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Local adipocytes enable estrogen-dependent breast cancer growth: Role of leptin and aromatase.

Liu E, Samad F, Mueller BM - Adipocyte (2013)

Bottom Line: Here we describe a unique animal model to study interactions between adipocytes and breast cancer cells in the tumor microenvironment.Our results suggest that local interactions between adipocytes and tumor cells are sufficient to promote the growth of hormone-dependent breast cancer.We also demonstrate that leptin signaling in adipocytes induces aromatase expression, expected to result in higher estrogen in the microenvironment thus enabling mammary tumorigenesis.

View Article: PubMed Central - PubMed

Affiliation: Torrey Pines Institute for Molecular Studies; San Diego, CA USA.

ABSTRACT
The importance of the microenvironment in breast cancer growth and progression is becoming increasingly clear. Adipocytes are abundant in the mammary microenvironment, and recent studies show that adipocytes produce endocrine, inflammatory, and angiogenic factors that have tremendous potential to affect adjacent breast cancer cells. Yet, the extent to which local adipocyte function contributes to the pathogenesis of breast cancer is largely unexplored. Here we describe a unique animal model to study interactions between adipocytes and breast cancer cells in the tumor microenvironment. Our results suggest that local interactions between adipocytes and tumor cells are sufficient to promote the growth of hormone-dependent breast cancer. We also demonstrate that leptin signaling in adipocytes induces aromatase expression, expected to result in higher estrogen in the microenvironment thus enabling mammary tumorigenesis.

No MeSH data available.


Related in: MedlinePlus

Figure 2. Aromatase and leptin receptor expression in F442A cells in vitro. (A) Western blot of basal and leptin-induced aromatase protein expression in F442A undifferentiated pre-adipocytes and differentiated adipocytes. F442A pre-adipocytes or confluent, differentiated adipocytes in 24-well plates were incubated with mouse leptin (PeproTech, 100 nM), leptin-triple mutant antagonist (leptin TA; Prospec, 250 nM) or buffer as control for 6 h under typical cell culture conditions. Aromatase protein expression was determined by western blot analysis using a standard protocol with anti-CPY19 (C-16; Santa Cruz Biotechnology) as primary antibody to detect aromatase. Western blot for actin is shown as loading control. (B) Leptin receptor expression in F442A pre-adipocytes vs. F442A adipocytes indicating an increase in the long form of LepR (LepR-1) in adipocytes compared with pre-adipocytes. Antibody to detect mouse LepR by western blotting was NB120-5593 (Novus Biologicals).
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Figure 2: Figure 2. Aromatase and leptin receptor expression in F442A cells in vitro. (A) Western blot of basal and leptin-induced aromatase protein expression in F442A undifferentiated pre-adipocytes and differentiated adipocytes. F442A pre-adipocytes or confluent, differentiated adipocytes in 24-well plates were incubated with mouse leptin (PeproTech, 100 nM), leptin-triple mutant antagonist (leptin TA; Prospec, 250 nM) or buffer as control for 6 h under typical cell culture conditions. Aromatase protein expression was determined by western blot analysis using a standard protocol with anti-CPY19 (C-16; Santa Cruz Biotechnology) as primary antibody to detect aromatase. Western blot for actin is shown as loading control. (B) Leptin receptor expression in F442A pre-adipocytes vs. F442A adipocytes indicating an increase in the long form of LepR (LepR-1) in adipocytes compared with pre-adipocytes. Antibody to detect mouse LepR by western blotting was NB120-5593 (Novus Biologicals).

Mentions: Adipocytes secrete many growth factors, hormones, and other bioactive molecules that can directly support tumorigenesis.1-3 Since proliferation, growth, and progression of hormone-responsive breast cancer are driven by estrogen, we reasoned that F442A adipocytes may enable growth of hormone-dependent breast cancer by providing local estrogen. In postmenopausal women estrogen is derived from the activity of aromatase, an enzyme of the cytochrome p450 superfamily. Aromatase converts androgens into estrogens and preferentially mediates conversion of adrenal androstenedione into estrone.11,12 While aromatase is highly expressed in ovarian follicles, in postmenopausal women the primary site of aromatase activity and estrogen production is the adipose tissue. Thus after menopause, peripheral aromatase activity and plasma estrogen levels correlate with body-mass index,13 and adipose-derived estrogen is thought to be a major contributor to obesity-related postmenopausal breast cancer risk and progression. Lowering of plasma estrogen levels with aromatase inhibitors has therapeutic benefit as adjuvant treatment in women with estrogen receptor-positive breast cancer14 and as first line treatment in postmenopausal women with advanced cancer.15 However, the extent to which plasma estrogen levels are sufficient to support hormone-dependent breast cancer is unclear. In postmenopausal women, local estrogen levels in breast cancer tissue are 10-fold higher than in plasma, suggesting increased local estrogen production.16 Indeed, breast cancer tissues have considerable aromatase activity17,18 and express aromatase in different cell types including tumor, stromal, endothelial cells, and adipocytes.19 Interestingly, tissue-specific promoters and different transcription factors control aromatase expression in different cell types including tumor cells and adipocytes.20 In mouse models, overexpression of aromatase in mouse mammary epithelia leads to hyperplasia in the absence of circulating estrogen21 and modulates tumor development in HER2/neu transgenic mice.22 Overexpression of aromatase in the human breast cancer cell line MCF-7 enables breast cancer growth in nude mice, which can be blocked by aromatase inhibitor.23 While these observations argue for a role of local aromatase activity in breast cancer, the contribution and regulation of adipocyte-produced aromatase in the tumor microenvironment and the extent to which adipocyte aromatase contributes to cancer pathogenesis is not known. We determined aromatase expression in vitro in undifferentiated F442A pre-adipocytes and in F442A adipocytes differentiated using a cocktail of 1 µM dexamathasone and 1 µg/ml insulin. Western blot analysis showed that undifferentiated F442A pre-adipocytes express very low levels of aromatase whereas high levels of aromatase was observed in fully differentiated F442A adipocytes (Fig. 2A).


Local adipocytes enable estrogen-dependent breast cancer growth: Role of leptin and aromatase.

Liu E, Samad F, Mueller BM - Adipocyte (2013)

Figure 2. Aromatase and leptin receptor expression in F442A cells in vitro. (A) Western blot of basal and leptin-induced aromatase protein expression in F442A undifferentiated pre-adipocytes and differentiated adipocytes. F442A pre-adipocytes or confluent, differentiated adipocytes in 24-well plates were incubated with mouse leptin (PeproTech, 100 nM), leptin-triple mutant antagonist (leptin TA; Prospec, 250 nM) or buffer as control for 6 h under typical cell culture conditions. Aromatase protein expression was determined by western blot analysis using a standard protocol with anti-CPY19 (C-16; Santa Cruz Biotechnology) as primary antibody to detect aromatase. Western blot for actin is shown as loading control. (B) Leptin receptor expression in F442A pre-adipocytes vs. F442A adipocytes indicating an increase in the long form of LepR (LepR-1) in adipocytes compared with pre-adipocytes. Antibody to detect mouse LepR by western blotting was NB120-5593 (Novus Biologicals).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
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Figure 2: Figure 2. Aromatase and leptin receptor expression in F442A cells in vitro. (A) Western blot of basal and leptin-induced aromatase protein expression in F442A undifferentiated pre-adipocytes and differentiated adipocytes. F442A pre-adipocytes or confluent, differentiated adipocytes in 24-well plates were incubated with mouse leptin (PeproTech, 100 nM), leptin-triple mutant antagonist (leptin TA; Prospec, 250 nM) or buffer as control for 6 h under typical cell culture conditions. Aromatase protein expression was determined by western blot analysis using a standard protocol with anti-CPY19 (C-16; Santa Cruz Biotechnology) as primary antibody to detect aromatase. Western blot for actin is shown as loading control. (B) Leptin receptor expression in F442A pre-adipocytes vs. F442A adipocytes indicating an increase in the long form of LepR (LepR-1) in adipocytes compared with pre-adipocytes. Antibody to detect mouse LepR by western blotting was NB120-5593 (Novus Biologicals).
Mentions: Adipocytes secrete many growth factors, hormones, and other bioactive molecules that can directly support tumorigenesis.1-3 Since proliferation, growth, and progression of hormone-responsive breast cancer are driven by estrogen, we reasoned that F442A adipocytes may enable growth of hormone-dependent breast cancer by providing local estrogen. In postmenopausal women estrogen is derived from the activity of aromatase, an enzyme of the cytochrome p450 superfamily. Aromatase converts androgens into estrogens and preferentially mediates conversion of adrenal androstenedione into estrone.11,12 While aromatase is highly expressed in ovarian follicles, in postmenopausal women the primary site of aromatase activity and estrogen production is the adipose tissue. Thus after menopause, peripheral aromatase activity and plasma estrogen levels correlate with body-mass index,13 and adipose-derived estrogen is thought to be a major contributor to obesity-related postmenopausal breast cancer risk and progression. Lowering of plasma estrogen levels with aromatase inhibitors has therapeutic benefit as adjuvant treatment in women with estrogen receptor-positive breast cancer14 and as first line treatment in postmenopausal women with advanced cancer.15 However, the extent to which plasma estrogen levels are sufficient to support hormone-dependent breast cancer is unclear. In postmenopausal women, local estrogen levels in breast cancer tissue are 10-fold higher than in plasma, suggesting increased local estrogen production.16 Indeed, breast cancer tissues have considerable aromatase activity17,18 and express aromatase in different cell types including tumor, stromal, endothelial cells, and adipocytes.19 Interestingly, tissue-specific promoters and different transcription factors control aromatase expression in different cell types including tumor cells and adipocytes.20 In mouse models, overexpression of aromatase in mouse mammary epithelia leads to hyperplasia in the absence of circulating estrogen21 and modulates tumor development in HER2/neu transgenic mice.22 Overexpression of aromatase in the human breast cancer cell line MCF-7 enables breast cancer growth in nude mice, which can be blocked by aromatase inhibitor.23 While these observations argue for a role of local aromatase activity in breast cancer, the contribution and regulation of adipocyte-produced aromatase in the tumor microenvironment and the extent to which adipocyte aromatase contributes to cancer pathogenesis is not known. We determined aromatase expression in vitro in undifferentiated F442A pre-adipocytes and in F442A adipocytes differentiated using a cocktail of 1 µM dexamathasone and 1 µg/ml insulin. Western blot analysis showed that undifferentiated F442A pre-adipocytes express very low levels of aromatase whereas high levels of aromatase was observed in fully differentiated F442A adipocytes (Fig. 2A).

Bottom Line: Here we describe a unique animal model to study interactions between adipocytes and breast cancer cells in the tumor microenvironment.Our results suggest that local interactions between adipocytes and tumor cells are sufficient to promote the growth of hormone-dependent breast cancer.We also demonstrate that leptin signaling in adipocytes induces aromatase expression, expected to result in higher estrogen in the microenvironment thus enabling mammary tumorigenesis.

View Article: PubMed Central - PubMed

Affiliation: Torrey Pines Institute for Molecular Studies; San Diego, CA USA.

ABSTRACT
The importance of the microenvironment in breast cancer growth and progression is becoming increasingly clear. Adipocytes are abundant in the mammary microenvironment, and recent studies show that adipocytes produce endocrine, inflammatory, and angiogenic factors that have tremendous potential to affect adjacent breast cancer cells. Yet, the extent to which local adipocyte function contributes to the pathogenesis of breast cancer is largely unexplored. Here we describe a unique animal model to study interactions between adipocytes and breast cancer cells in the tumor microenvironment. Our results suggest that local interactions between adipocytes and tumor cells are sufficient to promote the growth of hormone-dependent breast cancer. We also demonstrate that leptin signaling in adipocytes induces aromatase expression, expected to result in higher estrogen in the microenvironment thus enabling mammary tumorigenesis.

No MeSH data available.


Related in: MedlinePlus