Experiments with fluorescent chromosome staining in Burkitt tumors

c-MYC impairs immunogenicity of human B cells

Deregulation of c-myc expression through chromosomal translocation is essential in the pathogenesis of Burkitt's lymphoma (BL). A characteristic feature of BL cells, compared to Epstein-Barr Virus (EBV)-immortalized B cells, is their lack of immunogenicity. To study the contribution of EBV genes and of the c-MYC protein to this phenotype, we have generated a conditional B cell system in which the viral proliferation program and expression of c-myc can be regulated independently of each other. In cells proliferating due to exogenous c-myc overexpression, the cell surface phenotype, the pattern of proliferation in single cell suspension, and the immunological characteristics of BL cells could be completely recapitulated. Yet, it had remained open whether nonimmunogenicity is the default phenotype when EBNA2 and LMP1 are switched off, or whether c-MYC actively contributes to immunosuppression. We provide evidence also for the latter by showing that c-MYC down-regulates genes of the NF-kappaB and interferon pathway in a dose-dependent fashion. c-MYC acts at at least two different levels, the level of interferon induction as well as at the level of action of type I and type II interferons on their respective target promoters. c-MYC does not block the interferon pathway completely, it shifts the balance and increases the threshold of interferon induction and action.

A new translocation in chronic myelogenous leukemia

A reciprocal translocation involving chromosomes Nos. 3 and 22 has been found in a patient with seemingly Ph-negative chronic myelogenous leukemia (CML). G-band analysis revealed, that deletion in No. 22 occurred at the same point, as in the typical cases of the disease. It was concluded, that breakage in No. 22 at a specific site with spatial disjunction of the resulting segments might be the crucial cytogenetic event in the genesis of CML, the Philadelphia chromosome not being an obligatory result of the rearrangement.

Chromosomes and causation of human cancer and leukemia. X. Banding patterns in cancerous effusions

Cells from five cancer effusions (two ovarian carcinomas, two lung cancers, and one carcinoma of the breast) were analyzed by G-, C-, and Q-banding techniques. The following observations were made: 1) The origin of some marker chromosomes could be traced accurately by these banding techniques. 2) Several chromosomes, which appeared normal with conventional staining techniques, were found to be re-arranged ones and, hence, abnormal. 3) Chromosomes No. 1, No. 3 and No. 11 were the most frequently involved in aberrations, whereas No. 12, No. 13, No. 17-20, and No. 22 Were least frequently involved. Only in one case each was the X chromosome or the Y chromosome involved in aberrations. The Y chromosome was found to be missing in all cancer cells of one lung cancer. 4) Each effusion had characteristic markers, invariably present in each cell, whether the cells were near diploid, or polyploid. 5) No common markers were observed in the two ovarian carcinomas studied, whereas the two lung cancers had a few common markers.