Lack of correlation between DNA copy number and mRNA expression levels of c-myc in gamma-radiation-induced mouse thymic lymphomas by using quantitative real-time PCR

ABSTRACT

Background. It is well documented that over-expressionof the c-myc proto-oncogene occurs in thevast majority of mouse thymic lymphomas inducedby gamma-irradiation, evidencing the importance of thisgene in T-cell lymphomagenesis. However, it remainsunknown whether elevated levels of c-mycexpression are driven by extra c-myc copy numbers.Materials and methods. Here we use a quantitativetest on the basis of real-time PCR to determine thecellular copy number of c-myc in a set of 14 g-radiation-induced thymic lymphomas obtained from(C57BL/6J x BALB/cJ) F1 hybrid mice with increasedmRNA c-myc expression.Results. Since 5 out of 14 (35.7%) cases had no extracopy numbers of c-myc, gene amplification was obviouslynot the cause of c-myc over-expression inthese tumours. In the remaining 9 tumours, c-mycover-expression was also accompanied with extraDNA copy numbers. Therefore, c-myc amplificationmight be a consequence of the genomic instabilitysubsequent to the up-regulation of c-myc. However,linear regression analysis showed a lack of correlationbetween increasing DNA copy numbers andmRNA over expression of c-myc in these tumours (r= 0.029, p = 0.94).Conclusion. De-regulation of c-myc does not necessarilyimply amplification of this gene in these tumours.This report is, to our knowledge, the firstone comparing c-myc amplification with expressionin lymphomas of the T-cell lineage

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