RESUMO
BACKGROUND: Although DHFR gene amplification has long been known as a major mechanism for methotrexate (MTX) resistance in cancer, the early changes and detailed development of the resistance are not yet fully understood. METHODS: We performed genomic, transcriptional and proteomic analyses of human colon cancer cells with sequentially increasing levels of MTX-resistance. RESULTS: The genomic amplification evolved in three phases (pre-amplification, homogenously staining region (HSR) and extrachromosomal DNA (ecDNA)). We confirm that genomic amplification and increased expression of DHFR, with formation of HSRs and especially ecDNAs, is the major driver of resistance. However, DHFR did not play a detectable role in the early phase. In the late phase (ecDNA), increase in FAM151B protein level may also have an important role by decreasing sensitivity to MTX. In addition, although MSH3 and ZFYVE16 may be subject to different posttranscriptional regulations and therefore protein expressions are decreased in ecDNA stages compared to HSR stages, they still play important roles in MTX resistance. CONCLUSION: The study provides a detailed evolutionary trajectory of MTX-resistance and identifies new targets, especially ecDNAs, which could help to prevent drug resistance. It also presents a proof-of-principal approach which could be applied to other cancer drug resistance studies.
Assuntos
Resistencia a Medicamentos Antineoplásicos , Amplificação de Genes , Metotrexato , Tetra-Hidrofolato Desidrogenase , Humanos , Metotrexato/farmacologia , Resistencia a Medicamentos Antineoplásicos/genética , Tetra-Hidrofolato Desidrogenase/genética , Tetra-Hidrofolato Desidrogenase/metabolismo , Linhagem Celular Tumoral , Neoplasias do Colo/genética , Neoplasias do Colo/tratamento farmacológico , Neoplasias do Colo/patologia , Antimetabólitos Antineoplásicos/farmacologia , Regulação Neoplásica da Expressão Gênica/efeitos dos fármacos , Genômica/métodosRESUMO
AIM: To investigate the association between loss of heterozygosity (LOH) on chromosome 18 and sporadic gastric cancer. METHODS: Multiplex PCR was used to screen 14 highly polymorphic microsatellite markers on chromosome 18 in 45 cases of primary gastric cancer. PCR products were separated on polyacrylamide gels and the electrophoresis maps were analyzed with Genescan and Genotyper. RESULTS: The LOH frequencies in gastric cancer at all 14 markers ranged from 10% to 58%. Eleven markers were found with over 20% LOH frequencies, in which 9 markers located in 18q, and 2 markers in 18p. Two overlapping deleted regions were identified: R1 between D18S61-D18S1161 at 18q22 (9cM) with 24% LOH frequency; R2 between D18S462-D18S70 at 18q22-23(6cM) with 32% LOH frequency. CONCLUSION: LOH of chromosome 18 (18q and 18p) may be involved in gastric tumorigenesis. Two overlapping deleted fragments suggested that there might be unidentified tumor suppressor genes in those two regions.