A new class of poly(ADP-ribose) (pADPr)-binding proteins, heterogeneous nuclear ribonucleoproteins (hnRNPs), has been identified by a proteomic approach using matrix-assisted laser-desorption-ionization time-of-flight ('MALDI-TOF') MS. Liquid-phase isoelectric focusing with a Rotofor cell (Bio-Rad) allowed pre-fractionation of proteins extracted from HeLa cells. Rotofor protein fractions were further separated by SDS/PAGE and then transferred to a PVDF membrane. pADPr-binding proteins were analysed by autoradiography of the protein blot after incubation with (32)P-labelled automodified pADPr polymerase-1 (PARP-1). Peptide mass fingerprinting of selected bands identified the most abundant pADPr-binding proteins as hnRNPs, a family of proteins that bind pre-mRNA into functional complexes involved in mRNA maturation and transport to the cytoplasm. Sequence homology database searching against a previously reported pADPr-binding sequence motif revealed that the hnRNPs contain a putative pADPr-binding sequence pattern [Pleschke, Kleczkowska, Strohm and Althaus (2000) J. Biol. Chem. 275, 40974-40980]. pADPr-binding assays performed with synthetic peptides by the dot-blot technique and with nitrocellulose-transferred recombinant hnRNPs confirmed the pADPr-binding protein identification and the specificity of the interaction. These results could establish a link between increased levels of pADPr in DNA damaged cells and the modified protein expression pattern resulting from altered mRNA trafficking.

No abstract

No abstract

Depending on the cell lines and cell types, dimethyl sulfoxide (Me 2 SO) can induce or block cell differentiation and apoptosis. Although Me 2 SO treatment alters many levels of gene expression, the molecular processes that are directly affected by Me 2 SO have not been clearly identified. Here, we report that Me 2 SO affects splice site selection on model pre-mRNAs incubated in a nuclear extract prepared from HeLa cells. A shift toward the proximal pair of splice sites was observed on pre-mRNAs carrying competing 5-splice sites or competing 3-splice sites. Because the activity of recombinant hnRNP A1 protein was similar when added to extracts containing or lacking Me 2 SO, the activity of endogenous A1 proteins is probably not affected by Me 2 SO. Notably, in a manner reminiscent of SR proteins, Me 2 SO activated splicing in a HeLa S100 extract. Moreover, the activity of recombinant SR proteins in splice site selection in vitro was improved by Me 2 SO. Polar solvents like DMF and formamide similarly modulated splice site selection in vitro but formamide did not activate a HeLa S100 extract. We propose that Me 2 SO improves ionic interactions between splicing factors that contain RS-domains. The direct impact of Me 2 SO on alternative splicing may explain, at least in part, the different and sometimes opposite effects of Me 2 SO on cell differentiation and apoptosis.Me 2 SO 1 is a polar solvent used to promote cell differentiation of tumor cell lines. For example, the treatment of mouse erythroleukemic and neuroblastoma cells with 2% Me 2 SO induces morphological changes and differentiation in red blood cells and neurons, respectively (e.g. see Refs. 1, 2). Me 2 SO also induces differentiation of the human U937 monoblast leukemia cell line into monocyte/macrophage (3) and stimulates the differentiation of a human ovarian adenocarcinoma cell line (4). Paradoxically, Me 2 SO prevents the terminal differentiation of myoblasts (5, 6), inhibits the differentiation of adipocytes (7), blocks the differentiation of antibody-producing plasma cells (8), and interferes with the differentiation of chick embryo chondrocytes (9). Whereas Me 2 SO has been used to induce apoptosis in some cell lines (10, 11), it inhibits cell density-dependent apoptosis of CHO cells (6). Thus, depending on the cell line, Me 2 SO can have completely different effects on differentiation and apoptosis.The cellular mechanisms that are affected by Me 2 SO remain unclear. Because Me 2 SO facilitates DNA uptake during transfection procedures (e.g. see Ref. 12), Me 2 SO has been proposed to affect the integrity of cell membranes. Because Me 2 SO alters protein kinase C activity and the expression of integrin complexes (6, 13), Me 2 SO may alter intracellular signaling processes, which in turn may have a broad impact on many aspects of gene expression. Me 2 SO treatment promotes changes in the abundance of certain mRNAs and in the ratio of spliced isoforms (14 -17). Among the genes reported to be affected in their alternative splicing is the NCAM pre-mR...