Biomedical subjects

Li Lan

Publications and source records attributed to Li Lan.

31 records · Page 2Linked to original sources

PubMed2005

Downregulation of major histocompatibility complex antigens in invading glioma cells: stealth invasion of the brain.

Invasion into surrounding brain tissue is a fundamental feature of gliomas and the major reason for treatment failure. The process of brain invasion in gliomas is not well understood. Differences in gene expression and/or gene products between invading and noninvading glioma cells may identify potential targets for new therapies. To look for genes associated with glioma invasion, we first employed Affymetrix microarray Genechip technology to identify genes differentially expressed in migrating glioma cells in vitro and in invading glioma cells in vivo using laser capture microdissection. We observed upregulation of a variety of genes, previously reported to be linked to glioma cell migration and invasion. Remarkably, major histocompatiblity complex (MHC) class I and II genes were significantly downregulated in migrating cells in vitro and in invading cells in vivo. Decreased MHC expression was confirmed in migrating glioma cells in vitro using RT-PCR and in invading glioma cells in vivo by immunohistochemical staining of human and murine glioblastomas for beta2 microglobulin, a marker of MHC class I protein expression. To the best of our knowledge, this report is the first to describe the downregulation of MHC class I and II antigens in migrating and invading glioma cells, in vitro and in vivo, respectively. These results suggest that the very process of tumor invasion is associated with decreased expression of MHC antigens allowing glioma cells to invade the surrounding brain in a 'stealth'-like manner.

Animals↗

PubMed2005

Suprabasal induction of ornithine decarboxylase in adult mouse skin is sufficient to activate keratinocytes.

To study the effects of de novo induction of ornithine decarboxylase (ODC) activity in adult, quiescent skin, we generated transgenic mice in which the suprabasal expression of an inducible form of the ODC protein fused to a modified estrogen receptor ligand-binding domain (ODCER) is driven by an involucrin promoter. After topical treatment with the inducing agent 4-hydroxytamoxifen (4OHT), ODC activity and putrescine levels were dramatically increased in the epidermis but not in the dermis of transgenic mice. 4OHT treatment stimulated both proliferation as measured by bromodeoxyuridine incorporation in basal epidermal cells and differentiation shown by increased expression of differentiation markers. Furthermore, induction of ODC activity did not rescue primary epidermal keratinocyte cultures isolated from ODCER2 mice from a calcium-triggered DNA synthesis block, as measured by [3H]thymidine incorporation. In vivo induction of epidermal ODC enzyme activity significantly stimulated the vascularization of ODCER transgenic skin. Increased expression of interleukin-1beta and keratin 6, markers of keratinocyte activation seen in wound healing, was also observed in 4OHT-treated transgenic skin. These results suggest that de novo suprabasal induction of ODC activity in adult mouse skin activates keratinocytes and stimulates vascularization in the dermal layer in a manner similar to skin undergoing wound healing.

Age Factors↗

PubMed2005

Flavopiridol downregulates hypoxia-mediated hypoxia-inducible factor-1alpha expression in human glioma cells by a proteasome-independent pathway: implications for in vivo therapy.

Angiogenesis is a critical step required for sustained tumor growth and tumor progression. The stimulation of endothelial cells by cytokines secreted by tumor cells such as vascular endothelial growth factor (VEGF) induces their proliferation and migration. This is a prominent feature of high-grade gliomas. The secretion of VEGF is greatly upregulated under conditions of hypoxia because of the transcription factor hypoxiainducible factor (HIF)-1alpha, which controls the expression of many genes, allowing rapid adaptation of cells to their hypoxic microenvironment. Flavopiridol, a novel cyclin-dependent kinase inhibitor, has been attributed with antiangiogenic properties in some cancer cell lines by its ability to inhibit VEGF production. Here, we show that flavopiridol treatment of human U87MG and T98G glioma cell lines decreases hypoxia-mediated HIF-1alpha expression, VEGF secretion, and tumor cell migration. These in vitro results correlate with reduced vascularity of intracranial syngeneic GL261 gliomas from animals treated with flavopiridol. In addition, we show that flavopiridol downregulates HIF-1alpha expression in the presence of a proteasome inhibitor, an agent that normally results in the accumulation and overexpression of HIF-1alpha. The potential to downregulate HIF-1alpha expression with flavopiridol treatment in combination with a proteasome inhibitor makes this an extremely attractive anticancer treatment strategy for tumors with high angiogenic activity, such as gliomas.

Animals↗

PubMed2005

[Effects of N-methyl-D-aspartate receptor in visceral, hypersensitivity in rats with colonic inflammation].

OBJECTIVE: To investigate the effects of N-methyl-D-aspartate receptor (NMDAR) in the spinal dorsal horn in visceral hypersensitivity in rats with colonic inflammation. METHODS: Seventy adult male Sprague-Dawley (SD) rats were randomly divided into the experimental group and the control group. Colonic inflammation was induced in the experimental rats by intraluminal administration of trinitrobenzenesulfonic acid (TNBS). Saline was administered intraluminally in the control rats. After 3, 7, 14, and 28 days of administration, abdominal contractions induced by inflation of a balloon colonically inserted were recorded in rats by implanting electrodes in the abdominal striated muscles. Immunohistochemistry method was used to study the expression of NMDAR1 and NMDAR2A/B in lumbarsacral spinal cord after inflammation. RESULTS: Colonic distension evoked a significant increase of abdominal contractions after 3, 7 and 14 days of TNBS administration. After 28 days of TNBS administration, abdominal contractions were still significantly increased in 2 TNBS-treated rats compared with the control rats. After 7 and 14 days of TNBS administration, NMDAR1 and NMDAR2A/B-immunoreactive cells were significantly increased compared with the control group (P <0.05). Twenty-eight days after TNBS administration, the number of NMDAR1-IR and NMDAR2A/B-IR neurons was still significantly increased in 4 TNBS-treated rats compared with the saline-treated rats (P < 0.05). CONCLUSION: NMDAR was involved in the transmission of visceral nociceptive stimuli. After the remission of colonic inflammation, increased expression of NMDAR1 and NMDAR2A/B in the spinal dorsal horn may induce persistent neuronal hyperactivity, which results in visceral hypersensitivity.

Animals↗

PubMed2005

[Effect of antisense survivin RNA transfection on the growth of ovarian carcinoma SKOV3 cells in vitro and in vivo].

OBJECTIVE: To study the inhibition effect of survivin antisense RNA on the growth of ovarian carcinoma SKOV3 cells, and the tumorigenic ability of the transfected SKOV3 cells implanted subcutaneously in nude mice. METHODS: The recombinant vector pcDNA3-SVVas was constructed by directed cloning of fragments of survivin cDNA into the vector. The ovarian carcinoma SKOV3 cells were transfected with pcDNA3-SVVas by lipofectamine 2000 (SKOV3/SVVas cells), and blank vector pcDNA3 as control (SKOV3/neo cells). The effect of survivin antisense RNA on cell growth was assessed by growth curve. The inhibition of expression of endogenous survivin protein and mRNA was evaluated by immunohistochemical stain and RT-PCR. The apoptosis of cells was assessed by flow cytometry. Twenty-four nude mice were divided into three groups, then SKOV3/SVVas, SKOV3/neo and SKOV3 cells were implanted subcutaneously. The growth of tumor was observed and the tumor volume calculated. RESULTS: The expression of survivin significantly decreased in SKOV3/SVVas cells in comparison to that in SKOV3 and SKOV3/neo cells. The growth of the SKOV3/SVVas cells became significantly slower than those of SKOV3 cells and SKOV3/neo cells (P < 0.01). The expression of survivin protein and mRNA in the SKOV3/SVVas cells were (37.5 +/- 1.0)% and 0.407 +/- 0.022 respectively, compared with SKOV3 [(81.2 +/- 0.4)%, 0.793 +/- 0.042] and SKOV3/neo [(80.4 +/- 0.8)%, 0.734 +/- 0.039]. The difference was significant (P < 0.01). After transfected with pcDNA3-SVVas, cells were found apoptosis in early stage by flow cytometry. The apoptosis rate was (27.4 +/- 9.6)%. There was significant difference between SKOV3/SVVas cells and SKOV3 cells, as well as between SKOV3/SVVas and SKOV3/neo cells (P < 0.05). The tumorigenic ability of SKOV3/SVVas cells was reduced. The first time that tumor could be detected in SKOV3/SVVas group, (14.0 +/- 1.0) days was significantly prolonged compared to SKOV3/neo, (6.1 +/- 0.8) days and SKOV3, (5.8 +/- 0.9) days (P < 0.01). In SKOV3/SVVas group, 5 of 8 nude mice were found tumor, the growth rate of tumor was slower compared with the other two groups. When compared in volume, the difference was significant (P < 0.01). CONCLUSIONS: Stable expression of survivin antisense RNA can effectively inhibit the growth of SKOV3 cells and reduce the expression of endogenous survivin proteins and mRNA, induce the apoptosis of cells. Survivin antisense RNA can inhibit the tumorigenesis of SKOV3 cells in nude mice.

Animals↗

PubMed2004

In situ analysis of repair processes for oxidative DNA damage in mammalian cells.

Oxidative DNA damage causes blocks and errors in transcription and replication, leading to cell death and genomic instability. Although repair mechanisms of the damage have been extensively analyzed in vitro, the actual in vivo repair processes remain largely unknown. Here, by irradiation with an UVA laser through a microscope lens, we have conditionally produced single-strand breaks and oxidative base damage at restricted nuclear regions of mammalian cells. We showed, in real time after irradiation by using antibodies and GFP-tagged proteins, rapid and ordered DNA repair processes of oxidative DNA damage in human cells. Furthermore, we characterized repair pathways by using repair-defective mammalian cells and found that DNA polymerase beta accumulated at single-strand breaks and oxidative base damage by means of its 31- and 8-kDa domains, respectively, and that XRCC1 is essential for both polymerase beta-dependent and proliferating cell nuclear antigen-dependent repair pathways of single-strand breaks. Thus, the repair of oxidative DNA damage is based on temporal and functional interactions among various proteins operating at the site of DNA damage in living cells.

Base Sequence↗

PubMed2004

UV light-induced DNA damage and tolerance for the survival of nucleotide excision repair-deficient human cells.

DNA damage can cause cell death unless it is either repaired or tolerated. The precise contributions of repair and tolerance mechanisms to cell survival have not been previously evaluated. Here we have analyzed the cell killing effect of the two major UV light-induced DNA lesions, cyclobutane pyrimidine dimers (CPDs) and 6-4 pyrimidine-pyrimidone photoproducts (6-4PPs), in nucleotide excision repair-deficient human cells by expressing photolyase(s) for light-dependent photorepair of either or both lesions. Immediate repair of the less abundant 6-4PPs enhances the survival rate to a similar extent as the immediate repair of CPDs, indicating that a single 6-4PP lesion is severalfold more toxic than a CPD in the cells. Because UV light-induced DNA damage is not repaired at all in nucleotide excision repair-deficient cells, proliferation of these cells after UV light irradiation must be achieved by tolerance of the damage at replication. We found that RNA interference designed to suppress polymerase zeta activity made the cells more sensitive to UV light. This increase in sensitivity was prevented by photorepair of 6-4PPs but not by photorepair of CPDs, indicating that polymerase zeta is involved in the tolerance of 6-4PPs in human cells.

Blotting, Western↗

PubMed2004

Functional and physical interactions between ERCC1 and MSH2 complexes for resistance to cis-diamminedichloroplatinum(II) in mammalian cells.

Bulky DNA lesions are mainly repaired by nucleotide excision repair (NER), in which the interaction of ERCC1 with XPA protein recruits the ERCC1-XPF complex, which acts as a structure-specific endonuclease in the repair process. However, additional functions besides NER have been suggested for the ERCC1-XPF complex, because ERCC1- or XPF-deficient rodent cells are significantly more sensitive to DNA interstrand cross-linking (ICL) agents such as cis-diamminedichloroplatinum(II) (CDDP) than any other NER-deficient cells and because ERCC1-deficient mice suffer a more severe phenotype than XPA-deficient mice. By using RNA interference we show here that suppression of ERCC1 expression increases the sensitivity of xeroderma pigmentosum group A (XPA)-deficient human cells to CDDP but not to UV. This increased sensitivity to CDDP is observed in mouse cells defective in Xpa as well but not in cells defective both in Xpa and the mismatch repair gene Msh2. These data suggest that ERCC1 and MSH2 are involved co-operatively in CDDP resistance in mammalian cells. As a possible molecular basis, we show further a physical interaction between endogenous ERCC1 and MSH2 complexes in HeLa cell extracts. Using tagged ERCC1 in COS7 cells, the minimum region in ERCC1 necessary for the immuno-precipitation of MSH2 is turned out to be the carboxyl-terminal domain between the 184th and 260th amino acid, which is partly overlapping with the XPF-binding domain of ERCC1. This interaction may be important in additional functions of ERCC1-XPF including the repair of CDDP-induced DNA damage.

Animals↗

PubMed2004

Estimating three-class ideal observer decision variables for computerized detection and classification of mammographic mass lesions.

We are using Bayesian artificial neural networks (BANNs) to classify mammographic masses in schemes for computer-aided diagnosis, and we are extending this methodology to a three-class classification task. We investigated whether a BANN can estimate ideal observer decision variables to distinguish malignant, benign, and false-positive computer detections. Five features were calculated for 63 malignant and 29 benign computer-detected mass lesions, and for 1049 false-positive computer detections, in 440 mammograms randomly divided into a training and testing set. A BANN was trained on the training set features and applied to the testing set features. We then used a known relation between three-class ideal observer decision variables and that used by a two-class ideal observer when two of three classes are grouped into one class, giving one decision variable for distinguishing malignant from nonmalignant detections, and a second for distinguishing true-positive from false-positive computer detections. For comparison, we grouped the training data into two classes in the same two ways and trained two-class BANNs for these two tasks. The three-class BANN decision variables were essentially identical in performance to the specifically trained two-class BANNs, with the average difference in area under the ROC curves being less than 0.0035 and no differences in area being statistically significant. Thus, the BANN outputs obey the same theoretical relationship as do the three-class and two-class ideal observer decision variables, which is consistent with the claim that the three-class BANN output can provide good estimates of the decision variables used by a three-class ideal observer.

Breast Neoplasms↗

PubMed2004

Computerized analysis of mammographic parenchymal patterns for assessing breast cancer risk: effect of ROI size and location.

The long-term goal of our research is to develop computerized radiographic markers for assessing breast density and parenchymal patterns that may be used together with clinical measures for determining the risk of breast cancer and assessing the response to preventive treatment. In our earlier studies, we found that women at high risk tended to have dense breasts with mammographic patterns that were coarse and low in contrast. With our method, computerized texture analysis is performed on a region of interest (ROI) within the mammographic image. In our current study, we investigate the effect of ROI size and ROI location on the computerized texture features obtained from 90 subjects (30 BRCA1/BRCA2 gene-mutation carriers and 60 age-matched women deemed to be at low risk for breast cancer). Mammograms were digitized at 0.1 mm pixel size and various ROI sizes were extracted from different breast regions in the craniocaudal (CC) view. Seventeen features, which characterize the density and texture of the parenchymal patterns, were extracted from the ROIs on these digitized mammograms. Stepwise feature selection and linear discriminant analysis were applied to identify features that differentiate between the low-risk women and the BRCA1/BRCA2 gene-mutation carriers. ROC analysis was used to assess the performance of the features in the task of distinguishing between these two groups. Our results show that there was a statistically significant decrease in the performance of the computerized texture features, as the ROI location was varied from the central region behind the nipple. However, we failed to show a statistically significant decrease in the performance of the computerized texture features with decreasing ROI size for the range studied.

Algorithms↗

PubMed2004

Computerized interpretation of breast MRI: investigation of enhancement-variance dynamics.

The advantages of breast MRI using contrast agent Gd-DTPA in the diagnosis of breast cancer have been well established. The variation of interpretation criteria and absence of interpretation guidelines, however, is a major obstacle for applications of MRI in the routine clinical practice of breast imaging. Our study aims to increase the objectivity and reproducibility of breast MRI interpretation by developing an automated interpretation approach for ultimate use in computer-aided diagnosis. The database in this study contains 121 cases: 77 malignant and 44 benign masses as revealed by biopsy. Images were obtained using a T1-weighted 3D spoiled gradient echo sequence. After the acquisition of the precontrast series, Gd-DTPA contrast agent was injected intravenously by power injection with a dose of 0.2 mmol/kg. Five postcontrast series were then taken with a time interval of 60 s. Each series contained 64 coronal slices with a matrix of 128 x 256 pixels and an in-plane resolution of 1.25 x 1.25 mm2. Slice thickness ranged from 2 to 3 mm depending on breast size. The lesions were delineated by an experienced radiologist as well as independently by computer using an automatic volume-growing algorithm. Fourteen features that were extracted automatically from the lesions could be grouped into three categories based on (I) morphology, (II) enhancement kinetics, and (III) time course of enhancement-variation over the lesion. A stepwise feature selection procedure was employed to select an effective subset of features, which were then combined by linear discriminant analysis (LDA) into a discriminant score, related to the likelihood of malignancy. The classification performances of individual features and the combined discriminant score were evaluated with receiver operating characteristic (ROC) analysis. With the radiologist-delineated lesion contours, stepwise feature selection yielded four features and an Az value of 0.80 for the LDA in leave-one-out cross-validation testing. With the computer-segmented lesion volumes, it yielded six features and an Az value of 0.86 for the LDA in the leave-one-out testing.

Algorithms↗

PubMed2003

Spatial and temporal cellular responses to single-strand breaks in human cells.

DNA single-strand breaks (SSB) are one of the most frequent DNA lesions produced by reactive oxygen species and during DNA metabolism, but the analysis of cellular responses to SSB remains difficult due to the lack of an experimental method to produce SSB alone in cells. By using human cells expressing a foreign UV damage endonuclease (UVDE) and irradiating the cells with UV through tiny pores in membrane filters, we created SSB in restricted areas in the nucleus by the immediate action of UVDE on UV-induced DNA lesions. Cellular responses to the SSB were characterized by using antibodies and fluorescence microscopy. Upon UV irradiation, poly(ADP-ribose) synthesis occurred immediately in the irradiated area. Simultaneously, but dependent on poly(ADP-ribosyl)ation, XRCC1 was translocated from throughout the nucleus, including nucleoli, to the SSB. The BRCT1 domain of XRCC1 protein was indispensable for its poly(ADP-ribose)-dependent recruitment to the SSB. Proliferating cell nuclear antigen and the p150 subunit of chromatin assembly factor 1 also accumulated at the SSB in a detergent-resistant form, which was significantly reduced by inhibition of poly(ADP-ribose) synthesis. Our results show the importance of poly(ADP-ribosyl)ation in sequential cellular responses to SSB.

Cell Nucleus↗

PubMed2002

Rapid eye movement-localized apnea in a female patient with chronic insomnia.

A middle-aged female patient with chronic insomnia showed rapid eye movement (REM)- localized obstructive sleep apnea. She visited the Sleep Disorders Clinic and complained of insomnia with loud snoring. Once, in the past, her sleep complaints had disappeared after weight reduction but, 6 months later, she complained of excessive daytime sleepiness. Overnight polysomnography revealed REM-localized apnea. Careful follow up is strongly recommended for a female patient with chronic insomnia who shows REM-localized apnea.

Disorders of Excessive Somnolence↗