Characteristics of the RNA synthesized in vitro by the normal human small lymphocyte and the changes induced by phytohemagglutinin stimulation

Phosphorylated nucleolar Tau protein is related to the neuronal in vitro differentiation

Tau is a multifunctional protein, originally identified as a cytoplasmic protein associated with microtubules. It is codified by the MAPT gene, and the alternative splicing, in the neuronal cells, results in six different isoforms. Tau was subsequently observed in the cell nucleus, where its function is not yet clearly understood. Here, we studied the MAPT gene and the cellular localization of the AT8 and Tau-1 epitopes of Tau protein, in the SK-N-BE cell line, which differentiates in neuronal-like cells after retinoic acid treatment. These epitopes correspond to the phosphorylated Ser202/Thr205 and unphosphorylated Pro189/Gly207 amino acid residues, respectively, possibly involved in conformational changes of the protein. Our results demonstrated the presence of the smaller Tau isoform (352 amino acids), whose amount increases in differentiated SK-N-BE cells, with Tau-1/AT8 nuclear distribution related to the differentiation process. Tau-1 showed a spot-like nucleolar localization, in both replicative and differentiated cells, while AT8 was only detected in the differentiated cells, diffusely occupying the entire nucleolar region. Moreover, in the replicative cells exposed to actinomycin-D, AT8 and Tau-1 move to the nucleolar periphery and colocalize, in few spots, with the upstream binding transcription factor (UBTF). Our results, also obtained with lymphocytes exposed to the mitogenic compound phytohaemagglutinin, indicate the AT8 epitope of Tau as a marker of neuronal cell differentiation, whose presence in the nucleolus appears to be related to rDNA transcriptional inactivation.

The effects of lectin transformation on cytoplasmic polyadenylated RNA from human lymphocytes

The translational activity of cytoplasmic poly(A)+ RNA from resting human lymphocytes was approximately 20% of that from phytohemagglutinin-transformed lymphocytes in a rabbit reticulocyte lysate assay. Translation assays in the presence of cap analogues suggested that the mRNA from resting cells was relatively deficient in functional 5'-terminal cap structures. Neither mRNA fraction inhibited the translation of globin mRNA in the cell-free assay, and both preparations were essentially pure as shown by hybridisation with [3H]poly(U). The size distribution and poly(A) tail length of poly(A)+ RNA was similar in the resting and transformed cell and both preparations directed the synthesis of peptides of molecular weight 15 000 to 90 000. Two dimensional gels of total proteins from resting and transformed lymphocytes showed predominantly quantitative changes. However cross-hydridising cDNA and mRNA from resting and transformed cells after the common sequences have been removed by hydroxylapatite chromatography showed that about 4% of the cytoplasmic poly(A)+ RNA from transformed lymphocytes was not present in resting cells. This difference may result from transformation-specific gene expression.

Comparison of RNA and DNA synthesis, spontaneous and PHa induced, between blood lymphoid cells of newborn infants, older infants, and adults. A study of scintillation counting and by autoradiography

Spontaneous and PHA induced RNA and DNA synthesis was measured qualitatively by autoradiography and quantitatively by scintillation counting in blood lymphoic cells of newborn infants, older infants, and adults. Spontaneous RNA synthesis was found in transitional cells, large phagocytic lymphoid cells and lymphocytes. Transitional cells and phagocytic lymphoid cells also synthesized DNA spontaneously. Quantitatively, spontaneous RNA synthesis was active in both newborn infants and in adults, but significantly less so in older infants. PHA stimulation for 18 h increased RNA synthesis significantly in blood lymphoid cells of newborn infants and adults, and to a much lesser but still significant degree in older infants. Spontaneous DNA synthesis was significantly greater in newborn infants than in older infants and adults. PHA stimulation for 18 h had no effect on thymidine incorporation in any of the groups studied.

Adenylate-rich sequences of heterogeneous nuclear RNA from normal and chronic lymphocytic leukaemia lymphocytes

Rapidly labelled high molecular weight heterogeneous nuclear RNA (Hn RNA) from normal and chronic lymphocytic leukaemia (CLL) lymphocytes has been fractionated into two classes by chromatography on poly (U) sephasose. The (+) Hn RNA is bound to poly (U) sepharose and contains both a long poly (A) segment (100-200 nucleotides) and shorter (A) rich sequences (approximately 20-30 nucleotides. (-) Hn RNA is not bound to poly (U) sepharose and lacks the longer poly (A) segment but does contain shorter (A) rich sequences. Partial association of the short (A) rich segments with double-stranded regions was found for both classes of Hn RNA but was most pronounced in (-) Hn RNA from high WBC cases of CLL. Both classes of Hn RNA from CLL lymphocytes contain varying but generally higher amounts of the short (A) rich fraction than those in normals. Similar amounts of the longer poly (A) segments were found in (+) Hn RNA from both CLL and normal lymphocytes.

Double stranded ribonuclease activity in human lymphocyte nuclei

Ribonuclease activity directed against the synthetic duplex polyrC:polyI was detected in nuclear extracts from both unstimulated and PHA-stimulated human lymphocytes. In the latter cells, the activity was about twice that of small lymphocytes.

Heterogeneous nuclear rna from lymphocytes of chronic lymphocytic leukaemia: adenylate-rich and double-stranded regions

Rapidly labelled high molecular weight nuclear RNA from lymphocytes of chronic lymphocytic leukaemia was analysed for ribonuclease-stable adenylate-rich and double-stranded regions. The polyadenylate content corresponds to 0.4-0.5 percent and the content of double-stranded sequences to 2-4 percent of the total nucleotides. Partial association of polyadenylate segments with double-stranded regions was found by comparative analysis of (3H)-adenosine and (3H)-uridine labelled ribonuclease-stable RNA before and after thermal denaturation. Comparison with normal lymphocytes shows lower proportions of polyadenylate-containing RNA binding to poly(U)-Sepharose in leukaemia cells than in normals. Partial degradation of rapidly labelled high molecular weight RNA was found in leukaemia cases with low white cell counts.