title: A single internalization signal from the di-leucine family is critical for constitutive endocytosis of the type II TGF-beta receptor.
abstract: Endocytosis has an important contribution to the regulation of the surface expression levels of many receptors. In spite of the central role of the transforming growth factor beta (TGF-beta) receptors in numerous cellular and physiological processes, their endocytosis is largely unexplored. Current information on TGF-beta receptor endocytosis relies exclusively on studies with chimeric constructs containing the extracellular domain of the GM-CSF receptors, following the internalization of the GM-CSF ligand; the conformation and interactions of the chimeric receptors (and therefore their endocytosis) may differ considerably from those of the native TGF-beta receptors. Furthermore, there are no data on the potential endocytosis motif(s) of the TGF-beta receptors or other receptor Ser/Thr kinases. Here, we report the use of type II TGF-beta receptors, myc-tagged at their extracellular terminus, to investigate their endocytosis. Employing fluorescent antibody fragments to label exclusively the cell surface myc-tagged receptors exposed to the external milieu, made it possible to follow the internalization of the receptors, without the complications that render labeling with TGF-beta (which binds to many cellular proteins) unsuitable for such studies. The results demonstrate that the full-length type II TGF-beta receptor undergoes constitutive endocytosis via clathrin-coated pits. Using a series of truncation and deletion mutants of this receptor, we identified a short peptide sequence (I(218)I(219)L(220)), which conforms to the consensus of internalization motifs from the di-leucine family, as the major endocytosis signal of the receptor. The functional importance of this sequence in the full-length receptor was validated by the near complete loss of internalization upon mutation of these three amino acids to alanine.
authors: Dept of Neurobiochemistry, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel.
authors: M
authors: M
authors: Ehrlich
authors: A
authors: A
authors: Shmuely
authors: Y I
authors: YI
authors: Henis
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D001483:Base Sequence; D019556:COS Cells; D017931:DNA Primers; D004705:Endocytosis; D007930:Leucine / Q000737:chemistry / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D016296:Mutagenesis; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D017931:DNA Primers; D018125:Receptors, Transforming Growth Factor beta; D007930:Leucine