Biomedical subjects

E V Schmidt

Publications and source records attributed to E V Schmidt.

At least 37 records · Page 2Linked to original sources

PubMed1996

Happenstance, circumstance or enemy action: cyclin D1 in breast, eye and brain.

Two recent reports of mice homozygously deleted for cyclin D1 provide unequivocal evidence that the critical G1 cyclin, cyclin D1, is by itself rate-limiting for growth in some mammalian tissues. Cyclin D1 knockout mice are small and exhibit behavioral abnormalities. Specific hypoplasias of retinal and mammary tissues suggest an unusual dependence on cyclin D1 function for tissue growth in those organs. The odd coincidences that cyclin D1 functions as the retinoblastoma gene kinase, together with associations between increased cyclin D1 expression and breast cancer, suggest, but do not prove, a special function of cyclin D1 in those tissues.

Abnormalities, Multiple↗

PubMed1996

MYC family ties.

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Adaptor Proteins, Signal Transducing↗

PubMed1996

An essential E box in the promoter of the gene encoding the mRNA cap-binding protein (eukaryotic initiation factor 4E) is a target for activation by c-myc.

The mRNA cap-binding protein (eukaryotic initiation factor 4E [eIF4E]) binds the m7 GpppN cap on mRNA, thereby initiating translation. eIF4E is essential and rate limiting for protein synthesis. Overexpression of eIF4E transforms cells, and mutations in eIF4E arrest cells in G, in cdc33 mutants. In this work, we identified the promoter region of the gene encoding eIF4E, because we previously identified eIF4E as a potential myc-regulated gene. In support of our previous data, a minimal, functional, 403-nucleotide promoter region of eIF4E was found to contain CACGTG E box repeats, and this core eIF4E promoter was myc responsive in cotransfections with c-myc. A direct role for myc in activating the eIF4E promoter was demonstrated by cotransfections with two dominant negative mutants of c-myc (MycdeltaTAD and MycdeltaBR) which equally suppressed promoter function. Furthermore, electrophoretic mobility shift assays demonstrated quantitative binding to the E box motifs that correlated with myc levels in the electrophoretic mobility shift assay extracts; supershift assays demonstrated max and USF binding to the same motif. cis mutations in the core or flank of the eIF4E E box simultaneously altered myc-max and USF binding and inactivated the promoter. Indeed, mutations of this E box inactivated the promoter in all cells tested, suggesting it is essential for expression of eIF4E. Furthermore, the GGCCACGTG(A/T)C(C/G) sequence is shared with other in vivo targets for c-myc, but unlike other targets, it is located in the immediate promoter region. Its critical function in the eIF4E promoter coupled with the known functional significance of eIF4E in growth regulation makes it a particularly interesting target for c-myc regulation.

Animals↗

PubMed1996

Inhibitory effect of hepatocyte growth factor on metastasis of hepatocellular carcinoma in transgenic mice.

Hepatocyte growth factor (HGF) has different effects on different cell types. Recently, it has been reported that HGF has an anti-proliferative effect against tumor cells including hepatocellular carcinoma (HCC) cells. To clarify whether HGF inhibits the metastasis of HCC cells in vivo, we examined the metastatic potential of HCC cells into liver where HGF was highly expressed in transgenic animals. Three HCC cell lines including HuH7, Hep3B and FaO cells were transplanted into liver through the portal vein in chimeric mice or HGF transgenic mice and athymic nude mice (HGF/nude). The incidence of liver metastasis and number of metastatic tumors were significantly lower in mice expressing HGF (HGF/nude), compared with their siblings expressing no HGF (+/nude) (p < 0.05 and p = 0.002, respectively). These data suggest that HGF really inhibits metastasis of HCC cells in vivo.

Animals↗

PubMed1995

Eukaryotic translation initiation factor 4E regulates expression of cyclin D1 at transcriptional and post-transcriptional levels.

Regulation of the cell cycle is orchestrated by cyclins and cyclin-dependent kinases. We have demonstrated previously that overexpression of eukaryotic translation initiation factor 4E (eIF-4E) in NIH 3T3 cells growing in 10% fetal calf serum leads to highly elevated levels of cyclin D1 protein without significant increase in cyclin D1 mRNA levels, suggesting that a post-transcriptional mechanism is involved. (Rosenwald, I. B., Lazaris-Karatzas, A., Sonenberg, N., and Schmidt, E. V. (1993) Mol. Cell. Biol. 13, 7358-7363). In the present research, we did not find any significant effect of eIF-4E on polysomal distribution of cyclin D1 mRNA. However, the total amount of cyclin D1 mRNA associated with polysomes was significantly increased by eIF-4E overexpression. Further, we determined that the levels of both cyclin D1 protein and mRNA are increased in serum-deprived cells overexpressing eIF-4E. Nuclear run-on experiments demonstrated that the rate of the cyclin D1 transcription is not down-regulated in serum-deprived cells overexpressing eIF-4E. Thus, elevated levels of eIF-4E may lead to increased transcription of the cyclin D1 gene, and this effect becomes visible when serum deprivation down-regulates the rate of cyclin D1 mRNA synthesis in control cells. However, artificial overexpression of cyclin D1 mRNA in serum-deprived cells in the absence of eIF-4E overexpression did not cause the elevation of cyclin D1 protein, and this overexpressed cyclin D1 mRNA accumulated in the nucleus, suggesting that one post-transcriptional role of eIF-4E is to transport cyclin D1 mRNA from the nucleus to cytoplasmic polysomes.

3T3 Cells↗

PubMed1995

A rat gastrin-human gastrin chimeric transgene directs antral G cell-specific expression in transgenic mice.

Gastrin gene expression in the gastrointestinal tract is under both developmental and spatial regulation. In the mature animal, gastrin, an important regulator of parietal acid secretion, is expressed primarily in G cells of the antrum. To determine whether specific promoter elements can direct expression to the gastric antrum in vivo, 450 nucleotides of the proximal rat gastrin promoter were cloned and used to construct a rat gastrin-human gastrin reporter chimeric transgene, which was injected into the mouse germ line. Northern blot analysis, in situ hybridization, and double-label immunocytochemistry studies demonstrated expression of the transgene specifically in antral G cells. Low levels of transgene expression were observed in the ileum and colon, where immunohistochemical studies demonstrated colocalization in enteroendocrine cells expressing peptide YY. The same 450-nucleotide rat gastrin promoter, when joined to the human growth hormone gene, did not result in antral expression. Similarly, a human gastrin-human gastrin reporter transgene also did not achieve antral expression, although it did express in the liver. These results suggest that cis-acting elements present in both the basal 450-nucleotide rat gastrin promoter and the intragenic sequences of the human gastrin gene are necessary to direct expression of a transgene specifically to antral G cells.

Amino Acid Sequence↗

PubMed1995

Cyclin D1 (PRAD1) protein expression in breast cancer: approximately one-third of infiltrating mammary carcinomas show overexpression of the cyclin D1 oncogene.

Amplification of chromosome 11q13 has been observed in 10-20% of breast carcinomas and numerous other tumors, including squamous cell carcinomas of the head, neck, and esophagus; transitional cell carcinomas of the urinary bladder; and epithelial ovarian tumors. Cyclin D1/PRAD1 is a likely "driver" gene for this amplicon because of its role in cell cycle control and because it has been specifically implicated as an oncogene in parathyroid adenomas and B-cell lymphomas with 11q13 translocation breakpoints. We examined cyclin D1 protein expression in 48 consecutive cases of infiltrating mammary carcinoma using an affinity-purified polyclonal antisera to cyclin D1 and a microwave/citrate buffer antigen retrieval system. Staining data were correlated with clinicopathological features, protein detection by immunoblots, and 11q13 DNA amplification. Definite nuclear staining was seen in 17/48 (35%) tumors (16 infiltrating ductal carcinomas, predominantly grade 2/3, and one infiltrating lobular carcinoma). There was no nuclear staining of normal breast epithelium, fat cells, or admixed lymphocytes. Tumors with overexpression of cyclin D1 were estrogen receptor-positive (P < .005) and usually progesterone receptor-positive (P < .005) but otherwise were similar to other negative cases in the study group. Correlation between Western blot and immunostaining data was excellent (P < .01). Five of the 22 cases studied showed 11q13 DNA amplification as well as increased levels of cyclin D1 protein by Western blot and immunostaining. Four cases with increased cyclin D1 protein by both western blots and immunohistochemistry did not have detectable 11q13 amplification. Nuclear cyclin D1 protein can be detected in approximately one-third of infiltrating breast carcinomas using an immunohistochemical technique on formalin-fixed, paraffin-embedded tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1995

Characterization of double transgenic mice expressing hepatocye growth factor and transforming growth factor alpha.

Hepatocyte growth factor (HGF) and transforming growth factor alpha (TGF alpha) are potent mitogens for mature hepatocytes in primary culture (Nakamura, et al. 1984, Mead et al., 1989). However, these cytokines have completely different effects on tumor cell growth (Jhappan et al., 1990, Shiota et al, 1992). To clarify dual effects of these cytokines in liver, we developed double transgenic mice of HGF and TGF alpha using albumin promoter-HGF cDNA transgenic mice (AlbHGF) and metallothionein promoter-TGF alpha transgenic mice (MthTGF alpha). Double transgenic mice were examined on DNA synthesis, c-myc mRNA and occurrence of hepatocelular carcinoma (HCC). Higher labeling indices using BrDU were observed, in sequence, in AlbHGF mice, AlbHGF/MthTGF alpha, MthTGF alpha and wild type mice. Hepatic expression of c-myc mRNA in AlbHGF mice was elevated, compared to that in AlbHGF/MthTGF alpha or MthTGF alpha mice. After long-term observation, MthTGF alpha mice developed HCC in 6/10 (60%), whereas AlbHGF/MthTGF alpha mice developed HCC in 3/9 (33%). These data suggest that HGF is the potent mitogen, stimulating DNA synthesis and up-regulating c-myc mRNA. In addition, HGF may excert some inhibitory effect on occurrence of HCC by TGF alpha.

Animals↗

PubMed1995

Down-regulation of c-myc mRNA after completion of liver regeneration in transgenic mice expressing hepatocyte growth factor in liver.

Hepatocyte growth factor (HGF) is the potent mitogen for liver parenchymal cells. It has been demonstrated that HGF enhances liver regeneration in transgenic mice which express HGF highly and exclusively in hepatocytes. In HGF transgenic mice where DNA synthesis of hepatocytes is active, c-myc is induced through an increased transcription rate by HGF. Therefore, expression of c-myc is up-regulated by HGF in this condition. However, relations between c-myc, HGF and cell growth still remain unclear. To clarify regulatory mechanisms of c-myc, we measured c-myc mRNA, HGF mRNA, proliferating nuclear antigen (PCNA) mRNA, PCNA protein and labeling index after a two thirds partial hepatectomy in livers from transgenic mice which express HGF in liver. We found that expression of c-myc mRNA was high on day 1 and day 3, and decreased drastically on day 5 when liver regeneration had completed in HGF transgenic mice (Shiota, et al., 1994). Levels of PCNA protein and labeling index on day 1 after liver regeneration were higher in HGF transgenic mice than those of normal siblings, but no differences were observed between HGF transgenic and wild type ]nice on day 3. Endogenous expression of HGF was observed only on day 1, although transgene expression was almost constant during liver regeneration. These data suggest that cell-to-cell contact is more important for regulation of c-myc than levels of HGF mRNA.

Animals↗

PubMed1994

Functional cerebral imaging in the evaluation and radiotherapeutic treatment planning of patients with malignant glioma.

PURPOSE: Functional magnetic resonance imaging (MRI) and positron emission tomography are relatively new modalities of great potential value in the evaluation, treatment, and subsequent follow-up care of patients with malignant glioma. We report our experience with the incorporation of functional imaging data into radiation therapy three-dimensional (3-D) treatment planning. METHODS AND MATERIALS: Over a 24-month period, a total of 37 positron emission tomography and 29 functional MRI studies have been conducted on eight consecutive patients prior to, during, and following the completion of radiation therapy. Functional imaging was conducted prior to radiation therapy treatment planning and at approximate 3-month follow-up time intervals. RESULTS: In two patients, functional imaging provided additional information over conventional imaging modalities and resulted in subsequent modification of conventional radiation therapy treatment planning. CONCLUSION: Although it is premature to make definitive statements regarding the use of these new imaging parameters in the prognostic setting, functional imaging may likely prove to be a useful adjunct in the initial evaluation, radiation treatment planning, and follow-up care of patients with malignant glioma.

Adult↗

PubMed1994

Mammary hyperplasia and carcinoma in MMTV-cyclin D1 transgenic mice.

Physical associations between cyclins, viral oncogenes and tumour suppressor genes imply a central role for cyclins in growth control. Cyclin D1 was identified as a candidate oncogene (PRAD1) in tumour-specific DNA rearrangements and is suspected to be a contributor to several types of neoplasms including breast cancer. Cyclin D1 also rescues G1 cyclin-defective Saccharomyces cerevisiae, and is a growth-regulated gene. Despite evidence suggesting that cyclin D1 is an oncogene, its ability to transform cells directly in culture remains controversial. To evaluate its potential to deregulate growth in vivo in a physiologically relevant tissue we overexpressed cyclin D1 in mammary cells in transgenic mice. We report here that overexpression of cyclin D1 resulted in abnormal mammary cell proliferation including the development of mammary adenocarcinomas. We conclude that overexpression of cyclin D1 deregulates cell proliferation and can induce tumorigenic changes in mammary tissues, suggesting that cyclin D1 indeed plays an important oncogenic role in breast cancer.

Adenocarcinoma↗

PubMed1994

Hepatocyte growth factor regulates transforming growth factor alpha in HepG2 hepatic cells.

Hepatocyte growth factor (HGF) is an important paracrine regulator for liver growth, whereas it inhibits growth of tumor cells including hepatocellular carcinoma. In contrast, transforming growth factor alpha (TGF alpha) is a factor which stimulates hepatocyte growth and causes hepatocellular carcinoma in an autocrine fashion. To determine whether TGF alpha is affected by HGF, we examined the regulation of TGF alpha expression in response to exogenous HGF in HepG2 cells. We first examined TGF alpha mRNA and protein in the presence of HGF and found nearly a 3.6-fold increase in mRNA and a 2.5-fold increase in TGF alpha protein. This induction was dose-dependent and followed delayed kinetics. Nuclear run-on experiments suggested that the mechanism for this induction was an increase in transcription of TGF alpha mRNA. These data suggest that HGF may modulate TGF alpha expression and the interaction of these cytokines may play an important role in liver diseases.

Carcinoma, Hepatocellular↗

PubMed1994

Inhibitory effect of hepatocyte growth factor against FaO hepatocellular carcinoma cells may be associated with changes of intracellular signalling pathways mediated by protein kinase C.

Hepatocyte growth factor (HGF) stimulates growth of mature hepatocytes, whereas it inhibits growth of cancer cells including hepatocellular carcinoma (HCC) cells. However, the regulatory mechanisms for this phenomenon remains unclear. An important intermediary in HGF signal transduction in normal hepatocytes, c-myc, was not induced in FaO HCC cells after HGF stimulation, suggesting that intracellular signalling pathways of HGF in FaO HCC cells were different from those in normal hepatocytes. Protein kinase C (PKC) has been reported to be involved in signalling pathways of many growth factors. To study whether PKC is associated with this inhibitory mechanism, we studied the effects of HGF and/or 12-O-tetradecanoyl phorbol-13-acetate (TPA) on the growth of normal hepatocytes and FaO HCC cells. Consequently, HGF or TPA stimulated growth of normal hepatocytes, while equal doses of TPA or HGF inhibited growth of FaO HCC cells, respectively. In addition, TPA reversed the HGF effect in both normal hepatocytes and FaO HCC cells. These data suggest that an inhibitory effect of HGF on FaO HCC cells may be associated with changes of protein kinase C-mediated intracellular signalling pathways.

Animals↗

PubMed1994

Transfection of rat embryo cells with mutant p53 increases the intrinsic radiation resistance.

Dominant oncogenic sequences have been shown to modulate the intrinsic radiation sensitivity of cells of both human and murine tumor cell lines. Whether transfection with candidate tumor-suppressor genes can modulate intrinsic radiation sensitivity is unknown. The data presented here demonstrate that transfection of rat embryo cells with a mutant p53 allele can increase the intrinsic radiation resistance of cells in vitro. First, transfection with mutant p53 resulted in transformed cellular morphology. Second, the transfected clone and the corresponding pooled population of transfected clones were more resistant to ionizing radiation in vitro. Last, analyses of the parameters of cell kinetics suggested that the radiobiological effects were unlikely to be due to altered parameters of cell kinetics at the time of irradiation, suggesting that mutant p53 altered the intrinsic radiation resistance of transfected cells by a more direct mechanism. Further experimentation will be necessary to develop a mechanistic approach for the study of these alterations.

Animals↗

PubMed1994

Assessment of in vitro growth potential of hepatocytes expressing hepatocyte growth factor in an autocrine fashion.

We recently developed transgenic mice expressing hepatocyte growth factor (HGF) specific to hepatocytes. Hepatocytes of HGF transgenic mice showed a 2-fold increase of DNA labeling indices in vivo compared with those of wild type mice. To assess in vitro growth potential of hepatocytes from HGF transgenic mice, we studied the effects of epidermal growth factor (EGF), insulin or transforming growth factor beta (TGF beta) on DNA synthesis of hepatocytes derived from HGF transgenic or wild type mice, respectively. We found that DNA synthesis of hepatocytes from HGF transgenic mice was significantly enhanced, compared with that from wild type mice, respectively, and that its effect was additive with EGF or insulin. Further, growth-inhibitory effects of TGF beta on hepatocytes was greatly depressed in transgenic mice-derived hepatocytes, compared with that in wild type hepatocytes. These data suggest that the autocrine action of HGF is a potent stimulus for hepatocyte growth, and stress its importance as regulator of liver regeneration.

Animals↗

PubMed1994

Hepatocyte growth factor in transgenic mice: effects on hepatocyte growth, liver regeneration and gene expression.

Attention has recently been focused on hepatocyte growth factor as a major candidate factor in liver regeneration because it is the most potent known mitogen for hepatocytes in vitro. However, hepatocyte growth factor also displays diverse activities in vitro as scatter factor, as an epithelial morphogen, as a pluripotent mitogen and as a growth inhibitor. Consequently, we developed transgenic mice that expressed hepatocyte growth factor under the control of albumin regulatory sequences to examine its in vivo role in hepatocyte growth. Hepatocytes of these mice expressed increased levels of hepatocyte growth factor as an autocrine growth factor. Hepatocyte growth factor was a potent stimulus for liver repair; the livers of hepatocyte growth factor-transgenic mice recovered completely in half the time needed for their normal siblings after partial hepatectomy. This transgenic model also enabled us to study the chronic effects of hepatocyte growth factor expression. During several months of observation, the labeling index of hepatocytes in albumin-hepatocyte growth factor mice was doubled, and liver DNA content was increased compared with that in wild-type mice. To identify intermediate signaling pathways for hepatocyte growth factor that might regulate this increased growth response, we examined transgenic mice for changes in expression of genes that are known to be regulated during liver regeneration. We found that levels of c-myc and c-jun mRNA were increased in the hepatocyte growth factor-transgenic mice. In additional experiments the increased c-myc expression was the consequence of increased transcription rates as seen in nuclear run-on and myc-CAT reporter gene experiments. We conclude that hepatocyte growth factor increases growth and repair processes when expressed for long periods in the liver and that c-myc and c-jun may be important intermediaries in the hepatocyte growth response caused by hepatocyte growth factor.

Animals↗

PubMed1993

Increased expression of eukaryotic translation initiation factors eIF-4E and eIF-2 alpha in response to growth induction by c-myc.

Although activation of c-myc is a critical step in the development of lymphomas and other tumors, its normal function(s) in cell growth remain obscure because few myc-regulated genes are known. myc expression normally increases in response to mitogens and peaks in G1 when additional protein synthesis is required for cell-cycle progression. Protein synthesis is controlled by the availability of translation initiation factors, including the mRNA cap binding protein (eIF-4E) and the alpha subunit of the eIF-2 complex that binds the initiator Met-tRNA. Consequently we examined eIF-4E and eIF-2 alpha for evidence of regulation by c-myc. Expression of eIF-4E and eIF-2 alpha correlated with c-myc expression in fibroblasts after growth stimulation. In addition, expression of eIF-4E and eIF-2 alpha was increased in myc-transformed rat embryo fibroblasts but was not increased in ras-transformed cells. Transcription rates of eIF-4E and eIF-2 alpha mRNAs were regulated by c-myc in cells expressing an estrogen receptor-Myc fusion protein. Finally, electrophoretic mobility-shift assays identified a sequence element in the eIF-2 alpha promoter, TCCGCAT-GCGCG, which was specifically retarded by extracts of myc-expressing cells. c-myc is thought to deregulate the growth of cancer cells by activating transcription, suggesting that specific genes regulated by c-myc should also function as oncogenes. In previous studies these translation initiation factors could induce neoplastic growth because overexpression of eIF-4E-transformed cells and inhibition of a suppressor of eIF-2 alpha (eIF-2 alpha kinase) also caused malignant transformation. Our studies suggest that one important biological function of c-myc may be to increase cell growth by increasing expression of eIF-4E and eIF-2 alpha.

3T3 Cells↗

PubMed1993

Overexpression of CD3 eta during thymic development does not alter the negative selection process.

To elucidate the role of CD3 eta in thymic development and to determine whether CD3 eta is involved in the negative selection process, CD3 eta was overexpressed > 100 fold in transgenic (tg) mice using a Thy-1 promoter and regulatory elements. CD3 eta was readily observed in the majority of cortical thymocytes and in a fraction of medullary thymocytes in tg mice by immunohistochemical staining with an anti-CD3 eta-specific mAb. In contrast, endogenous CD3 eta levels were too low to detect in normal littermates. Flow cytometric analysis demonstrated an increased level of TCR on thymocytes with intermediate TCR density in tg animals and parallel biochemical studies showed a marked increased in TCR-associated CD3 zeta-eta heterodimers and CD3 eta-eta homodimers relative to controls. Despite this change in surface TCR phenotype, there was no significant alteration in the total numbers or proportion of CD4+CD8+ double-positive or CD4+CD8- or CD4-CD8+ single-positive thymocytes or peripheral T cells. Percentages of SP V beta 5, V beta 6, and V beta 8 thymocytes in tg animals were unaltered compared to normal littermates when backcrossed either to C57BL/6 (H-2b) or DBA/2 (H-2d) backgrounds. Furthermore, induction of DNA fragmentation with anti-CD3 epsilon mAb treatment in vivo was not significantly different for tg and normal littermates. Collectively, these data imply that CD3 eta is not a limiting component of the negative selection process.

Animals↗