Petr Starostik

Acquirement of Rituximab Resistance in Lymphoma Cell Lines Is Associated with Both Global CD20 Gene and Protein Down-Regulation Regulated at the Pretranscriptional and Posttranscriptional Levels

Acquirement of resistance to rituximab has been observed in lymphoma patients. To define mechanisms associated with rituximab resistance, we developed various rituximab-resistant cell lines (RRCL) and studied changes in CD20 expression/structure, lipid raft domain (LRD) reorganization, calcium mobilization, antibody-dependent cellular cytotoxicity, and complement-mediated cytotoxicity (CMC) between parental and RRCL. Significant changes in surface CD20 antigen expression were shown in RRCL. Decreased calcium mobilization and redistribution of CD20 into LRD were found in RRCL. Western blotting identified a unique 35 kDa protein band in RRCL, which was not seen in parental cells and was secondary to an increase in surface and cytoplasmic expression of IgM light chains. CD20 gene expression was decreased in RRCL. In vitro exposure to PS341 increased CD20 expression in RRCL and minimally improved the sensitivity to rituximab-associated CMC. Our data strongly suggest that the acquisition of rituximab resistance is associated with global gene and protein down-regulation of the CD20 antigen affecting LRD organization and downstream signaling. CD20 expression seems to be regulated at the pretranscriptional and posttranscriptional levels. Proteasome inhibition partially reversed rituximab resistance, suggesting the existence of additional mediators of rituximab resistance. Future research is geared to identify drugs and/or biological agents that are effective against RRCL.

Chromosome 6 Suffers Frequent and Multiple Aberrations in Thymoma

Thymoma is the most frequent tumor arising in human thymus. In this study, we performed a detailed mapping of deleted regions on chromosome 6 shown previously to harbor the most frequent genetic aberrations in this cancer. We analyzed 40 thymomas using 41 microsatellites. Two hundred ninety-four (23.5%) of 1253 informative genotypes showed loss of heterozygosity (LOH), only 39 (2.4%) were positive for microsatellite instability (MSI). Genetic aberrations on chromosome 6 were found in 31 of 40 cases (77.5%) in five hot spots. The most frequent LOHs (48.6%) occurred in region 6q25.2 within a 0.7-Mb interval flanked by markers D6S441 and D6S290. Another hot spot showing LOH in 32.4% of tumors was located between markers D6S442 and D6S1708 (0.4 Mb apart) on 6q25.2-25.3, just 1.1 Mb from the D6S441-D6S290 deletions. The third hot spot (30%) showing LOH appeared in region 6p21.31 including the MHC locus (markers D6S1666-D6S1560, 1 Mb apart). The fourth hot spot (26.3%) was detected on 6q14.1-14.3 (D6S1596-D6S284, 5.2 Mb apart). Some tumors (21.6%) showed LOHs within a fifth hot spot on 6q21 (D6S447-D6S1592, 0.3 Mb apart). Thus, several tumor suppressor genes on chromosome 6 seem to be involved in the pathogenesis of thymoma.

Spiradenocylindroma of the kidney: Clinical and genetic findings suggesting a role of somatic mutation of the CYLD1 gene in the oncogenesis of an unusual renal neoplasm

We describe the morphology and comparative genomic hybridization findings in a tumor for which we propose the term “spiradenocylindroma” of the kidney. The tumor arose in the wall of a renal cyst in an otherwise healthy male patient who had a favorable clinical course after nephrectomy. Tumor cells formed either large nodules exhibiting a solid or trabecular architecture with conspicuous perivascular spaces or cylindromatous small tumor cell islands arranged in a jigsaw pattern. Focally, there were interspersed tubular structures and tumor cell rosettes with central deposits of periodic acid–Schiff-positive material. A minor tumor component showed epidermoid differentiation. The tumor cells were strongly positive for cytokeratins 5/6, high molecular weight cytokeratins 34&bgr;E12 and AE1/3, and E-cadherin, but only weakly positive for cytokeratins 7, 8, 18, 19, and epithelial membrane antigen. Focal reactivity for actin, vimentin, and S-100 protein or lysozyme and &agr; 1 -antichymotrypsin within tubular and cylindromatous areas suggested myoepithelial and apocrine differentiation, respectively. By comparative genomic hybridization, the only abnormality was loss of the long arm of chromosome 16 and gain of genetic material on the short arm of chromosome 16, suggesting isochromosome i(16p). This finding is unique among renal neoplasms and implies loss of heterozygosity at 16q12–13 of the CYLD1 gene that is critically involved in the oncogenesis of familial cylindromatosis and some sporadic spiradenocylindromas. We conclude that somatic mutation of the CYLD1 gene outside the skin can have a role in the oncogenesis of tumors with cylindromatous features.

High Frequency of Genetic Aberrations in Enteropathy-Type T-Cell Lymphoma

To define genetic aberrations playing a role in the development of enteropathy-type T-cell lymphoma (ETL), we examined 26 such tumors using a battery of 47 microsatellite markers. The most frequent aberration (seen in 40% of informative genotypes) was amplification of genomic material in region 9q34 encompassing c-abl and Notch-1 gene loci. Other frequent amplifications were detected in regions 5q33.3–34 and 7q31 (both in more than 30%). Multiple losses of heterozygosity were detected in 6p24, 7p21, 17q23–25, regions containing putative tumor suppressor genes, and in the p53 locus in 17p13.1. Analysis of the pattern of occurrence of these aberrations revealed existence of two ETL subgroups: one of them characterized by the 9q34 aberration and another smaller one showing allelic imbalances in 3q27. These two aberrations were mutually exclusive. Microsatellite instability (MSI) was detected in 69% of the examined lymphomas; the percentage of MSI-positive genotypes per tumor ranged from 2% to 12%. The spectrum of genetic alterations detected showed patterns dependent on morphology. Monomorpic ETLs displayed frequently biallelic TCR-γ gene rearrangement (p = 0078, χ2 test). They showed a different pattern and fewer allelic imbalances (no 3q27, 4q28, 13q14, fewer 5q21, or 5q33.3–34 aberrations) and a lower frequency of MSI than pleomorphic ETLs.

Thymic Epithelial Tumors Can Develop along Two Different Pathogenetic Pathways

To investigate genetic abnormalities associated with the development of thymic epithelial tumors, we performed microsatellite analysis of 26 thymomas belonging to three different World Health Organization types (A, B3, and C) using 48 repeats. The most frequent aberration seen was loss of heterozygosity (LOH) in the region 6q23.3-25.3 detected in 11 tumors (45.8% of informative cases). Further consistent LOHs were detected in regions 3p22-24.2, 3p14.2 (FHIT gene locus), 5q21 (APC), 6p21, 6q21-22.1, 7p21-22, 8q11.21-23, 13q14 (RB), and 17p13.1 (p53). Microsatellite instability was extremely rare, occurring in one type B3 thymoma only, although, at 12.5% of the analyzed loci. Comparing the allelotypes of the analyzed thymomas, we were able to identify two pathogenetic pathways these tumors develop along, characterized by the 6q23.3-25.3 and 5q21 LOHs, respectively. The APC aberration on 5q21 showed significant associations with LOH in the 3p22-24.2, 13q14, and 17p13.1 regions. Interestingly, type A thymomas presented with consistent LOH in the region 6q23.3-25.5 only, they did not reveal any aberrations in the APC, RB, and p53 gene loci or regions 3p22-24.2 and 8q11.21-23. The absence of these aberrations might be the reason for the well-known benign behavior of type A thymomas as compared to types B3 and C tumors.

Hypoxia-inducible factor-1α protein expression is associated with poor survival in normal karyotype adult acute myeloid leukemia

We examined the predictive impact of HIF-1α protein expression on clinical outcome of 84 normal karyotype acute myeloid leukemia (NK-AML) patients (median age 66.5 years) at our institute. Thirty percent of NK-AML cells expressed cytoplasmic HIF-1α. In univariate analysis, low HIF-1α (≤ 5%, n = 66) was associated with improved event-free survival (p = 0.0453, HR = 0.22). Multivariate analysis incorporating age, complete remission, FLT3-ITD mutation, and marrow blast percentage demonstrated that HIF-1α was independently associated with poorer overall and event-free survival. HIF-1α expression correlated with VEGF-C but not VEGF-A, marrow angiogenesis, FLT3 ITD or NPM1 mutations. These results support HIF-1α as an outcome marker for NK-AML.

Loss of Fas (CD95/APO-1) Regulatory Function Is an Important Step in Early MALT-Type Lymphoma Development

Fas (CD95, APO-1) mutations were found in autoimmune diseases and some lymphomas, suggesting impairment of Fas-mediated cell death signaling that may cause tumor development. Because mucosa-associated lymphoid tissue (MALT)-type lymphoma B cells recognize autoantigens and proliferate in response to antigen and T cell-mediated signals, it is suggestive that autoreactive B cell lymphoma precursor cells may have escaped the Fas-mediated checkpoint that normally operates in healthy individuals. Using different biochemical, molecular, and functional approaches, we analyzed the Fas signaling in malignant B cells from seven MALT-type lymphomas that were additionally characterized for the t(11;18)(q21;q21) and four gastric diffuse large B cell lymphomas (DLBL). All DLBLs and three of seven MALT-type lymphomas were resistant to Fas-mediated apoptosis in vitro. Moreover, four of five MALT-type lymphomas analyzed and one of three DLBLs analyzed showed mutations in Fas mRNA transcripts but no loss of heterozygosity in the Fas promotor region. Alternative mechanisms of resistance to apoptosis, such as decreased expression of Fas or production of soluble Fas were not operative. Therefore, it is suggestive that a subgroup of MALT-type lymphoma B cells, irrespective of t(11;18)(q21;q21), escape the censoring Fas pathway by mutating and inactivating Fas. This identifies a key regulatory step in early MALT-type lymphomagenesis.

The Role of Microsatellite Instability in Gastric Low- and High-Grade Lymphoma Development

DNA mismatch repair genes and their dysfunction as evidenced by microsatellite instability (MSI) play an important role in the pathogenesis of a variety of tumors, most prominently hereditary nonpolyposis colorectal cancer (HNPCC). However, their role in development of extranodal lymphomas has not been established yet. We therefore evaluated for MSI 25 gastric low-grade marginal-zone B-cell lymphomas of mucosa-associated lymphoid tissue type and 31 gastric high-grade diffuse large B-cell lymphomas (DLBCLs) with 29 and 118 microsatellites, respectively. Compared with HNPCC, the overall level of MSI was much lower with a mean of 2.6% MSI-positive repeats in the DLBCLs; the frequency of MSI showed a tendency to increase with age (P = 0.01), as did MSI variability (P = 0.02). Low-grade mucosa-associated lymphoid tissue lymphomas displayed even less MSI (sevenfold) than DLBCLs (P = 0.009). MSI frequency thus increases with the transition from low- to high-grade disease and with age; it does not seem to initiate lymphomagenesis. Other microsatellites than those typically mutated in HNPCC frequently revealed MSI in these lymphomas, especially dinucleotide repeats on chromosomes 3, 5, and 18. To facilitate rapid screening of lymphomas for MSI and to establish a tool for future MSI frequency comparisons, we recommend to use repeats D3S1261, D3S1530, D5S346, D17S250, D18S474, and DCC.

Amplification of NOTCH1 and ABL1 gene loci is a frequent aberration in enteropathy-type T-cell lymphoma

We have shown previously that amplification of chromosomal region 9q34 is the most frequent aberration in enteropathy-type T-cell lymphoma (ETL). To determine the minimum amplified 9q34 region and identify possible candidate gene(s), we performed a detailed microsatellite screening and quantitative real-time PCR (QPCR) on 26 ETL cases. Microsatellite analysis revealed allelic imbalance in both ABL1 and NOTCH1 gene loci (microsatellites D9S290–D9S1847 and D9S158 flanking the former and latter genes, respectively) localized in the band 9q34. The results were confirmed by TaqMan-based QPCR showing amplification of ABL1 and NOTCH1 exons in 50% and 65% of cases, respectively. Amplifications of the NOTCH1 gene were more frequent than of the ABL1 gene; moreover, the analyzed NOTCH1 exon consistently displayed higher levels of amplification than ABL1 coding sequences. From 9q34 known genes, NOTCH1 could thus be the primary target of genomic DNA amplification in ETL.

Multiparameter flow cytometry for the diagnosis and monitoring of small GPI-deficient cellular populations†

Glycosyl‐phosphatidylinositol (GPI)‐negative blood cells are diagnostic for Paroxysmal Nocturnal Hemoglobinuria (PNH). Marrow failure states are often associated with GPI‐negative cell populations. Quantification of small clonal populations of GPI‐negative cells influences clinical decisions to administer immunosuppressive therapy in marrow failure states (aplastic anemia or myelodysplastic syndrome) and to monitor minimal residual disease after allogeneic blood or marrow transplantation (BMT). We studied the reliability of high‐resolution flow cytometry markers operating at the limits of detection.