title: The Jak1 SH2 domain does not fulfill a classical SH2 function in Jak/STAT signaling but plays a structural role for receptor interaction and up-regulation of receptor surface expression.
abstract: The presence of a Src homology 2 (SH2) domain sequence similarity in the sequence of Janus kinases (Jaks) has been discussed since the first descriptions of these enzymes. We performed an in depth study to determine the function of the Jak1 SH2 domain. We investigated the functionality of the Jak1 SH2 domain by stably reconstituting Jak1-defective human fibrosarcoma cells U4C with endogenous amounts of Jak1 in which the crucial arginine residue Arg466 within the SH2 domain has been replaced by lysine. This mutant still binds to the receptor subunits gp130 and OSMR. Moreover, the SH2 R466K mutation does not affect the subcellular distribution of Jak1 as assessed by cell fractionation and confocal microscopy of cells expressing endogenous levels of non-tagged or a yellow fluorescent protein (YFP)-tagged Jak1-R466K, respectively. Likewise, the signaling capacity of Jak1 was not affected by this point mutation. However, we found that the SH2 domain is structurally important for cytokine receptor binding and surface expression of the OSMR.
authors.affiliation: Institut für Biochemie, Uniklinik Aachen, Pauwelsstrasse 30, 52074 Aachen, Germany.
authors.forename: Simone
authors.initials: S
authors.lastname: Radtke
authors.forename: Serge
authors.initials: S
authors.lastname: Haan
authors.forename: Angela
authors.initials: A
authors.lastname: Jörissen
authors.forename: Heike M
authors.initials: HM
authors.lastname: Hermanns
authors.forename: Sandra
authors.initials: S
authors.lastname: Diefenbach
authors.forename: Tanya
authors.initials: T
authors.lastname: Smyczek
authors.forename: Hildegard
authors.initials: H
authors.lastname: Schmitz-Vandeleur
authors.forename: Peter C
authors.initials: PC
authors.lastname: Heinrich
authors.forename: Iris
authors.initials: I
authors.lastname: Behrmann
authors.forename: Claude
authors.initials: C
authors.lastname: Haan
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D045744:Cell Line, Tumor; D002645:Chickens; D002522:Chlorocebus aethiops; D004330:Drosophila; D005354:Fibrosarcoma; D005399:Fishes; D006801:Humans; D007372:Interferons / Q000378:metabolism; D015850:Interleukin-6 / Q000378:metabolism; D053613:Janus Kinase 1; D008253:Macaca mulatta; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017434:Protein Structure, Tertiary; D011505:Protein-Tyrosine Kinases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D013552:Swine; D015854:Up-Regulation / Q000502:physiology; D018909:src Homology Domains / Q000502:physiology*
chemical_list: D015850:Interleukin-6; D011956:Receptors, Cell Surface; D007372:Interferons; D011505:Protein-Tyrosine Kinases; C507904:JAK1 protein, human; C507905:Jak1 protein, mouse; C507906:Jak1 protein, rat; D053613:Janus Kinase 1