PKCθ promotes c-Rel–driven mammary tumorigenesis in mice and humans by repressing estrogen receptor α synthesis
Karine Belguise, Gail E. Sonenshein
Karine Belguise, Gail E. Sonenshein
Published December 3, 2007
Citation Information: J Clin Invest. 2007;117(12):4009-4021. https://doi.org/10.1172/JCI32424.
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Research Article Oncology

PKCθ promotes c-Rel–driven mammary tumorigenesis in mice and humans by repressing estrogen receptor α synthesis

Abstract

The vast majority of primary human breast cancer tissues display aberrant nuclear NF-κB c-Rel expression. A causal role for c-Rel in mammary tumorigenesis has been demonstrated using a c-Rel transgenic mouse model; however, tumors developed with a long latency, suggesting a second event is needed to trigger tumorigenesis. Here we show that c-Rel activity in the mammary gland is repressed by estrogen receptor α (ERα) signaling, and we identify an epigenetic mechanism in breast cancer mediated by activation of what we believe is a novel PKCθ-Akt pathway that leads to downregulation of ERα synthesis and derepression of c-Rel. ERα levels were lower in c-Rel–induced mammary tumors compared with normal mammary gland tissue. PKCθ induced c-Rel activity and target gene expression and promoted growth of c-Rel- and c-RelxCK2α–driven mouse mammary tumor–derived cell lines. RNA expression levels of PKCθ and c-Rel target genes were inversely correlated with ERα levels in human breast cancer specimens. PKCθ activated Akt, thereby inactivating forkhead box O protein 3a (FOXO3a) and leading to decreased synthesis of its target genes, ERα and p27Kip1. Thus we have shown that activation of PKCθ inhibits the FOXO3a/ERα/p27Kip1 axis that normally maintains an epithelial cell phenotype and induces c-Rel target genes, thereby promoting proliferation, survival, and more invasive breast cancer.

Authors

Karine Belguise, Gail E. Sonenshein

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Figure 5

PKCθ inhibits ERα expression and activity.

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PKCθ inhibits ERα expression and activity. (A) WCEs from ERα-positive an...
(A) WCEs from ERα-positive and ERα-negative human breast cancer cell lines were subjected to immunoblotting for PKCθ, position as indicated. (B) Box plots of data from the Wang et al. (30) (top panel) and Chin et al. (31) (bottom panel) carcinoma microarray datasets (reporter number 210039_s_at) were accessed using the ONCOMINE Cancer Profiling Database and were plotted on a log scale. A Student’s t test performed directly through the Oncomine 3.0 software showed the difference in PKCθ expression between the 2 groups was significant (Wang et al. [ref. 30] dataset: P = 8.3 × 10–6 and Chin et al. [ref. 31] dataset: P = 5.4 × 10–4). (C) MCF7 and ZR75 cells were transfected in 6-well plates with 2 μg PKCθ-A/E or EV. WCEs were subjected to immunoblotting. (D) ZR75 and MCF7 cells were transfected in 12-well plates with 0.1 μg ERE2-tk-Luc, β-gal, and 0.2 or 0.4 μg PKCθ-A/E or EV. The values represent the mean ± SD of normalized luciferase activities. (E) WCEs from C were subjected to immunoblotting for RARα, PR-A, and β-actin. (F) rel-3875 and rel-3983 cells were transfected in 6-well plates with 2 μg PKCθ-K/R or EV. WCEs were subjected to immunoblotting. (G) rel-3875 cells were transfected in 12-well plates with 0.1 μg ERE-Luc, β-gal, and 0.4 μg PKCθ-K/R (+) or EV (–). (H) ZR75 and MCF7 cells were transfected in 12-well plates with 0.1 μg proB-Luc, β-gal, and 0.2 or 0.4 μg PKCθ-A/E or EV. The values represent the mean ± SD of normalized luciferase activities.