Regions of mouse mammary tumor virus superantigen involved in interaction with the major histocompatibility complex class II I-A molecule

To study the major histocompatibility complex class II I-E dependence of mouse mammary tumor virus (MMTV) superantigens, we constructed hybrids between the I-E-dependent MMTV(GR) and the I-E-independent mtv-7 superantigens and tested them in vivo. Our results suggest that, although the C-terminal third mediates I-A interaction, additional binding sites are located elsewhere in the superantigen.

Exogenous mouse mammary tumor virus proviral DNA isolated from a kidney adenocarcinoma cell line contains alterations in the U3 region of the long terminal repeat

Mouse mammary tumor virus (MMTV) is a B-type retrovirus which induces predominantly mammary carcinomas after a relatively long latency period. To date, very little is known about the reasons for the strict tissue specificity of MMTV. The BALB/cf/Cd strain of mice, which was infected with milk-borne MMTV (C3H), shows a high incidence of kidney adenocarcinomas, and our data suggest that MMTV might be involved in the formation of these tumors. Newly integrated exogenous MMTV proviruses were found in the genome of transplanted tumor cells as well as in the DNA of a cell line derived from one tumor, but not in normal cells of BALB/cf/Cd mice. The MMTV DNA in these tumor cells was transcribed and viral RNA synthesis was strongly stimulated by glucocorticoid hormones. Viral structural polypeptides, comparable in size and antigenicity to MMTV polypeptides of infected mammary tumor cells were synthesized and processed normally in the cell line and were organized correctly into intracytoplasmic particles. Heteroduplex analysis of the molecularly cloned MMTV proviral DNAs of kidney and mammary tumor origin revealed a high degree of homology in the gag, pol, and env genes. A striking difference, however, was observed in the U3 region of the two LTRs that might relate to the different tissue specificity of the two viruses.

A new site of integration for mouse mammary tumor virus proviral DNA common to BALB/cf(C3H) mammary and kidney adenocarcinomas

The BALB/cf/Cd substrain of mice, developed by inbreeding and selection, shows a 70% incidence of spontaneous kidney adenocarcinomas. Initially foster-nursed on C3H mothers, these mice no longer produce mammary tumors, but there is evidence that mouse mammary tumor virus (MMTV) is involved in the formation of these renal carcinomas. We identified a chromosomal region called int-41, representing a locus interrupted by the integration of an exogenous MMTV provirus in a BALB/c mammary tumor. We found a DNA rearrangement and transcriptional activation in the domain specified by the int-41 probe in one primary kidney adenocarcinoma. A 5.2-kb int-41 specific mRNA was detected in the kidney tumor cell line established from a transplantable renal adenocarcinoma. This mRNA hybridized with MMTV and int-41 specific probes suggesting that it is a hybrid molecule composed of MMTV-LTR sequences covalently linked to host cell RNA. This mRNA was strongly stimulated by the presence of glucocorticoid hormone in the culture medium. Our data are compatible with the hypothesis that the int-41 chromosomal domain is involved in the neoplastic transformation of epithelial cells from different organs.