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Q. Gao's Lab
Qingshen Gao, M.D. Assistant Professor
q-gao@northwestern.edu, Phone: 224.364.7531, Fax: 224.364.7402
Recent Publications:
Journal of Cell Biology 2005 in press
Centrobin: a novel daughter centriole-associated protein that is required for centriole duplication
Chaozhong Zou, Jun Li, Yujie Bai, William T. Gunning, David E. Wazer, Vimla Band, Qingshen Gao
In mammalian cells the centrosome consists of a pair of centrioles and amorphous pericentriolar material. The pair of centrioles, which is the core component of centrosomes, duplicates once per cell cycle. Centrosomes play a pivotal role in orchestrating formation of the bipolar spindle during mitosis. Recent studies have linked centrosomal activity on centrioles or centriole-associated structures to cytokinesis and cell cycle progression through G1 into the S phase. In this study, we have identified centrobin as a centriole-associated protein, which asymmetrically localizes to the daughter centriole. Silencing of centrobin expression by siRNA inhibited centriole duplication and resulted in centrosomes with one or no centriole, demonstrating that centrobin is required for centriole duplication. Furthermore, inhibition of centriole duplication by centrobin depletion led to impaired cytokinesis.
Cancer Res. 2005 Jun 1;65(11):4747-53. | Abstract | PDF
BRCA2 Suppresses Cell Proliferation via Stabilizing MAGE-D1
Xin-xia Tian, Deepak Rai, Jun Li, Chaozhong Zou, Yujie Bai, David Wazer, Vimla Band and Qingshen Gao
Here we found that BRCA2 binds and stabilizes MAGE-D1, a member of the MAGE gene family of proteins. Expression of BRCA2 and MAGE-D1 synergistically suppresses cell proliferation independently of the p53 pathway. Using two MAGE-D1 RNA interferences and two cell lines expressing low or undetectable levels of MAGE-D1, we further showed that the expression of MAGE-D1 is required for BRCA2-mediated suppression of cell proliferation, indicating that MAGE-D1 is a downstream target of BRCA2 and that BRCA2 suppresses cell proliferation via stabilizing MAGE-D1. Importantly, MAGE-D1 protein expression was reduced in 6 of 16 breast carcinoma cell lines tested as compared with untransformed immortal mammary epithelial cell lines, suggesting that suppression of MAGE-D1 expression may be involved in the tumorigenesis of a subset of sporadic breast cancers.
Oncogene; October 3, 2005 | Abstract | PDF
DSS1 is required for the stability of BRCA2
Jun Li, Chaozhong Zou, Yujie Bai, David Wazer, Vimla Band and Qingshen Gao
Here, we developed a modified Western blotting protocol that detects endogenous DSS1 protein, and used it to study the function of DSS1 and its interaction with BRCA2 in mammalian cells. We found that essentially all BRCA2 in human cell lines is associated with DSS1. Importantly, we found that RNAi knockdown of DSS1 in human cell lines led to dramatic loss of BRCA2 protein, mainly due to its increased degradation. Furthermore, the stability of BRCA2 mutant devoid of the DSS1-binding domain is unaffected by the depletion of DSS1. Most notably, like BRCA2 depletion, DSS1 depletion also led to hypersensitivity to DNA damage. These results demonstrated that the stability of BRCA2 protein in mammalian cells depends on the presence of DSS1. Deletion or mutation of DSS1 or suppression of its expression by other mechanisms are therefore potential causative mechanisms for human breast and ovarian cancer. Such mechanisms may be relevant to sporadic as well as familiar breast cancer where BRCA1 and BRCA2 mutations are not present.
Research Focus:
My research focuses on studying the BRCA2 functions in mammary epithelial biology and carcinogenesis. It has been estimated that BRCA2 accounts for 30 percent of hereditary breast cancers. Recent studies indicate that BRCA2 plays a role in DNA double strand break repair, G2/M checkpoint control, regulation of transcription and regulation of centrosome duplication. However, how BRCA2 functions in these pathways and how BRCA2 germline mutations lead specifically to the development of breast cancer remains undefined.
Dissect the BRCA2 pathway. As BRCA2 is an enormous protein, it is conceivable that there are more proteins with which BRCA2 interacts than previously identified. Identifying the proteins that form complexes with BRCA2 will provide important insight into the function of BRCA2. Using three C-terminal fragments of BRCA2 as baits, numerous novel BRCA2 binding proteins have been identified using yeast two hybrid screen. Characterization of these binding proteins should provide important insight into the function pathway of BRCA2.
Determine the susceptibility of BRCA2 Heterozygous Normal Mammary Epithelial Cells to Radiation Induced Transformation. In addition to surgery and systemic therapy, radiation therapy is one of the most important components of breast cancer management. Lumpectomy and radiation therapy remains a standard of care option for the majority of patients with early stage breast cancer. It is estimated that about 40-60% breast cancer patients with early stage disease will undergo radiation treatment. However, development of radiation-induced secondary malignancy after successful radiotherapy of a prior cancer has been well documented. It is generally accepted among radiation oncologists that, for most patients, this is an unavoidable complication. However, for specific population of patients such as BRCA2 germline mutation carriers, the risk of radiation induced secondary breast cancer warrants further investigation.
Since BRCA2 plays important roles in the DNA damage response, it is reasonable to hypothesize that radiation treatment of breast cancer patients who inherit one defective copy of the BRCA2 gene may pose greater risk of radiation-induced secondary cancer. The BRCA2 knock out mouse models have very limited value to ratify this hypothesis, since transformation of murine cells is significantly different from that of human cells. Clinical study is hindered by small number of patients with documented BRCA2 status, long term follow up, and interference of multigenic effects. One pair of normal human mammary epithelial cell strains with identical genetic background and different BRCA2 status will be an ideal system to assess the susceptibility of BRCA2 heterozygous normal human mammary epithelial cells to radiation induced transformation.
We are in the process of generating a normal human mammary epithelial cell strain with one allele of BRCA2 disrupted by targeted recombination. And we will examine the susceptibility of BRCA2 +/- human mammary epithelial cells and their parental cells to radiation-induced transformation.
Publications:
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BRCA2 suppresses cell proliferation via stabilizing MAGE-D1. |
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Meng G, Zhao Y, Nag A, Zeng M, Dimri G, Gao Q, Wazer DE, Kumar R, Band H, Band V. |
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Human ADA3 binds to estrogen receptor (ER) and functions as a coactivator for ER-mediated transactivation. |
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Singh L, Gao Q, Kumar A, Gotoh T, Wazer DE, Band H, Feig LA, Band V. |
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The high-risk human papillomavirus type 16 E6 counters the GAP function of E6TP1 toward small Rap G proteins. |
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Zeng M, Kumar A, Meng G, Gao Q, Dimri G, Wazer D, Band H, Band V. |
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Human papilloma virus 16 E6 oncoprotein inhibits retinoic X receptor-mediated transactivation by targeting human ADA3 coactivator. |
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Human papillomavirus oncoprotein E6 inactivates the transcriptional coactivator human ADA3. |
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Gao Q, Kumar A, Singh L, Huibregtse JM, Beaudenon S, Srinivasan S, Wazer DE, Band H, Band V. |
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Human papillomavirus E6-induced degradation of E6TP1 is mediated by E6AP ubiquitin ligase. |
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Human papillomavirus type 16 E6-induced degradation of E6TP1 correlates with its ability to immortalize human mammary epithelial cells. |
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Multiple genetic changes are required for efficient immortalization of different subtypes of normal human mammary epithelial cells. |
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Gao Q, Kumar A, Srinivasan S, Singh L, Mukai H, Ono Y, Wazer DE, Band V. |
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PKN binds and phosphorylates human papillomavirus E6 oncoprotein. |
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Liu Y, Chen JJ, Gao Q, Dalal S, Hong Y, Mansur CP, Band V, Androphy EJ. |
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Multiple functions of human papillomavirus type 16 E6 contribute to the immortalization of mammary epithelial cells. |
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The E6 oncoproteins of high-risk papillomaviruses bind to a novel putative GAP protein, E6TP1, and target it for degradation. |
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Abrogation of wild-type p53-mediated transactivation is insufficient for mutant p53-induced immortalization of normal human mammary epithelial cells. |
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Mutant p53-induced immortalization of primary human mammary epithelial cells. |
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Mutational analysis of human papillomavirus type 16 E6 demonstrates that p53 degradation is necessary for immortalization of mammary epithelial cells. |
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Immortalization of distinct human mammary epithelial cell types by human papilloma virus 16 E6 or E7. |
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Tumor cell-specific loss of p53 protein in a unique in vitro model of human breast tumor progression. |
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Loss of p53 protein during radiation transformation of primary human mammary epithelial cells. |
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Synthesis of DNA, rRNA, and protein by Rickettsia prowazekii growing in untreated or gamma interferon-treated mouse L929 cells. |
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