First name
Lucia
Last name
Casoli
Year of Study
Research Center
Thesis Title
Myc-dependent transcriptional programs in mammary epithelial cells
Thesis Abstract
The transcriptional programs governing the decision of mammary epithelial
stem and progenitor cells to self-renew or differentiate are still not completely
outlined. Previous evidences pointed out the role of Myc, and in particular of
its repressive activity with Miz1, in these processes. Since the presence of
stem-like cells within the tumor, the so-called cancer stem cells (CSCs), is
now considered crucial for tumor initiation and maintenance, clarifying this
aspect of Myc biology could be relevant in understanding its contribution to
the genesis of breast cancer. Here, we used RNA-seq technology to profile
the transcriptional programs regulated by Myc in two different settings. First,
we studied immortalized mammary epithelial cells, in which we induced either
Myc loss or gain of function. In this setting, Myc contributed to the positive and
negative regulation of different sets of genes. Activated genes are involved in
proliferation, metabolism, ribosomal biogenesis, mitochondrial organization,
chromatin modification, RNA processing and modification. Repressed genes,
on the other hand, were mainly involved in lysosome and vesicle-mediated
transport, angiogenesis, cell death, extracellular matrix interaction, cell
adhesion regulation, epithelial development and morphogenesis. Second, we
studied the effect of Myc activation in mammosphere cultures, which provide
a measure of stem cell activity. We demonstrate that Myc, when
overexpressed, is able to promote self-renewal of mammary epithelial stem
cells, as assessed by increased mammosphere expansion, and confirmed by
mammary gland reconstitution assays in vivo. This activity of Myc is in part
dependent on the interaction with the co-repressor protein Miz1, since the
Myc mutant V394D (hereby Myc VD), impaired in Miz1 binding, is defective in
promoting self-renewal. Overexpression of Myc in mammospheres was
associated with the de-regulated expression of about three thousand genes,
with similar numbers of up- and down-regulated genes. A group of around
nine hundred genes was specifically repressed by Myc WT and not by the VD
mutant. Surprisingly, the overlap between the groups of regulated genes in
those mammary epithelial cells in adhesion or grown as mammospheres was
limited, illustrating the context-dependency of Myc-dependent responses.
Thus, transcriptional repression via Miz1 may constitute one of the
mechanisms through which Myc sustains mammary epithelial cell selfrenewal.
We are currently setting a functional screen, among genes
repressed in a Miz1-dependent manner, to identify those that are critical in
this process. Our study shall shed light on the mechanisms through which
Myc regulates self-renewal in mammary epithelial stem and progenitor cells.
Understanding this could be crucial in order to clarify the physiopathological
roles of Myc in the mammary gland.
stem and progenitor cells to self-renew or differentiate are still not completely
outlined. Previous evidences pointed out the role of Myc, and in particular of
its repressive activity with Miz1, in these processes. Since the presence of
stem-like cells within the tumor, the so-called cancer stem cells (CSCs), is
now considered crucial for tumor initiation and maintenance, clarifying this
aspect of Myc biology could be relevant in understanding its contribution to
the genesis of breast cancer. Here, we used RNA-seq technology to profile
the transcriptional programs regulated by Myc in two different settings. First,
we studied immortalized mammary epithelial cells, in which we induced either
Myc loss or gain of function. In this setting, Myc contributed to the positive and
negative regulation of different sets of genes. Activated genes are involved in
proliferation, metabolism, ribosomal biogenesis, mitochondrial organization,
chromatin modification, RNA processing and modification. Repressed genes,
on the other hand, were mainly involved in lysosome and vesicle-mediated
transport, angiogenesis, cell death, extracellular matrix interaction, cell
adhesion regulation, epithelial development and morphogenesis. Second, we
studied the effect of Myc activation in mammosphere cultures, which provide
a measure of stem cell activity. We demonstrate that Myc, when
overexpressed, is able to promote self-renewal of mammary epithelial stem
cells, as assessed by increased mammosphere expansion, and confirmed by
mammary gland reconstitution assays in vivo. This activity of Myc is in part
dependent on the interaction with the co-repressor protein Miz1, since the
Myc mutant V394D (hereby Myc VD), impaired in Miz1 binding, is defective in
promoting self-renewal. Overexpression of Myc in mammospheres was
associated with the de-regulated expression of about three thousand genes,
with similar numbers of up- and down-regulated genes. A group of around
nine hundred genes was specifically repressed by Myc WT and not by the VD
mutant. Surprisingly, the overlap between the groups of regulated genes in
those mammary epithelial cells in adhesion or grown as mammospheres was
limited, illustrating the context-dependency of Myc-dependent responses.
Thus, transcriptional repression via Miz1 may constitute one of the
mechanisms through which Myc sustains mammary epithelial cell selfrenewal.
We are currently setting a functional screen, among genes
repressed in a Miz1-dependent manner, to identify those that are critical in
this process. Our study shall shed light on the mechanisms through which
Myc regulates self-renewal in mammary epithelial stem and progenitor cells.
Understanding this could be crucial in order to clarify the physiopathological
roles of Myc in the mammary gland.
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