LOSS OF A PUTATIVE TUMOR-SUPPRESSOR LOCUS AFTER GAMMA-RAY-INDUCED NEOPLASTIC TRANSFORMATION OF HELA X SKIN FIBROBLAST HUMAN CELL HYBRIDS

The nontumorigenic HeLa x skin fibroblast hybrid cell line, CGL1, can be induced to re-express HeLa tumor-associated cell surface antigen, p 75-IAP (intestinal alkaline phosphatase), with resulting neoplastic tr ansformation, by exposure to gamma radiation. This has allowed the hum an hybrid system to be developed into a quantitative in vitro model fo r radiation-induced neoplastic transformation of human cells. Recently , several gamma-ray-induced IAP-expressing mutants (GIMs) of the nontu morigenic HeLa x skin fibroblast hybrid CGL1 were isolated and all wer e tumorigenic when injected subcutaneously into nude mice (Mendonca et al., Cancer Res. 51, 4455-4462, 1991). Control cell lines which were negative for p75-IAP (CONs) were also isolated from irradiated populat ions, and none were found to be tumorigenic. We have now begun to inve stigate the molecular basis of radiation-induced neoplastic transforma tion in this system by studying the potential genetic linkage between p75/IAP expression, tumorigenicity and damage to a putative tumor supp ressor locus on fibroblast chromosome 11. Previous analysis of rare sp ontaneous segregants has indicated that this locus is involved in the regulation of tumorigenicity and in the expression of the HeLa tumor-a ssociated cell surface marker intestinal alkaline phosphatase (p75-IAP ) in this system, Therefore, analysis by restriction fragment length p olymorphism and chromosome painting have been performed for chromosome 11, and for chromosome 13 as a control, for the p75/IAP-positive GIM and p75/IAP-negative CON cell lines. We report that in five of eight o f the GIMs large-scale damage to the fibroblast chromosome Il's is evi dent (four GIMs have lost one complete copy of a fibroblast chromosome 11 and one GIM has both copies of fibroblast chromosome 11 heavily da maged). None of the CONs, however (0/5), have lost a complete copy of either fibroblast chromosome 11. No large-scale damage to the control chromosome 13's was detected in the GIMs or CONs, The data further sug gest that both copies of fibroblast chromosome 11 contain an active lo cus and that radiation-induced loss of either fibroblast chromosome 11 will result in neoplastic transformation in this system. We conclude that it is the loss of a putative tumor suppressor locus on fibroblast chromosome 11 which is responsible at least in part for radiation-ind uced neoplastic transformation of these human hybrid cells. (C) 1995 b y Radiation Research Society