When used as the initial treatment for chronic lymphocytic leukemia, fludarabine yields higher response rates and a longer duration of remission and progression-free survival than chlorambucil.

Key Points MCL cells are mobilized into the peripheral blood of patients treated with the BTK inhibitor ibrutinib. Ibrutinib dose-dependently inhibits BCR- and chemokine-mediated adhesion and migration of MCL cells.

Bruton tyrosine kinase (Btk) has a welldefined role in B-cell development, whereas its expression in osteoclasts (OCs) further suggests a role in osteoclastogenesis.

No abstract

Moesin, a member of the ezrin-radixin-moesin (ERM) family of membrane/cytoskeletal linkage proteins, is known to be threonine-phosphorylated at Thr 558 in activated platelets within its conserved putative actinbinding domain. The pathway leading to this phosphorylation step and its control have not been previously elucidated. We have detected and characterized reactions leading to moesin phosphorylation in human leukocyte extracts. In vitro phosphorylation of endogenous moesin, which was identified by peptide microsequencing, was dependent on phosphatidylglycerol (PG) or to a lesser extent, phosphatidylinositol (PI), but not phosphatidylserine (PS) and diacylglycerol (DAG). Analysis of charge shifts, phosphoamino acid analysis, and stoichiometry was consistent with a single phosphorylation site. By using mass spectroscopy and direct microsequencing of CNBr fragments of phospho-moesin, the phosphorylation site was identified as KYKT*LRQIR (where * indicates the phosphorylation site) (Thr 558 ), which is conserved in the ERM family. Recombinant moesin demonstrated similar in vitro phospholipid-dependent phosphorylation compared with the endogenous protein. The phosphorylation site sequence of moesin displays a high degree of conservation with the pseudosubstrate sequences of the protein kinase C (PKC) family. We identified the kinase activity as PKCon the basis of immunodepletion of the moesin kinase activity and copurification of PKC-with the enzymic activity. We further demonstrate that PKC-displays a preference for PG vesicles over PI or PS/DAG, with minimal activation by DAG, as well as specificity for moesin compared with myelin basic protein, histone H1, or other cellular proteins. Expression of a human His 6 -tagged PKC-in Jurkat cells and purification by Ni 2؉ chelate chromatography yield an active enzyme that phosphorylates moesin. PG vesicle binding experiments with expressed PKC-and moesin demonstrate that both bind to vesicles independently of one another. Thus, PKC-is identified as a major kinase within cells with specificity for moesin and with activation under non-classical PKC conditions. It appears likely that this activity corresponds to a specific intracellular pathway controlling the function of moesin as well as other ERM proteins.Moesin is a member of the ERM 1 family of actin cytoskeletalmembrane linkage proteins. Although closely related, there is evidence that these proteins have distinct functions, based upon their patterns of intracellular and tissue distribution. Moesin is named for its association with extracellular extensions (membrane-organizing-extension spike protein). ERM proteins have N-terminal membrane-binding domains and Cterminal actin-binding domains. Relatively little is known about their intracellular control, although phosphorylation of moesin Thr 558 by an unidentified kinase in activated platelets has recently been described (1). This residue is within the previously identified actin-binding domain of ezrin, which is highly conserved in moesin (2).This laboratory has be...