Modulation of TGF-beta Signaling in Mammary Epithelial Cells

Institution: University of California, Irvine
Investigator(s): Xiaoman Xu, B.S. -
Award Cycle: 2005 (Cycle 11) Grant #: 11GB-0143 Award: $73,723
Award Type: Dissertation Award
Research Priorities
Biology of the Breast Cell>Biology of the Normal Breast: the starting point



Initial Award Abstract (2005)

Transforming Growth Factor-beta (TGF-β) strongly inhibits the growth of mammary epithelial cells. Although it has tumor suppressor function, TGF-β can promote invasion and metastases of tumor cells at later stages of breast cancer progression. To develop effective TGF-β based drugs for treatment, it is important to understand the “switch” that converts it from a tumor suppressor to a tumor promoter. LM04, a gene regulatory protein (transcription factor) that our laboratory studies, is highly expressed during development of the mammary gland. Interfering with its function inhibits mammary gland development in mice. LM04 is overexpressed in over half of breast cancer cases, indicating that it may play a cancer-promoting role in breast cancer. We believe that the differential effects of TGF-β on epithelial vs. cancer cell may be regulated by LM04

In preliminary experiments, I have discovered that increasing the expression of LM04 in mammary gland cells enhances the response of the cells to TGF-β. I plan to test whether LM04 can alter TGF-β responses in breast cancer cells and to understand the underlying mechanisms. Next, we will test our hypothesis in the context of a whole animal model, using genetically modified mice. Our work on genetically modified mice will be the most definitive test of the hypothesis that LM04 plays roles in mammary gland development and cancer. This approach is possible, since we have access to mice with mutations in both LM04 and TGF-β

Understanding the relationship between LMO4 and TGF-β will be useful, because TGF-β therapeutics are being developed. The use of whole animal models having genetic defects for these genes is best way to study the processes at the molecular level in a system that most closely mimics the normal breast development.




Final Report (2007)

Transforming Growth Factor-beta (TGFβ ) is a growth factor which strongly inhibits the growth of mammary epithelial cells. Although it has tumor suppressor function, TGß can promote invasion and metastases of tumor cells at later stages of breast cancer progression. To develop effective TGF based drugs for treatment, it is important to understand the switch that converts it from a tumor suppressor to a tumor promoter. LM04, a gene regulatory protein we have been working on, is highly expressed during development of the mammary gland and interfering with its function inhibits mammary gland development in mice. LMO4 is overexpressed in over half of breast cancer cases, indicating that it may play an oncogenic role in breast cancer. LMO proteins function by associating with transcription factors, which are proteins that regulate gene expression. Based on our preliminary work, I proposed that the LMO4 gene may be one of the modulators of TGFβ responsiveness in breast cancer.

First, we tested the ability of LMO4 to modulate biological effects of TGFβ in breast epithelial cells. My studies show that LMO4 affects cell growth by enhancing the inhibitory effect of TGFβ on cell proliferation. Next, we defined how LMO4 modifies the expression of a panel of TGFβ target genes and to understand the mechanism whereby LMO4 alters TGFβ -mediated transcriptional responses. Our results suggest that both upregulation and knockout of LMO4 is capable of enhancing TGFβ -stimulated transcription, indicating that LMO4 regulates the transcriptional response to TGFβ in a biphasic manner. Furthermore, LMO4 can associate with the endogenous TGFβ -responsive Plasminogen Activator Inhibitor (PAI)-1 gene promoter in a TGFβ -dependent manner, which suggests that such interactions may mediate the effects of LMO4 on TGFβ signaling. I also found that BMP7 (Bone morphogenetic protein 7, a member of the TGF-β superfamily of proteins) is a direct target gene of LM04.

Our results define a new function for LMO4 as a co-activator in TGFβ signaling, and provide a potential novel mechanism for LM04-mediated regulation in breast development and breast cancer progression.




Symposium Abstract (2007)
The LIM-only protein 4 (LMO4) transcription factor plays critical roles in mammalian development, and has been proposed to play roles in epithelial oncogenesis, including breast cancer. As LMO4 is highly expressed in the epithelial compartments at locations of active mesenchymal-epithelial interactions, we reasoned that LMO4 might act by modulating pathways involved in mesenchymal-epithelial signaling. One candidate is the transforming growth factor-beta (TGFβ) cytokine pathway, which plays important roles both in development and cancer. Our results show that the transcriptional response to TGFβ in epithelial cells is sensitive to LMO4 levels; both up- and down-regulation of LMO4 can enhance TGFβ signaling as assessed by a TGFβ-responsive reporter gene. Furthermore, LMO4 can interact with the MH1 and linker domains of receptor-mediated Smad proteins, and associate with the endogenous TGFβ-responsive Plasminogen Activator Inhibitor-1 gene promoter in a TGFβ-dependent manner, suggesting that such interactions may mediate the effects of LMO4 on TGFβ signaling. When introduced into mammary epithelial cells, LMO4 potentiated the growth-inhibitory effects of TGFβ. These results define a new function for LMO4 as a co-activator in TGFβ signaling, and provide a potential novel mechanism for LMO4-mediated regulation in development and oncogenesis.

LMO4 can interact with Smad proteins and modulate transforming growth factor-beta signaling in epithelial cells. Oncogene. 2006 May 11;25 (20): 2920-30.
Periodical:Oncogene
Index Medicus: Oncogene
Authors: Lu Z, Lam KS, Wang N, Xu X, Cortes M, Andersen B.
Yr: 2006 Vol: 25 Nbr: Abs: Pg:2920-2930

The LIM-only factor LMO4 regulates expression of the BMP7 gene through an HDAC2-dependent mechanism, and controls cell proliferation and apoptosis of mammary epithelial cells.
Periodical:Oncogene
Index Medicus: Oncogene
Authors: Wang N, Lin KK, Lu Z, Lam KS, Newton R, Xu X, Yu Z, Gill GN, Andersen B
Yr: 2007 Vol: 26 Nbr: 44 Abs: Pg:6431-41