Exogenous mouse mammary tumor virus (MMTV) infection induces endogenous MMTV sag expression
1Department of Microbiology, University of Texas at Austin 78712-1095, USA.
Abstract:
The mouse mammary tumor virus (MMTV) superantigen (Sag) protein is involved in the transmission of milk-borne MMTV from virus-infected milk in the gut to the target mammary gland tissue. Using an RT-PCR assay for in vivo MMTV infection, BALB/c or C3H mice nursed on C3H MMTV-infected mothers showed sag mRNA expression in intestine, spleen, and thymus as early as 1 day after infection, whereas uninfected BALB/c control animals had approximately 10- to 30-fold lower sag expression. Further fractionation experiments with small intestine indicated that sag expression occurred in gut-associated lymphoid cells. Restriction enzyme digestion of PCR products indicated that the sag mRNA detected was derived from the endogenous MMTVs, and sequencing analysis confirmed that the PCR products were derived from endogenous MTv-6. Expression of C3H-specific mRNA was detectable in BALB/cfC3H or C3H tissues by RNase protection or by RT-PCR. Endogenous MMTV sag expression was low in spleen and undetectable in thymocytes of C3H MMTV-infected C57BL/6 mice, a strain resistant to C3H MMTV tumorigenesis and defective for MHC class II I-E molecules. The RT-PCR assay for sag mRNA appears to measure the Sag-induced stimulation previously predicted for milk-borne MMTV infection. Together these data suggest that exogenous MMTV sag expression is minimal, but sufficient to rapidly stimulate transcription of endogenous MMTV sag mRNA in B- and T-cells in an MHC class II I-E-dependent manner. The endogenous sag expression on maternal lymphocytes may increase the number of proliferating T-cells available for milk-borne MMTV infection.
Insights
Mouse mammary tumor virus (MMTV) superantigen (Sag) rapidly stimulates endogenous MMTV sag mRNA in B- and T-cells. This MHC class II I-E-dependent process may enhance milk-borne MMTV infection by increasing T-cells.
Area of Science:
- Virology
- Immunology
- Genetics
Background:
- Mouse mammary tumor virus (MMTV) is transmitted via milk.
- The MMTV superantigen (Sag) protein plays a role in MMTV transmission from the gut to mammary glands.
- Understanding Sag's role is crucial for controlling MMTV infection.
Purpose of the Study:
- To investigate the expression and regulation of MMTV superantigen (Sag) mRNA following milk-borne MMTV infection.
- To determine the cell types and mechanisms involved in Sag mRNA induction.
- To assess the role of MHC class II I-E molecules in Sag expression.
Main Methods:
- Reverse transcription-polymerase chain reaction (RT-PCR) assay for in vivo MMTV infection.
- Fractionation of small intestine tissues.
- Restriction enzyme digestion and sequencing of PCR products.
- RNase protection assays.
Main Results:
- Sag mRNA was rapidly detected in the intestine, spleen, and thymus of infected mice.
- Sag expression was primarily localized to gut-associated lymphoid cells.
- Detected sag mRNA originated from endogenous MMTVs, specifically MTv-6.
- Exogenous MMTV sag minimally stimulated endogenous MMTV sag mRNA transcription in B- and T-cells in an MHC class II I-E-dependent manner.
Conclusions:
- Exogenous MMTV Sag is sufficient to rapidly induce endogenous MMTV sag mRNA transcription.
- This induction is MHC class II I-E-dependent and occurs in B- and T-cells.
- Endogenous sag expression on maternal lymphocytes may facilitate milk-borne MMTV infection by increasing T-cell proliferation.
