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The expression of human lymphotoxin (LT) alpha/beta cell-surface complex was studied in human B-cell lines as well as in normal and neoplastic human B lymphocytes. In the absence of TNF receptors, only the human hairy-cell leukemia (HCL)-derived cell line JOK-I revealed constitutive cell-surface expression of LT but not TNF-alpha. Immunoprecipitation experiments with anti-LT monoclonal antibody (MAb) 9B9 from cell-surface radioiodinated JOK-I cells revealed that a cell-surface lymphotoxin molecule (25 kDa) is expressed in association with a 33-kDa molecule. Enzymatic digestion with F/N-glycosidase and O-glycosidase showed that both proteins contained N-linked carbohydrate residues, whereas only the 25-kDa molecule contained O-linked sugar residues. Analysis of mRNA expression revealed specific transcripts of LT-alpha and LT-beta in JOK-I cells. Resting tonsillar B cells did not express cell-surface LT. However, LT-beta mRNA was observable in unstimulated tonsillar B cells, whereas LT-alpha mRNA, cell-surface LT and LT secretion could only be detected upon in vitro activation. Thus LT-beta and alpha appear to be sequentially expressed in human B cells. Neoplastic B cells from chronic lymphocytic leukemia (BCLL), being devoid of constitutive cell-surface LT expression, could be induced to express surface LT by in vitro stimulation with Staphylococcus aureus Cowan I (SAC). Constitutive LT-beta transcripts, however, could also be detected in 4 out of 5 cases of BCLL. In contrast, human HCL cells displayed constitutive cell expression of lymphotoxin-alpha and beta. These findings demonstrate that cell-surface LT-alpha is expressed in association with LT-beta on activated normal B cells and neoplastic B cells representing an activated state. more...

Synaptophysin (SY) is an integral membrane protein of presynaptic small (30-80-nm) translucent vesicles also present in dispersed neuroendocrine cells. As the occurrence of this type of vesicle is specific for two major pathways of differentiation, the neuronal and neuroendocrine-epithelial information on the regulation of SY synthesis should contribute to an understanding of regulatory principles common to both pathways. Isolation and comparison of the complete rat and human single-copy genes showed that despite the difference in size (16 kb in rat vs. 13 kb in man) intron/exon boundaries are precisely conserved. Surprisingly, intron VI is located in the 3'-noncoding region in both species. The major transcriptional start point, as determined by primer extension and S1-nuclease protection analyses in rat pheochromocytoma-derived PC12 cells and rat brain, mapped to a site 27 nt 5' of the first methionine codon. Unexpectedly, the 5' upstream region is devoid of any TATA or CAAT boxes, but shows instead typical features of 'housekeeping' genes, i.e., G + C-rich islands and four Sp1-binding motifs. Using 'nuclear run-on' assays, we have identified examples in which SY synthesis is regulated at the transcriptional level. Reporter gene constructs showed that approx. 1.2 kb of the immediate upstream region contains promoter enhancer elements that were, however, insufficient to confer cell-type specific expression, whereas sequences farther upstream were able to suppress thymidine kinase promoter activity in a cell-type-dependent fashion. more...