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NF-kappa B signaling is required for the maintenance of normal B lymphocytes, whereas dysregulated NF-kappa B activation contributes to B cell lymphomas. The events that regulate NF-kappa B signaling in B lymphocytes are poorly defined. Here, we demonstrate that PKC-beta is specifically required for B cell receptor (BCR)-mediated NF-kappa B activation. B cells from protein kinase C-beta (PKC-beta)-deficient mice failed to recruit the I kappa B kinase (IKK) complex into lipid rafts, activate IKK, degrade I kappa B or up-regulate NF-kappa B-dependent survival signals. Inhibition of PKC-beta promoted cell death in B lymphomas characterized by exaggerated NF-kappa B activity. Together, these data define an essential role for PKC-beta in BCR survival signaling and highlight PKC-beta as a key therapeutic target for B-lineage malignancies.

Polyadenylic acid [poly(A)] segments containing 150 to 250 nucleotides appear to be covalently linked to heterogeneous nuclear RNA (HnRNA) and messenger RNA (mRNA) in eucaryotic cells. The poly(A) is synthesized in the nucleus, and is probably linked initially to HnRNA that is ultimately transported as mRNA to the cytoplasm. Studies with inhibitors of RNA or poly(A) synthesis indicate that synthesis of poly(A) segments is independent of transcription. The poly(A) marker may prove useful to elucidate mRNA modification and transport in eucaryotic cells.s

ABSrRACT The most abundant of the stable small nuclear RNAs of eukaryotic cells, U-1 small nuclear RNA, is exactly complementary to the consensus sequences at RNA splice sites.We propose that this RNA is the recognition component of the nuclear RNA splicing enzyme and forms base pairs with both ends of an intron so as to align them for cutting and splicing.Intramolecular RNA splicing, first discovered for the adenovirus-specific RNA (1-3), occurs in the expression of numerous eukaryotic genes (4). At present there are three known classes of DNA sequences at splice sites, found in genes for a chloroplast tRNA (5), yeast tRNAs (6), and vertebrate mRNAs (7-9). Each class has distinctive sequence characteristics. For the splice sites of vertebrate genes, comparisons of a limited set of sequences (7,8) showed that introns were flanked in every case by 5'-/ G-T-(intron)-A-G/-3'. Subsequent sequences have borne this out (9) and have shown that the 5' ("upstream") and 3' ("downstream") ends of introns have approximately the following consensus or "optimal" sequences: 5'-(exon)-A-G/G-T-A-A-G-T-A-(intron) -T-T-T-T-Y-T-T-T-T-T-T-C-T-T-N-C-A-G/G-(exon)-3'.The upstream and downstream splice sites in nuclear RNA molecules presumably must be brought together for RNA splicing to occur. This could be achieved by intramolecular base pairing, but no appropriate complementary structures have been found reproducibly in the vicinity of splice sites (10). We propose an alternative mechanism in which upstream and downstream splicing sites form base pairs with another RNA molecule which could be a structural component of the splicing enzyme(s). There may be an example comparable to this proposed splicing system in RNase P of Escherichia coli, which is a site-specific RNase with an essential RNA component (I1).THE MODEL We considered that such an effector RNA might be found among the discrete; stable, small nuclear RNAs (snRNAs) that are ubiquitous in eukaryotic cells (12). Sequences have been reported for several of these (13-17). When we compared the sequence of U-i snRNA from rat hepatoma (13) with sequences of the optimal splice site (Fig. 1), we discovered that the first 10 nucleotides after the U-1 RNA cap are perfectly complementary to the 9 nucleotides of the optimal upstream site and to the tetranucleotide C-A-G/G from the optimal downstream site. The next 11 nucleotides of U-I are purine-rich and can be aligned with the pyrimidine-rich segment of the downstream site. This striking complementarity with splicing sites is not found in any of the other snRNAs now sequenced, which are U-2 (14), 4.5S (15), and adenovirus VA-I RNAs (16,17). We therefore propose that U-1 snRNA in the RNA splicing complex forms base pairs with both ends of an intron in a large nuclear RNA molecule as shown in Fig. 2, bringing

A 6.8-kilobase DNA fragment containing the sequence coding for the constant region of the mouse immunoglobulin gamma1 heavy chain was cloned from total cellular DNA. Electron microscopic and nucleotide sequencing studies showed that the three protein domains and the hinge region are encoded in separate DNA segments.

Activation of the TCL1 oncogene has been implicated in T cell leukemias/lymphomas and recently was associated with AIDS diffuse large B cell lymphomas (AIDS-DLBCL). Also, in nonmalignant lymphoid tissues, antibody staining has shown that mantle zone B cells expressed abundant Tcl1 protein, whereas germinal center (GC; centrocytes and centroblasts) B cells showed markedly reduced expression. Here, we analyze isolated B cell subsets from hyperplastic tonsil to determine a more precise pattern of Tcl1 expression with development. We also examine multiple B cell lines and B lymphoma patient samples to determine whether different tumor classes retain or alter the developmental pattern of expression. We show that TCL1 expression is not affected by Epstein-Barr virus (EBV) infection and is high in naïve B cells, reduced in GC B cells, and absent in memory B cells and plasma cells. Human herpesvirus-8 infected primary effusion lymphomas (PEL) and multiple myelomas are uniformly TCL1 negative, whereas all other transformed B cell lines tested express moderate to abundant TCL1. This observation supports the hypothesis that PEL, like myeloma, usually arise from post-GC stages of B cell development. Tcl1 protein is also detected in most naïve/GC-derived B lymphoma patient samples (23 of 27 [85%] positive), whereas most post-GC-derived B lymphomas lack expression (10 of 41 [24%] positive). These data indicate that the pattern of Tcl1 expression is distinct between naïve/GC and post-GC-derived B lymphomas (P < 0.001) and that the developmental pattern of expression is largely retained. However, post-GC-derived AIDS-DLBCL express TCL1 at a frequency equivalent to naïve/GC-derived B lymphomas in immune-competent individuals (7 of 9 [78%] positive), suggesting that TCL1 down-regulation is adversely affected by severe immune system dysfunction. These findings demonstrate that TCL1 expression in B cell lymphoma usually reflects the stage of B cell development from which they derive, except in AIDS-related lymphomas.

Messenger RNA from HeLa cells contains, as part of the polynucleotide chain, RNase-resistant sequences that are labeled by adenosine but not by uridine. Heterogeneous nuclear RNA also contains adenylate-rich RNase-resistant regions, but in lower proportion than messenger RNA. Hybridization to DNA of 32P-labeled messenger RNA reveals that some of the adenylate-rich region is included in the rapidly-hybridizing fraction.