Involvement of mouse mammary tumor virus in spontaneous and hormone-induced mammary tumors in low-mammary-tumor mouse strains

Abstract

The involvement of the mouse mammary tumor virus (MTV) in spontaneous and hormone-induced mammary tumors in low-mammary-tumor mouse strains was studied by comparing the amounts of MTV RNA and MTV DNA sequences in mammary tumors and other tissues of mice with an without hormonal treatments. The following results were obtained. (i) Mammary tumors which appeared in C3H mice as a result of an infection with MTV contained more MTV DNA compared with noninfected organs; these mammary tumors also contained more MTV RNA than was present in lactating mammary gland cells. (ii) Hormonal stimulation by administration of excessive amounts of prolactin via hypophyseal isografts in C3Hf and O20 mice resulted in an increased expression of MTV RNA in the mammary glands. This elevated level of MTV RNA expression was, however, not maintained in the hormone-induced mammary tumors. (iii) Spontaneous mammary tumors in BALB/c mice contained similar levels of MTV DNA and MTV RNA sequences as were found in other cells of these animals.

Lack of induction of murine mammary tumor virus expression in cultured mammary glands treated with chemical carcinogens

“…Treatment with either 1 ng DMBA or 1 pg FAA at days 3 to 4 had apparently no effect on this level. This value is comparable to the previously reported amounts of MuMTV RNA in the mammary glands of BALB/c mice (Varmus et al, 1973;Michalides et al, 1978a;Dudley et al, 19786;Long et al, 1980). A set of RNA hybridization curves is shown in Figure 2u.…”

“…The mammary glands of BALB/c mice have barely detectable levels of endogenous MuMTV RNA in vivo (Varmus et al, 1973;Michalides et al, 1978a;Dudley et al, 1978b;Long et al, 1980). Using the whole-organ culture system, we therefore undertook to determine if elevations in the steady-state levels of MuMTV RNA and protein result from the treatment of the mammary glands with either of the two chemical carcinogens, DMBA or FAA.…”

“…Despite the elevated transcription of endogenous viral genes found in mammary tumors induced by combined treatments with urethane and X-rays in BALBk mice, little viral protein has been detected (Michalides et al, 1979). Also, increased levels of both viral RNA and protein have been reported to occur in mammary tumors resulting from hormonal stimulation in BALB/c mice (McGrath et al, 1978;Michalides et al, 1979), although not in tumors induced by hormones or chemicals in other strains (Michalides et al, 1978a;Smith et al, 1978;Nusse et al, 1980). In contrast, other investigators have found little or no induction of viral RNA in BALBk mammary tumors caused by non-viral agents, or in the cell lines derived from those tumors (Dudley et al, 1978a;Dusing-Swartz et al, 1979).…”

Idiopathic mammary tumors in BALB/c mice

“…Molecular hybridization procedures have been employed in several laboratories to determine the number of MuMTV DNA and MuMTV RNA copies per cell in various mouse tissues. Many studies (Drohan et al, 1977;Michalides et al, 1976;Morris et al, 1977;and Varmus et al, 1973) have shown that virus-induced mammary tumors such as those that occur in RIII, C3H, A, and BALB/cfC3H mice contain higher amounts of both MuMTV DNA and MuMTV RNA sequences than those found in other body tissues. However, Varmus ef al.…”

Effect of parity regimen on the rate of occurrence of mammary tumors in a, C3H, and RIII mice

“…These examples, in addition to the findings of this report, emphasize the effect of genetic differences among mouse strains on the occurrence of mammary carcinoma and the differences in the etiology of the disease in mic; and in humans. In most mammary tumors in the mouse, MuMTV is an important etiological factor, but there is evidence that in some strains mammary tumors can occur without additional MuMTV expression (Michalides et a/., 1978;Moore ef al., 1979). In an occasional feral mouse, even the MuMTV genome is missing (Cohen and Varmus, 1979).…”