| 1. |
- Gisselsson Nord, David, et al.
(författare)
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Telomere dysfunction triggers extensive DNA fragmentation and evolution of complex chromosome abnormalities in human malignant tumors
- 2001
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Ingår i: Proceedings of the National Academy of Sciences. - : Proceedings of the National Academy of Sciences. - 1091-6490 .- 0027-8424. ; 98:22, s. 12683-12688
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Tidskriftsartikel (refereegranskat)abstract
- Although mechanisms for chromosomal instability in tumors have been described in animal and in vitro models, little is known about these processes in man. To explore cytogenetic evolution in human tumors, chromosomal breakpoint profiles were constructed for 102 pancreatic carcinomas and 140 osteosarcomas, two tumor types characterized by extensive genomic instability. Cases with few chromosomal alterations showed a preferential clustering of breakpoints to the terminal bands, whereas tumors with many changes showed primarily interstitial and centromeric breakpoints. The terminal breakpoint frequency was negatively correlated to telomeric TTAGGG repeat length, and fluorescence in situ hybridization with telomeric TTAGGG probes consistently indicated shortened telomeres and >10% of chromosome ends lacking telomeric signals. Because telomeric dysfunction may lead to formation of unstable ring and dicentric chromosomes, mitotic figures were also evaluated. Anaphase bridges were found in all cases, and fluorescence in situ hybridization demonstrated extensive structural rearrangements of chromosomes, with terminal transferase detection showing fragmented DNA in 5-20% of interphase cells. Less than 2% of cells showed evidence of necrosis or apoptosis, and telomerase was expressed in the majority of cases. Telomeric dysfunction may thus trigger chromosomal fragmentation through persistent bridge-breakage events in pancreatic carcinomas and osteosarcomas, leading to a continuous reorganization of the tumor genome. Telomerase expression is not sufficient for completely stabilizing the chromosome complement but may be crucial for preventing complete genomic deterioration and maintaining cellular survival.
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| 2. |
- Heidenblad, Markus, et al.
(författare)
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Detailed genomic mapping and expression analyses of 12p amplifications in pancreatic carcinomas reveal a 3.5-Mb target region for amplification.
- 2002
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Ingår i: Genes, Chromosomes and Cancer. - : Wiley. - 1045-2257. ; 34:2, s. 211-223
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Tidskriftsartikel (refereegranskat)abstract
- Previous cytogenetic and comparative genomic hybridization (CGH) analyses have shown that the gain of chromosome arm 12p is frequent in pancreatic carcinomas. We investigated 15 pancreatic carcinoma cell lines using CGH, fluorescence in situ hybridization (FISH), and semiquantitative polymerase chain reaction (PCR) to characterize 12p amplifications in detail. The CGH analysis revealed gains of 12p in four of the cell lines and local amplification within 12p11-12 in six cell lines. By FISH analysis, using precisely mapped YAC clones, the commonly amplified region was found to be approximately 5 Mb. The amplified segment extended from YAC 753f12, covering the KRAS2 locus, to YAC 891f1, close to the centromere. A semiquantitative PCR methodology was used to estimate genomic copy numbers of 14 precisely mapped expressed sequence tags (ESTs) and sequence-tagged sites, located within this interval. The level of amplification ranged from two- to 12-fold. The produced gene copy profiles revealed a 3.5-Mb segment with various local amplifications. This region includes KRAS2 and ranges from D12S1617 to sts-N38796. Two of the cell lines (primary and metastatic tumor from the same patient) showed amplification peaks within the distal region of this segment, two had peaks within the proximal region, one showed subpeaks in both regions, and one displayed amplification of the entire region. Chromosome segment-specific cDNA array analysis of 29 expressed sequences within the whole interval between D12S1617 and sts-N38796 indicated overexpression of four ESTs, two corresponding to DEC2 and PPFIBP1, and two to ESTs with unknown function. Expression analysis of these and of KRAS2 showed specific overexpression in the six cell lines with local 12p amplifications. These findings indicate two target regions within the 3.5-Mb segment in 12p11-12, one proximal including PPFIBP1, and one distal including KRAS2.
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| 3. |
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| 4. |
- Jonson, Tord, et al.
(författare)
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Altered expression of TGFB receptors and mitogenic effects of TGFB in pancreatic carcinomas
- 2001
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Ingår i: International Journal of Oncology. - 1019-6439. ; 19:1, s. 71-81
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Tidskriftsartikel (refereegranskat)abstract
- Alteration of the transforming growth factor beta (TGFB) signalling pathway is important in pancreatic carcinogenesis, as shown by the frequent inactivation of the downstream target SMAD4. We recently analysed a series of pancreatic carcinoma cell lines with respect to alterations of five SMAD genes involved in TGFB signalling, and showed that SMAD4 was structurally rearranged in 42% of these. This pathway may, however, also be affected by alterations of genes whose products regulate the activation of TGFB as well as of TGFB receptor genes. We therefore studied the expression of UPA, UPAR, IGF2R, ALK5 (TGFBR1), TGFBR2, TGFBR3, ENG, ALK1, TGFB1, TGFB2, and TGFB3 in a series of 14 pancreatic carcinoma cell lines. We also analysed ALK5 and TGFBR2 for mutations, cell surface localisation of TGFBR2 and ENG, and TGFB1 response. No mutations of ALK5 or TGFBR2 were found. However, 4 cell lines were methylated within the ALK5 promoter region. ALK5 expression was strongly reduced in 9 cases, whereas TGFBR2 expression was increased in 12 of the cell lines. The TGFB signalling associated receptors ENG and ALK1 were co-expressed in 4 of the cell lines. There was no evidence for disruption of the UPAR-IGF2R TGFB activating pathway. The response to TGFB1 was analysed in 12 cell lines, and 6 of these (50%) showed increased proliferation. The cell lines stimulated by TGFB showed frequent mutations of SMAD4, KRAS2, and TP53, as well as frequent absence of CDKN2B expression. These results suggest that the ALK5-SMAD4 part of the TGFB signalling pathway is a major target for inactivation in pancreatic carcinomas, that the expression of TGFBR2, TGFBR3, and receptors involved in TGFB activation are maintained, and that alterations of components of the TGFB signalling pathway may be accompanied by a positive effect of TGFB on cell growth.
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| 5. |
- Jonson, Tord, et al.
(författare)
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Characterization of genomically amplified segments using PCR: optimizing relative-PCR for reliable and simple gene expression and gene copy analyses
- 2000
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Ingår i: Genes, Chromosomes and Cancer. - 1045-2257. ; 29:2, s. 192-199
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Tidskriftsartikel (refereegranskat)abstract
- Gene amplification is one of the mechanisms for oncogene activation in solid tumors. The size of the amplified regions may vary considerably among individual tumors, and more than one gene may be affected within the same amplicon. The main objective in analyzing genomic amplifications has therefore been to map the shortest region involved and to identify genes with increased expression as a result of the increased gene copy number. To facilitate such an analysis, we have developed simple polymerase chain reaction (PCR) procedures using the internal standards beta-actin (ACTB) and L1Hs for gene expression and gene copy number analyses, respectively. We used cDNA derived from pancreatic carcinoma cell lines, and genomic DNA extracted from the same cell lines, as templates in the gene expression and in the gene copy number analyses, respectively. To determine the optimal number of PCR cycles, dilution series of the templates were made. Furthermore, competing primers were used to adjust for differences in target sequence levels. We show that by these simple means it is possible to determine optimal conditions for expression analyses. In addition, the procedure was adapted for the analysis of gene copy number changes at the genomic level using L1Hs as the internal standard. This PCR method makes it possible to produce detailed gene copy number profiles of amplified genomic regions.
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| 6. |
- Jonson, Tord
(författare)
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Molecular studies of pancreatic cancer: Characterization of the transforming growth factor beta signaling pathway
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the present thesis, genetic abnormalities in pancreatic cancer were studied, with special emphasis on alterations of components involved in the transforming growth factor beta (TGFB) signaling pathway. In the first study, fluorescence in situ hybridization and cytogenetic analyses revealed aberrations of chromosome 18 in all 13 pancreatic carcinoma cell lines studied, in particular frequent breaks close to the centromere of chromosome arm 18q. The results suggested the presence of at least one tumor suppressor gene (TSG) at 18q, one candidate being SMAD4, which is a key component of the TGFB signaling pathway. The second study was initiated to investigate the role of five SMAD genes involved in TGFB signaling, i.e., the potential TSGs SMAD2 (18q), SMAD3 (15q), and SMAD4 (18q), as well as the putative oncogenes SMAD6 (15q) and SMAD7 (18q). Loss of heterozygosity and mutation analyses revealed frequent loss of 18q material and SMAD4 inactivations in 5 of 12 cases, whereas no mutations of SMAD2, SMAD3, SMAD6, or SMAD7 were detected. In the third study, the TGFB receptors were investigated. No mutations of TGFBR2 or ALK5 (TGFBR1) were found, expression of TGFBR2 and TGFB3 was maintained or increased, whereas ALK5 was downregulated. The response to TGFB was analyzed in 12 pancreatic carcinoma cell lines, half of which responded by an increase in proliferation. In the fourth study, filter-based microarrays were used to study TGFB induced gene expression alterations. The results demonstrated that pancreatic cancer cell lines with SMAD4 mutations still respond to TGFB treatment. In addition, a gradual inverse gene expression pattern as compared to TGFB sensitive control cells was observed in the pancreatic carcinoma cell lines that correlated with reduced sensitivity to TGFB growth inhibition. In the fifth study, polymerase chain reaction (PCR) protocols for gene expression and gene copy analyses were developed. In summary, the results of the present thesis suggest that partial inactivation of the TGFB signaling pathway, e.g., SMAD4 inactivation and downregulated ALK5 expression, in conjunction with other genetic alterations gradually alter the ability of pancreatic tumor cells to be growth inhibited by TGFB. The most important finding was the detected ability of half of the investigated cell lines to be growth stimulated by TGFB, thus providing a basis for future investigations of the biphasic effects of TGFB observed during the progression of many different tumor types.
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| 7. |
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| 8. |
- Kadigrobov, Anatoli M., 1937, et al.
(författare)
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Giant lasing effect in magnetic nanoconductors
- 2004
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Ingår i: Europhysics Letters. - : IOP Publishing. - 1286-4854 .- 0295-5075. ; 67:6, s. 948-954
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Tidskriftsartikel (refereegranskat)abstract
- We propose a new principle for a compact solid-state laser in the 1–100 THz regime. This is a frequency range where attempts to fabricate small-size lasers up to now have met severe technical problems. The proposed laser is based on a new mechanism for creating spin-flip processes in ferromagnetic conductors. The mechanism is due to the interaction of light with conduction electrons; the interaction strength, being proportional to the large exchange energy, exceeds the Zeeman interaction by orders of magnitude. On the basis of this interaction, a giant lasing effect is predicted in a system where a population inversion has been created by tunneling injection of spin-polarized electrons from one ferromagnetic conductor to another—the magnetization of the two ferromagnets having different orientations. Using experimental data for ferromagnetic manganese perovskites with nearly 100% spin polarization, we show the laser frequency to be in the range 1–100 THz. The optical gain is estimated to be of order 107 cm−1, which exceeds the gain of conventional semiconductor lasers by 3 or 4 orders of magnitude. A relevant experimental study is proposed and discussed.
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| 9. |
- Mertens, Fredrik, et al.
(författare)
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Retained heterodisomy for chromosome 12 in atypical lipomatous tumors: implications for ring chromosome formation.
- 2004
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Ingår i: Cytogenetic and Genome Research. - : S. Karger AG. - 1424-859X .- 1424-8581. ; 106:1, s. 33-38
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Tidskriftsartikel (refereegranskat)abstract
- Atypical lipomatous tumor (ALT) is an intermediate malignant mesenchymal tumor that is characterized by supernumerary ring chromosomes and/or giant rod-shaped marker chromosomes (RGMC). Fluorescence in situ hybridization ( FISH) and molecular genetic analyses have disclosed that the RGMCs always contain amplified sequences from the long arm of chromosome 12. Typically, RGMCs are the sole clonal changes and so far no deletions or other morphologic aberrations of the two normal-appearing chromosomes 12 that invariably are present have been detected. The mechanisms behind the formation of the RGMCs are unknown, but it could be hypothesized that RGMC formation is preceded by trisomy 12 or, alternatively, that ring formation of one chromosome 12 is followed by duplication of the remaining homolog. The latter scenario would always result in isodisomy for the two normal-appearing chromosomes 12, whereas the former would yield isodisomy in one-third of the cases. In order to investigate these possible mechanisms behind ring formation, we studied polymorphic loci on chromosome 12 in 14 cases of ALT showing one or more supernumerary ring chromosomes and few or no other clonal aberrations at cytogenetic analysis. The molecular genetic analyses showed that the tumor cells always retained both parental copies of chromosome 12, thus refuting the trisomy 12 and duplication hypotheses. Copyright (C) 2004 S. Karger AG, Basel.
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