Colorectal cancer is the second leading cause of cancer-related deaths in the United States with 112,000 new cases diagnosed per year and approximately 52,000 deaths estimated in 2007. Dysregulation of Akt and protein kinase C (PKC) contributes to tumorigenesis by promoting cell proliferation and inhibiting apoptosis. The signaling activation process of Akt and PKC has been studied in great detail. However, little is known about how the signals are turned off once activated. Recently, we have identified a family of novel protein phosphatases, PHLPP (PH domain Leucine-rich-repeats Protein Phosphatase) that directly dephosphorylates Akt and PKC. However, the role of PHLPP in cancer has not been defined. In the preliminary studies, we found that loss of PHLPP expression occurs with high frequency in human colorectal cancer specimens. Furthermore, our studies have suggested that PHLPP plays a role in regulating cell polarity. In light of our findings, the central hypothesis driving this proposal is that PHLPP serves as a tumor suppressor by regulating cell polarity in addition to its ability of turning off the growth signaling activated by Akt and PKC. The long-term goal of our studies is to better understand the physiological role of PHLPP and its contribution to colon cancer development and progression in vivo.
The Specific Aims are:
Aim 1 : To define the molecular mechanism of PHLPP downregulation. The goal of this aim is to investigate the potential mechanism leading to PHLPP downregulation in cancer. We will test the hypothesis that the expression level of PHLPP is controlled by the ubiquitin proteasome pathway in cells, and preventing PHLPP degradation leads to upregulation of the protein.
Aim 2 : To determine the role PHLPP in maintaining cell polarity. We hypothesize that PHLPP exerts its function as a tumor suppressor by regulating cell polarity and cell growth. The functional effect of PHLPP on establishing epithelial cell polarity will be determined. To elucidate the underlying mechanism, we will test the hypothesis that PHLPP is required for epithelial junction formation by modulating PKC activity via binding to the polarity protein Scribble.
Aim 3 : To delineate the role of PHLPP in tumorigenesis in vivo. The hypothesis driving this aim is that loss of PHLPP expression contributes to the initiation and progression of colorectal tumors. We will address the question whether there is an increase of tumor incidence when PHLPP is knocked out, both basally and in combination with other carcinogenic factors. Furthermore, we will assess the contribution of altered cell polarity in normal development of gut epithelium and tumor initiation using the knockout mice.

Public Health Relevance

Colorectal cancer is the second leading cause of cancer-related deaths in the United States with 148,000 new cases diagnosed per year and approximately 50,000 deaths estimated in 2007 and, among many contributing factors, aberrant protein phosphorylation resulting from hyperactivation of oncogenic signaling mediated by protein kinases such as Akt and PKC, is a key cause of colorectal cancer. We recently identified a novel protein phosphatase PHLPP that directly dephosphorylates Akt and PKC and terminates the growth signals activated by these kinases. We propose to determine the functional importance of PHLPP as a tumor suppressor in colorectal cancer and the results from this study will provide significant insights into the development of potential cancer therapy using PHLPP as a novel target.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA133429-06
Application #
8495058
Study Section
Molecular Oncogenesis Study Section (MONC)
Program Officer
Yassin, Rihab R,
Project Start
2009-04-01
Project End
2015-02-28
Budget Start
2013-03-01
Budget End
2014-02-28
Support Year
6
Fiscal Year
2013
Total Cost
$245,467
Indirect Cost
$79,833
Name
University of Kentucky
Department
Biochemistry
Type
Schools of Medicine
DUNS #
939017877
City
Lexington
State
KY
Country
United States
Zip Code
40506
Li, Xin; Gao, Tianyan (2014) mTORC2 phosphorylates protein kinase C? to regulate its stability and activity. EMBO Rep 15:191-8
Jiang, Kai; Liu, Yajuan; Fan, Junkai et al. (2014) Hedgehog-regulated atypical PKC promotes phosphorylation and activation of Smoothened and Cubitus interruptus in Drosophila. Proc Natl Acad Sci U S A 111:E4842-50
Li, Xin; Stevens, Payton D; Liu, Jianyu et al. (2014) PHLPP is a negative regulator of RAF1, which reduces colorectal cancer cell motility and prevents tumor progression in mice. Gastroenterology 146:1301-12.e1-10
Zaytseva, Yekaterina Y; Elliott, Victoria A; Rychahou, Piotr et al. (2014) Cancer cell-associated fatty acid synthase activates endothelial cells and promotes angiogenesis in colorectal cancer. Carcinogenesis 35:1341-51
Liu, Jianyu; Stevens, Payton D; Eshleman, Nichole E et al. (2013) Protein phosphatase PPM1G regulates protein translation and cell growth by dephosphorylating 4E binding protein 1 (4E-BP1). J Biol Chem 288:23225-33
Li, X; Stevens, P D; Yang, H et al. (2013) The deubiquitination enzyme USP46 functions as a tumor suppressor by controlling PHLPP-dependent attenuation of Akt signaling in colon cancer. Oncogene 32:471-8
Wen, Yang-An; Stevens, Payton D; Gasser, Michael L et al. (2013) Downregulation of PHLPP expression contributes to hypoxia-induced resistance to chemotherapy in colon cancer cells. Mol Cell Biol 33:4594-605
Gulhati, Pat; Bowen, Kanika A; Liu, Jianyu et al. (2011) mTORC1 and mTORC2 regulate EMT, motility, and metastasis of colorectal cancer via RhoA and Rac1 signaling pathways. Cancer Res 71:3246-56
Ojeda, Luis; Gao, Junling; Hooten, Kristopher G et al. (2011) Critical role of PI3K/Akt/GSK3? in motoneuron specification from human neural stem cells in response to FGF2 and EGF. PLoS One 6:e23414
Liu, Jianyu; Stevens, Payton D; Li, Xin et al. (2011) PHLPP-mediated dephosphorylation of S6K1 inhibits protein translation and cell growth. Mol Cell Biol 31:4917-27

Showing the most recent 10 out of 15 publications