SEN6, A LOCUS FOR SV40-MEDIATED IMMORTALIZATION OF HUMAN-CELLS, MAPS TO 6Q26-27

Normal cells show a Limited lifespan in culture and the phenotype of c ellular senescence, Tumors and tumor cell lines have typically overcom e this form of growth suppression and grow continuously as immortal ce ll lines in culture, We have exploited the DNA virus SV40 to study the mechanism by which human fibroblasts overcome senescence and become i mmortal, Multiple steps have now been identified, including inactivati on of cellular growth suppressors through direct interaction with SV40 large T antigen and through mutation of a gene on chromosome 6 (desig nated SEN6), In this study, we sublocalize the site of SEN6 to 6q26-27 based on molecular genetic analysis, Twelve SV40-immortalized fibrobl ast cell lines share a deletion in this area based on assessment for l oss of heterozygostiy (LOH) for seven informative markers on 6q, Two i mmortal cell lines (AR5 and HALneo) appeared to have retained separate single copies of chromosome 6 despite the fact that they are both der ived from the same preimmortal SV40-transformant and should share the same mutated allele of SEN6 (Hubbard-Smith et al., 1992), Detailed ana lysis by polymerase chain reaction, restriction fragment length polymo rphism and fluorescence in situ hybridization shows, however, that alt hough they differ for 17 markers from the centromere to 6q26, they sha re AR5 derived sequences (eight markers) distal to 6q26 including the minimal deletion region, further supporting the assignment of SEN6 to this region, Since human tumors including non-Hodgkins lymphoma, mamma ry carcinoma and ovarian carcinoma show LOH in 6q26-27, inactivation o f SEN6 may be responsible for immortalization of these tumors as well.