Molecular analysis of endogenous retrovirus-related sequences in chemically transformed NIH 3T3 cells

The mouse genome contains hundreds of copies of endogenous retrovirus-related sequences. Structural similarities between the endogenous proviruses and transposable gene elements suggest that the retrovirus-related elements may be capable of movement within the genome. Movement and insertion of these sequences at new genetic loci could lead to activation of cellular oncogenes.

A search for rearrangements of two types of endogenous proviral elements in chemically transformed NIH 3T3 cells is described in this dissertation. Chemically transformed cell clones were isolated by selection of chemically treated NIH 3T3 cells in soft agar. In contrast to other reports, no evidence of ras gene activation was found in these cells. Southern blotting analysis did not detect rearrangements of the endogenous MuLV-related sequences. The transformed cells, however, did not contain two male-specific IS-type element bands observed in normal NIH 3T3 and male liver DNA preparationss. Examination of inde pendent subclones of untransformed NIH 3T3 cells suggested that the chemically transformed cell clones were derived from a subpopulation in the original NIH 3T3 cell line which did not possess male-specific sequences. Thus, rearrangement of the male-specific IS-type elements probably was not involved in the transformation of the NIH 3T3 cell clones.

Additional studies were performed to characterize the male-specific IS-type element. Southern blotting of genomic DNAs and molecular cloning of a portion of this element revealed that it is a structurally unique member of the IS-type element gene family. A hybridization probe derived from this element will facilitate cloning and molecular analysis of the IS-type elements.