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

• Published in: Clinical & translational oncology Vol. 8; no. 5; p. 349
• Main Authors: Santos, J, Vaquero, C, Reyes, J, López-Nieva, P, Matabuena, M, Villa, M, Fernández, P, Fernández-Piqueras, J
• Format: Journal Article
• Language: English
• Published: Italy 01-05-2006
• Subjects: Animals; Cell Transformation, Neoplastic - genetics; Cell Transformation, Neoplastic - radiation effects; Computer Systems; Crosses, Genetic; DNA, Neoplasm - genetics; Gamma Rays - adverse effects; Gene Amplification; Gene Dosage; Genes, myc; Lymphoma - etiology; Lymphoma - genetics; Mice; Mice, Inbred BALB C; Mice, Inbred C57BL; Neoplasms, Radiation-Induced - etiology; Neoplasms, Radiation-Induced - genetics; Polymerase Chain Reaction; RNA, Messenger - biosynthesis; RNA, Messenger - genetics; RNA, Neoplasm - biosynthesis; RNA, Neoplasm - genetics; Thymus Neoplasms - etiology; Thymus Neoplasms - genetics
• ISSN: 1699-048X
• DOI: 10.1007/s12094-006-0181-y

It is well documented that over-expression of the c-myc proto-oncogene occurs in the vast majority of mouse thymic lymphomas induced by gamma-irradiation, evidencing the importance of this gene in T-cell lymphomagenesis. However, it remains unknown whether elevated levels of c-myc expression are driven by extra c-myc copy numbers.
Here we use a quantitative test on the basis of real-time PCR to determine the cellular 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 increased mRNA c-myc expression.
Since 5 out of 14 (35.7%) cases had no extra copy numbers of c-myc, gene amplification was obviously not the cause of c-myc over-expression in these tumours. In the remaining 9 tumours, c-myc over-expression was also accompanied with extra DNA copy numbers. Therefore, c-myc amplification might be a consequence of the genomic instability subsequent to the up-regulation of c-myc. However, linear regression analysis showed a lack of correlation between increasing DNA copy numbers and mRNA over expression of c-myc in these tumours (r = 0.029, p = 0.94).
De-regulation of c-myc does not necessarily imply amplification of this gene in these tumours. This report is, to our knowledge, the first one comparing c-myc amplification with expression in lymphomas of the T-cell lineage.