Patterns of adenosine deaminase, ecto-5'-nucleotidase, poly(A)polymerase and surface light chain expression in chronic lymphocytic leukemias

The levels of activity of three enzymes have been measured in the circulating malignant lymphocytes of 47 patients with B chronic lymphocytic leukemia (CLL). These were the purine degradative enzymes, adenosine deaminase (ADA) and ecto-5'-nucleotidase (5'NT) and the enzyme responsible for the polyadenylation of mRNA, poly(A) polymerase. The patterns of activity of the above enzymes and the expression of surface immunoglobulin light chains were examined. A heterogeneity in the specific activity of the enzymes was observed which could not be attributed to variations of the percentage of B lymphocytes. A positive correlation was found between ADA and poly(A)polymerase activity (r = 0.383, p less than 0.01). Furthermore, the expression of immunoglobulin light chain phenotype was inversely related to 5'NT specific activity; CLL cases in which less than 20% of the cells expressed lambda chain phenotype, presented 5'NT specific activity of 16.7 +/- 3.3 (S.E.) nmol/h/10(6) cells, whereas in CLL cases with more than 20% of the cells expressing this phenotype the enzyme specific activity was 4.8 +/- 1.6 (S.E.) nmol/h/10(6) cells (p less than 0.02). These findings suggest that the simultaneous determination of enzymatic activities and immunological markers, might be useful in defining subsets in CLL and the subsequent clinical treatment.     

Surface expression of Bcl-2 in chronic lymphocytic leukemia and other B-cell leukemias and lymphomas without a breakpoint t(14;18)

Since its discovery in follicular lymphoma cells at the breakpoint t(14;18), Bcl-2 has been studied extensively in many basic and clinical science settings. Bcl-2 can locate as an integral mitochondrial membrane component, where its primary role is to block apoptosis by maintaining membrane integrity. Here we show that Bcl-2 also can position on the outer cell surface membrane of B cells from patients with chronic lymphocytic leukemia (B-CLL) and certain other leukemias that do not classically possess the chromosomal breakpoint t(14;18). Although low levels of Bcl-2 can be detected on the surface membrane of apparently healthy leukemic and normal B cells, expression of Bcl-2 correlates best with spontaneous or induced apoptosis. Notably, upon induction of apoptosis, B-CLL cells were much more efficient in upregulating surface Bcl-2 than normal B cells. It is not clear if this surface membrane expression is a passive consequence of the apoptotic process or an active attempt by the B cell to abort cell death by stabilizing the plasma membrane.     

Biology of chronic lymphocytic leukemia

B-cell chronic lymphocytic leukemia (CLL) lies at the cross-roads of hematology, immunology and oncology for at least three major reasons: (a) it is the prototype of human malignancies that primarily involve defects in the induction of apoptosis; (b) CLL patients develop a severe immunodeficiency with progressive hypogammaglobulinemia; and (c) they have a high prevalence of autoimmune phenomena. Recent advances in the biology of the malignant cell in CLL lead to a scenario comprised of two basic elements: first, CLL cells are optimally organized to survive in their niches because their ability to undergo apoptosis is severely hampered; second, they have a microenvironment-dependence that promotes their extended survival, a situation that arises most probably through direct cell-to-cell contacts. In addition, CLL cells themselves are the major accessory cells in CLL, but are inefficient antigen-presenting cells. This latter defect may provide a clue to reinterpret the events of immunodeficiency and autoimmunity.     

ZAP70 in chronic lymphocytic leukaemia

The protein tyrosine kinase zeta-chain associated protein kinase (ZAP70), normally expressed in T cells and a subset of B cells, is solely expressed in poor prognosis chronic lymphocytic leukaemia and implicated in enhanced B cell receptor signalling. As a result, the expression of this protein provides an ideal prognostic marker for the disease. A previous study has shown differential CpG methylation of a 5' region of ZAP70 in leukaemic lymphoid cells, although no further epigenetic studies have been reported. Further investigation into the expression of ZAP70 may therefore provide targets for therapies.     

Polyamine metabolism in chronic lymphocytic leukemia

We have previously shown that polyamines have profound effects on lymphocyte proliferation and function. We now report that the proliferative response of cultured lymphocytes from patients with chronic lymphocytic leukemia is abrogated by the addition of diacetyldiaminohexane (HMBA), the 6-carbon analogue of diacetylputrescine. In addition, this study demonstrates the post-translational modification of proteins by polyamines in CLL-lymphocytes, a decrease in the uptake of exogenous spermidine by CLL-lymphocytes which have been exposed to HMBA, and the significant conversion of spermidine to N1-acetylspermidine in CLL-lymphocytes.     

Lymphocyte cholesterol synthesis in chronic lymphocytic leukemia

Studies in B and T lymphocytes from two patients with B cell chronic lymphocytic leukemia (CLL) showed that the rate of cholesterol synthesis and hydroxymethylglutaryl (HMG)-CoA reductase activity in the malignant cell--the B lymphocyte--did not differ from that in normals, before or after the treatment. Cholesterol synthesis and HMG-CoA reductase activity in T cells, on the other hand, from one patient (H.E.) before therapy, were only one-fifth of that in normals and in the other patient (J.R.) receiving treatment. Following chemotherapy and treatment with prednisone, T lymphocytes from H.E. exhibited normal cholesterol metabolism.     

Molecular pathogenesis of chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is unique among malignancies since it represents an accumulation of B-lymphocytes resistant to apoptosis. Several factors are thought to confer this unusual feature to a CLL B-cell. Misbalance between cytoplasmic pro-survival and pro-death molecules, such as Bcl-2, Mcl-1 and alike, appears to be one of the key factors defining B-cell longevity. Autocrine pathways, such as vascular endothelial growth factor-receptor pathway, also contribute to survival. The role of B-cell receptor (BCR) is less straightforward. In the last decade it became clear that CLL does not constitute a uniform disease, but, based on the prevalence of mutations in the BCR heavy chain (IgVH), can be classified into two distinct subgroups. Several molecular markers correlate with IgVH mutations. Some of them, like zeta-chain associated protein kinase, are also involved in BCR signaling and influence cell cycle. Yet the primary pathogenic event leading to increased proliferation and survival in CLL is difficult to ascertain. Molecules involved in BCR signaling pathways and cytoplasmic pro-survival players probably act in concert to confer resistance to apoptosis. In this respect, the role of the B-CLL environment, which includes nurse-like cells and T-cells, cannot be underestimated. Nurse-like cells provide stimuli necessary for perpetuation of life in CLL. On the other hand, abnormal T-cell function, whether it is excessive immunosuppression delivered by regulatory T-cells or insufficient anti-tumor immunity rendered by T-helpers, allows malignant CLL cells to go unnoticed by the cellular immune system.