Biomedical subjects

Xiao Zeng

Publications and source records attributed to Xiao Zeng.

7 recordsLinked to original sources

PubMed2006

Chronic restraint stress modulates expression of genes in murine spleen.

Psychological and physical stress can alter the immune system in both humans and animals. We have reported that mice subjected to chronic 12-h daily physical restraint for 2 days showed dramatic apoptosis in splenocytes. To identify genes that contribute to the splenocyte apoptosis, we compare gene expression in the spleens of restrained and unstressed mice using oligo microarrays consisting of 226 genes. We report here that mice subjected to chronic 12-h daily physical restraint for 2 days exhibited significantly altered expression of 50 of 226 genes. These genes included pro-apoptotic genes. We selected 5 genes of interest and confirmed the microarray results by real-time PCR. In this study, we identify a potentially important component of pro-apoptotic activity in restraint stress and suggest a possible target for anti-apoptotic therapy to protect splenocytes against stress-induced apoptosis.

Adaptor Proteins, Signal Transducing↗

PubMed2006

Differential roles of phosphoinositide-dependent protein kinase-1 and akt1 expression and phosphorylation in breast cancer cell resistance to Paclitaxel, Doxorubicin, and gemcitabine.

3-Phosphoinositide-dependent protein kinase-1 (PDK1) and Akt1 are two closely related components of the phosphatidylinositol-3 kinase (PI3K) pathway, which is aberrantly regulated in breast cancer. Despite the importance of PDK1, few studies have evaluated it as a potential target for cancer therapy compared with studies of Akt1. We hypothesized that PDK1 is a superior target in the PI3K pathway. To test this, we first used a mouse mammary cell line retrovirally infected to express human PDK1 or Akt1 for comparative studies of treatment with paclitaxel, doxorubicin, and gemcitabine. Overexpression of PDK1 or Akt1 conferred similar resistance to treatment with paclitaxel or doxorubicin compared with control cells. However, the PDK1-overexpressing cells were more resistant to gemcitabine than were the Akt1-overexpressing cells. We next correlated the expression and activation-specific phosphorylation of PDK1 and Akt1 with the cytotoxic effects of the same agents in several human breast cancer cell lines. Cells with high levels of phosphorylated PDK1 were more resistant to gemcitabine-induced apoptosis than cells expressing high levels of phosphorylated Akt1. To further validate this observation, we used small interfering RNA oligonucleotides to selectively knock down PDK1 or Akt1 expression in MCF7 human breast cancer cells. We found that knockdown of PDK1 expression sensitized MCF7 cells to gemcitabine-induced apoptosis more effectively than did knockdown of Akt1 expression in the same cells. Our findings show that PDK1 may be a superior alternative to Akt1 as a target for sensitizing breast cancer cells to chemotherapeutic agents, particularly gemcitabine.

3-Phosphoinositide-Dependent Protein Kinases↗

PubMed2006

3-phosphoinositide-dependent protein kinase-1 (PDK1) promotes invasion and activation of matrix metalloproteinases.

BACKGROUND: Metastasis is a major cause of morbidity and mortality in breast cancer with tumor cell invasion playing a crucial role in the metastatic process. PDK1 is a key molecule that couples PI3K to cell proliferation and survival signals in response to growth factor receptor activation, and is oncogenic when expressed in mouse mammary epithelial cells. We now present evidence showing that PDK1-expressing cells exhibit enhanced anchorage-dependent and -independent cell growth and are highly invasive when grown on Matrigel. These properties correlate with induction of MMP-2 activity, increased MT1-MMP expression and a unique gene expression profile. METHODS: Invasion assays in Matrigel, MMP-2 zymogram analysis, gene microarray analysis and mammary isografts were used to characterize the invasive and proliferative function of cells expressing PDK1. Tissue microarray analysis of human breast cancers was used to measure PDK1 expression in invasive tumors by IHC. RESULTS: Enhanced invasion on Matrigel in PDK1-expressing cells was accompanied by increased MMP-2 activity resulting from stabilization against proteasomal degradation. Increased MMP-2 activity was accompanied by elevated levels of MT1-MMP, which is involved in generating active MMP-2. Gene microarray analysis identified increased expression of the ECM-associated genes decorin and type I procollagen, whose gene products are substrates of MT1-MMP. Mammary fat pad isografts of PDK1-expressing cells produced invasive adenocarcinomas. Tissue microarray analysis of human invasive breast cancer indicated that PDK1pSer241 was strongly expressed in 90% of samples. CONCLUSION: These results indicate that PDK1 serves as an important effector of mammary epithelial cell growth and invasion in the transformed phenotype. PDK1 mediates its effect in part by MT1-MMP induction, which in turn activates MMP-2 and modulates the ECM proteins decorin and collagen. The presence of increased PDK1 expression in the majority of invasive breast cancers suggests its importance in the metastatic process.

3-Phosphoinositide-Dependent Protein Kinases↗

PubMed2005

cDNA expression profiling reveals elevated gene expression in cell clusters overlying focally disrupted myoepithelial cell layers: implications for breast tumor invasion.

BACKGROUND: Our previous studies revealed that a subset of mammary ductal carcinoma in situ (DCIS) contained focally disrupted myoepithelial (ME) cell layers that were predominantly overlain by estrogen receptor (ER) negative cells, which showed a substantially higher rate of cell proliferation and genetic alterations than adjacent ER positive cells within the same duct. This study attempted to assess whether these cells also had a different expression profile on tumor progression related genes. DESIGN: Consecutive sections were made from frozen tissues of 30 DCIS with focally disrupted ME cell layers and associated ER negative cell clusters. ER negative and adjacent ER positive cells within the same duct were microdissected for RNA extraction and amplification. Amplified RNA was converted to biotin-labeled cDNAs and interrogated with 'Cancer PathwayFinder' arrays. RESULTS: Cells within each or among ER negative clusters were immunohistochemically and morphologically similar, whereas they differed substantially from adjacent cells within the same duct. Of 20-paired informative ER negative and positive cells, 15 genes were differentially expressed. Of which, 11(73.3%) were higher in ER negative, 2 (13.3%) were higher in ER positive, and 2 (13.3%) were equal in these cells (p <0.01). Of 11 up-regulated genes in ER negative cells, 8 indirectly or directly promote proliferation and progression, and 3 promote apoptosis. CONCLUSION: ER negative cell clusters showed a significantly higher expressing frequency of multiple tumor progression related genes than their adjacent ER positive counterparts, suggesting that they are likely to be biologically more aggressive and have a greater potential for invasion.

Breast Neoplasms↗

PubMed2003

Transformation of mammary epithelial cells by 3-phosphoinositide- dependent protein kinase-1 activates beta-catenin and c-Myc, and down-regulates caveolin-1.

3-phosphoinositide-dependent protein kinase-1 (PDK1) plays a pivotal role in coupling growth factor receptor signaling to tumor cell proliferation, survival, and invasion. Protein kinase C (PKC) alpha, but not Akt1, was found previously to be downstream of PDK1-mediated transformation of mammary epithelial cells. To determine the basis for its oncogenic activity, signal transduction pathways mediated by PDK1 in mammary epithelial cells were investigated. beta-Catenin/T-cell factor-dependent promoter activity was markedly activated in PDK1- and PKCalpha-expressing cells, but not in Akt1-expressing cells, which resulted in increased levels of the beta-catenin/T-cell factor target genes c-myc and cyclin D1. In contrast, caveolin-1, of which the transcription is suppressed by c-myc, was down-regulated in PDK1- and PKCalpha-expressing, but not in Akt1-expressing cells. Analysis of 16 breast cancer cell lines established that caveolin-1 expression was either absent or reduced compared with breast epithelial cells, and that PDK1 was elevated in all of the cell lines. Interestingly, all of the cell lines known to be invasive expressed caveolin-1 to some degree, whereas, 5 of 6 cell lines that are not invasive did not express caveolin-1. Therefore, it appears that a concomitant gain of c-myc function and a loss or reduction of caveolin-1 are major determinants of PDK1- and PKCalpha-mediated mammary oncogenesis.

3-Phosphoinositide-Dependent Protein Kinases↗

PubMed2003

Hypomutable regions of yeast TFIIB in a unigenic evolution test represent structural domains.

As genome sequences of many organisms - including humans - are being decoded, there is a great need for genetic tools to analyze newly discovered genes/proteins. A 'unigenic evolution' approach has been previously proposed for dissecting protein domains, which is based on the assumption that functionally important regions of a protein may tolerate missense mutations less well than other regions. We describe a unigenic evolution analysis of general transcription factor IIB (TFIIB) - a protein that is well characterized both structurally and functionally - to better understand the molecular basis of this genetic approach. The overall distribution profile of hypomutable regions within yeast TFIIB correlates extremely well with the known compact structural domains, suggesting that the unigenic evolution approach can help reveal structural properties of a protein. We further show that a small region located immediately carboxyl-terminal to the zinc ribbon motif is functionally important despite its strong hypermutability. Our study further demonstrates the usefulness of the unigenic evolution approach in dissecting protein domains, but suggests that the mutability of different regions of a protein in such a test is determined primarily by their structural properties.

Amino Acid Sequence↗

PubMed2002

Transformation of mammary epithelial cells by 3-phosphoinositide-dependent protein kinase-1 (PDK1) is associated with the induction of protein kinase Calpha.

3-Phosphoinositide-dependent protein kinase 1 (PDK1) is a mediator of multiple signaling pathways coupled to growth factor receptor activation in human cancers. To evaluate the role of PDK1 in mammary gland oncogenesis, COMMA-1D mouse mammary epithelial cells were retrovirally transduced with PDK1, and transformation was measured by anchorage-independent growth in soft agar. PDK1-expressing cells exhibited a high degree of transformation that was associated with the activation of Akt1 and an elevation of protein kinase Calpha (PKCalpha) expression. Cells overexpressing Akt1 did not exhibit anchorage-independent growth, whereas PKCalpha overexpression produced significant transformation, although to a lesser extent compared with PDK1. Coexpression of Akt1 and PKCalpha led to a more than additive effect on transformation activity. Isografts of either PDK1- or PKCalpha-expressing cells but not Akt1-expressing cells in syngeneic mice led to formation of poorly differentiated mammary carcinomas. PDK1 was highly expressed in a majority of human breast cancer cell lines. These results suggest that activation of PDK1 can lead to mammary tumorigenesis, in part through PKCalpha, and that PDK1 expression may be an important target in human breast cancer.

3-Phosphoinositide-Dependent Protein Kinases↗