Abstract
Megalin is a member of the LDL receptor gene family that plays an important role in forebrain development and in cellular vitamin D metabolism through endocytic uptake of vitamin D metabolites. Similar to other receptors in this gene family, megalin is believed to functionally interact with intracellular proteins through adaptors that bind to the receptor tail and regulate its endocytic and signal transducing activities. Using yeast two-hybrid screens, we identified a novel scaffold protein with tetratrico peptide repeats, the megalin-binding protein (MegBP) that associates with the receptor. The binding site of MegBP was mapped to an N-terminal region on the receptor tail harboring a proline-rich peptide element. MegBP binding did not block the endocytic activity of the receptor; however, overexpression resulted in cellular lethality. In further screens, we identified proteins that bound to MegBP and thus might be recruited to the megalin tail. MegBP-interacting partners included several transcriptional regulators such as the SKI-interacting protein (SKIP), a co-activator of the vitamin D receptor. These finding suggest a model whereby megalin directly participates in transcriptional regulation through controlled sequestration or release of transcription factors via MegBP.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Adaptor Proteins, Signal Transducing*
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Adaptor Proteins, Vesicular Transport / genetics
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Adaptor Proteins, Vesicular Transport / isolation & purification*
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Amino Acid Sequence / genetics
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Animals
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Base Sequence / genetics
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Binding Sites / physiology
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Carrier Proteins / genetics
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Carrier Proteins / isolation & purification*
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Carrier Proteins / metabolism
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Cell Line
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Cell Membrane / metabolism*
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DNA, Complementary / analysis
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DNA, Complementary / genetics
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Endocytosis / physiology*
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Eukaryotic Cells / metabolism*
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Genes, Regulator / physiology*
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Humans
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Ligands
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Low Density Lipoprotein Receptor-Related Protein-2 / genetics
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Low Density Lipoprotein Receptor-Related Protein-2 / isolation & purification*
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Low Density Lipoprotein Receptor-Related Protein-2 / metabolism*
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Mice
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Molecular Sequence Data
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Nuclear Matrix-Associated Proteins / genetics
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Nuclear Matrix-Associated Proteins / isolation & purification*
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Peptides / genetics
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Peptides / metabolism
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Protein Binding / physiology
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Protein Structure, Tertiary / physiology
Substances
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Adaptor Proteins, Signal Transducing
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Adaptor Proteins, Vesicular Transport
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Carrier Proteins
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DNA, Complementary
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LRP2BP protein, human
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Ligands
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Low Density Lipoprotein Receptor-Related Protein-2
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Nuclear Matrix-Associated Proteins
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Peptides
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SPHKAP protein, human
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megalinbinding protein, mouse