Abstract
BackgroundTo sustain cell growth, cancer cells exhibit an altered metabolism characterized by increased lipogenesis. Stearoyl-CoA desaturase-1 (SCD-1) catalyzes the production of monounsaturated fatty acids that are essential for membrane biogenesis, and is required for cell proliferation in many cancer cell types. Although estrogen is required for the proliferation of many estrogen-sensitive breast carcinoma cells, it is also a repressor of SCD-1 expression in liver and adipose. The current study addresses this apparent paradox by investigating the impact of estrogen on SCD-1 expression in estrogen receptor-α-positive breast carcinoma cell lines.MethodsMCF-7 and T47D mammary carcinomas cells and immortalized MCF-10A mammary epithelial cells were hormone-starved then treated or not with 17β-estradiol. SCD-1 activity was assessed by measuring cellular monounsaturated/saturated fatty acid (MUFA/SFA) ratios, and SCD-1 expression was measured by qPCR, immunoblot, and immunofluorescence analyses. The role of SCD-1 in cell proliferation was measured following treatment with the SCD-1 inhibitor A959372 and following SCD-1 silencing using siRNA. The involvement of IGF-1R on SCD-1 expression was measured using the IGF-1R antagonist AG1024. The expression of SREBP-1c, a transcription factor that regulates SCD-1, was measured by qPCR, and by immunoblot analyses.Results17β-estradiol significantly induced cell proliferation and SCD-1 activity in MCF-7 and T47D cells but not MCF-10A cells. Accordingly, 17β-estradiol significantly increased SCD-1 mRNA and protein expression in MCF-7 and T47D cells compared to untreated cells. Treatment of MCF-7 cells with 4-OH tamoxifen or siRNA silencing of estrogen receptor-α largely prevented 17β-estradiol-induced SCD-1 expression. 17β-estradiol increased SREBP-1c expression and induced the mature active 60 kDa form of SREBP-1. The selective SCD-1 inhibitor or siRNA silencing of SCD-1 blocked the 17β-estradiol-induced cell proliferation and increase in cellular MUFA/SFA ratios. IGF-1 also induced SCD-1 expression, but to a lesser extent than 17β-estradiol. The IGF-1R antagonist partially blocked 17β-estradiol-induced cell proliferation and SCD-1 expression, suggesting the impact of 17β-estradiol on SCD-1 expression is partially mediated though IGF-1R signaling.ConclusionsThis study illustrates for the first time that, in contrast to hepatic and adipose tissue, estrogen induces SCD-1 expression and activity in breast carcinoma cells. These results support SCD-1 as a therapeutic target in estrogen-sensitive breast cancer.
Highlights
To sustain cell growth, cancer cells exhibit an altered metabolism characterized by increased lipogenesis
Following de novo fatty acid biosynthesis, the enzyme stearoyl-CoA desaturase-1 (SCD-1) catalyzes the introduction of the first double bond in the cis-delta 9 position of saturated fatty acyl-CoA producing monounsaturated fatty acids (MUFA) that are essential for membrane biogenesis as they contribute to cell membrane fluidity [17]
In this study we sought to investigate an apparent paradox where Stearoyl-CoA desaturase-1 (SCD-1) is highly expressed in breast cancers and appears to be required for appropriate cell division, SCD-1 expression is repressed in liver and adipose tissue in response to estrogen, a principal driver of growth in estrogen receptors (ER)-α-positive breast cancer
Summary
Reagents Cell culture media (DMEM/F12, RPMI-1640, phenol red-free RPMI-1640), FBS, and charcoal-stripped FBS were purchased from Thermo Fisher Scientific. As described previously [42, 43], before treatments cells were cultured for one week in phenol red-free medium supplemented with 10 % charcoal-stripped FBS (5 % for MCF-10A cells) to starve cells from steroid hormones (starvation medium). Cells that had been starved as above for 7 days were resuspended in PBS containing 5 μM of CFSE diluted in DMSO, were incubated for 20 min at 37 °C followed by 3 washes with phenol redfree media to remove free dye remaining in the solution. Immunocytochemistry MCF-7 cells grown on glass cover slips at approximately 60 % confluence were incubated in starvation medium (phenol red-free medium and charcoal-stripped FBS), followed by a 5-day treatment or not with 2nM 17β-ED as described above. (b) Following one week of incubation in phenol red-free medium containing charcoal-stripped FBS, cells were treated with 2nM 17β-ED or its vehicle EtOH (Ctrl) for 5 days. Differences in treatments were analyzed using Student’s t-test or 1-way ANOVA tests with Tukey’s post-hoc test, performed with GraphPad Prism Version 6.0 software
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