Akt1 Is Essential for Postnatal Mammary Gland Development, Function, and the Expression of Btn1a1

Akt1, a serine-threonine protein kinase member of the PKB/Akt gene family, plays critical roles in the regulation of multiple cellular processes, and has previously been implicated in lactation and breast cancer development. In this study, we utilized Akt1+/+ and Akt1−/− C57/Bl6 female mice to assess the role that Akt1 plays in normal mammary gland postnatal development and function. We examined postnatal morphology at multiple time points, and analyzed gene and protein expression changes that persist into adulthood. Akt1 deficiency resulted in several mammary gland developmental defects, including ductal outgrowth and defective terminal end bud formation. Adult Akt1−/− mammary gland composition remained altered, exhibiting fewer alveolar buds coupled with increased epithelial cell apoptosis. Microarray analysis revealed that Akt1 deficiency altered expression of genes involved in numerous biological processes in the mammary gland, including organismal development, cell death, and tissue morphology. Of particular importance, a significant decrease in expression of Btn1a1, a gene involved in milk lipid secretion, was observed in Akt1−/− mammary glands. Additionally, pseudopregnant Akt1−/− females failed to induce Btn1a1 expression in response to hormonal stimulation compared to their wild-type counterparts. Retroviral-mediated shRNA knockdown of Akt1 and Btn1a1 in MCF-7 human breast epithelial further illustrated the importance of Akt1 in mammary epithelial cell proliferation, as well as in the regulation of Btn1a1 and subsequent expression of ß-casein, a gene that encodes for milk protein. Overall these findings provide mechanistic insight into the role of Akt1 in mammary morphogenesis and function

Structure-Function Analysis of Human TYW2 Enzyme Required for the Biosynthesis of a Highly Modified Wybutosine (yW) Base in Phenylalanine-tRNA

Posttranscriptional modifications are critical for structure and function of tRNAs. Wybutosine (yW) and its derivatives are hyper-modified guanosines found at the position 37 of eukaryotic and archaeal tRNAPhe. TYW2 is an enzyme that catalyzes α-amino-α-carboxypropyl transfer activity at the third step of yW biogenesis. Using complementation of a ΔTYW2 strain, we demonstrate here that human TYW2 (hTYW2) is active in yeast and can synthesize the yW of yeast tRNAPhe. Structure-guided analysis identified several conserved residues in hTYW2 that interact with S-adenosyl-methionine (AdoMet), and mutation studies revealed that K225 and E265 are critical residues for the enzymatic activity. We previously reported that the human TYW2 is overexpressed in breast cancer. However, no difference in the tRNAPhe modification status was observed in either normal mouse tissue or a mouse tumor model that overexpresses Tyw2, indicating that hTYW2 may have a role in tumorigenesis unrelated to yW biogenesis

The effect Akt2 deletion on tumor development in Pten+/− mice

The serine/threonine kinase Akt is frequently activated in human cancers and is considered an attractive therapeutic target. However, the relative contributions of the different Akt isoforms to tumorigenesis, and the effect of their deficiencies on cancer development are not well understood. We had previously shown that Akt1 deficiency is sufficient to markedly reduce the incidence of tumors in Pten+/− mice. Particularly, Akt1 deficiency inhibits endometrial carcinoma and prostate neoplasia in Pten+/− mice. Here, we analyzed the effect of Akt2 deficiency on the incidence of tumors in Pten+/− mice. Relative to Akt1, Akt2 deficiency had little-to-no effect on the incidence of prostate neoplasia, endometrial carcinoma, intestinal polyps and adrenal lesions in Pten+/− mice. However, Akt2 deficiency significantly decreased the incidence of thyroid tumors in Pten+/−, which correlates with the relatively high level of Akt2 expression in the thyroid. Thus, unlike Akt1 deletion, Akt2 deletion is not sufficient to markedly inhibit tumorigenesis in Pten+/− mice in most tested tissues. The relatively small effect of Akt2 deletion on the inhibition of tumorigenesis in Pten+/− mice could be explained, in part, by an insufficient decrease in total Akt activity, due to the relatively lower Akt2 versus Akt1 expression, and relatively high blood insulin levels in Pten+/−Akt2−/− mice. The relatively high blood insulin levels in Pten+/−Akt2−/− mice may elevate the activity of Akt1, and possibly Akt3, thus, limiting the reduction of total Akt activity and preventing this activity from dropping to a threshold level required to inhibit tumorigenesis

Vav3 oncogene activates estrogen receptor and its overexpression may be involved in human breast cancer

<p>Abstract</p> <p>Background</p> <p>Our previous study revealed that Vav3 oncogene is overexpressed in human prostate cancer, activates androgen receptor, and stimulates growth in prostate cancer cells. The current study is to determine a potential role of Vav3 oncogene in human breast cancer and impact on estrogen receptor a (ERα)-mediated signaling axis.</p> <p>Methods</p> <p>Immunohistochemistry analysis was performed in 43 breast cancer specimens and western blot analysis was used for human breast cancer cell lines to determine the expression level of Vav3 protein. The impact of Vav3 on breast cancer cell growth was determined by siRNA knockdown of Vav3 expression. The role of Vav3 in ERα activation was examined in luciferase reporter assays. Deletion mutation analysis of Vav3 protein was performed to localize the functional domain involved in ERα activation. Finally, the interaction of Vav3 and ERα was assessed by GST pull-down analysis.</p> <p>Results</p> <p>We found that Vav3 was overexpressed in 81% of human breast cancer specimens, particularly in poorly differentiated lesions. Vav3 activated ERα partially via PI3K-Akt signaling and stimulated growth of breast cancer cells. Vav3 also potentiated EGF activity for cell growth and ERα activation in breast cancer cells. More interestingly, we found that Vav3 complexed with ERα. Consistent with its function for AR, the DH domain of Vav3 was essential for ERα activation.</p> <p>Conclusion</p> <p>Vav3 oncogene is overexpressed in human breast cancer. Vav3 complexes with ERα and enhances ERα activity. These findings suggest that Vav3 overexpression may aberrantly enhance ERα-mediated signaling axis and play a role in breast cancer development and/or progression.</p

Evaluation of the cancer chemopreventive efficacy of rice bran in genetic mouse models of breast, prostate and intestinal carcinogenesis

Brown rice is a staple dietary constituent in Asia, whereas rice consumed in the Western world is generally white, obtained from brown rice by removal of the bran. We tested the hypothesis that rice bran interferes with development of tumours in TAg, TRansgenic Adenocarcinoma of the Mouse Prostate (TRAMP) or ApcMin mice, genetic models of mammary, prostate and intestinal carcinogenesis, respectively. Mice received rice bran (30%) in AIN-93G diet throughout their post-weaning lifespan. In TAg and TRAMP mice, rice bran did not affect carcinoma development. In TRAMP or wild-type C57Bl6/J mice, dietary rice bran increased kidney weight by 18 and 20%, respectively. Consumption of rice bran reduced numbers of intestinal adenomas in ApcMin mice by 51% (P<0.01), compared to mice on control diet. In parallel, dietary rice bran decreased intestinal haemorrhage in these mice, as reflected by increased haematocrit. At 10% in the diet, rice bran did not significantly retard ApcMin adenoma development. Likewise, low-fibre rice bran (30% in the diet) did not affect intestinal carcinogenesis, suggesting that the fibrous constituents of the bran mediate chemopreventive efficacy. The results suggest that rice bran might be beneficially evaluated as a putative chemopreventive intervention in humans with intestinal polyps

Maternal consumption of canola oil suppressed mammary gland tumorigenesis in C3(1) TAg mice offspring

<p>Abstract</p> <p>Background</p> <p>Maternal consumption of a diet high in omega 6 polyunsaturated fats (n-6 PUFA) has been shown to increase risk whereas a diet high in omega 3 polyunsaturated fats (n-3 PUFA) from fish oil has been shown to decrease risk for mammary gland cancer in female offspring of rats. The aim of this study was to determine whether increasing n-3 PUFA and reducing n-6 PUFA by using canola oil instead of corn oil in the maternal diet might reduce the risk for breast cancer in female offspring.</p> <p>Methods</p> <p>Female SV 129 mice were divided into two groups and placed on diets containing either 10% w/w corn oil (which is 50% n-6 PUFA, control diet) or 10% w/w canola oil (which is 20% n-6 PUFA, 10% n-3 PUFA, test diet). After two weeks on the diets the females were bred with homozygous C3(1) TAg transgenic mice. Mother mice consumed the assigned diet throughout gestation and nursing of the offspring. After weaning, all female offspring were maintained on the control diet.</p> <p>Results</p> <p>Compared to offspring of mothers fed the corn oil diet (CO/CO group), offspring of mothers fed the canola oil diet (CA/CO group) had significantly fewer mammary glands with tumors throughout the experiment. At 130 days of age, the CA/CO group had significantly fewer tumors per mouse (multiplicity); the tumor incidence (fraction of mice with any tumor) and the total tumor weight (per mouse that developed tumor) was less than one half that of the CO/CO group. At 170 days of age, the total tumor weight per mouse was significantly less in the CA/CO group and if a tumor developed the rate of tumor growth rate was half that of CO/CO group. These results indicate that maternal consumption of canola oil was associated with delayed appearance of mammary gland tumors and slowed growth of the tumors that developed.</p> <p>Conclusions</p> <p>Substituting canola oil for corn oil is an easy dietary change for people to make; such a change to the maternal diet may decrease risk for breast cancer in the daughter.</p

Mammary Involution and Breast Cancer Risk: Transgenic Models and Clinical Studies

Postlactational involution is the process following weaning during which the mammary gland undergoes massive cell death and tissue remodeling as it returns to the pre-pregnant state. Lobular involution is the process by which the breast epithelial tissue is gradually lost with aging of the mammary gland. While postlactational involution and lobular involution are distinct processes, recent studies have indicated that both are related to breast cancer development. Experiments using a variety of rodent models, as well as observations in human populations, suggest that deregulation of postlactational involution may act to facilitate tumor formation. By contrast, new human studies show that completion of lobular involution protects against subsequent breast cancer incidence

Key signalling nodes in mammary gland development and cancer. Signalling downstream of PI3 kinase in mammary epithelium: a play in 3 Akts

The protein serine/threonine kinase Akt, also known as protein kinase B (PKB), is arguably the most important signalling nexus in the cell. Akt integrates a plethora of extracellular signals to generate diverse outcomes, including proliferation, motility, growth, glucose homeostasis, survival, and cell death. The phosphatidylinositol 3-kinase (PI3K)/Akt pathway is the second most frequently mutated pathway in cancer, after p53, and mutations in components of this pathway are found in around 70% of breast cancers. Thus, understanding how Akt relays input signals to downstream effectors is critically important for the design of therapeutic strategies to combat breast cancer. In this review, we will discuss the various signals upstream of Akt that impact on its activity, how Akt integrates these signals and modulates the activity of downstream targets to control mammary gland development, and how mutations in components of the pathway result in breast cancer