Infection of tissues of mA3+/+ and −/− mice after milk-borne transmission of MMTV. A) and B) RT-qPCR analysis of DNA isolated from spleen and non-lactating mammary gland, respectively, using MMTV- and GAPDH-specific primers; shown are the MMTV values normalized to GAPDH. All error bars represent SD from the averages of the mice analyzed at each time point. From 6 to 19 mice were analyzed for each time point. *, p ≤ 0.02; ** p ≤ 0.001; #, p ≤ 0.01; comparison is between mA3 +/+ and −/− at each time point. C) Mammary tumor incidence in MMTV-infected mA3 −/− and +/+ mice after milk-borne infection. Shown are Kaplan-Meier survival curves that were computed for age at tumor onset. The p-value for the test that these two curves are significantly different (null hypothesis of equality) was <0.0001. N = 26 mA3 −/− mice, 29 mA3 +/+ mice.

Virus isolated from mA3 −/− milk is more infectious than that isolated from mA3 +/+ milk. A) Virions were isolated from the milk of MMTV-infected mA3 −/− and +/+ mice and RNA isolated from equal amounts of milk was subjected to reverse-transcribed RT-qPCR. Error bars represent the SD of 11 mA3−/− and 9 mA3+/+ milk samples. B) Western blot analysis of APOBEC3 in tissues and virions. Lanes 1 and 2, 293T cells transfected with expression vectors containing the BL/6 delta exon 5 (−5) or BALB/c + exon 5 (+5) cDNAs; lanes 3 and 4, splenic extracts from mA3 +/+ mice; lanes 5 and 6, splenic extracts from mA3 −/− mice; lane 7 and 8, virions isolated from the mammary tissue of mA3 +/+ (A3+, lane 7) or −/− (A3−, lane 8) mice. The top panel was probed with rabbit anti-mouse APOBEC3 antisera then stripped and re-probed with goat anti-MMTV antisera (middle panel); the bottom panel is a duplicate blot of the same extracts probed with anti-β-actin. A cross-reacting protein that is present in the tissue extracts of both +/+ and −/− mice is indicated by a dotted arrow; this protein was detected in some, but not all virus preparations irrespective of the presence of APOBEC3 (not shown). C) Various dilutions of virus isolated from mA3 −/− and +/+ milk were used to infect 293-mTFR1 cells in triplicate, DNA was isolated from the infected cells and subjected to RT-qPCR for MMTV and GAPDH. The numbers presented were normalized to the amount of virion RNA as measured in A). Error bars represent SD from 3 replicate wells. p ≤ 0.001 for both dilutions.

APOBEC3G protein is made in human MECs. A) Western blots of lysates made from the different MECs following 48 hr treatment with (+) or without (−) progesterone. Also included are lysates prepared from 293T (APOBEC3G-) and H9 (APOBEC3+) cells. Arrow points to APOBEC3G. B) Indirect immunofluorescence of HS578T and T47D cells, using anti-APOBEC3G antisera. Cells were counterstained with DAPI. Left panel: IF plus DAPI; right panel, IF alone.

APOBEC3G made in MECs is packaged into HIV. A) HS578T (left) and T47D (right) cells were transduced with PNL-Luc that contained (+ vif) or lacked (− vif) the vif gene and a vector bearing the VSV G protein. Twenty-four hrs post-transduction, progesterone was added to the media, as indicated (+) or left untreated (−) and 24 hr later, virus was harvested from the cell supernatants and used to infect NP2 cells, in the absence or presence of AZT, as indicated. In addition, p24 levels were measured by ELISA. Twenty-four after infection, luciferase assays were performed on lysates prepared from the NP2 cells. RLUs were normalized to the p24 levels in the virus preparations. Error bars represent SD from 3 replicate infections. *, NS; **, p ≤ 0.05; #, p ≤ 0.001. This experiment was performed 3 times with similar results. B) The virion preparations were analyzed by Western blots, using anti-p24 antisera. Virions prepared in PNL-Luc+vif-transduced 293T cells were included as positive controls.

Adoptive transfer of lymphocytes into mA3 +/+ and −/− mice. Five mice of each genotype were lethally irradiated, reconstituted with bone marrow mA3+/+ mice, infected with MMTV and then sacrificed 9 weeks after irradiation. A) FACS analysis of reconstituted mice. PBLs were isolated from the individual mice at sacrifice and stained with the indicated antibodies. Error bars represent SD from the average for the 5 mice of each genotype. B) RNA was isolated from the spleen, lymph nodes (LN) and mammary gland (MG) and subjected to reverse-transcribed PCR with primers specific for APOBEC3. C) DNA was isolated from the indicated tissue and subjected to RT-qPCR specific for exogenous MMTV(RIII) sequences. Values were normalized to GAPDH. This experiment was repeated 2 additional times with similar results.

APOBEC3G is made in human mammary epithelial cells. A) RNA was isolated from MCF7, MCF10, HS578T and T47D mammary cell lines, and from seven different primary mammary gland samples from normal, non-lactating females (P1 – P7) and subjected to reverse transcribed RT-qPCR, using primers to APOBEC3G. All values were normalized to GAPDH. The values for the HS578T cell line were set at 1.0 and the results from the other cells and tissues are normalized to this value. B) Reverse transcribed RT-qPCR analysis of RNA isolated from the indicated cell lines after 48 hr treatment with estrogen (E), progesterone (P), or dexamethasone (D); - indicates untreated cells. Error bars represent the SD of 3 replicate wells of each cell line/treatment. *, NS; **, p ≤ 0.04; #, p ≤ 0.01; +, p ≤ 0.02. See also Figures S1, S2 and S3.

APOBEC3G protein is made in primary human mammary tissue. Indirect IF of primary mammary tissue was performed, using rabbit anti-APOBEC3G antisera in the absence (α-A3G) or presence (α-A3G +r3G) of recombinant APOBEC3G protein. An enlargement of the outlined area of the lumen is shown to the right of the top panel. Yellow arrow, luminal epithelial cells; white arrow, stromal cell.