ACTIVATION OF THE MAS ONCOGENE INVOLVES COUPLING TO HUMAN ALPHOID SEQUENCES

We have shown previously that mouse NIH3T3 cells transfected with DNA from a human ovarian carcinoma were rendered tumourigenic by an activa ted mas oncogene in four independent transfection experiments. In all cases the 5'-noncoding region was rearranged in comparison to the orig inal ovarian tumour DNA. We now report that in all four transfectants the newly acquired sequences consist of human centromeric alpha satell ite repeat DNA. In at least three transfectants the alphoid DNA origin ates from the centromere of chromosome three. Analysis of the sequence s of the recombination site in one transfectant revealed that a homolo gous sequence of five base pairs (CAGCA) is present in both parental s trands, and might thus have contributed to the recombinational event. To establish a conclusive role for alphoid DNA in the activation of ma s, we performed a co-transfection experiment in NIH3T3 cells with clon ed alphoid DNA and the mas coding sequence. We show that the transfect ants expressing a transformed phenotype contain amplified mas linked t o alphoid DNA. NIH3T3 cells transfected with plasmids that contained a lphoid sequences cloned directly upstream of the mas coding sequence, and injected into nude mice, gave rise to tumours with amplified mas s equences (7/7). In six of these tumours the alphoid sequences were amp lified as well. Our data suggest a novel mechanism of oncogene activat ion: recombination with normal alphoid repeat DNA resulting in amplifi cation of the oncogene.