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The molecular diagnosis of Gaucher disease has been difficult

Mitogen-activated protein (MAP) kinase pathways are three-kinase modules that mediate diverse cellular processes and have been highly conserved among eukaryotes. By using a functional complementation screen in yeast, we have identified a human MAP kinase kinase kinase (MAPKKK) that shares homology with members of the mixed lineage kinase (MLK) family and therefore was called MRK (MLK-related kinase). We report the structure of the MRK gene, from which are generated two splice forms of MRK, MRK-␣ and MRK-␤, encoding for proteins of 800 and 456 amino acids, respectively. By using a combination of solid phase protein kinase assays, transient transfections in cells, and analysis of endogenous proteins in stably transfected Madin-Darby canine kidney cells, we found that MRK-␤ preferentially activates ERK6/p38␥ via MKK3/MKK6 and JNK through MKK4/MKK7. We also show that expression of wild type MRK increases the cell population in the G 2 /M phase of the cell cycle, whereas dominant negative MRK attenuates the G 2 arrest caused by ␥-radiation. In addition, exposure of cells to ␥-radiation induces MRK activity. These data suggest that MRK may mediate ␥-radiation signaling leading to cell cycle arrest and that MRK activity is necessary for the cell cycle checkpoint regulation in cells.

The growth factor independence-1 (Gfi1) transcription factor is required for proper development of neuroendocrine cells, sensory neurons, and blood. Patients with mutations in Gfi1 exhibit severe congenital neutropenia (SCN) or non-immune chronic idiopathic neutropenia of adults. Gfi1 was initially described as an oncoprotein that mediates tumor progression in a mouse model of leukemia; however, recent data suggest that Gfi1 may act as either an oncogene or an anti-proliferative tumor suppressor gene depending on the cell type. Here we review the latest literature on Gfi1, and emphasize its role in the hematopoietic, sensory and neuroendocrine systems.

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DNA damage induced by ionizing radiation (IR) activates a complex cellular response that includes checkpoints leading to cell cycle arrest. The stress-activated mitogen-activated protein kinase (MAPK) p38␥ has been implicated in the G 2 phase checkpoint induced by IR. We recently discovered MRK as a member of the MAPK kinase kinase family that activates p38␥. Here we investigated the role of MRK in the checkpoint response to IR. We identified autophosphorylation sites on MRK that are important for its kinase activity. A phosphospecific antibody that recognizes these sites showed that MRK is activated upon IR in a rapid and sustained manner. MRK depletion by RNA interference resulted in defective S and G 2 checkpoints induced by IR that were accompanied by reduced Chk2 phosphorylation and delayed Cdc25A degradation. We also showed that Chk2 is a substrate for MRK in vitro and is phosphorylated at Thr 68 by active MRK in cells. MRK depletion also increased sensitivity to the killing effects of IR. In addition, MRK depletion reduced IR-induced activation of p38␥ but had no effect on p38␣ activation, indicating that MRK is a specific activator of p38␥ after IR. Inhibition of p38␥ by RNA interference, however, did not impair IR-induced checkpoints. Thus, in response to IR MRK controls two independent pathways: the Chk2-Cdc25A pathway leading to cell cycle arrest and the p38␥ MAPK pathway.

Abstracttional insights into the effect of mutations of the splice consensus sequences on splicing. Gaucher disease is due to mutations involving the glucocerebrosidase gene. A closely homologous pseudogene is located -16 kD downstream from the functional gene. Sequence analysis of clones from cDNA libraries made from skin fibroblast cultures showed several independent clones with the sequence of an aberrantly processed pseudogene message. Examination of cellular RNA from lymphoblasts or fibroblasts obtained from thirteen Gaucher disease patients, one Gaucher disease heterozygote, and four normal subjects showed that the pseudogene was consistently transcribed, and that in some cases the level of transcription seemed to be approximately equal to that of the functional gene. The transcription of the pseudogene must be taken into account when attempting to detect mutations of glucocerebrosidase by the study of cDNA libraries. (J.

We have applied a molecular biology approach to the identification of human monoclonal antibodies. Human peripheral blood lymphocyte mRNA was converted to cDNA and a select subset was amplified by the polymerase chain reaction. These products, containing coding sequences for numerous immunoglobulin heavy-and K light-chain variable and constant region domains, were inserted into modified bacteriophage A expression vectors and introduced into Escherichia coli by infection to yield a combinatorial immunoexpression library. Clones with binding activity to tetanus toxoid were identified by filter hybridization with radiolabeled antigen and appeared at a frequency of 0.2% in the library. These human antigen binding fragments, consisting of a heavy-chain fragment covalently linked to a light chain, displayed high affinity of binding to tetanus toxoid with equilibrium constants in the nanomolar range but did not cross-react with other proteins tested. We estimate that this human immunoexpression library contains 20,000 clones with high aftmity and specificity to our chosen antigen.