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E T Liu

Publications and source records attributed to E T Liu.

At least 37 records · Page 2Linked to original sources
PubMed2000

Risk of breast cancer according to the status of HER-2/neu oncogene amplification.

We examined risk factors for breast cancer after subdividing cases based on the presence of HER-2/neu oncogene amplification in their tumors. Data were from the Carolina Breast Cancer Study, a population-based, case-control study of 577 invasive breast cancer patients, diagnosed during 1993-1996 and ages 20-74 years, and 790 controls frequency-matched on race and age. Information on breast cancer risk factors was obtained from structured personal interviews. About 20% of paraffin-embedded tissues from the breast cancers of cases were identified as positive for HER-2/neu amplification (HER-2/neu+) by differential PCR. Early age at menarche, higher waist:hip ratio, and family history of breast or ovarian cancer were associated with elevated odds ratios (ORs) for both HER-2/neu+ and HER-2/neu- breast cancers. Breastfeeding for at least 1 year was inversely associated with HER-2/neu+ breast cancer [OR, 0.3; 95% confidence interval (CI), 0.1-0.7] more so than HER-2/neu- breast cancer (OR, 0.8; 95% CI, 0.5-1.2). Most of the remaining risk factors had ORs around 1.0 for both HER-2/neu+ and HER-2/neu- breast cancers, although a few exhibited possible associations with one disease subtype in analyses stratified by menopausal status. These study results suggest that most recognized breast cancer risk factors do not operate through HER-2/neu amplification in breast carcinogenesis. Differential effects of long-term breastfeeding by HER-2/neu amplification status have been observed in earlier studies and are provocative; however, the direction and magnitude of the associations have not been consistent.

Adult↗
PubMed1999

BRCA1-associated growth arrest is RB-dependent.

BRCA1 is a susceptibility gene for breast and ovarian cancer with growth-inhibitory activity for which the mechanism of action remains unclear. When introduced into cells, BRCA1 inhibits growth of some but not all cell lines. In an attempt to uncover the mechanism of growth suppression by BRCA1, we examined a panel of cell lines for their ability to reduce colony outgrowth in response to BRCA1 overexpression. Of all variables tested, only those cells with wild-type pRb were sensitive to BRCA1-induced growth suppression. In cells with an intact rb gene, inactivation of pRb by HPV E7 abrogates the growth arrest imposed by BRCA1. In accordance with these observations, we found that BRCA1 could not suppress BrdUrd uptake in primary fibroblasts from rb-/- mice and exhibited an intermediate ability to inhibit DNA synthesis in rb+/- as compared with rb+/+ cells. We further found that the BRCA1 protein complexes with the hypophosphorylated form of pRb. This binding is localized to amino acids 304-394 of BRCA1 protein and requires the ABC domain of pRb. In-frame deletion of BRCA1 fragment involved in interaction with pRb completely abolished the growth-suppressive property of BRCA1. Although it has been reported that BRCA1 interacts with p53, we find the p53 status did not affect the ability of BRCA1 to suppress colony formation. Our data suggest that the growth suppressor function of BRCA1 depends, at least in part, on Rb.

Adenoviridae↗
PubMed1999

Biologic and biochemical analyses of p16(INK4a) mutations from primary tumors.

BACKGROUND: Point mutations in the tumor suppressor gene p16(INK4a) (also known as p16, CDKN2, MTS1, and INK4a) are found in many tumor types. Because the function of the products of these naturally occurring mutants has not been fully explored, we investigated the functional activities of a wide range of naturally occurring p16 mutant proteins. METHODS: Sixteen cancer-associated p16 mutant proteins, resulting from missense mutations, were characterized for their ability to bind and inhibit the cyclin-dependent kinases (CDK4 and CDK6) and to induce cell cycle arrest in G(1) phase. RESULTS/CONCLUSIONS: Among 16 mutants analyzed, nine had detectable functional defects. Three mutants (D84V, D84G, and R87P) had defects in CDK binding, kinase inhibition, and cell cycle arrest. The corresponding mutations are located in the third ankyrin repeat in a highly conserved region believed to form the CDK binding cleft. Three mutants (P48L, D74N, and R87L) had defects in kinase inhibition and cell cycle arrest. Among the 10 mutants with normal CDK binding and inhibitory activity, three mutants (N71S, R80L, and H83Y) had defects only in their ability to induce cell cycle arrest. Thus, p16 mutant proteins that retain CDK4 and CDK6 binding may have more subtle functional defects. All nine mutations leading to functional impairments mapped to the central portion of the p16 protein. Ankyrin repeats II and III appear more critical to p16 function, and mutations in ankyrin repeats I and IV are less likely to disrupt p16 function.

Amino Acid Sequence↗
PubMed1999

P57 (KIP2) polymorphisms and breast cancer risk.

A previous report in this journal has suggested that germline deletions in the proline-alanine-rich (PAPA-repeat) region of P57 (KIP2) are associated with increased risk of a variety of cancers, including breast cancer. We have analyzed the association of P57 PAPA-repeat deletion polymorphisms and breast cancer risk as part of a population-based case-control study of breast cancer. We have not observed an association between the presence of one or two copies of deletion polymorphisms in P57 and breast cancer risk (adjusted odds ratio: 1.1, 95% confidence interval: 0.6-2.0). Further investigation is necessary to determine the functional significance of P57 deletion polymorphisms and their potential relationship with disease.

Breast Neoplasms↗
PubMed1999

Axl-gas6 interaction counteracts E1A-mediated cell growth suppression and proapoptotic activity.

The adenovirus type 5 early region 1A gene (E1A) has previously been known as an immortalization oncogene because E1A is required for transforming oncogenes, such as ras and E1B, to transform cells in primary cultures. However, E1A has also been shown to downregulate the overexpression of the Her-2/neu oncogene, resulting in suppression of transformation and tumorigenesis induced by that oncogene. In addition, E1A is able to promote apoptosis induced by anticancer drugs, irradiation, and serum deprivation. Many tyrosine kinases, such as the epidermal growth factor receptor, Her-2/Neu, Src, and Axl, are known to play a role in oncogenic signals in transformed cells. To study the mechanism underlying the E1A-mediated tumor-suppressing function, we exploited a modified tyrosine kinase profile assay (D. Robinson, F. Lee, T. Pretlow, and H.-J. Kung, Proc. Natl. Acad. Sci. USA 93:5958-5962, 1996) to identify potential tyrosine kinases regulated by E1A. Reverse transcription (RT)-PCR products were synthesized with two degenerate primers derived from the conserved motifs of various tyrosine kinases. A tyrosine kinase downregulated by E1A was identified by analyzing the AluI-digested RT-PCR products. We isolated the DNA fragment of interest and found that E1A negatively regulated the expression of the transforming receptor tyrosine kinase Axl at the transcriptional level. To study whether downregulation of the Axl receptor is involved in E1A-mediated growth suppression, we transfected axl cDNA into E1A-expressing cells (ip1-E1A) to establish cells that overexpressed Axl. The Axl ligand Gas6 triggered a greater mitogenic effect in these ip1-E1A-Axl cells than in ip1-E1A control cells and protected the Axl-expressing cells from serum deprivation-induced apoptosis. These results indicate that downregulation of the Axl receptor by E1A is involved in E1A-mediated growth suppression and E1A-induced apoptosis and thereby contributes to E1A's antitumor activities.

Adenovirus E1A Proteins↗
PubMed1998

erbB-2, p53, and efficacy of adjuvant therapy in lymph node-positive breast cancer.

BACKGROUND: We have previously reported that high expression of the erbB-2 gene (also known as HER-2/neu and ERBB2) in breast cancer is associated with patient response to dose-intensive treatment with cyclophosphamide, doxorubicin (Adriamycin), and 5-flurouracil (CAF) on the basis of short-term follow-up of 397 patients (set A) with axillary lymph node-positive tumors who were enrolled in Cancer and Leukemia Group B (CALGB) protocol 8541. METHODS: To validate those findings, we conducted immunohistochemical analyses of erbB-2 and p53 protein expression in an additional cohort of 595 patients (set B) from CALGB 8541, as well as a molecular analysis of erbB-2 gene amplification in tumors from all patients (sets A and B). Marker data were compared with clinical, histologic, treatment, and outcome data. RESULTS: Updated analyses of data from set A (median follow-up, 10.4 years) showed an even stronger interaction between erbB-2 expression and CAF dose, by use of either immunohistochemical or molecular data. A similar interaction between erbB-2 expression and CAF dose was observed in all 992 patients, analyzed as a single group. However, for set B alone (median follow-up, 8.2 years), results varied with the method of statistical analysis. By use of a proportional hazards model, the erbB-2 expression-CAF dose interaction was not significant for all patients. However, in the subgroups of patients randomly assigned to the high- or the moderate-dose arms, significance was achieved. When patient data were adjusted for differences by use of a prognostic index (to balance an apparent failure of randomization in the low-dose arm), the erbB-2 expression-CAF dose interaction was significant in all patients from the validation set B as well. An interaction was also observed between p53 immunopositivity and CAF dose. CONCLUSIONS: The hypothesis that patients whose breast tumors exhibit high erbB-2 expression benefit from dose-intensive CAF should be further validated before clinical implementation. Interactions between erbB-2 expression, p53 expression, and CAF dose underscore the complexities of predictive markers where multiple interactions may confound the outcome.

Adult↗
PubMed1998

Identification of a large Myc-binding protein that contains RCC1-like repeats.

The protooncogene MYC plays an important role in the regulation of cellular proliferation, differentiation, and apoptosis and has been implicated in a variety of human tumors. MYC and the closely related MYCN encode highly conserved nuclear phosphoproteins (Myc and NMyc) that apparently function as transcription factors in the cell. We have identified a large and highly conserved nuclear protein that interacts directly with the transcriptional activating domain of Myc (designated "protein associated with Myc" or Pam). Pam contains an extended amino acid sequence with similarities to a protein known as regulator of chromosome condensation (RCC1), which may play a role in the function of chromatin. The gene encoding Pam (PAM) is expressed in all of the human tissue examined, but expression is exceptionally abundant in brain and thymus. Pam binds specifically to Myc, but not NMyc. The region in Myc required for binding to Pam includes a domain that is essential for the function of Myc and that is frequently mutated in Burkitt's lymphomas. PAM is located within a 300-kb region on chromosome 13q22.

Adaptor Proteins, Signal Transducing↗
PubMed1998

Determinants for transformation induced by the Axl receptor tyrosine kinase.

The Axl receptor tyrosine kinase is a transforming oncogene in NIH3T3 cells. In order to define structural requirements of the Axl receptor necessary for transformation we passaged recombinant retroviruses carrying the axl cDNA in NIH3T3 cells, generating randomly mutated axl variants. Using this strategy, we have isolated three axl viral strains (1B1, SV8, and FFa4) that show augmented 3T3 cell transforming capacity associated with elevated p140Axl. Upon sequencing, the 1B1 and SV8 proviruses possessed only silent mutations, making p140Axl overexpression the most likely explanation for their increased transformation activity. However, the characterization of FFa4 revealed a deletion of sequences encoding the carboxy-terminal 45 amino acids leading to the generation of a chimeric transcript comprised of a truncated Axl receptor with a segment of the 3' UTR region. Mutational analysis revealed that the transforming activity of FFa4 was specific to the formation of the chimeric receptor rather than to the carboxyl-terminal truncation. Intriguingly, none of the viral strains were able to transform the murine cell lines NR-6 and 32D despite equivalent expression of surface p140Axl protein. Further analysis showed that Axl's transforming potential is dependent on the host cell type, the presence of a putative pp190 as a facilitator for transformation, and the level of p140Axl expression. Taken together, these results underscore the complexity of Axl biology which is dependent on receptor stoichiometry and the cellular background.

3T3 Cells↗
PubMed1998

GAS6 induces Axl-mediated chemotaxis of vascular smooth muscle cells.

Atherosclerosis and arterial restenosis are disease processes involving the accumulation of vascular smooth muscle cells following vascular injury. Key events leading to these processes are migration and proliferation of these cells. Here, we demonstrate that GAS6, encoded by the growth arrest-specific gene 6, induces a directed migration (chemotaxis) of both rat and human primary vascular smooth muscle cells while showing only marginal mitogenic potential in human vascular smooth muscle cells. GAS6 stimulation induces Axl autophosphorylation in human vascular smooth muscle cells, indicating that specific GAS6-Axl interactions may be associated with GAS6-directed chemotaxis. To test this hypothesis, vascular smooth muscle cells overexpressing Axl were generated by gene transfer and assessed for their ability to migrate along a GAS6 gradient. These Axl overexpressors exhibited 2-5-fold increased sensitivity to GAS6-induced chemotaxis. Furthermore, vascular smooth muscle cells expressing the kinase dead mutant of Axl or exposure to the soluble Axl extracellular domain showed attenuated GAS6-induced migration. Taken together, these results suggest that GAS6 is a novel chemoattractant that induces Axl-mediated migration of vascular smooth muscle cells. The separation of mitogenesis from migration provided by this study may enhance the molecular dissection of cell migration in vascular damage.

Animals↗
PubMed1998

Juvenile myelomonocytic leukemia (JMML) with the hematologic phenotype of severe beta thalassemia.

A 3-year-old Filipino-American child with recurrent fever, splenomegaly, anemia, and thrombocytopenia, was found to have a hemoglobin F level of 76.9%. His reticulocyte count was elevated (4.3%), and erythroblasts were present in his peripheral blood. The child's erythrocytes were microcytic (MCV 66.9 fl) but his serum ferritin level was normal. His bone marrow at initial presentation demonstrated normal cellularity without an increase in blast cells. The disease progressed with worsening anemia, leukocytosis, and thrombocytopenia, with increased blasts in his marrow and the appearance of a mediastinal mass. His liver, spleen, and lymph nodes were found to be infiltrated with myeloblasts, supporting a diagnosis of juvenile myelomonocytic leukemia (JMML). Analysis of the child's Hb F showed a Ggamma/Agamma ratio of 2.2, which was within the characteristic range for JMML. A globin synthesis study using blood reticulocytes showed an alpha/non-alpha globin synthesis ratio of 2.24, typical of severe homozygous beta thalassemia. Southern blot analysis of blood-leukocyte DNA from the patient and his parents demonstrated no apparent abnormality in the beta-globin gene promoter or coding regions. The elevated level of Hb F in this child with JMML appeared to be part of an acquired Cooley's anemia-like hematologic phenotype.

Child, Preschool↗
PubMed1998

Perspective on BRCA1.

In a very real sense, the search for a breast cancer susceptibility gene reflects the rapid evolution of molecular genetics as a field and the power of molecular technology to accelerate the pace of discovery. This search began with the study of blood proteins through biochemical analysis; the number of loci accessible was limited, and very few consistent results were obtained (1). Then came recombinant DNA technology. The number of available markers, and the information they provide, has grown rapidly over the years. The same is true for the development of new, high-throughput genotyping methods and associated informatics systems and statistical methods, making gene mapping more feasible. For BRCA1, it took five years and 183 markers to identify the chromosomal location as 17q21 (2). It took an additional four years before BRCA1 was cloned (3). In contrast, BRCA2 was localized to chromosome 13q12-13 two months before the cloning of BRCA1 was reported; less than two years later, BRCA2 was cloned (4,5). Characterization of these two genes is still underway, in part, because of unanticipated complexity. This complexity plays out at multiple levels, including the relationship between phenotype and genotype within and between the populations studied, biological function(s), and social consequences. The reviews presented in this issue reflect the breadth of impact that the discovery of the BRCA genes has had on science, medicine, and law. As with most great discoveries, the identification of BRCA1 has forced us to question the fundamentals of our belief systems: what is a mutation, what is a tumor suppressor, what is righteous, and what is ethical?

Journal Article↗
PubMed1997

GAS6 mediates adhesion of cells expressing the receptor tyrosine kinase Axl.

Axl is a receptor tyrosine kinase that contains both immunoglobulin and fibronectin III repeats in its extracellular domain reminiscent of cell adhesion molecules. Expression of the receptor tyrosine kinase Axl in the 32D myeloid cell line permits aggregation of cells in response to treatment with the native ligand GAS6; this aggregation was not observed in untreated 32D-Axl cells nor in treated parental cells. This aggregation can be blocked by the addition of excess Axl extracellular domain peptide and does not require intracellular Axl kinase activity. Cell surface binding activity of GAS6 was mapped to distinct plasma membrane interacting domains that are separate from the GAS6 motifs that engage the Axl receptor. This suggests that aggregation is mediated by a heterotypic intercellular mechanism whereby cell-bound GAS6 interacts with Axl receptor on an adjacent cell. This mechanism is supported by our observation that GAS6 binds to 32D parental cells which then permits their aggregation with untreated 32D-Axl cells. We have recently demonstrated that the GAS6-Axl interaction does not initiate mitogenesis in 32D cells. When considered with the adhesion results, these data suggest that an important biological function of the Axl-GAS6 interaction is to mediate cell-cell binding.

Animals↗
PubMed1997

Human chondrocyte expression of growth-arrest-specific gene 6 and the tyrosine kinase receptor axl: potential role in autocrine signaling in cartilage.

OBJECTIVE: To determine if human articular chondrocytes express the axl tyrosine kinase receptor and its ligand Gas-6, a protein product of growth-arrest-specific gene 6, and to determine if Gas-6 and axl function in the regulation of chondrocyte growth and survival. METHODS: The presence of Gas-6 and axl was examined in situ in human articular cartilage by immunohistochemistry and in vitro in cell culture studies using primary human chondrocytes and immortalized human chondrocytes. The ability of recombinant Gas-6 to mediate adhesion of chondrocytes and to stimulate chondrocyte axl phosphorylation was determined. Studies of the role of Gas-6 and axl in cell proliferation and survival were also performed. RESULTS: Both Gas-6 and axl were detected in cartilage by immunohistochemical staining. Gas-6 and axl messenger RNA (mRNA) and protein were also detected in cultures of primary and immortalized human chondrocytes. Compared with cells cultured in medium containing 10% serum, Gas-6 mRNA levels were increased in immortalized chondrocytes cultured in serum-free medium, while axl expression decreased. Chondrocytes attached to Gas-6-coated plastic, and the attachment was blocked by a soluble Ig fusion protein containing the axl extracellular domain. Recombinant human Gas-6 and serum-free conditioned medium from primary and immortalized human chondrocyte cultures stimulated chondrocyte axl tyrosine phosphorylation. A mitogenic effect was noted both when immortalized chondrocytes were stimulated with recombinant Gas-6 or when they were made to overexpress axl by transfection. Addition of recombinant Gas-6 to serum-free medium resulted in increased survival of primary chondrocytes cultured at low density in agarose. CONCLUSION: These findings present evidence for an autocrine signaling pathway in cartilage involving Gas-6 and the axl tyrosine kinase adhesion receptor. Stimulation of axl by Gas-6 may play an important role in the control of chondrocyte growth and survival.

3T3 Cells↗
PubMed1996

BRCA1 protein level is not affected by peptide growth factors in MCF10A cell line.

The breast cancer susceptibility gene (BRCA1) has been identified as a putative tumor suppressor on chromosome 17. We raised antibody against Ring-finger domain of BRCA1. The antibody recognizes a specific BRCA1 protein doublet of about 220 kD. The majority of BRCA1 protein is localized to the nuclear fraction of untreated MCF10A cells. Though BRCA1 is thought to be a growth suppressor gene, no change in BRCA1 protein level was found when MCF10A cells were arrested by growth factor deprivation or stimulation of cell proliferation by re-addition of growth factors. Furthermore the subcellular localization of the BRCA1 protein does not change throughout the cell cycle. These results suggest that BRCA1 may not be directly involved in the regulation of the cell cycle of breast cancer cell line.

BRCA1 Protein↗
PubMed1996

Internal sequence variations in the Ha-ras variable number tandem repeat rare and common alleles identified by minisatellite variant repeat polymerase chain reaction.

In this report, we describe the sequence allelotyping of the Ha-ras variable number tandem repeat (VNTR) region using a minisatellite variant repeat (MVR)-PCR approach. This method permits the rapid identification of internal sequence variations among the VNTR alleles, exploiting the presence of two polymorphic sites within the 28-bp repeat subunits that give rise to four distinct repeat types. Using MVR-PCR, 20 to 25 repeats at the 5' end of the VNTR can be sequenced rapidly and reliably. MVR typing of the common alleles a1, a2, a3, and a4 shows that the first six repeats at the 5' end of each allele constitutes an invariant region. Beginning with repeat 7, characteristic "signature" MVR patterns emerge for each common allele. The a1 and a2 common alleles were found to consist of specific repeat types 1, 2, and 3, whereas a3 and a4 contain an additional repeat type 4 not present in the smaller alleles. MVR typing of rare-length alleles indicates that they are comprised of disorganized sequences, although they usually bear a resemblance to one of the common alleles at the 5'-most end. These results suggest that the rare alleles may be generated from recombination or gene conversion-type events involving the common progenitor alleles. MVR typing could, therefore, improve the ascertainment of rare Ha-ras alleles and may provide molecular insights into the genesis of cancer-associated alleles.

Alleles↗