After the intraportal injection of EGF, the EGF receptor (EGFR) is rapidly internalized into hepatic endosomes where it remains largely receptor bound (Lai et al., 1989. J. Cell Biol. 109:2751-2760). In the present study, we evaluated the phosphotyrosine content of EGFRs at the cell surface and in endosomes in order to assess the consequences of internalization. Quantitative estimates of specif...

Herpes simplex virus 1 encodes at least four genes whose functions include blocking apoptosis induced by exogenous agents (e.g., sorbitol, Fas ligand, and BAD protein) or replication-incompetent mutants (e.g., the d120 mutant lacking both copies of the alpha 4 gene). U(S)3, one of these four genes, encodes a serine-threonine kinase that has been demonstrated to block apoptosis induced by proapo...

The immunomodulatory drug FTY720 is phosphorylated in vivo, and the resulting FTY720 phosphate as a ligand for sphingosine-1-phosphate receptors is responsible for the unique biological effects of the compound. So far, phosphorylation of FTY720 by murine sphingosine kinase (SPHK) 1a had been documented. We found that, while FTY720 is also phosphorylated by human SPHK1, the human type 2 isoform ...

The development of acquired resistance to antihormonal agents in breast cancer is a major therapeutic problem. We have developed a tamoxifen-resistant (TAM-R) MCF-7 breast cancer cell line to investigate the mechanisms behind this condition. Both epidermal growth factor receptor (EGFR) and c-erbB2 mRNA and protein expression were increased in TAM-R compared with wild-type MCF-7 cells, whereas c...

EphA2 is activated through phosphorylation on serine 897 (S897) by Akt to promote cancer cell motility and invasion, independently of stimulation by ephrin, its ligand. Here we show that S897 phosphorylation of EphA2 strengthens the interaction between EphA2 and Ephexin4, a guanine nucleotide exchange factor for the small GTPase RhoG. S897A mutation of EphA2 abolished the EphA2/Ephexin4-mediate...

Protein phosphorylation is a fundamental mechanism regulating nearly every aspect of cellular life. Several secreted proteins are phosphorylated, but the kinases responsible are unknown. We identified a family of atypical protein kinases that localize within the Golgi apparatus and are secreted. Fam20C appears to be the Golgi casein kinase that phosphorylates secretory pathway proteins within S...

Cytokine-mediated phosphorylation of Erk (pErk), ribosomal S6 (pS6), and Stat5 (pStat5) in CD34 /CD117 blast cells in normal bone marrow from 9 healthy adult donors were analyzed over 60 minutes. Treatment with stem cell factor (SCF), Flt3-ligand (FL), IL-3, and GM-CSF and measurement by multiparametric flow cytometry yielded distinctive, highly uniform phosphoprotein kinetic profiles despite a...

and the activated signalling pathways investigated. To ensure equivalent activation of downstream pathways by each ligand, phosphorylated-smad2 levels were assayed by Western blot. Up to 100-fold higher concentrations of Xnr1 than ActivinA were required to induce equivalent levels of phosphorylation of smad2. The expression of well-known downstream targets of Activin and Xnr1 was assayed by qua...

To improve our understanding of uranium toxicity, the determinants of uranyl affinity in proteins must be better characterized. In this work, we analyzed the contribution of a phosphoryl group on uranium binding affinity in a protein binding site, using the site 1 EF-hand motif of calmodulin. The recombinant domain 1 of calmodulin from A. thaliana was engineered to impair metal binding at site ...