Chromosomal and in vitro culture studies in a case of primary plasma cell leukemia

Histone H1 depletion triggers an interferon response in cancer cells via activation of heterochromatic repeats

Histone H1 has seven variants in human somatic cells and contributes to chromatin compaction and transcriptional regulation. Knock-down (KD) of each H1 variant in breast cancer cells results in altered gene expression and proliferation differently in a variant specific manner with H1.2 and H1.4 KDs being most deleterious. Here we show combined depletion of H1.2 and H1.4 has a strong deleterious effect resulting in a strong interferon (IFN) response, as evidenced by an up-regulation of many IFN-stimulated genes (ISGs) not seen in individual nor in other combinations of H1 variant KDs. Although H1 participates to repress ISG promoters, IFN activation upon H1.2 and H1.4 KD is mainly generated through the activation of the IFN response by cytosolic nucleic acid receptors and IFN synthesis, and without changes in histone modifications at induced ISG promoters. H1.2 and H1.4 co-KD also promotes the appearance of accessibility sites genome wide and, particularly, at satellites and other repeats. The IFN response may be triggered by the expression of noncoding RNA generated from heterochromatic repeats or endogenous retroviruses upon H1 KD. In conclusion, redundant H1-mediated silencing of heterochromatin is important to maintain cell homeostasis and to avoid an unspecific IFN response.

The recurrent IgH translocations are highly associated with nonhyperdiploid variant multiple myeloma

Aneuploid is ubiquitous in multiple myeloma (MM), and 4 cytogenetic subcategories are recognized: hypodiploid (associated with a shorter survival), pseudodiploid, hyperdiploid, and near-tetraploid MM. The hypodiploid, pseudodiploid, and near-tetraploid karyotypes can be referred to as the nonhyperdiploid MM. Immunoglobulin heavy-chain (IgH) translocations are seen in 60% of patients. We studied the relation between aneuploidy and IgH translocations in MM. Eighty patients with MM and abnormal metaphases were studied by means of interphase fluorescent in situ hybridization (FISH) to detect IgH translocations. We also studied a second cohort of 199 patients (Eastern Cooperative Oncology Group [ECOG]) for IgH translocations, chromosome 13 monosomy/deletions (Delta13), and ploidy by DNA content. Mayo Clinic patients with abnormal karyotypes and FISH-detected IgH translocation were more likely to be nonhyperdiploid (89% versus 39%, P <.0001). Remarkably, 88% of tested patients with hypodiploidy (16 of 18) and 90% of tested patients with tetraploidy (9 of 10) had an IgH translocation. ECOG patients with IgH translocations were more likely to have nonhyperdiploid MM by DNA content (68% versus 21%, P <.001). This association was seen predominantly in patients with recurrent chromosome partners to the IgH translocation (11q13, 4p16, and 16q23). The classification of MM into hyperdiploidy and nonhyperdiploidy is dictated largely by the recurrent (primary) IgH translocations in the latter.

Cytogenetic and fluorescence in situ hybridization studies in four cases of plasma cell leukemia

We present a cytogenetic and fluorescence in situ hybridization (FISH) study, using centromeric probes for chromosomes 3, 7, 11, and 18, TP53 gene (17p13), and RB-1 locus (13q14) DNA probes, in four cases of plasma cell leukemia (PCL). Among the four cases, three presented monosomy of the RB-1 locus and one monoallelic deletion of the TP53 gene. The present report shows the usefulness of the FISH technique to detect abnormalities not previously observed by conventional cytogenetics.

Molecular cytogenetic abnormalities in multiple myeloma and plasma cell leukemia measured using comparative genomic hybridization

Comparative genomic hybridization (CGH) was used to identify recurrent regions of DNA sequence loss and gain in 21 multiple myeloma (MM) and plasma cell leukemia (PCL) primary tumor specimens and cell lines. Multiple regions of non-random sequence loss and gain were observed in 8/8 primary advanced stage tumors and 13/13 cell lines. Identification of sequence copy number changes was facilitated by statistical analyses that reduce subjectivity associated with identification of copy number changes and by requiring that sequence changes are visible using both red- and green-labeled tumor DNA. Loss of sequence on 13q and 14q and gain of sequence on 1q and chromosome 7 occurred in 50-60% of the population. In general, cell lines carry more and larger regions of sequence gain and loss than primary tumors. Regions of sequence copy number change that recur among MM cell lines and primary tumors include, in order of prevalence, enh(1q12qter), dim(13), enh(7), enh(3q22q29), enh(11q13.3qter), dim(14q11.2q31), enh(8q21qter), enh(3p25pter), dim(17p11.2p13), and dim(6q22.1q23). Population distributions of genome-wide changes in primary tumors reveal "hot-spots" of sequence loss from 13q12.1-q21, 13q32-q34, 14q11.2-q13, and 14q23-q31. Genomic changes detected using CGH are consistent with those identified using banding analyses, although recurrent involvement of additional regions of the genome are also evident. A higher prevalence of genomic changes is visible using CGH compared to banding. Identification of recurrent regions of sequence gain and loss provides opportunities to identify regions of the genome that may be involved in the malignant phenotype and/or disease progression.