Stefan Einhorn

Cloning of two candidate tumor suppressor genes within a 10 kb region on chromosome 13q14, frequently deleted in chronic lymphocytic leukemia

Previous studies have indicated the presence of a putative tumor suppressor gene on chromosome 13q14, commonly deleted in patients with B-cell chronic lymphocytic leukemia (B-CLL). We have previously defined a minimally deleted region of 130 kb centromeric to the marker D13S272, and constructed a PAC and cosmid contig encompassing this area. In the present study we have made a detailed restriction and transcriptional map of the region of interest. Using these tools we have screened a panel of 206 primary CLL clones and three cell lines. In five CLL cases we found limited deletions defining the region of interest to an area of no more than 10 kb. Two adjacent genes, termed Leu1 and Leu2 (leukemia-associated gene 1 and 2), were mapped to the minimally deleted region, with several patients showing deletion borders within these genes. The Leu1 and Leu2 genes show little homology to previously published genes at the nucleotide and expected translated amino acid sequence level. Mutational analysis of the Leu1 and 2 genes in 170 CLL samples revealed no small intragenic mutations or point mutations. However, in all cases of 13q14 loss examined, the first exon of both genes, which are only 300 bp apart, were deleted. We conclude that the Leu1 and Leu2 genes are strong candidates as tumor suppressor gene(s) involved in B-CLL leukemogenesis.

Mechanisms of Interferon-alpha induced apoptosis in malignant cells.

Interferon alpha (IFNα) has been used in the treatment of several types of cancer for almost 30 years, yet the mechanism(s) responsible for its anti-tumoral action remains unknown. A variety of cellular responses, including inhibition of cell growth and induction of apoptosis are induced by IFNs, and apoptotic induction by this cytokine has been proposed to be of importance for both its anti-tumoral in addition to its anti-viral responses. The aim of the present study was to delineate the pathways activated during IFNα-induced apoptosis in malignant cell lines. We found that apoptosis induced by IFNα was associated with activation of caspases-1, -2, -3, -8 and -9 and that this activation was a critical event. Caspase-3 activation was dependent on activity of caspases-8 and -9, moreover, activation of caspase-8 seems to be the upstream event in IFNα-induced caspase cascade. We also found loss of mitochondrial membrane potential as well as release of cytochrome c post IFN-treatment, clearly implicating the involvement of mitochondria in IFN-mediated apoptosis. Furthermore, IFNα-induced apoptosis was found to be independent on interactions between the Fas-receptor and its ligand. These studies form the basis for further investigations aiming to improve IFN therapy and the development of future strategies to overcome the IFN resistance observed in some malignancies.

Molecular mechanisms underlying interferon-α-induced G0/G1 arrest: CKI-mediated regulation of G1 Cdk-complexes and activation of pocket proteins

One prominent effect of IFNs is their cell growth-inhibitory activity. The mechanism behind this inhibition of proliferation is still not fully understood. In this study, the effect of IFN-α treatment on cell cycle progression has been analysed in three lymphoid cell lines, Daudi, U-266 and H9. Examination of the growth-arrested cell populations shows that Daudi cells accumulate in a G0-like state, whereas U-266 cells arrest later in G1. H9 cells are completely resistant to IFN-αs cell growth-inhibitory effects. The G0/G1-phase arrest is preceded by a rapid induction of the cyclin-dependent kinase inhibitors (CKIs), p21 and p15. In parallel, the activities of the G1 Cdks are significantly reduced. In addition to p21/p15 induction, IFN-α regulates the expression of another CKI, p27, presumably by a post-transcriptional mechanism. In the G1 Cdk-complexes, there is first an increased binding of p21 and p15 to their respective kinases. At longer exposure times, when Cdk-bound p15 and p21 decline, p27 starts to accumulate. Furthermore, we found that IFN-α not only suppresses the phosphorylation of pRb, but also alters the phosphorylation and expression of the other pocket proteins p130 and p107. These data suggest that induction of p21/p15 is involved in the primary IFN-α response inhibiting G1 Cdk activity, whereas increased p27 expression is part of a second set of events which keep these Cdks in their inactive form. Moreover, elevated levels of p27 correlated with a dissociation of cyclin E/Cdk2-p130 or p107 complexes to yield cyclin E/Cdk2-p27 complexes. In resistant H9 cells, which possess a homozygous deletion of the p15/p16 genes and lack p21 protein expression, IFN-α causes no detectable changes in p27 expression and, furthermore, no effects are observed on either pocket proteins in this cell line. Taken together, these data suggest that the early decline in G1 Cdk activity, subsequent changes in phosphorylation of pocket proteins, and G1/G0 arrest following IFN-α treatment, is not primarily due to loss of the G1 kinase components, but result from the inhibitory action of CKIs on these complexes.

Induction of Cip/Kip and Ink4 cyclin dependent kinase inhibitors by interferon-α in hematopoietic cell lines

One prominent effect of IFNs is their cell growth inhibitory activity. The exact molecular mechanism behind this inhibition of proliferation remains to be elucidated. Possible effectors for IFN-induced growth inhibition are the recently discovered cyclin-dependent kinase inhibitors. The effect of IFN-α treatment on the members of the Ink4 and Cip/Kip families of Cdk inhibitors was investigated in three hematopoietic cell lines Daudi, U-266 and H9. Two of these cell lines, Daudi and U-266, respond to IFN-α by G1 arrest, whereas the H9 cell line is not growth arrested by IFN-α. We show that a p53-independent upregulation of p21 mRNA occurs following IFN-α treatment in all three cell lines. In Daudi and U-266 cells, the mRNA induction is accompanied by an increase in p21 protein, followed by an increased binding of p21 to Cdk2 and a subsequent decrease in Cdk2 activity, temporally coinciding with G1 arrest. In both these cell lines, there was also an increased binding of p21 to Cdk4. In contrast, p21 protein was not expressed in H9 cells, despite high levels of p21 mRNA following IFN-α treatment. In U-266 cells, IFN-α increased not only p21 but also p15 mRNA and protein levels, followed by an increased association of p15 with Cdk4. Furthermore, IFN-α treatment caused a four- to sixfold induction of the p16 E1β transcript in U-266 cells. Expression levels of the other Ink4 and Cip/Kip Cdk inhibitors were not induced by IFN treatment in any of the cell lines. We conclude that IFN-α can act as a potent regulator of Cdk-inhibitor expression, correlating with decreased Cdk activity and cell growth inhibition. One mechanism for resistance to IFN may be loss of the ability of cells to upregulate these proteins.

Involvement of the Ink4 proteins p16 and p15 in T-lymphocyte senescence.

Little is known about the molecular background to senescence in T-lymphocytes. In fibroblast systems replicative senescence has been shown to correlate with a number of changes in the expression of the proteins normally regulating progression through the G1 phase of the cell cycle, and recently the Ink4 inhibitor p16 was implicated as a central regulator of replicative senescence in human fibroblasts. It has, however, been claimed that p16 is not expressed in T-lymphocytes. In the present study we have analysed G1 regulating proteins in ageing human T-lymphocytes. We show that PHA and IL-2 stimulated T-lymphocytes cease to proliferate after around 20 population doublings, these cells can not thereafter be restimulated to growth, and were also found to exhibit markers for senescence. We found that T-lymphocytes accumulate p16 and p15 protein during successive population doublings and display high levels of these proteins as they enter into replicative senescence. There was also an increased binding of p16 to the Cdk6 kinase in senescent cells, and a decreased Cdk6 as well as Cdk2 kinase activity. The levels of other G1 regulating proteins were also altered in the senescent cells, such as slightly elevated levels of p21/WAF1, and downregulation of Cdk2 and cyclinD3. The levels of p27/Kip1 is down regulated in proliferating cells but rise to approximately 15% of the levels in un-stimulated quiescent cells. As a high proportion of T-cell childhood acute lymphoblastic leukaemias have deletions of both p15 and p16, our data suggest that inactivation of these genes makes it possible for leukemic cells to avoid senescence.

Prognostic importance of p15INK4B and p16INK4 gene inactivation in childhood acute lymphocytic leukemia.

PURPOSE The present study explores the prognostic importance of p16INK4/p15INK4B gene inactivation in childhood acute lymphocytic leukemia (ALL). MATERIALS AND METHODS Cells from 79 pediatric ALL patients were investigated for inactivation of the p15INK4B and p16INK4 genes or loss of heterozygosity (LOH) for chromosome 9p markers by use of Southern hybridization, restriction fragment length polymorphism (RFLP) analysis, microsatellite analysis as well as single-strand conformation polymorphism (SSCP) analysis, and nucleotide sequencing of the p15INK4B and p16INK4 genes. Genetic data were correlated to clinical outcome and established prognostic factors. RESULTS Inactivation of the p15INK4B and/or p16INK4 genes by homozygous deletion or loss of one allele and mutation of the other was detected in 24 cases (30%). Another 12 patients (15%) showed loss of one allele. A statistically significant correlation was found between inactivation of the p15INK4B/p16INK4 genes and poor prognosis (P < .01). Furthermore, inactivation proved to be an independent factor that predicted relapse, ranking second to WBC count. The trend toward overrepresentation of treatment failure was strongest in the high-risk (HR) group patients with p16INK4/p15INK4B gene inactivation. Patients with deletion of genetic material on 9p21 and normal coding sequence of the remaining p16INK4 and p15INK4B genes had a similar prognosis to that of nondeleted cases. CONCLUSION The data suggest that analysis of p15INK4B/p16INK4 genes may contribute prognostic information in pediatric ALL.

Interferon and malignant disease how does it work and why doesn't it always?

Since their first use at the clinic almost 30 years ago. interferons (IFNS) have become an accepted therapy in a range of malignancies. Although IFN All induce remissions in some patients, they are of no benefit, or at best, lead only to minor improvements in the great majority of patients. This review considers possible mechanisms underlying the antitumour effects of IFN, and discusses possible reasons for resistance to IFN therapy in patients with malignant disease.

Amplification of multiple regions of chromosome 12, including 12q13–15, in chronic lymphocytic leukaemia

Abstract: Trisomy 12 is a frequent abnormality in chronic lymphocytic leukaemia (CLL). The biological importance of trisomy 12 is still poorly understood but it has been suggested that one or several genes are duplicated leading to malignant transformation. We present a case with amplification of 12q13–22 found in a clinically aggressive relapse of CLL. A smaller region, 12q13–15, was amplified most frequently and a YAC containing the MDM2 gene gave the highest number of signals. Additionally, in a subclone an amplicon containing at least 5 copies of a cosmid from 12q23–24 was detected. The case shows that small duplications of chromosome 12, not revealed by cytogenetic analysis, may occur in CLL. Also, it shows that cytogenetic clonal evolution can occur in CLL without morphological evidence of blast transformation. Our results indicate that the 12q13–15 region carries an important gene for CLL progression.

Therapeutic effects of low‐dose cytosine arabinoside, alpha‐interferon, 1α‐hydroxyvitamin D3 and retinoic acid in acute leukemia and myelodysplastic syndromes

62 evaluable patients with myelodysplastic syndromes (MDS) or acute leukemia were treated with different combinations of low dose ara‐C, α‐interferon (IFN), 1α‐hydroxyvitamin D3 (vit D3) and retinoic acid. The aim was to study the efficacy and toxicity of each combination. The overall rate was 44%. Of these, 50% responded favorably to the combination of IFN, vit D3 and retinoic acid (IDR), which was comparable to the response rate of 43% for low‐dose ara‐C. The results of the IDR treatment may be explained by additive or synergistic effects between the separate drugs in the combination. Ara‐C and IDR treatment was generally well‐tolerated but interferon gave more side effects than any other drug used in the study. Evaluation of the full combination of ara‐C, IFN, vit D3 and retinoic acid was not possible because of toxicity. Marrow hypoplasia was infrequent (5/27 patients) in cases responding favorably to treatment. Complete remissions were not longer than partial remissions or significant responses.

Human leukocyte interferon therapy for advanced ovarian carcinoma.

Daily intramuscular injections of 3 X 10(6) international units of human leukocyte interferon were given to five patients with advanced ovarian carcinoma, all of whom previously received other forms of treatment. Ascitic fluid production ceases in two out of two patients. According to the criteria specified by Young and DeVita a partial response was observed in one patient and in two other patients the disease was stable for more than 1 year. Side effects of the interferon therapy were relatively mild. The introduction of interferon therapy was followed by an increase in the natural killer cell activity of peripheral blood lymphocytes in all three patients examined. Natural killer cell activity decreased after cessation of interferon therapy in the one patient where this was tested.