The first member of the myc gene family, the v-myc gene, was isolated from the avian myelocytomatosis virus MC29. 1-3 Its cellular homologue, the c-myc gene, is evolutionarily well conserved between different species.4-11 Two other closely related genes, N-myc and L-myc, have also been cloned and characterized. 12-19 The N-myc gene was isolated from a human neuroblastoma cell line,12 and the L-myc gene from a human small cell lung cancer (SCLC) cell line,13 where they appeared amplified. The c-myc, N-myc, and L-myc genes all consist of three exons which are located within less than 7 kb in distinct chromosomal regions 8q24,20 2p23-24,21 and Ip32,22 respectively. In contrast to the protein-coding sequences, the long noncoding portions of the corresponding mRNAs are not well conserved between the different myc genes. In addition, there are considerable differences in the regulatory regions of these genes.18.104.22.168 The myc gene family appears to contain at least three other functional members, the P-, R-, and B-myc genes, as well as an inactive pseudogene, L-myc ‘I’.25,26 The c-myc, N-myc, and L-myc genes have all been found to be amplified in human tumors. Amplifications of the c-myc gene are most common among the three genes, and are particularly frequent in SCLC cell lines13.27-30 and in breast cancer. 3 N-myc amplifications are common in neuroblastoma,15.32 SCLC,37 and retinoblastoma,33 Cases of N-myc amplification have also been detected in adenocarcinoma of the lung,34 astrocytoma,35 and rhabdomyosarcoma,36 L-myc amplifications have so far been discovered only in SCLC.29,37,38 Altogether, 35 to 40% ofestablished SCLC cell lines have amplified one of the three members of the myc gene family. It is also curious that in cell lines established from other types of human lung cancer, amplification of only c-myc has been detected. 39-41 Amplifications usually lead to enhanced myc mRNA and protein expression. 27 Some reports indicate that amplification of the c-myc gene correlates with the phenotypic properties of the corresponding cells. 29 ,42,43 The so-called variant SCLC cell lines carrying an amplified c-myc gene grow faster, more loosely aggregated, and they have an increased cloning efficiency when compared to typical SCLC lines. Curiously, contrary to the resuls from cell lines, c-myc amplifications are not very common in primary SCLC tumors. 34,38,44-47 This could suggest a role for c-myc amplification as a relatively late event during tumor progression, or indicate a selection for c-myc amplified cell clones during the establishment of continuously growing cell lines. Nonetheless, the basis for the discrepancy between the in vitro and the in vivo situation remains to be determined. © 1991 by CRC Press, Inc.
|Titel på gästpublikation||Growth Regulation and Carcinogenesis|
|Redaktörer||Walter R. Paukovits|
|Status||Publicerad - 2018|
|MoE-publikationstyp||A3 Del av bok eller annan forskningsbok|
- 3122 Cancersjukdomar
- 3111 Biomedicinska vetenskaper