The myc family of oncogenes and their presence and importance in small-cell lung carcinoma and other tumour types.

The myc family of cellular oncogenes, c-myc, N-myc, encodes three highly related, cell cycle specific, nuclear phospho-proteins. All are able to transform primary rat embryo fibroblasts when cotransfected with the c-ras oncogene. Myc family genes are differentially expressed with respect to tissue type and developmental stage and dramatic changes in their expression coincide with critical developmental transitions in many cell lineages. Their conservation as distinct genes over a large phylogenetic distance and their unique pattern of expression in developing embryos support the view that each member of the myc family may have an important and discrete biological activity. The nuclear localization and the presence of contiguous regions containing the basic region/helix-loop-helix/leucine zipper motifs suggest that myc-encoded proteins are involved in gene expression during growth and differentiation. The role of myc-oncogene amplification and/or overexpression in tumourigenesis is still not clear, but application of new biotechnological tools as transfection vectors and the antisense strategy may lead to a better understanding of the importance of the myc family of oncogenes. Transfection of cells with oncogenes in expression vectors conferring high levels of oncoprotein are used to analyze the influence of overexpression of the oncogene, while incubation with an appropriate antisense oligonucleotide leading to an inhibition of oncogene expression may give some clues to the necessity, function and importance of the oncogene. These two techniques have proven to be useful tools in the illumination of the function of these ubiquitous (proto-) oncogenes and probably will help to clarify at least a part of their role in, for instance, apoptosis, tumourigenesis and the development of resistance to antitumour drugs.