5
0
-AMP-activated protein kinase (AMPK) regulates progesterone receptor
transcriptional activity in breast cancer cells
Li Wu
a
, Xiao-jie Huang
a
, Cheng-hong Yang
a
, Si-si Deng
b
, Min Qian
a
, Yi Zang
b,
⇑
, Jia Li
a,b,
⇑
a
School of Life Sciences, East China Normal University, 3663 North Zhongshan Road, Shanghai 200062, China
b
National Center for Drug Screening, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 189 Guo Shou Jing Road, Shanghai 201203, China
article info
Article history:
Received 23 October 2011
Available online 10 November 2011
Keywords:
Progesterone receptor
AMPK
AICAR
Metformin
Compound C
abstract
The steroid hormone progesterone is an essential regulator of the cellular processes that are required for
the development and maintenance of reproductive function. The diverse effects of progesterone are med-
iated by the progesterone receptor (PR). The functions of the PR are regulated not only by ligands but also
by modulators of various cell signaling pathways. However, it is not clear which energy state regulates PR
activity. AMP-activated protein kinase (AMPK), a serine/threonine protein kinase, is a key modulator of
energy homeostasis. Once activated by an increasing cellular AMP:ATP ratio, AMPK switches off ATP-
consuming processes and switches on ATP-producing processes. We found that both 5-aminoimidaz-
ole-4-carboxamide 1-b-
D
-ribofuranoside (AICAR) and metformin, traditional pharmacological activators
of AMPK, inhibited the PR pathway, as evidenced by progesterone response element (PRE)-driven lucif-
erase activity and PR target gene expression. Compound C, an inhibitor of AMPK, partly but significantly
reversed the anti-PR effects of AICAR and metformin. The downregulation of endogenous AMPK by small
interfering RNAs (siRNAs) stimulated PR activity. AMPK activation by AICAR decreased the progesterone-
induced phosphorylation of PR at serine 294 and inhibited the recruitment of PR to an endogenous PRE.
Taken together, our data suggest that AMPK, an energy sensor, is involved in the regulation of PR
signaling.
Ó 2011 Elsevier Inc. All rights reserved.
1. Introduction
The steroid hormone progesterone is produced by the ovarian
corpus luteum and by the placental syncytiotrophoblast during
the second trimester of pregnancy. Progesterone is a vital compo-
nent in the complicated regulation of reproduction, differentiation
and development. The diverse effects of progesterone on its target
tissues are mediated by the progesterone receptor (PR). Human PR
is expressed from a single gene as two proteins, PR-A and PR-B,
with distinct functional activities both in vitro and in vivo. In many
cell types, PR-B is a stronger transcriptional activator than PR-A.
The activity of PR is regulated not only by its ligands but also by
modulators of various cell signaling pathways [1]. It is not known
whether a metabolic regulator could trigger PR regulation.
AMP-activated protein kinase (AMPK) is a serine/threonine pro-
tein kinase that is a key modulator of energy homeostasis and a
responsor to physiological and pathological change (e.g., exercise,
low glucose, hypoxia, and ischemia), hormones (e.g., leptin, adipo-
nectin and resistin) and pharmaceuticals (AICAR, metformin and
berberine) [2]. AMPK is a heterotrimeric protein consisting of a cat-
alytic
a
subunit and regulatory b and
c
subunits in a 1:1:1 stoichi-
ometric ratio [3]. Once activated by cellular stresses that increase
the AMP:ATP ratio, AMPK phosphorylates and inactivates a num-
ber of metabolic enzymes involved in ATP-consuming processes,
such as fatty acid, cholesterol and protein synthesis, while activat-
ing ATP-producing processes, such as fatty acid oxidation and glu-
cose uptake, thereby restoring the AMP:ATP ratio [2]. Thus, AMPK
is generally termed a metabolic ‘energy sensor’ of the cell.
Interestingly, recent studies have revealed a non-metabolic
function of AMPK. AMPK is switched on by stresses that disturb en-
ergy balance, and it triggers both acute responses and longer-term
adaptations by affecting gene expression, including inducing cell
cycle arrest at the G1/S transition by phosphorylating p53 [4]
and p21 [5], regulating apoptosis by phosphorylating p27 [6], reg-
ulating reproductive hormone secretion [7], and even extending
0006-291X/$ - see front matter Ó 2011 Elsevier Inc. All rights reserved.
doi:10.1016/j.bbrc.2011.11.018
Abbreviations: PR, progesterone receptors; PRE, progesterone response element;
ACC, acetyl-CoA carboxylase; AICAR, 5-aminoimidazole-4-carboxamide 1-b-
D
-
ribofuranoside; AMPK, 5
0
-AMP-activated protein kinase; FOXO, forkhead box, class
O; HDAC5, histone deacetylase 5; HMGR, 3-hydroxy-3-methylglutaryl-CoA reduc-
tase; MTS/PMS, 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl-2-(4-sul
fophe-nyl)-2H-tetrazolium)/phenazine methosulfate; SGK, serum and glucocorti-
coid-inducible kinase; siRNA, small interfering RNA; FKBP54, 54 kDa progesterone
receptor-associated immunophilin.
⇑
Corresponding authors at: 189 Guo Shou Jing Road, Shanghai 201203, China.
Fax: +86 21 50800721.
E-mail addresses: yzang@mail.shcnc.ac.cn (Y. Zang), jli@mail.shcnc.ac.cn (J. Li).
Biochemical and Biophysical Research Communications 416 (2011) 172–177
Contents lists available at SciVerse ScienceDirect
Biochemical and Biophysical Research Communications
journal homepage: www.elsevier.com/locate/ybbrc