Roger Weil

Repression of nuclear lamin A and C gene expression in human acute lymphoblastic leukemia and non-Hodgkin's lymphoma cells

The lamins A, B and C which are differentially expressed during ontogenesis and differentiation are karyoskeletal proteins forming a polymeric meshwork at the inner nuclear membrane. Using Northern blot analyses we investigated the steady state levels of the three lamin specific RNA transcripts in neoplastic cells derived from 16 untreated patients with acute lymphoblastic leukemia (ALL) or non-Hodgkins lymphoma (NHL) and in ALL and NHL established cell lines. Whereas lamin B mRNA was present in all, lamin A and C transcripts were observed in none of the malignant cell samples except one of a common-ALL patient (precursor B-ALL, cytoplasmic mu chain negative). All three lamin mRNAs were detected in normal peripheral blood lymphocytes, however, only after mitogenic stimulation with concanavalin A. Our results provide evidence that expression of lamin A and C is repressed in neoplastic blast cells derived from patients with ALL or NHL and suggest that lamin A and C gene repression is not related to cell proliferation but might be relevant to the differentiated stages of the lymphoid cells in vivo.

Cyclosporin A and FK506 prevent the derepression of the IL-2 gene in mitogen-induced primary T lymphocytes.

In resting primary T lymphocytes the interleukin 2 (IL-2) gene is silenced by a repressor binding to the Pud element spanning positions -292 to -264 upstream of the cap site. Upon T-cell activation, this silencer is displaced by a positive transcription factor (TF) and the gene is derepressed and transcribed. Cyclosporin A (CsA) and FK506 interfere with normal derepression of the IL-2 gene. Both drugs exert no direct effect on basal transcription of the IL-2 or control viral genes. Direct addition does not abolish the active state of positive TFs present in proteins from activated T cells. However, if T cells are activated in the presence of either drug, their proteins not only fail to derepress, but efficiently and irreversibly silence IL-2 transcription. DNA-protein binding data show that proteins present in drug-treated cells form retarded complexes corresponding in size to the silencer and positive TF. Thus, in drug-treated cells a functional silencer persists, and a positive TF-like factor appears which is functionally abnormal. Moreover, drug-treated T cells appear to form a component that prevents functioning of normal positive TF.

The relation between potyoma T-antigen and increased 5S RNA synthesis in cell-free extracts from polyoma-infected mouse kidney cell cultures

In polyoma-infected mouse kidney cell cultures 5S RNA synthesis began to increase around 16 h, i.e. 7-9 h after the onset of polyoma T-antigen synthesis. The rate of polyoma-induced 5S RNA synthesis reached a maximum plateau around 25 h when it was 1.8-2.0 times higher than in mock-infected parallel cultures. Stimulation of 5S RNA synthesis in vivo thus coincided in time with the increase in total cellular RNA and protein. Cell-free extracts (S100) prepared at 15 h from mock-(S100-M) or polyoma-infected (S100-Py) mouse kidney cell cultures were indistinguishable with respect to protein concentration and 5S RNA synthesis, using a cloned somatic Xenopus borealis 5S gene as template. S100-Py extracted 25 h after infection contained 30% more protein and synthesized 1.5-2.0 times more 5S RNA than S100-M. Complete removal of the polyoma T-antigens from S100-Py by 3 cycles of immunoprecipitation with hamster anti-T serum remained without effect on stimulated 5S RNA synthesis. However, a linear relationship between 5S RNA synthesis and protein concentration of S100-M and S100-Py was observed.