Possible role of Abb gene in mouse resistance to EL4 metastases

Hidden variables: unstable Abeta chain genes encoding antigen recognition structures in tumor survivors

Novel single exon genes Abeta4-7 comprising the Abeta6 gene family have been cloned from mouse mutants surviving transplantable metastatic tumors. Their protein coding sequences are similar to H2-Ab cDNA which encodes antigen-binding molecules of antigen presenting cells (APC); their promoters and/or signal sequences are unrelated to Ab sequences but found in other eukaryotic genes. Abeta4(b) protein was demonstrated on macrophages and B cells that are APC. The Abeta6(w302) appears to be an ancient gene ancestral to major histocompatibility complex (MHC) class II beta genes. However, unlike the MHC class II, the Abeta4-7 genes are not involved in skin graft rejection. Despite inbreeding, the Abeta6(w302) locus remains unfixed in several strains of mice. The number of Abeta genes and their alleles varied between individual mice; they do not map into the H2 region but appear to be scattered over the genome. The Abeta6 gene family is molecularly unstable in Abeta6(w302)-positive (but not in Abeta6(w302)-negative) mice which are somatic mosaics for these genes. Biological features of Abeta4-7 genes make them remarkably different from the classical MHC gene system. All available evidence strongly suggests that these genes control susceptibility/resistance to the spread of metastatic tumors.

Screening mouse mutations for resistance to cancer metastasis

To search for host genes for resistance/susceptibility to cancer metastasis, mutation analysis was employed. Ten putative mutants of resistance to lymphoma EL4 and four putative mutants of resistance to sarcoma MCA/77-23 of C57BL/6J (B6) mice were produced. These mutants were designated S (for "survivor") mutants; they do not reject parental strain B6 skin grafts. S-mutants resist moderate tumor cell doses: TD50 values in them were increased by a factor of 12 to 600. Genetic linkage tests showed that five S-mutants were linked to mouse major histocompatibility complex (H-2) and five other S-mutants were not linked to this locus. A group of H-2-linked S-mutants resisting EL4 and a mutant, S-87/2, resisting MCA/77-23 were tested for resistance to spontaneous metastases of the same two tumors, EL4 and MCA/77-23. Two of the mutants, S-31 (lymphoma-resisting) and S-87/2 (sarcoma-resisting), were shown to carry mutations of mouse gene(s) for resistance to tumor metastases. In both of these mutants resistance to the original tumor transplant coexisted with highly increased susceptibility to metastasis. These mutants are a new tool to study genes for resistance to cancer metastasis and of mechanism of resistance controlled by each individual gene.