scholarly journals Estrogen Receptor-Alpha and p53 Status as Regulators of AMPK and mTOR in Luminal Breast Cancer

Cancers ◽  
2021 ◽  
Vol 13 (14) ◽  
pp. 3612
Author(s):  
Nishant Gandhi ◽  
Chetan C. Oturkar ◽  
Gokul M. Das

Luminal breast cancer (LBC) driven by dysregulated estrogen receptor-alpha (ERα) signaling accounts for 70% of the breast cancer cases diagnosed. Although endocrine therapy (ET) is effective against LBC, about one-third of these patients fail to respond to therapy owing to acquired or inherent resistance mechanisms. Aberrant signaling via ERα, oncogenes, growth factor receptors, and mutations in tumor suppressors such as p53 impinge on downstream regulators such as AMPK and mTOR. While both AMPK and mTOR have been reported to play important roles in determining sensitivity of LBC to ET, how the ERα-p53 crosstalk impinges on regulation of AMPK and mTOR, thereby influencing therapeutic efficacy remains unknown. Here, we have addressed this important issue using isogenic breast cancer cell lines, siRNA-mediated RNA knockdown, and different modes of drug treatments. Interaction of p53 with ERα and AMPK was determined by in situ proximity ligation assay (PLA), and endogenous gene transcripts were analyzed by quantitative real-time polymerase chain reaction (qRT-PCR). Further, the effect of concurrent and sequential administration of Fulvestrant–Everolimus combination on colony formation was determined. The studies showed that in cells expressing wild type p53, as well as in cells devoid of p53, ERα represses AMPK, whereas in cells harboring mutant p53, repression of AMPK is sustained even in the absence of ERα. AMPK is a major negative regulator of mTOR, and to our knowledge, this is the first study on the contribution of AMPK-dependent regulation of mTOR by ERα. Furthermore, the studies revealed that independent of the p53 mutation status, combination of Fulvestrant and Everolimus may be a viable first line therapeutic strategy for potentially delaying resistance of ERα+/HER2− LBC to ET.

2004 ◽  
Vol 24 (19) ◽  
pp. 8681-8690 ◽  
Author(s):  
Shangqin Guo ◽  
Gail E. Sonenshein

ABSTRACT The expression status of the estrogen receptor alpha (ERα) and that of the epidermal growth factor receptor Her-2/neu frequently correlate inversely in breast cancers. While ERα-dependent cancers respond to antiestrogen therapy, Her-2/neu-overexpressing cancers typically display resistance to antiestrogens and poor prognosis. In this report we have explored the mechanism linking the loss of expression of ERα in breast cancer cells with overexpression of Her-2/neu, which signals constitutively via a phosphatidylinositol 3-kinase (PI3K)/Akt kinase pathway. We identify for the first time the Forkhead box protein FOXO3a (formerly termed FKHRL-1), which is inactivated by Akt, as a key regulator of ERα gene transcription. In breast cancer cell lines, expression of ERα was correlated with active FOXO3a levels. Ectopic FOXO3a expression induced ERα protein levels and promoter activity, while a dominant negative FOXO3a decreased ERα levels. By using transient transfection, mobility shift assays, and site-directed mutagenesis, two major functional Forkhead binding sites were identified in the human ERα promoter B. A chromatin immunoprecipitation assay confirmed FOXO3a binding at these two sites. Ectopic FOXO3a induced estrogen response element-driven reporter activity and expression of ERα target genes. The constitutively activated myristylated Akt reduced ERα expression, whereas agents that negatively affect the PI3K/Akt pathway, i.e., wortmannin, celecoxib, and the green tea polyphenol epigallocatechin-3 gallate, induced ERα. Thus, FOXO3a represents an important intracellular mediator of ERα expression, suggesting possible therapeutic intervention strategies for Her-2/neu-overexpressing refractory breast tumors.


Cancers ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 2799
Author(s):  
Aaron Waddell ◽  
Iqbal Mahmud ◽  
Haocheng Ding ◽  
Zhiguang Huo ◽  
Daiqing Liao

Estrogen receptor alpha (ER) is the oncogenic driver for ER+ breast cancer (BC). ER antagonists are the standard-of-care treatment for ER+ BC; however, primary and acquired resistance to these agents is common. CBP and p300 are critical ER co-activators and their acetyltransferase (KAT) domain and acetyl-lysine binding bromodomain (BD) represent tractable drug targets, but whether CBP/p300 inhibitors can effectively suppress ER signaling remains unclear. We report that the CBP/p300 KAT inhibitor A-485 and the BD inhibitor GNE-049 downregulate ER, attenuate estrogen-induced c-Myc and Cyclin D1 expression, and inhibit growth of ER+ BC cells through inducing senescence. Microarray and RNA-seq analysis demonstrates that A-485 or EP300 (encoding p300) knockdown globally inhibits expression of estrogen-regulated genes, confirming that ER inhibition is an on-target effect of A-485. Using ChIP-seq, we report that A-485 suppresses H3K27 acetylation in the enhancers of ER target genes (including MYC and CCND1) and this correlates with their decreased expression, providing a mechanism underlying how CBP/p300 inhibition downregulates ER gene network. Together, our results provide a preclinical proof-of-concept that CBP/p300 represent promising therapeutic targets in ER+ BC for inhibiting ER signaling.


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