize novel monensin-resistant (Monr-31) and compactin-resistant (MF-2) Chinese hamster cell mutants with altered LDL receptors.
- To determine if these mutants belong to previously identified complementation groups or represent a new class.
Main Methods:
- Generating and analyzing monensin-resistant (Monr-31) and compactin-resistant (MF-2) Chinese hamster cell mutants.
- Investigating O-linked glycosylation of LDL receptors in these mutants.
- Performing cell-cell hybridization experiments with known ldl mutants and the novel mutants.
Main Results:
- Monr-31 and MF-2 cells exhibit altered O-linked sugar chains on their LDL receptors, with MF-2 showing a 5000-dalton reduction in mature receptor size due to glycosylation changes.
- Hybridization of MF-2 and Monr-31 yielded cells with aberrant sugar chains, indicating they belong to the same complementation group.
- Hybridization with previously classified ldl mutants (ldlA-D) resulted in wild-type LDL receptors, suggesting Monr-31 and MF-2 represent a new class of LDL receptor mutant.
- Both mutants were confirmed to be defective in LDL internalization, leading to their classification as 'int' mutants.
Conclusions:
- The monensin- and compactin-resistant mutants (Monr-31 and MF-2) define a new complementation group ('int' mutants) affecting LDL receptor function.
- This discovery suggests a novel etiology for hypercholesterolemia, warranting examination of clinical cases for this specific defect.