Multiple active X chromosomes in myelofibrosis with myeloid metaplasia

Aberrant expression of X-linked genes RbAp46, Rsk4, and Cldn2 in breast cancer

The consequence of activation status or gain/loss of an X-chromosome in terms of the expression of tumor suppressor genes or oncogenes in breast cancer has not been clearly addressed. In this study, we investigated the activation status of the X-chromosomes in a panel of human breast cancer cell lines, human breast carcinoma, and adjacent mammary tissues and a panel of murine mammary epithelial sublines ranging from low to high invasive potentials. Results show that most human breast cancer cell lines were homozygous, but both benign cell lines were heterozygous for highly polymorphic X-loci (IDS and G6PD). On the other hand, 60% of human breast carcinoma cases were heterozygous for either IDS or G6PD markers. Investigation of the activation status of heterozygous cell lines revealed the presence of only one active X-chromosome, whereas most heterozygous human breast carcinoma cases had two active X-chromosomes. Furthermore, we determined whether or not an additional active X-chromosome affects expression levels of tumor suppressor genes and oncogenes. Reverse transcription-PCR data show high expression of putative tumor suppressor genes Rsk4 and RbAp46 in 47% and 79% of breast carcinoma cases, respectively, whereas Cldn2 was down-regulated in 52% of breast cancer cases compared with normal adjacent tissues. Consistent with mRNA expression, immunostaining for these proteins also showed a similar pattern. In conclusion, our data suggest that high expression of RbAp46 is likely to have a role in the development or progression of human breast cancer. The activation status of the X-chromosome may influence the expression levels of X-linked oncogenes or tumor suppressor genes.

The causes and consequences of random and non-random X chromosome inactivation in humans

X chromosome (X) inactivation is a remarkable biological process including the choice and cis-limited inactivation of one X, as well as the stable maintenance of this silencing by epigenetic chromatin alterations. The process results in females generally being mosaic for two populations of cells--one with each parental X active. In this review, we discuss recent advances in our understanding of how inactivation works, as well as the causes and clinical implications of deviations from random inactivation.

Twenty-six patients with hematologic disorders and X chromosome abnormalities. Frequent idic(X)(q13) chromosomes and Xq13 anomalies associated with pathologic ringed sideroblasts

In our experience, acquired structurally abnormal X chromosomes are found in about 1% of patients with hematologic disorders who have a chromosomally abnormal clone. Over a 10-year period, we identified 26 patients with hematologic disorders who had an acquired X chromosome abnormality. In 13 of these patients, the breakpoints were at Xq13, and in 13 the had idic(X)(q13) chromosomes. The 13 patients with Xq13 breakpoints were all older females, and 12 had pathologic ringed sideroblasts with dysmyelopoietic syndromes or a history of these syndromes. Among the 13 patients with breakpoints other than Xq13, seven were male and six were female; only one of these patients had pathologic ringed sideroblasts, and all of these patients had a variety of hematologic disorders. Xq13 may contain genes that, when altered by the formation of chromosome abnormalities, may be associated with neoplastic disorders involving pathologic ringed sideroblasts.

Cytogenetic studies in twelve patients with primary myelofibrosis and myeloid metaplasia

Chromosome studies on bone marrow and/or peripheral blood cells without phytohemagglutinin were performed on 12 patients with primary myelofibrosis with myeloid meta-plasia (PMMM) between 1980 and 1984. Abnormal clones were found in six patients (50%). In five cases the abnormal clone involved the long arm of chromosome #7, two of which also had partial trisomy of chromosome #1 and trisomy of 9. Additional abnormalities involving chromosomes #3, #5, #11, #13, #15, and #21 were each found once. Review of the literature showed few studies on the cytogenetics of PMMM. No specific chromosomal pattern can be established; however, abnormalities described are nonrandom.

Evolution of karyotypic abnormalities and C-MYC oncogene amplification in human colonic carcinoma cell lines

Cell lines (COLO 320 DM and COLO 320 HSR), established from a human neuroendocrine tumor, contain an amplified cellular oncogene (c-myc). We have previously shown that the homogeneously staining regions (HSRs) of a marker chromosome in the COLO 320 HSR cells that evolved in culture from COLO 320 DM cells contain amplified c-myc. Molecular hybridization in situ has now been used to demonstrate that the HSRs are on both arms of what was once an X chromosome. We also show that amplified c-myc copies are present in the isolated double minute chromosomes (DMs) of the COLO 320 DM cells that were characteristic of the tumor cells initially established from the patient. The results suggest that the amplified c-myc appeared first as DMs and was subsequently transposed to engender HSRs on an X chromosome. The initial COLO 320 tumor cell may have acquired two "early replicating" (i.e., active) X chromosomes and lost the "late replicating" (i.e., inactive) X.

Isochromosome X in acute myeloblastic leukemia

An aberrant leukemic clone with a 46,X,i(Xq) karyotype appeared at the first relapse of the disease in a case of acute myeloblastic leukemia (AML). The DNA replication pattern displayed asynchronous late termination within the homologous arms of the isochromosome in all investigated metaphases. The origin of asynchrony in the isochromosome's DNA replication pattern is discussed.

Abnormalities of chromosome 13 in myelofibrosis

19 patients with myelofibrosis, primary or following polycythaemia vera were studied cytogenetically. Bone marrow cells, unstimulated and stimulated cells from peripheral blood were investigated. 7 patients were found to have clonal aberrations, 3 of whom had a structural rearrangement of chromosome 13. In 2 additional cases single mitoses with 13q- were found. Reviewing the files on patients previously studied in our laboratory, 2 more patients with 13q- markers were noted. Both had had haematologic disorders in which fibrosis of the bone marrow can be found, but this feature could not be evaluated retrospectively, because no biopsies had been taken. Our data and those found in the literature suggest that rearrangements of 13q12----q22 are often associated with myelofibrosis, both in its primary form or following polycythaemia vera.

Trisomy X as a possible initial chromosome change in a gastric cancer

Primary and metastatic gastric tumors from a patient previously treated for five different cancers were cytogenetically examined by G-banding. Both types of tumors had cells with a 47,XX, +X karyotype; in addition, the primary tumor had a second clone with a 48,XX, +X, +12 karyotype. No other abnormality was found in either tumor. The lymphocytes of this patient revealed a normal female diploid karyotype.