Efficient internalization of IL-2 depends on the distal portion of the cytoplasmic tail of the IL-2R common gamma-chain and a lymphoid cell environment.
The common gamma-chain (gammac), a subunit of the IL-2R, is essential for high affinity ligand binding and signal transduction due to Jak3 association to gammac. Another consequence of IL-2/IL-2R interaction is rapid receptor-mediated endocytosis of the receptor-ligand complex. In the present study, we establish that this rapid endocytosis of IL-2 in a T cell tumor line is dependent upon the cytoplasmic tail of gammac. Deletion mutants of the cytoplasmic tail mapped this activity to 9 aa of gammac, 45-54 aa distal to the transmembrane region. In contrast, ligand-independent constitutive endocytosis of gammac occurred more slowly and was dependent upon a PEST sequence in a more membrane-proximal region of the cytoplasmic tail of gammac. Thus, this receptor subunit may use distinct sorting signals for its constitutive regulation and ligand-induced endocytosis. Rapid endocytosis of IL-2 was inhibited by the tyrosine kinase inhibitor genistein, implicating a role for a signal transduction pathway in IL-2 internalization. However, one T cell line bearing a mutant gammac exhibited impaired endocytosis of IL-2, despite normal IL-2-induced Jak/STAT activation. Furthermore, inefficient endocytosis of IL-2 was noted after transfection of the COS7 epithelial cell line with the IL-2R, and further reconstitution of these cells with Jak/STAT proteins did not enhance this internalization. Collectively, these latter findings indicate that rapid endocytosis of IL-2 is dependent upon cellular signaling in lymphoid cell environment that is not solely a consequence of the presence of the Jak/STAT pathway.
Yu
A
A
Department of Microbiology and Immunology, University of Miami School of Medicine, Miami, FL 33136, USA.
Olosz
F
F
Choi
C Y
CY
Malek
T R
TR
D000818:Animals; D003593:Cytoplasm / Q000235:genetics / Q000276:immunology / Q000378:metabolism / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000502:physiology; D004789:Enzyme Activation / Q000276:immunology; D007376:Interleukin-2 / Q000378:metabolism*; D053613:Janus Kinase 1; D053616:Janus Kinase 3; D008214:Lymphocytes / Q000276:immunology* / Q000378:metabolism*; D051379:Mice; D008894:Milk Proteins; D009928:Organ Specificity / Q000235:genetics / Q000276:immunology; D011505:Protein-Tyrosine Kinases / Q000378:metabolism / Q000502:physiology; D018121:Receptors, Cytokine / Q000235:genetics / Q000502:physiology*; D015375:Receptors, Interleukin-2 / Q000235:genetics / Q000502:physiology*; D050799:STAT5 Transcription Factor; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology; D015534:Trans-Activators / Q000502:physiology; D014162:Transfection; D014407:Tumor Cells, Cultured
D004268:DNA-Binding Proteins; D007376:Interleukin-2; D008894:Milk Proteins; D018121:Receptors, Cytokine; D015375:Receptors, Interleukin-2; D050799:STAT5 Transcription Factor; D015534:Trans-Activators; D011505:Protein-Tyrosine Kinases; C507905:Jak1 protein, mouse; C507935:Jak3 protein, mouse; D053613:Janus Kinase 1; D053616:Janus Kinase 3