Bcl-X
L
mediates epidermal growth factor dependent cell survival in HC11 mammary
epithelial cells
Leonardo Romorini
a,c
, Omar A. Coso
b,c
, Adali Pecci
a,c,
⁎
a
Departamento de Química Biológica, Universidad de Buenos Aires, Buenos Aires, Argentina
b
Departamento de Fisiología, Biología Molecular y Celular, Universidad de Buenos Aires, Buenos Aires, Argentina
c
IFIBYNE-CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina
abstractarticle info
Article history:
Received 29 July 2008
Received in revised form 18 November 2008
Accepted 2 December 2008
Available online 11 December 2008
Keywords:
Mammary epithelial cell
Apoptosis
EGF
MAPKs
Bcl-XL
Bad
Apoptosis is the predominant process controlling cell deletion during post-lactational mammary gland
remodeling. The members of the Bcl-2 protein family, whose expression levels are under the control of
lactogenic hormones, internally control this mechanism. Epidermal growth factor (EGF) belongs to a family of
proteins that act as survival factors for mammary epithelial cells upon binding to specific membrane tyrosine
kinase receptors. Expression of EGF peaks during lactation and dramatically decreases in the involuting
mammary gland. Though it was suggested that the protective effect of EGF is mediated through the
phosphatidylinositol-3-kinase (PI3K) or MEK/ERK kinases activities, little is known about the downstream
mechanisms involved on the anti-apoptotic effect of EGF on mammary epithelial cells; particularly the identity
of target genes controlling apoptosis. Here, we focused on the effect of EGF on the survival of mammary
epithelial cells. We particularly aimed at the characterization of the signaling pathways that were triggered by
this growth factor, impinge upon expression of Bcl-2 family members and therefore have an impact on the
regulation of cell survival. We demonstrate that EGF provokes the induction of the anti-apoptotic isoform Bcl-
X
L
and the phosphorylation and down-regulation of the pro-apoptotic protein Bad. The activation of JNK and
PI3K/AKT signaling pathways promotes the induction of Bcl-X
L
while AKT activation also leads to Bad
phosphorylation and down-regulation. This protective effect of EGF correlates mainly with the up-regulation of
Bcl-X
L
than with the down-regulation of Bad. In fact, HC11 cells unable to express bcl-X, die even in the presence
of EGF. In this context, Bcl-X
L
emerges as a key anti-apoptotic molecule critical for mediating EGF cell survival.
© 2008 Elsevier B.V. All rights reserved.
1. Introduction
Apoptosis is a tightly regulated and highly efficient process. It
occurs throughout the development and growth of the mammary
gland, as was described by several authors. The most dramatic
changes due to programmed cell death occur during post-lactational
involution, when the glandular secretory tissue of the lactating
mammary gland is remodeled [1–3]. Particularly, it has been reported
that 72 h involuting glands show reduced size, low milk content, and a
restructured tissue organization with high amounts of dead cells and
the presence of immune infiltrates.
Apoptosis can be triggered by diverse stimuli that ignite signals
converging into a common cell death machinery. This process is
controlled at several intracellular check points. One of these is mainly
regulated by different members of the Bcl-2 family, which can play
opposite functions on programmed cell death. This family of proteins
is defined by the presence of up to four conserved motifs known as
Bcl-2 homology domains (BH1–BH4). In addition to Bcl-2, a number of
other proteins like Bcl-X
L
, Bcl-w and Mcl1, have an anti-apoptotic
effect. On the other hand, the members of the pro-apoptotic group can
be divided into two subgroups: the Bax-subfamily consisting mainly of
Bax and Bak, which contain domains BH1, BH2 and BH3 and the
members of the BH3-only subfamily, which possess only the BH3
motif, like Bad, Bid, Bim, etc. [4].
Mammary gland tissue expresses a number of different Bcl-2
relatives including Bcl-X (the most abundant), Bax, Bak, Bad, Bcl-w,
Bfl-1 and Bcl-2 [5,6]. These proteins play a critical role in the control of
apoptosis in the mammary epithelium and their expression levels are
under the control of lactogenic hormones. While Bcl-2 is expressed in
the nonpregnant and early pregnancy mammary gland, the expression
of Bax remains high during pregnancy, is down-regulated during
lactation, and is again up-regulated at the start of involution [5]. In this
sense, stimulation of bcl-2 expression and suppression of bax, were
suggested as key events in the anti-apoptotic action of prolactin in
mammary epithelial cells [7,8]. On the other hand, Bak, Bad, Bcl-w, and
Bfl-1 are also up-regulated during involution [5].
The activity of some members of the Bcl-2 family may also be
regulated by phosphorylation. In particular, phosphorylation of Bad on
residues Ser-112, Ser-136, Ser-155 and Ser-170 promotes its binding to
14-3-3 proteins, and its subsequent cytosolic sequestration. Importantly,
Biochimica et Biophysica Acta 1793 (2009) 496–505
⁎ Corresponding author. Departamento de Química Biológica, Universidad de Buenos
Aires, Buenos Aires, Argentina. Tel./fax: +54 11 4576 3342.
E-mail address: apecci@qb.fcen.uba.ar (A. Pecci).
0167-4889/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.bbamcr.2008.12.002
Contents lists available at ScienceDirect
Biochimica et Biophysica Acta
journal homepage: www.elsevier.com/locate/bbamcr