Limits...
SirT1 modulates the estrogen-insulin-like growth factor-1 signaling for postnatal development of mammary gland in mice.

Li H, Rajendran GK, Liu N, Ware C, Rubin BP, Gu Y - Breast Cancer Res. (2007)

Bottom Line: The effect of exogenous estrogen was also examined by subcutaneous implantation of a slow-releasing pellet in the subscapular region.SirT1 deficiency deregulates the expression of IGF-1 binding protein-1 and attenuates the effect of IGF-1 signals, including estrogen-stimulated local IGF-1 signaling for the onset of ductal morphogenesis.These findings suggest that the enzymatic activity of SirT1 may influence both normal growth and malignant growth of mammary epithelial cells.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Radiation Oncology, University of Washington School of Medicine, Seattle, WA 98195, USA.

ABSTRACT

Introduction: Estrogen and insulin-like growth factor-1 (IGF-1) play important roles in mammary gland development and breast cancer. SirT1 is a highly conserved protein deacetylase that can regulate the insulin/IGF-1 signaling in lower organisms, as well as a growing number of transcription factors, including NF-kappaB, in mammalian cells. Whether SirT1 regulates the IGF-1 signaling for mammary gland development and function, however, is not clear. In the present study, this role of SirT1 was examined by studying SirT1-deficient mice.

Methods: SirT1-deficient (SirT1(ko/ko)) mice were generated by crossing a new strain of mice harboring a conditional targeted mutation in the SirT1 gene (SirT1(co/co)) with CMV-Cre transgenic mice. Whole mount and histology analyses, immunofluorescence staining, immunohistochemistry, and western blotting were used to characterize mammary gland development in virgin and pregnant mice. The effect of exogenous estrogen was also examined by subcutaneous implantation of a slow-releasing pellet in the subscapular region.

Results: Both male and female SirT1(ko/ko) mice can be fertile despite the growth retardation phenotype. Virgin SirT1(ko/ko) mice displayed impeded ductal morphogenesis, whereas pregnant SirT1(ko/ko) mice manifested lactation failure due to an underdeveloped lobuloalveolar network. Estrogen implantation was sufficient to rescue ductal morphogenesis. Exogenous estrogen reversed the increased basal level of IGF-1 binding protein-1 expression in SirT1(ko/ko) mammary tissues, but not that of IkappaB alpha expression, suggesting that increased levels of estrogen enhanced the production of local IGF-1 and rescued ductal morphogenesis. Additionally, TNFalpha treatment enhanced the level of the newly synthesized IkappaB alpha in SirT1(ko/ko) cells. SirT1 deficiency therefore affects the cellular response to multiple extrinsic signals.

Conclusion: SirT1 modulates the IGF-1 signaling critical for both growth regulation and mammary gland development in mice. SirT1 deficiency deregulates the expression of IGF-1 binding protein-1 and attenuates the effect of IGF-1 signals, including estrogen-stimulated local IGF-1 signaling for the onset of ductal morphogenesis. These findings suggest that the enzymatic activity of SirT1 may influence both normal growth and malignant growth of mammary epithelial cells.

Show MeSH

Related in: MedlinePlus

Pregnancy-induced ductal morphogenesis. (a) Whole mount analysis of mammary gland development. Upper panel: wild-type (+/+) mice show terminal end buds (TEBs) at the onset of puberty, elongated ducts (virgin mice), site branching during pregnancy (P13), and lobuloalveolar structures for milk production on lactation day 1 (L1). Lower panel: virgin SirT1ko/ko (ko/ko) mice show impeded ductal morphogenesis. Pregnancy-induced ductal morphogenesis manifests transitional TEBs, ductal elongation, and side branching with variety in three SirT1ko/ko mice on L1. All scale bars = 200 μm. (b) Western blot analysis of both insulin-like growth factor-1 binding protein-1 (IGFBP-1) and IκBα in mammary tissues of male mice, virgin mice, and L1 female mice of wild type (+/+) and SirT1ko/ko (ko/ko). Actin is used as a loading control. Lower panel scores the estimated density of indicated lineages of cells in the protein extracts, which are based on the morphological analyses in (a).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC1851382&req=5

Figure 3: Pregnancy-induced ductal morphogenesis. (a) Whole mount analysis of mammary gland development. Upper panel: wild-type (+/+) mice show terminal end buds (TEBs) at the onset of puberty, elongated ducts (virgin mice), site branching during pregnancy (P13), and lobuloalveolar structures for milk production on lactation day 1 (L1). Lower panel: virgin SirT1ko/ko (ko/ko) mice show impeded ductal morphogenesis. Pregnancy-induced ductal morphogenesis manifests transitional TEBs, ductal elongation, and side branching with variety in three SirT1ko/ko mice on L1. All scale bars = 200 μm. (b) Western blot analysis of both insulin-like growth factor-1 binding protein-1 (IGFBP-1) and IκBα in mammary tissues of male mice, virgin mice, and L1 female mice of wild type (+/+) and SirT1ko/ko (ko/ko). Actin is used as a loading control. Lower panel scores the estimated density of indicated lineages of cells in the protein extracts, which are based on the morphological analyses in (a).

Mentions: To characterize the developmental defect leading to lactation failure, we analyzed the mammary glands of SirT1ko/ko female mice on lactation day 1. Terminal end buds (TEBs) are club-shaped transitional structures (see Figure 3a, upper panel). In wild-type female mice, TEBs form and precede ductal elongation and branching at the onset of puberty [17,24,25]. When TEBs/ducts reach the edge of mammary fat pads, TEBs regress as shown in the virgin mice in Figure 3a (upper panel). Interestingly, the transitional TEBs can be readily identified in SirT1ko/ko female mice on lactation day 1, manifesting as either newly formed TEBs or as TEBs attached to developing ductal and alveolar structures (Figure 3a, lower panel). Moreover, SirT1ko/ko mice displayed varying degrees of ductal development, ranging from a lack of any ductal structure to a fully developed ductal network, the latter of which is comparable with the morphology and cellularity of wild-type mammary tissues on day 13 of pregnancy (Figure 3a). These observations indicated that pregnancy could rescue impeded ductal morphogenesis in virgin SirT1ko/ko mice.


SirT1 modulates the estrogen-insulin-like growth factor-1 signaling for postnatal development of mammary gland in mice.

Li H, Rajendran GK, Liu N, Ware C, Rubin BP, Gu Y - Breast Cancer Res. (2007)

Pregnancy-induced ductal morphogenesis. (a) Whole mount analysis of mammary gland development. Upper panel: wild-type (+/+) mice show terminal end buds (TEBs) at the onset of puberty, elongated ducts (virgin mice), site branching during pregnancy (P13), and lobuloalveolar structures for milk production on lactation day 1 (L1). Lower panel: virgin SirT1ko/ko (ko/ko) mice show impeded ductal morphogenesis. Pregnancy-induced ductal morphogenesis manifests transitional TEBs, ductal elongation, and side branching with variety in three SirT1ko/ko mice on L1. All scale bars = 200 μm. (b) Western blot analysis of both insulin-like growth factor-1 binding protein-1 (IGFBP-1) and IκBα in mammary tissues of male mice, virgin mice, and L1 female mice of wild type (+/+) and SirT1ko/ko (ko/ko). Actin is used as a loading control. Lower panel scores the estimated density of indicated lineages of cells in the protein extracts, which are based on the morphological analyses in (a).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1851382&req=5

Figure 3: Pregnancy-induced ductal morphogenesis. (a) Whole mount analysis of mammary gland development. Upper panel: wild-type (+/+) mice show terminal end buds (TEBs) at the onset of puberty, elongated ducts (virgin mice), site branching during pregnancy (P13), and lobuloalveolar structures for milk production on lactation day 1 (L1). Lower panel: virgin SirT1ko/ko (ko/ko) mice show impeded ductal morphogenesis. Pregnancy-induced ductal morphogenesis manifests transitional TEBs, ductal elongation, and side branching with variety in three SirT1ko/ko mice on L1. All scale bars = 200 μm. (b) Western blot analysis of both insulin-like growth factor-1 binding protein-1 (IGFBP-1) and IκBα in mammary tissues of male mice, virgin mice, and L1 female mice of wild type (+/+) and SirT1ko/ko (ko/ko). Actin is used as a loading control. Lower panel scores the estimated density of indicated lineages of cells in the protein extracts, which are based on the morphological analyses in (a).
Mentions: To characterize the developmental defect leading to lactation failure, we analyzed the mammary glands of SirT1ko/ko female mice on lactation day 1. Terminal end buds (TEBs) are club-shaped transitional structures (see Figure 3a, upper panel). In wild-type female mice, TEBs form and precede ductal elongation and branching at the onset of puberty [17,24,25]. When TEBs/ducts reach the edge of mammary fat pads, TEBs regress as shown in the virgin mice in Figure 3a (upper panel). Interestingly, the transitional TEBs can be readily identified in SirT1ko/ko female mice on lactation day 1, manifesting as either newly formed TEBs or as TEBs attached to developing ductal and alveolar structures (Figure 3a, lower panel). Moreover, SirT1ko/ko mice displayed varying degrees of ductal development, ranging from a lack of any ductal structure to a fully developed ductal network, the latter of which is comparable with the morphology and cellularity of wild-type mammary tissues on day 13 of pregnancy (Figure 3a). These observations indicated that pregnancy could rescue impeded ductal morphogenesis in virgin SirT1ko/ko mice.

Bottom Line: The effect of exogenous estrogen was also examined by subcutaneous implantation of a slow-releasing pellet in the subscapular region.SirT1 deficiency deregulates the expression of IGF-1 binding protein-1 and attenuates the effect of IGF-1 signals, including estrogen-stimulated local IGF-1 signaling for the onset of ductal morphogenesis.These findings suggest that the enzymatic activity of SirT1 may influence both normal growth and malignant growth of mammary epithelial cells.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Radiation Oncology, University of Washington School of Medicine, Seattle, WA 98195, USA.

ABSTRACT

Introduction: Estrogen and insulin-like growth factor-1 (IGF-1) play important roles in mammary gland development and breast cancer. SirT1 is a highly conserved protein deacetylase that can regulate the insulin/IGF-1 signaling in lower organisms, as well as a growing number of transcription factors, including NF-kappaB, in mammalian cells. Whether SirT1 regulates the IGF-1 signaling for mammary gland development and function, however, is not clear. In the present study, this role of SirT1 was examined by studying SirT1-deficient mice.

Methods: SirT1-deficient (SirT1(ko/ko)) mice were generated by crossing a new strain of mice harboring a conditional targeted mutation in the SirT1 gene (SirT1(co/co)) with CMV-Cre transgenic mice. Whole mount and histology analyses, immunofluorescence staining, immunohistochemistry, and western blotting were used to characterize mammary gland development in virgin and pregnant mice. The effect of exogenous estrogen was also examined by subcutaneous implantation of a slow-releasing pellet in the subscapular region.

Results: Both male and female SirT1(ko/ko) mice can be fertile despite the growth retardation phenotype. Virgin SirT1(ko/ko) mice displayed impeded ductal morphogenesis, whereas pregnant SirT1(ko/ko) mice manifested lactation failure due to an underdeveloped lobuloalveolar network. Estrogen implantation was sufficient to rescue ductal morphogenesis. Exogenous estrogen reversed the increased basal level of IGF-1 binding protein-1 expression in SirT1(ko/ko) mammary tissues, but not that of IkappaB alpha expression, suggesting that increased levels of estrogen enhanced the production of local IGF-1 and rescued ductal morphogenesis. Additionally, TNFalpha treatment enhanced the level of the newly synthesized IkappaB alpha in SirT1(ko/ko) cells. SirT1 deficiency therefore affects the cellular response to multiple extrinsic signals.

Conclusion: SirT1 modulates the IGF-1 signaling critical for both growth regulation and mammary gland development in mice. SirT1 deficiency deregulates the expression of IGF-1 binding protein-1 and attenuates the effect of IGF-1 signals, including estrogen-stimulated local IGF-1 signaling for the onset of ductal morphogenesis. These findings suggest that the enzymatic activity of SirT1 may influence both normal growth and malignant growth of mammary epithelial cells.

Show MeSH
Related in: MedlinePlus