Acquired genomic aberrations associated with methotrexate resistance vary with background genomic instability
ABSTRACT Tumors vary widely in chromosomal level genome instability. To gain a better understanding of the underlying defects which foster specific types of aberrations, we investigated the response of cells of related genetic backgrounds to challenge with methotrexate. We studied mismatch repair deficient HCT116 cells, two derivatives also deficient in XRCC5 (HCT116 Ku86+/-) or BLM (HCT116 BLM-/-), and mismatch repair competent HCT116+chr3 cells. We show that colony formation occurred at a significantly higher frequency in HCT116 cells and HCT116 Ku86+/- cells compared to HCT116 BLM-/- and HCT116+chr3 cells. Visible colonies arose most rapidly in HCT116 Ku86+/- cells, whereas they formed most slowly in HCT116+chr3 cells. Copy number changes acquired by the methotrexate resistant HCT116 and HCT116 BLM-/- cells most often included whole chromosome gains or losses or no acquired copy number changes, whereas resistance in HCT116+chr3 and HCT116 Ku86+/- cells was associated with amplification of DHFR and copy number transitions leading to increased copy number of DHFR, respectively. The additional copies of DHFR were present on unstable chromosomes and organized as inverted repeats in HCT116+chr3 cells, while they were most often present as direct repeats in HCT116 Ku86+/- cells. These observations suggest that different mutational mechanisms promote drug resistance in these genetic backgrounds; mismatch repair deficiency in HCT116, high rates of chromosomal instability in HCT116 Ku86+/-, and low rates of chromosomal instability in HCT116+chr3. On the other hand, it appears that loss of BLM function suppresses the mismatch repair mutator mechanism in mismatch repair and BLM deficient HCT116 BLM-/- cells.
SourceAvailable from: Tae-Hoon Chung[Show abstract] [Hide abstract]
ABSTRACT: Multiple myeloma (MM) is characterized by complex genetic abnormalities whose complexity signifies varying degree of chromosomal instability (CIN). In this study, we introduced a novel CIN measure, chromosome instability genome event count (CINGEC), which considered both copy number aberrations and interstitial breakpoints from high-resolution genome-wide assays. When assessed in two aCGH MM datasets, higher CINGEC was associated with poor survival. We then derived a CINGEC-associated gene expression profile (GEP) signature, CINGECS, using a dataset that has both aCGH and GEP. Genes in CINGECS were mainly involved in DNA damage responses besides in aneuploidy and other generic oncogenic processes contrary to other CIN associated GEP signatures. Finally, we confirmed its survival association in three GEP datasets that encompassed newly diagnosed patients treated with transplant-based protocol with or without novel agents for induction as well as relapsed patients treated with bortezomib. Furthermore, CINGECS was independent of many GEP-based prognostic signatures. In conclusion, our novel CIN measure has definite biological and clinical significance in myeloma.PLoS ONE 06/2013; 8(6):e66361. DOI:10.1371/journal.pone.0066361 · 3.53 Impact Factor
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ABSTRACT: Methotrexate (MTX) has been widely used for the treatment of cancer and rheumatoid arthritis (RA). Aspirin (ASA) is a non-selective cyclooxygenase (COX) inhibitor that contributes to the treatment of inflammatory conditions such as RA. It has been observed that the antitumor effect of ASA can be attributed to inhibition of cell cycle progression, induction of apoptosis and inhibition of angiogenesis. In the present study, we revealed that the treatment with a combination of MTX and ASA resulted in antagonism of the cytotoxic effect as demonstrated by SRB and colony formation assays. ASA alleviated the MTX-mediated S phase accumulation and recovered the G1 phase. MTX-mediated accumulation of the S phase marker cyclin A was also alleviated by ASA. Notably, FAS protein levels were upregulated by MTX in A549 cells. The antagonism of MTX efficacy caused by ASA was accompanied by altered expression of caspase-3, Bcl-2 and FAS but not dihydrofolate reductase (DHFR). This suggests that the alteration of caspase-3, Bcl-2 and FAS was involved in the antagonism between ASA and MTX. Exogenously added folic acid reversed the MTX-mediated DHFR inhibition following either MTX or MTX + ASA treatments. Most importantly, we demonstrated for the first time that the commonly used non-steroidal anti-inflammatory drug for headache ASA and possibly other COX-1/2 inhibitors can produce a strong antagonistic effect on the growth inhibition of lung cancer cells when administered in combination with MTX. The clinical implication of our finding is obvious, i.e., the clinical efficacy of MTX therapy can be compromised by ASA and their concomitant use should be avoided.Oncology Reports 06/2013; 30(3). DOI:10.3892/or.2013.2561 · 2.19 Impact Factor
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ABSTRACT: It is becoming increasingly apparent that splicing defects play a key role in cancer, and that alterations in genomic splicing elements promote aberrant splicing. Alternative splicing increases the diversity of the human transcriptome and increases the numbers of functional gene products. However, dysregulation that leads to aberrant pre-mRNA splicing can contribute to cancer. Hyaluronan (HA), known to be an important component of cancer progression, is synthesized by hyaluronan synthases (HASs). In cancer cells, hyaluronan synthase 1 (HAS1) pre-mRNA is abnormally spliced to generate a family of aberrant splice variants (HAS1Vs) that synthesize extracellular and intracellular HA. HAS1Vs are clinically relevant, being found almost exclusively in malignant cells. Expression of aberrant HAS1Vs predicts poor survival in multiple myeloma. In this review, we summarize the unusual properties of HAS1Vs and their relationship to cancer. HAS1Vs form heterogeneous multimers with normally spliced HAS1 as well as with each other and with HAS3. Aberrant variants of HAS1 synthesize HA. Extracellular HA synthesized by HAS1Vs is likely to promote malignant spread. We speculate that synthesis of intracellular HA plays a fundamental and early role in oncogenesis by promoting genetic instability and the emergence of viable cancer variants that lead to aggressive disease.Advances in Cancer Research 01/2014; 123:67-94. DOI:10.1016/B978-0-12-800092-2.00003-4 · 4.26 Impact Factor