T7 RNA Polymerase Functions In Vitro without Clustering

Many nucleic acid polymerases function in clusters known as factories. We investigate whether the RNA polymerase (RNAP) of phage T7 also clusters when active. Using ‘pulldowns’ and fluorescence correlation spectroscopy we find that elongation complexes do not interact in vitro with a Kd<1 µM. Chromosome conformation capture also reveals that genes located 100 kb apart on the E. coli chromosome do not associate more frequently when transcribed by T7 RNAP. We conclude that if clustering does occur in vivo, it must be driven by weak interactions, or mediated by a phage-encoded protein

A recurrent germline PAX5 mutation confers susceptibility to pre-B cell acute lymphoblastic leukemia

Somatic alterations of the lymphoid transcription factor gene PAX5 (also known as BSAP) are a hallmark of B cell precursor acute lymphoblastic leukemia (B-ALL)1–3, but inherited mutations of PAX5 have not previously been described. Here we report a new heterozygous germline variant, c.547G>A (p.Gly183Ser), affecting the octapeptide domain of PAX5 that was found to segregate with disease in two unrelated kindreds with autosomal dominant B-ALL. Leukemic cells from all affected individuals in both families exhibited 9p deletion, with loss of heterozygosity and retention of the mutant PAX5 allele at 9p13. Two additional sporadic ALL cases with 9p loss harbored somatic PAX5 substitutions affecting Gly183. Functional and gene expression analysis of the PAX5 mutation demonstrated that it had significantly reduced transcriptional activity. These data extend the role of PAX5 alterations in the pathogenesis of pre-B cell ALL and implicate PAX5 in a new syndrome of susceptibility to pre-B cell neoplasia

mRNA Secondary Structures Fold Sequentially But Exchange Rapidly In Vivo

Self-cleavage assays of RNA folding reveal that mRNA structures fold sequentially in vitro and in vivo, but exchange between adjacent structures is much faster in vivo than it is in vitro

CD32B on Clonal Plasma Cells in Systemic Light-Chain Amyloidosis (AL) and Multiple Myeloma (MM): A Target for Immunotherapy in Both Disorders and a Prognostic Marker in MM

Abstract Despite stem cell transplant and new therapies, nearly all patients with AL and MM die of disease or complications of treatment. Novel approaches that selectively kill clonal plasma cells are needed. CD32B, the inhibitory Fcγ receptor IIB, is a member of the Fc receptor (FcR) family on chromosome 1q. B-cells and some monocytes and dendritic cell subtypes express cell-surface CD32B, which has a cytoplasmic inhibitory motif important in regulating immune responses. Unlike the CD32B2 isoform on myeloid cells, CD32B1 on B-cells is not internalized, making it a suitable target for monoclonal antibody (MAb) therapy (Blood 2006Jun6 Epub). CD32B has not previously been found on AL and MM plasma cells. We used purified CD138+ marrow and blood cells from AL, MM and plasma cell leukemia (PCL) patients, and 5 human MM cell lines, to evaluate CD32B gene and cell-surface expression with gene expression profiles (GEP) (Affymetrix U133 PLUS 2.0), RT-PCR for CD32B1 and B2, and flow-cytometry with the 2B6 MAb for CD32B. In AL, GEP showed that CD32B expression was significantly higher than other FcR genes (p98% of all AL plasma cells. In MM, public GEP data (http://lambertlab.uams) showed that CD32B expression was significantly higher than other FcR genes while RT-PCR showed CD32B1 message in CD138+ MM and PCL specimens but not in the RPMI 8226 cell line. Cytogenetic analysis then showed that 8226 cells lack t(4;14) but have 4 copies of 1q, implicating segmental uniparental tetrasomy of a mutant allele in the lack of CD32B message. Flow cytometry showed median 96% CD32B expression on CD138+ marrow cells from patients with normal or hyperdiploid cytogenetics, but significantly lower expression (median 69%, p=0.01) in patients with unfavorable cytogenetics (del 13, t(4;14)). CD32B expression was lower still on PCL specimens (median 10%) and nil on MM cell lines. We then investigated the GEP of sorted CD138+/CD32B+ and CD32B− fractions from MM patients. In CD138+/CD32B+ cells, CD45C and CXCR4 were overexpressed. In CD138+/CD32B− cells, genes on chromosome 1q were overexpressed, including those for cancer testis antigens and others possibly associated with biologic aggressivity (Cancer Cell2006;9:313). Notably, the CD32B-specific MAb 2B6 directs human mononuclear cell cytotoxicity against CD32B+ cell lines, reduces tumor growth and improves tumor-free survival in a mouse xenograft model. Moreover, an Fc-engineered humanized variant of 2B6 elicits ADCC-mediated specific cytotoxicity against a low-level CD32B+ MM cell line in vitro. In sum, these data show that CD32B is important in AL and MM; that CD32B on AL and the majority of MM plasma cells provides a target for MAb therapy; and that, given the results in MM, PCL and MM cell lines, CD32B expression is inversely related to biologic aggressivity. Genetic instability of chromosome 1q may provide a direct basis for this relationship thereby mechanistically linking CD32B expression in MM to prognosis. These data support further evaluation of CD32B and clinical studies of anti-CD32B MAb therapy in AL and MM