Signal Transduction by a CD16/CD7/Jak2 Fusion Protein (∗)

• Published in: The Journal of biological chemistry 1995-08, Vol.270 (31), p.18420-18427
• Main Authors: Sakai, Ikuya, Nabell, Lisle, Kraft, Andrew S.
• Format: Article
• Language: English
• Subjects: Animals; Antigens, CD - genetics; Antigens, CD - metabolism; Antigens, CD7; Antigens, Differentiation, T-Lymphocyte - genetics; Antigens, Differentiation, T-Lymphocyte - metabolism; B-Lymphocytes; Base Sequence; Calcium-Calmodulin-Dependent Protein Kinases - metabolism; Cell Line; Cross-Linking Reagents; Enzyme Activation; Hematopoietic Stem Cells; Janus Kinase 2; Mice; Molecular Sequence Data; Phosphoproteins - biosynthesis; Phosphorylation; Protein-Tyrosine Kinases - genetics; Protein-Tyrosine Kinases - metabolism; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-myc - biosynthesis; Receptors, IgG - genetics; Receptors, IgG - metabolism; Recombinant Fusion Proteins - metabolism; Signal Transduction; Transcription, Genetic
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.270.31.18420

The addition of interleukin-3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GM-CSF) to hormone-dependent cells induces tyrosine phosphorylation of Janus protein kinase 2 (Jak2) and activates its in vitro kinase activity. To explore the role of Jak2 in IL-3/GM-CSF-mediated signal transduction, we constructed a CD16/CD7/Jak2 (CD16/Jak2) fusion gene containing the external domain of CD16 and the entire Jak2 molecule and expressed this fusion protein using a recombinant vaccinia virus. The clustering of CD16/Jak2 fusion protein by cross-linking with an anti-CD16 antibody induced autophosphorylation of the fusion protein but did not induce the phosphorylation of either the endogenous Jak2 or the β chain. Cross-linking of CD16/Jak2 stimulates the tyrosine phosphorylation of a large group of proteins that are also phosphorylated after the addition of IL-3 or GM-CSF and include proteins of 145, 97, 67, 52, and 42 kDa. Closer analysis demonstrated that the CD16/Jak2 phosphorylates Shc, a 52-kDa protein, and the 145-kDa protein associated tightly with Shc, as well as mitogen-associated protein kinase (pp42). Electrophoretic mobility shift assays demonstrate that CD16/Jak2 activates the ability of signal transduction and activation of transcription (STAT) proteins to bind to an inferon-γ-activated sequence oligonucleotide in a manner similar to that seen after IL-3 treatment. Cross-linking of the CD16/Jak2 protein stimulated increases in c-fos and junB similar to IL-3 but did not cause major changes in the levels of the c-myc message, which normally increases after IL-3 treatment. Thus, a transmembrane CD16/Jak2 fusion is capable of activating protein phosphorylation and mRNA transcription in a manner similar but not identical to hematopoietic growth factors.