First name
Carolina
Last name
D'Alesio
Year of Study
Research Center
Thesis Title
Identification of novel epigenetic targets that sustain breast cancer growth
Thesis Abstract
Breast cancer is the second leading cause of tumor-related death in women, mainly due to
resistance to first line therapy, high risk of relapse and metastatic dissemination. Breast
cancer is a highly heterogeneous disease, which displays diverse biological
characteristics, clinical behaviour and prognosis. For these reasons, it has become
challenging the identification and characterization of novel genes responsible for breast
cancer initiation and progression. To identify new targets that sustain breast cancer
growth, we performed in vivo and in vitro shRNA screens in a human breast cancer cell
model. We screened two libraries targeting several chromatin remodeling enzymes
(around 200 in total), which are essential genes in breast cancer maintenance and
represent optimal druggable candidates. We identified approximately 70 genes that were
depleted in our screens, and among them, we selected five hits to validate the screens.
Remarkably, the silencing of each target gene significantly reduced tumor growth in vivo
and decreased proliferation, colony formation and migration in vitro, thus validating our
screens.
We deeply investigated the Chromodomain Helicase DNA binding Domain 4 (CHD4)
gene, whose silencing in breast cancer cells greatly reduces tumor growth, but does not
affect normal mammary epithelial proliferation and migration. We examined the role of
CHD4 in primary cells derived from spontaneous mammary tumors of MMTV/NeuT
transgenic mice. Upon CHD4 depletion, we confirmed a significant decrease of tumor
growth in vivo and cell proliferation and migration in vitro. Intriguingly, we demonstrated
that CHD4 silencing reduced tumor growth in vivo in a patient-derived xenopatient (PDX)
model of Luminal B drug-resistant breast carcinoma.
Moreover, we investigated the mechanism through which CHD4 promotes breast cancer
cell proliferation and we showed that CHD4 regulates cell cycle progression of breast
cancer cells. CHD4 depletion provokes a consistent accumulation of cells in the G0/G1
phase and a strong reduction of the S phase of the cell cycle, and an upregulation of p21.
In summary, RNAi screens allowed us to identify CHD4 as a critical target that sustains
human breast cancer. Importantly, we showed that CHD4 modulation does not modify
normal mammary cell proliferation and migration, suggesting that its targeting in tumor
cells might not impact on the surrounding normal tissues. Moreover, CHD4 is crucial in
almost any subtype of breast cancer, as shown by its effect on MMTV/NeuT and PDX
tumorigenesis. Finally, we demonstrated that CHD4 is a key regulator of breast cancer cell
cycle.
resistance to first line therapy, high risk of relapse and metastatic dissemination. Breast
cancer is a highly heterogeneous disease, which displays diverse biological
characteristics, clinical behaviour and prognosis. For these reasons, it has become
challenging the identification and characterization of novel genes responsible for breast
cancer initiation and progression. To identify new targets that sustain breast cancer
growth, we performed in vivo and in vitro shRNA screens in a human breast cancer cell
model. We screened two libraries targeting several chromatin remodeling enzymes
(around 200 in total), which are essential genes in breast cancer maintenance and
represent optimal druggable candidates. We identified approximately 70 genes that were
depleted in our screens, and among them, we selected five hits to validate the screens.
Remarkably, the silencing of each target gene significantly reduced tumor growth in vivo
and decreased proliferation, colony formation and migration in vitro, thus validating our
screens.
We deeply investigated the Chromodomain Helicase DNA binding Domain 4 (CHD4)
gene, whose silencing in breast cancer cells greatly reduces tumor growth, but does not
affect normal mammary epithelial proliferation and migration. We examined the role of
CHD4 in primary cells derived from spontaneous mammary tumors of MMTV/NeuT
transgenic mice. Upon CHD4 depletion, we confirmed a significant decrease of tumor
growth in vivo and cell proliferation and migration in vitro. Intriguingly, we demonstrated
that CHD4 silencing reduced tumor growth in vivo in a patient-derived xenopatient (PDX)
model of Luminal B drug-resistant breast carcinoma.
Moreover, we investigated the mechanism through which CHD4 promotes breast cancer
cell proliferation and we showed that CHD4 regulates cell cycle progression of breast
cancer cells. CHD4 depletion provokes a consistent accumulation of cells in the G0/G1
phase and a strong reduction of the S phase of the cell cycle, and an upregulation of p21.
In summary, RNAi screens allowed us to identify CHD4 as a critical target that sustains
human breast cancer. Importantly, we showed that CHD4 modulation does not modify
normal mammary cell proliferation and migration, suggesting that its targeting in tumor
cells might not impact on the surrounding normal tissues. Moreover, CHD4 is crucial in
almost any subtype of breast cancer, as shown by its effect on MMTV/NeuT and PDX
tumorigenesis. Finally, we demonstrated that CHD4 is a key regulator of breast cancer cell
cycle.
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