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An acceptor splice site mutation in intron 16 of the low density lipoprotein receptor gene leads to an elongated, internalization defective receptor

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Author: Lombardi, P. · Hoffer, M.J.V. · Top, B. · Wit, E. de · Gevers Leuven, J.A. · Frants, R.R. · Havekes, L.M.
Type:article
Date:1993
Institution: Gaubius Instituut TNO
Source:Atherosclerosis, 1-2, 104, 117-128
Identifier: 232339
Keywords: Denaturating gradient gel electrophoresis · Polymerase chain reaction · Complementary dna · Low density lipoprotein receptor · Case report · Dna sequence · Familial hypercholesterolemia · Gel electrophoresis · Mutation · Pedigree analysis · Polymerase chain reaction · Adult · Amino Acid Sequence · Base Sequence · Cells, Cultured · Electrophoresis · Female · Homozygote · Human · Hypercholesterolemia, Familial · Introns · Molecular Sequence Data · Pedigree · Point Mutation · Reading Frames · Receptors, LDL · RNA Splicing · Sequence Analysis, DNA · Support, Non-U.S. Gov't

Abstract

In this report, we describe the characterization of a mutation in the low density lipoprotein (LDL) receptor gene of a true homozygous familial hypercholesterolemic (FH) patient. The combined use of denaturing gradient gel electrophoresis (DGGE) and DNA sequence analysis revealed a unique A to G transition in the penultimate 3'-nucleotide of intron 16 of the LDL receptor gene, which disrupts the acceptor splice site. cDNA sequence analysis indicated that a cryptic splice site was activated in intron 16, upstream from the original splice site, leading to the inclusion of 62 nucleotides and a reading frame-shift. The resulting new translation product contains a stretch of 154 amino acids at the carboxy-terminal that have no resemblance to the normal receptor protein. To elucidate the biological effects of the mutation, the structural and functional properties of the mutated LDL receptor protein were studied. Immunoprecipitation of the newly synthesized LDL receptors showed that an aberrant precursor form of the LDL receptor protein was synthesized, about 10 kDa larger than normal, which is not further processed to the mature form. Some 50% of the normal LDL binding activity was found on the cell surface of the patient's fibroblasts, whereas internalization and degradation of LDL were abolished. Molecular Sequence Numbers: GENBANK: L06914, L06915, L06916, L06917, L06918, L06919, L22587, L22588, L22589, S70123; Chemicals/CAS: Receptors, LDL