LOW-FREQUENCY LOSS OF HETEROZYGOSITY IN MOLONEY MURINE LEUKEMIA VIRUS-INDUCED TUMORS IN BRAKF1 J MICE/

To identify potential involvement of tumor suppressor gene inactivatio n during leukemogenesis by Moloney murine leukemia virus (M-MuLV), a g enome-wide scan for loss of heterozygosity (LOH) in tumor DNAs was mad e, To assess LOH, it is best to study mice that are heterozygous at ma ny loci across the genome, Accordingly, we generated a collection of 5 2 M-MULV-induced tumor DNAs from C57BR/cdJ x AKR/JF(1) (BRAKF1) hybrid mice, By using direct hybridization with oligonucleotides specific fo r three different classes of endogenous MuLV-related proviruses, 48 ma rkers on 16 of 19 autosomes were simultaneously examined for allelic l oss, No allelic losses were detected, with the exception of a common l oss of markers on chromosome 4 in two tumors, The three autosomes that lacked informative endogenous proviral markers were also analyzed for LOH by PCR with simple-sequence length polymorphisms (SSLPs); one add itional tumor showed LOH on chromosome 15, Further screening with chro mosome 4 SSLPs identified one additional tumor with LOH on chromosome 4, Therefore, in total, the average fractional allelic loss was quite low (0.002), but the LOH frequency of 6% on chromosome 4 was highly st atistically significant (P < 0.0005), Detailed SSLP mapping of the thr ee tumors,vith LOH on chromosome 4 localized the region of common LOH to the distal 45 centimorgans, a region syntenic with human chromosome s 1 and 9, Candidate tumor suppressor genes, Mts1 (p16(INK4a)) and Mts 2 (p15(INK4b)), have been mapped to this region, but by Southern blot analysis, no homozygous deletions were detected in either gene, One of three tumors with LOH on chromosome 4 also showed a proviral insertio n near the c-myc proto oncogene. These results suggested that tumor su ppressor inactivation is generally infrequent in M-MuLV-induced tumors but that a subset of these tumors may have lost a tumor suppressor ge ne on chromosome 4.