Cleavage of the IPS-1/Cardif/MAVS/VISA does not inhibit T cell-mediated elimination of hepatitis C virus non-structural 3/4A-expressing hepatocytes.

BACKGROUND: Hepatitis C virus (HCV) effectively establishes persistent infection in human livers. The non-structural (NS) 3/4A complex participates in this process by cleavage of interferon beta (IFN beta) promoter stimulator-1 (IPS-1; also termed Cardif/MAVS/VISA), which inhibits responses to double stranded (ds) RNA. However, it is not known whether this effect extends beyond innate responses. AIMS: To test if HCV NS3/4A affects innate and adaptive immune responses in vivo. METHODS: NS3 levels were semi-quantified in human liver biopsies, transfected cells, and in transgenic (Tg) mouse livers by western blot. The effect of NS3/4A on dsRNA-mediated signalling and on the integrity of IPS-1 was analysed using in vitro translation, transfected cells and Tg mice. Cytotoxic T cell (CTL)-mediated clearance of transient firefly luciferase (FLuc)- and/or NS3/4A-Tg hepatocytes was determined using in vivo imaging and western blot. RESULTS: NS3 protein levels were in a comparable range (0.1-49 microg/g tissue) in infected human livers and Tg mouse livers. Importantly, these levels of NS3/4A reduced murine innate responses to synthetic dsRNA in vivo, supporting the possibility that this occurs also in infected humans. The likely explanation for this was the NS3/4A-mediated cleavage of mouse IPS-1, albeit less efficiently than human IPS-1. Despite this, FLuc- and/or NS3/4A-expressing murine hepatocytes were effectively eliminated by hepatic CTLs, utilising the classical molecules for virus-infected cell lysis, including CD8, IFN gamma, perforin and FasL. CONCLUSIONS: Although HCV NS3/4A inhibits the innate immunity, this does not prevent CTL-mediated clearance of NS3/4A-expressing hepatocytes in vivo. Thus, other HCV proteins are most likely responsible for interfering with the adaptive immunity.

Irreversible TrxR1 inhibitors block STAT3 activity and induce cancer cell death.

Because of its key role in cancer development and progression, STAT3 has become an attractive target for developing new cancer therapeutics. While several STAT3 inhibitors have progressed to advanced stages of development, their underlying biology and mechanisms of action are often more complex than would be expected from specific binding to STAT3. Here, we have identified and optimized a series of compounds that block STAT3-dependent luciferase expression with nanomolar potency. Unexpectedly, our lead compounds did not bind to cellular STAT3 but to another prominent anticancer drug target, TrxR1. We further identified that TrxR1 inhibition induced Prx2 and STAT3 oxidation, which subsequently blocked STAT3-dependent transcription. Moreover, previously identified inhibitors of STAT3 were also found to inhibit TrxR1, and likewise, established TrxR1 inhibitors block STAT3-dependent transcriptional activity. These results provide new insights into the complexities of STAT3 redox regulation while highlighting a novel mechanism to block aberrant STAT3 signaling in cancer cells.

Deletion of alpha-, beta-, and omega-interferon genes in malignant cells from children with acute lymphocytic leukemia.

Scanning densitometry and restriction fragment length polymorphism analysis were used to study the alpha-, beta-, gamma-, and omega-interferon (IFN) genes in malignant cells from 11 children with acute lymphocytic leukemia and in one cell line of T-cell origin. In the malignant cells of one patient there was a complete loss of alpha-, beta-, and omega-IFN genes, whereas in another patient one of the alleles of these genes had been deleted. Cytogenetic analysis revealed a deletion of the short arm of chromosome 9, i.e., the region containing the alpha-, beta-, and omega-IFN genes, in the latter patient. The normal cells of the patients with IFN gene deletions had two alleles of the alpha-, beta-, and omega-IFN genes. In cells from none of the patients could deletions or rearrangements of the gamma-IFN genes be detected. We conclude that in 2 of 11 patients with acute lymphocytic leukemia the malignant transformation is accompanied by loss of material on one or both chromosomes 9 and that the alpha-, beta-, and omega-IFN genes are included in these deletions.

Alpha-interferon receptors in malignant B-cells from patients with chronic lymphocytic leukemia: relation to induction of 2'-5'-oligoadenylate synthetase and blast transformation.

alpha-Interferon (IFN-alpha) induces blast transformation of malignant B-cells from approximately 65% of chronic lymphocytic leukemia patients. We have shown previously that induction of blast transformation correlates with induction of 2'-5'-oligoadenylate synthetase. In this paper we address the question of whether low responsiveness to IFN-alpha is associated with a reduced expression of the IFN receptor. IFN-alpha receptor expression was studied by the binding of radioiodinated IFN-alpha to peripheral blood malignant B-cells from 20 chronic lymphocytic leukemia patients and to blood cells from 5 healthy donors. Chronic lymphocytic leukemia cells from all 20 patients displayed high affinity IFN-alpha receptors [mean Kd, 62 +/- 9 (SE) pM] ranging between 110 and 850 binding sites/cell [mean, 416 +/- 51]. Nonmalignant mononuclear blood cells showed similar binding data (411 +/- 105 binding sites/cell; Kd 66 +/- 20 pM). Receptor expression did not correlate with the degree of blast transformation or with induction of 2'-5'-oligoadenylate synthetase. We conclude that the deficiency of IFN sensitivity is localized somewhere between signal transduction from the receptor and induction of 2'-5'-oligoadenylate synthetase.

Induction of Cip/Kip and Ink4 cyclin dependent kinase inhibitors by interferon-alpha 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-alpha 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-alpha by G1 arrest, whereas the H9 cell line is not growth arrested by IFN-alpha. We show that a p53-independent upregulation of p21 mRNA occurs following IFN-alpha 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-alpha treatment. In U-266 cells, IFN-alpha increased not only p21 but also p15 mRNA and protein levels, followed by an increased association of p15 with Cdk4. Furthermore, IFN-alpha treatment caused a four- to sixfold induction of the p16 E1beta 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-alpha 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.

Molecular mechanisms underlying interferon-alpha-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-alpha 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-alpha's 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-alpha 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-alpha 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-alpha 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-alpha 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-alpha treatment, is not primarily due to loss of the G1 kinase components, but result from the inhibitory action of CKIs on these complexes.

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.

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.

Gamma-IFN induced cell adhesion in chronic myelogenous leukemia cells.

Both gamma- and alpha-interferons (IFNs) have been shown to induce clinical responses in chronic myelogenous leukemia (CML). The mechanisms behind these effects are not known. In chronic phase CML, granulocytic progenitors normally found in the bone marrow only, are found extramedullary. A defect in the adhesion of CML cells, that may be responsible for this finding, has been described earlier. In this study, we have investigated whether IFN can restore the defect in CML cell adhesion. It was found that gamma-, but not alpha-IFN, strongly induced the adhesion of CML cells to other cells and to plastic in a majority of the patients. In parallel, an induction in the expression of the adhesion molecules ICAM-1 and LFA-1 was found, and blocking of these molecules by antibodies abolished the effect. The ability of gamma-IFN to restore the adhesive property of CML cells may add to the antitumor effects observed with gamma-IFN therapy in CML.

Interferon system defects in malignant T-cells.

Deletions of chromosome 9p21-22 occur in acute lymphocytic leukemia (ALL), melanoma and glioma. With some exceptions, these deletions include the alpha- and beta-interferon (IFN) genes. In this study, the frequency of alpha- and beta-IFN gene deletions was investigated in 17 T-cell lines, and losses of IFN genes were related to other aspects of the IFN system. Deletions of alpha-/beta-IFN genes were observed in 7/17 cell lines. In two cases the deletions were homozygous for both loci. In most cases aberrations of chromosome 9 were also apparent on cytogenetic analysis. An increased proportion (40% as compared to the expected 13%) of the remaining ten cell lines showed homozygosity for all five common polymorphic alpha-/beta-IFN markers, possibly implicating allelic deletion by loss of heterozygosity (LOH) in some of these clones. The cell lines showed a large variability in IFN production, IFN-alpha receptor number, susceptibility to IFN measured as induction of the enzyme 2',5' oligoadenylate synthetase and cell growth inhibition. No correlations between loss of IFN genes and IFN-producing capacity, or susceptibility to IFN, were found. Of the seven cell lines with a normal IFN-gene dosage and heterozygosity for the alpha- and beta-IFN genes, three had a deficiency in their IFN-producing capacity and one was also insensitive to growth inhibition by IFN. All IFN-producing cell lines predominantly produced beta-IFN.

Deletion of the Ink4-locus (the p16ink4a, p14ARF and p15ink4b genes) predicts relapse in children with ALL treated according to the Nordic protocols NOPHO-86 and NOPHO-92.

Inactivation of the Ink4 gene locus locus on 9p comprising the tumour suppressor gene p16ink4a and its neighbours p14ARF and p15ink4b is common in childhood acute lymphoblastic leukaemia (ALL), but the prognostic significance is controversial. DNA from 230 patients was retrospectively analysed by Southern blotting, single strand conformation polymorphism (SSCP) and sequencing techniques. The results were correlated with clinical characteristics and outcome. One hundred and ninety-four fully analysed patients, similarly treated using the Nordic NOPHO-86 or the current NOPHO-92 protocols, were included in the outcome analysis. Deletions approached a minimally deleted region between the p16ink4a and p15ink4b genes, making the p14ARF gene the most commonly deleted coding sequence. Bi-allelic deletion was associated with high white blood cell count (WBC) (P < 0.001), T cell phenotype (P < 0.001) and mediastinal mass (P < 0.001). Patients with Ink4 locus bi-allelic deletions had an inferior pEFS (P < 0.01) and multivariate analysis indicated that bi-allelic deletion of the p16ink4a and the p14ARF genes was an independent prognostic risk factor (P < 0.05). Sub-group analysis revealed a pronounced impact of deletion status for high-risk patients, ie with high WBC. Deletion-status and clinical risk criteria (WBC) could thus be combined to further differentiate risk within the high-risk group. The analysis of the Ink4 locus adds independent prognostic information in childhood ALL treated by Nordic protocols and may help in selection of patients for alternative treatment.

A cosmid and cDNA fine physical map of a human chromosome 13q14 region frequently lost in B-cell chronic lymphocytic leukemia and identification of a new putative tumor suppressor gene, Leu5.

B-cell chronic lymphocytic leukemia (B-CLL) is a human hematological neoplastic disease often associated with the loss of a chromosome 13 region between RB1 gene and locus D13S25. A new tumor suppressor gene (TSG) may be located in the region. A cosmid contig has been constructed between the loci D13S1168 (WI9598) and D13S25 (H2-42), which corresponds to the minimal region shared by B-CLL associated deletions. The contig includes more than 200 LANL and ICRF cosmid clones covering 620 kb. Three cDNAs likely corresponding to three different genes have been found in the minimally deleted region, sequenced and mapped against the contigged cosmids. cDNA clone 10k4 as well as a chimeric clone 13g3, codes for a zinc-finger domain of the RING type and shares homology to some known genes involved in tumorigenesis (RET finger protein, BRCA1) and embryogenesis (MID1). We have termed the gene corresponding to 10k4/13g3 clones LEU5. This is the first gene with homology to known TSGs which has been found in the region of B-CLL rearrangements.

Why do so many cancer patients fail to respond to interferon therapy?

Since their first use in the clinic some 25 years ago, interferons (IFNs) have become accepted therapy in a range of cancer forms. However, although in some patients they induce remission, in the great majority they are of no benefit or, at best, lead only to minor improvements. This review considers possible reasons for these failures.

In vivo induction of the interferon-stimulated protein 2'5'-oligoadenylate synthetase in tumor and peripheral blood cells during IFN-alpha treatment of metastatic melanoma.

Interferon-alpha (IFN-alpha) therapy induces a response in a proportion of patients with metastatic melanoma. However, the mechanism of the antitumor action and reason(s) for resistance to IFN therapy are not known. To investigate whether lack of clinical response may be due to resistance of the melanoma cells to IFN-alpha or to an inability of IFN-alpha to reach the tumor cells during treatment, we investigated the in vivo and in vitro susceptibility of primary tumor cells obtained through fine needle aspiration biopsies and peripheral blood mononuclear cells (PBMC) to the induction of the IFN-induced enzyme 2'5'-oligoadenylate synthetase (2'5'OAS) during initiation of IFN-alpha therapy in 10 patients with metastatic melanoma. None of the patients showed an objective response to IFN-alpha treatment. The melanoma cells from 2 of the 10 patients were resistant to IFN-induced enhancement of 2'5'OAS in vitro. This correlated well with the in vivo induction of 2'5'OAS in the malignant cells, as no in vivo induction was seen in the 2 patients whose malignant cells were resistant in vitro, whereas tumor cells from 7 of 8 of the remaining patients showed enhancement also in vivo. This study shows that it is possible to monitor the cellular susceptibility of tumor cells to IFN-alpha in vivo and that melanoma cells from a small percentage of patients are resistant to the cellular effects of IFN-alpha. Furthermore, the absence of a clinical response to IFN-alpha therapy in the majority of melanoma patients can be explained neither by impaired cellular susceptibility to IFN nor by an inability of IFN-alpha to reach the tumor.

Cytotoxic effect of interferon on primary malignant tumour cells. Studies in various malignancies.

It is a well established fact that interferon (IFN) can inhibit cell growth, but only recently has it been found that IFN can exert a direct cytotoxic effect on primary tumour cells. This was shown in malignant cells from patients with multiple myeloma. In this study the influence of IFN on the viability of primary malignant cells from patients with different malignancies was studied. As previously described a direct cytotoxic effect of IFN on multiple myeloma cells was observed. No major effects on cell viability could be found in malignant cells from patients with lymphoma, chronic lymphocytic leukaemia, hairy cell leukaemia, chronic myelogenous leukaemia and carcinoma. This indicates that the direct cytotoxic effect of IFN in multiple myeloma may be relatively specific for this malignancy. It could be due to a specific differentiation stage in the myeloma cells, specific genetic alterations and/or abrogation of an autocrine/paracrine loop.

Measurement of interferon sensitivity in tumour cells from fine-needle aspirations.

Previous studies have shown significant correlations between interferon (IFN) induced enhancement of the enzyme 2',5'-oligoadenylate (2',5'-A) synthetase in vitro and response to IFN therapy. A limitation of this and other predictive tests is the availability of malignant cells for culture. Malignant cells can be obtained from most palpable solid tumours by fine-needle aspiration. We investigated whether malignant cells from such aspirations can be used in a 2',5'-A synthetase assay. In 23/27 (85%) of the cases sufficient amounts of viable cells were obtained, containing a high proportion (greater than or equal to 90%) of tumour cells. In 13/23 tumour samples (57%) IFN-alpha significantly enhanced the 2',5'-A synthetase levels. The use of cells from the fine-needle aspirations for prediction of IFN sensitivity, makes the 2',5'-A synthetase test applicable in a wide range of tumours at a variety of disease stages.

Mechanisms of interferon-induced cell cycle arrest.

The interferons (IFNs) are a group of cytokines, which in addition to their antiviral activity are capable of modulating a variety of cellular responses. One such prominent effect of IFNs is their potent antimitogenic action, which can be observed both on malignant and non-malignant cells of many different origins. IFNs are also used in the clinic, mainly in malignant and viral diseases, and their cell growth -inhibitory effect has been suggested to be of major importance in their antitumour and antiviral action. The aim of the present review is to provide insight into the molecular mechanisms by which IFNs modulate cell cycle progression in various cell types. With the recent progress in our understanding of how the cell cycle is regulated at the molecular level, it has become possible to delineate intracellular effectors of IFN in this respect. Understanding the antiproliferative effects of IFN may not only help in understanding its antineoplastic and antiviral activities, but may also provide an insight into cell cycle regulation in general and aid in making IFNs a more useful tool in treating disease.

How do mutated oncogenes and tumor suppressor genes cause cancer?

In recent decades we have been given insight into the process that transforms a normal cell into a malignant cancer cell. It has been recognised that malignant transformation occurs through successive mutations in specific cellular genes, leading to the activation of oncogenes and inactivation of tumor suppressor genes. The further study of these genes has generated much of its excitement from the convergence of experiments addressing the genetic basis of cancer, together with cellular pathways that normally control important cellular regulatory programmes. In the present review the context in which oncogenes and tumor suppressor genes normally function as key regulators of physiological processes such as proliferation, cell death/apoptosis, differentiation and senescence will be described, as well as how these cellular programmes become deregulated in cancer due to mutations.

[Transcription map of the 13q14 region, frequently deleted in B-cell chronic lymphocytic leukemia patients]. / Transkriptsionnaia karta raiona 13q14, chasto utrachivaemogo u bol'nykh B-kletochnym khronicheskim limfoleikozom.

Deletions in the region located between the STS markers D13S1168 and D13S25 on chromosome 13 are the most frequent genomic changes in patients with B-cell chronic lymphocytic leukemia (B-CLL). After sequencing of this region, two novel candidate genes were identified: C13orf1 (chromosome 13 open reading frame 1) and PLCC (putative large CLL candidate). Analysis of the repeat distribution revealed two subregions differing in composition of repetitious DNA and gene organization. The interval D13S1168-D13S319 contains 131 Alu repeats accounting for 24.8% of its length, whereas the interval GCT16C05-D13S25, which is no more than 180 kb away from the former one is extremely poor in Alu repeats (4.1% of the total length). Both intervals contain almost the same amount of the LINE-type repeats L1 and L2 (20.3 and 21.24%, respectively). In the chromosomal region studied, 29 Alu repeats were found to belong to the evolutionary young subfamily Y, which is still capable of amplifying. A considerable proportion of repeats of this type with similar nucleotide sequences may contribute to the recombinational activity of the chromosomal region 13q14.3, which is responsible for its rearrangements in some tumors in humans.