Browsing by Subject "Rezeptor-Tyrosinkinasen"

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Posttranslationale Modifikationen der IL-6-Typ-Zytokin-Rezeptoren gp130 und LIFR und ihr Einfluss auf die Assoziation mit Detergenz-resistenten Membranmikrodomänen (DRM)
(2008) Ziegler, Inna; Graeve, Lutz
Post-translational modification of proteins is an important event in the regulation of cellular functions. Glycosylation or palmitoylation, but also ligand binding can affect the localization of proteins in membrane microdomains and thus affect signal transduction. The aim of this study was to analyze how posttranslational modifications of LIFR and the common signal transducer gp130 impact the translocation to detergent resistant membranes (DRMs, lipid rafts). Palmitoylation of cysteine residues within the transmembrane domain of a protein is considered to be one process that assists in the localization of proteins to DRMs. Gp130 has two cysteine residues C711 and C725 in its transmembrane domain. My studies indicate that these cysteine residues have no significant influence on lipid raft association of gp130. Contrary to our expectations, after isolation of DRMs with Brij 58 and Triton X-100 an increase of raft association of the C->A-mutants was detected. Partial DRM association of LIFR was confirmed by using Brij 58 and Triton X-100 protocols. Furthermore, two different N-glycosylation types of that receptor could be detected. The mannose-rich (precursor) species is preferentially found in non-DRMs and is degraded by Endo-Glycosidase Hf. The hybrid-type (mature) tends towards an association with DRMs. My results indicate that only the mature-type of LIFR was phosphorylated after LIF binding to the receptor complex in 3T3-L1 and HepG2 cells. Combined with other data from our workgroup these findings suggest that only the mature-type of LIFR is expressed at the plasma membrane surface and involved in signal transduction. After stimulation with LIF an increase of LIFR tyrosine phosphorylation was observed in DRMs in HepG2 cells. However, phosphorylation of gp130 was detected only in non-DRMs fractions after stimulation with LIF. The inconsistency of these results can be explained with methodical problems. Furthermore, the translocation of phosphorylated receptors described above could not confirmed in 3T3-L1 cells. In this cell line, the activation of gp130 and LIFR occurs in detergent-resistant membranes. These findings indicate differences between cell lines with respect to receptor activation and translocation within the plasma membrane on the one hand and demonstrate a differential sensitivity of raft subdomains to extraction by different detergents on the other hand.