Mutation, replicative infidelity of DNA and aneuploidy sequentially in the formation of malignant pleomorphic tumors

Abstract

Mutations are thought to be involved in tumor formation because (i) tumor cells transmit their abnormalities to their descendants; and (ii) many carcinogens are mutagens. Aneuploidy is thought to be involved in tumor formation because (i) it is a common phenomenon, especially among malignant neoplasms; (ii) certain particular types of tumors are associated with specific karyotypic changes; and (iii) many immortal tumor cell lines are hyperploid. In recent years, acquired somatic cell replicative infidelity of DNA (“mutator phenotype”) has been suggested as a mechanism of tumor formation, because more somatic genomic events occur in malignant tumor cells than could be caused by repeated exogenous mutagenic insults. Previously, theories of the genomic pathogenesis of tumors have involved these mechanisms individually. Here it is suggested that all three mechanisms may play roles in the formation of certain tumor types. For example, a sequence could occur such that first, a mutation affects genomic elements for control of growth, and for replicative fidelity of DNA, leading to “mutator phenotype”. Second, when replicative infidelity of DNA results in mutation of genomic elements for mitotic-andchromosomal stability, aneuploidy develops. Third, an asymmetric mitosis (in the course of the aneuploid stage) could produce occasional cells in which the “bad copy” is lost (or an extra “good copy” is gained) of the original genomic element which had supported replicative fidelity of DNA. These resulting cells would regain fidelity of replication of DNA, and hence could give rise to populations which are relatively genomically stable, hyperploid and immortal.