Receptor-mediated hydrolysis of plasma membrane messenger PIP2 leads to K+-current desensitization

Phosphatidylinositol bisphosphate (PIP2) directly regulates functions as diverse as the organization of the cytoskeleton, vesicular transport and ion channel activity. It is not known, however, whether dynamic changes in PIP2 levels have a regulatory role of physiological importance in such functions. Here, we show in both native cardiac cells and heterologous expression systems that receptor-regulated PIP2 hydrolysis results in desensitization of a GTP-binding protein-stimulated potassium current. Two receptor-regulated pathways in the plasma membrane cross-talk at the level of these channels to modulate potassium currents. One pathway signals through the betagamma subunits of G proteins, which bind directly to the channel. Gbetagamma subunits stabilize interactions with PIP2 and lead to persistent channel activation. The second pathway activates phospholipase C (PLC) which hydrolyses PIP2 and limits Gbetagamma-stimulated activity. Our results provide evidence that PIP2 itself is a receptor-regulated second messenger, downregulation of which accounts for a new form of desensitization.

Characterization of a novel silencer element in the human aromatase gene PII promoter

Approximately two thirds of breast cancer patients have estrogen-dependent carcinomas. The biosynthesis of estrogens is catalyzed by the microsomal enzyme aromatase. Mechanisms controlling human aromatase gene expression are complicated by the existence of multiple tissue specific promoters. The most proximally located Pll promoter is mainly active in ovarian granulosa cells. PlI can be switched on in human breast cancer cells. Since there are strong silencer elements located within the 3' portion of the PlI promoter, we propose that the function of these silencer elements could be reversed by breast cancer cell specific signals/factors, resulting in aberrant expression of aromatase. We have identified and characterized a novel silencer element, S2, which is upstream of S1, a silencer element recently identified by another group. S2, a 54-bp fragment 100% conserved between humans and rodents, functions in both orientation- and promoter-independent manners. The core region of S2 contains two consensus binding sites for members of the GATA transcription factors. GATA-4 was found to be expressed in three out of four human breast cancer cell lines examined by RT-PCR, and transfection with GATA-4 partially reversed the repressive function of S2. However, we were unable to demonstrate that DNA-protein complexes formed between nuclear extracts of human breast and ovarian cancer cells and S2 contain GATA-4 using a supershifting approach. We suggest that the expression of GATA-4, and more importantly, other yet to be identified GATA or GATA-related factor(s), are implicated in provoking aberrant expression of aromatase, and therefore, the biosynthesis of estrogens, in human breast cancer cells.

Structures and magnetism of two novel heptanuclear lanthanide-centered trigonal prismatic clusters: [LnCu6(mu 3-OH)3(HL)2(L)4](ClO4)2.25H2O (Ln = La, Tb; H2L = iminodiacetic acid)

The new heteronuclear iminodiacetic acid (H2L) complexes [LnCu6(mu 3-OH)3(HL)2(L)4](ClO4)(2).25H2O with Ln = La (1) and Tb (2) have been prepared in aqueous solution and characterized by single-crystal X-ray diffraction to be isomorphous (crystallographic data for 1 and 2: hexagonal, P63/m; a = b = 12.6425(14) A, c = 24.541(5) A, Z = 2 (1); a = b = 12.5802(9) A, c = 24.285(4) A, Z = 2 (2)). Ln3+ was found to be located in the center of the trigonal prismatic cage formed by six Cu2+ ions, with a tricapped trigonal prismatic coordination environment of nine O atoms. The magnetic properties of complexes 1 and 2 have been studied. The results indicate the presence of ferromagnetic couplings between Tb3+ and Cu2+ in compound 2.

[An autopsy case of thymic carcinoma producing various tumor markers and the examination of 222 autopsy cases of thymic malignant tumor in Japan]

The autopsy of a 76-year-old Japanese female patient, which revealed thymic carcinoma with various tumor markers such as NSE, CYFRA, and CA-125, is presented. The patient died from hepatic failure because the liver was overtaken by the tumors. At autopsy, the thymic carcinoma was found to have metastased only in the liver. From microscopical analyses and electron microscopical findings, we diagnosed poorly differenciated squamous cell carcinoma of thymic origin. In the histochemical analyses, the tumor cells were positively stained in CA 125, CA 19-9, EMA, NSE, AE 1, AE 3, CEA, S-100, glimerius and Bcl-2. These date suggest that the tumor cells produced various tumor markers. In 222 autopsy cases of thymic malignant tumor observed in Japan over a period of 4 years, the dominant pathohistological image was squamous cell carcinoma. It is interesting that the greatest number of combined malignant tumors with thymic malignancies were thyroid papillary carcinomas.

[Lycopene on cancer prevention]

Many epidemiological research indicate that there is an inverse correlation between the consumption of tomato products and the risk of cancer, especially the gastrointestinal cancer and prostate cancer. The biological features of lycopene, such as molecular structure, metabolism, tissue distribution and its anti-cancer function and possible mechanism are reviewed.

Genetic association study between alpha 1-antichymotrypsin polymorphism and Alzheimer disease in Chinese Han population

We investigated a common signal peptide polymorphism in the alpha 1-antichymotrypsin (ACT) gene in 125 sporadic Alzheimer disease (AD) patients and 141 healthy control subjects in Chinese Han population. We found no significant difference in the distribution of ACT polymorphism between AD cases and controls, and failed to detect any effects of ACT genotypes associated with AD. Thus, our data do not support the involvement of ACT polymorphism in the risk of AD in Chinese Han population. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:133-135, 2000.

Development of mouse dendritic cells from lineage-negative c-kit(low) pluripotent hemopoietic stem cells in vitro

Dendritic cells (DCs) are essential for the presentation of antigens in the primary immune response. To examine the generation of DCs from hemopoietic stem cells in the bone marrow (BM), lineage-negative (Lin-)/CD71- bone marrow cells (BMCs) from C57BL/6 mice were separated into major histocompatibility complex (MHC) class Ihigh/ c-kit(low) and MHC class Ihigh/c-kit(low)(phenotypically c-kit-negative, but c-kit message only detected by reverse transcriptase-polymerase chain reaction) populations. A large number of cells with the morphological, phenotypical, and functional characteristics of DCs was generated from both c-kit(low) and c-kit(low) populations when cultured with a combination of cytokines (GM-CSF, tumor necrosis factor-a [TNF-a], interleukin 7 [IL-7], IL-3, stem cell factor [SCF], and flt3 ligand); the cytokine combination studies revealed that SCF and IL-3 in addition to GM-CSF and TNF-a are essential for DCs to be generated from these primitive populations. To our surprise most (>80%) generated cells expressed high levels of DC surface markers such as DEC205 and MHC class II, and they were potent stimulators in the primary allogeneic T cell activation. The development of DCs from c-kit(<low) cells was slower than that from c-kit(low) cells. These results indicate that c-kit(<low) cells are more primitive than c-kit(low) cells, although both c-kit*(low) cells and c-kit(<low) cells can differentiate into DCs. It should be noted that the combination of these cytokines selectively induces DCs from both c-kit(<low) and c-kit(low) cells in vitro, suggesting that the ex vivo expansion of DCs using these primitive cells would be applicable to immunotherapy.

Differential calcium transport disturbances in renal membrane vesicles after cadmium-metallothionein injection in rats

Cadmium-metallothionein (CdMT) induced calciuria may result from disturbed calcium (Ca) transport through the renal tubular epithelium. The present study aimed at defining time of onset and the degree of disturbed calcium transport. Kidneys were obtained from rats at 4, 12 and 24 h after a single injection of CdMT (dose 0.4 mg Cd/kg b.w.), and compared to saline injected controls. Rapid-filtration 45Ca-assays were performed on basolateral and luminal membrane vesicles, isolated from kidney cortex using a sequential ultracentrifugation procedure. Luminal 45Ca uptake was increased at 4 h and then declined to about 80% of controls, suggesting an early phase perturbation of Ca absorption. Basolateral 45Ca uptake was reduced to less than 50% of controls, starting already at 4 h while 45Ca binding was reduced at 8 h. This may reflect an inhibited basolateral Ca pump mechanism after the binding step. Since the Ca pump normally expels Ca from the cell, an accumulation of intracellular calcium was indicated. Metal analysis verified a four-fold increase of Ca in kidney cortex at 24 h. This suggests that Cd impact on tubular cells involves disturbances on cellular absorption as well as expulsion of Ca.

Localization of the G protein betagamma complex in living cells during chemotaxis

Gradients of chemoattractants elicit signaling events at the leading edge of a cell even though chemoattractant receptors are uniformly distributed on the cell surface. In highly polarized Dictyostelium discoideum amoebas, membrane-associated betagamma subunits of heterotrimeric guanine nucleotide-binding proteins (G proteins) were localized in a shallow anterior-posterior gradient. A uniformly applied chemoattractant generated binding sites for pleckstrin homology (PH) domains on the inner surface of the membrane in a pattern similar to that of the Gbetagamma subunits. Loss of cell polarity resulted in uniform distribution of both the Gbetagamma subunits and the sensitivity of PH domain recruitment. These observations indicate that Gbetagamma subunits are not sufficiently localized to restrict signaling events to the leading edge but that their distribution may determine the relative chemotactic sensitivity of polarized cells.

Cadmium-induced apoptosis and changes in expression of p53, c-jun and MT-I genes in testes and ventral prostate of rats

Apoptosis and a change in the expression of p53, c-jun and MT-I genes occurred in rats exposed to cadmium in a way known to cause carcinogenesis in testes and ventral prostate. In situ end labelling (ISEL), DNA electrophoresis, and RT-PCR methods were used in present study. Adult male Wistar rats were given a single (s.c.) injection of 0, 5, 10, or 20 micromol/kg CdCl2. Then 12, 48 or 96 h after administration of cadmium, animals were sacrificed. It was observed that cadmium markedly induced apoptosis in the testes at the dose of 5 micromol/kg while 10 and 20 micromol/kg cadmium caused more necrosis than apoptosis. Apoptosis in the ventral prostate was markedly induced by all the doses of cadmium and there was an obvious time- and dose-dependent relationship between apoptotic index (AI) and cadmium treatment. Far fewer apoptotic cells appeared in liver, compared to the testes and ventral prostate. p53 mRNA expression was clearly enhanced in the ventral prostate but clearly suppressed in the testes by cadmium exposure, and the time- and dose-effect was very clear. The expression level of p53 in the liver was not affected by cadmium treatment. Cadmium-induced overexpression of c-jun gene appeared at 12 h in the liver, but not until 96 h in the testes and ventral prostate. Although the MT-I gene was found to be expressed in all tissues, marked induction by cadmium of the expression of MT-I gene was only observed in the liver. These results indicate: (1) that apoptosis is an early mechanism of acute tissue damage by cadmium in the testes and ventral prostate; (2) that p53 and c-jun genes may be involved in cadmium-induced cytotoxicity (apoptosis) and related carcinogenicity in male reproductive tissues; and (3) that the enhanced expression of MT-I in the liver could protect this organ from cadmium-induced cytotoxicity (apoptosis) and carcinogenicity.

The susceptibility to nephrotoxicity of streptozotocin-induced diabetic rats subchronically exposed to cadmium chloride in drinking water

Streptozotocin-induced diabetic rats and normal non-diabetic (ND) rats were exposed to cadmium chloride in drinking water in doses of 0, 50 and 100 ppm for 90 days. There was a dose-related increase in urinary protein and enzymes in the diabetic group, but an increase in proteinuria only in the high exposure subgroup of the ND group. It is suggested that diabetic rats induced by streptozotocin are more susceptible to cadmium nephrotoxicity than normal (ND) rats. Metallothionein synthesis in liver was estimated to be similar in both the diabetic and non-diabetic groups after exposure to cadmium. Less excretion of cadmium in urine and greater accumulation of cadmium in kidney were observed in the diabetic group, and this may be one of the mechanisms underlying the susceptibility of diabetic animals to the effects of cadmium. Further biochemical and histological studies are required in order to explain the detailed events involved in inducing such changes in the toxicokinetics of cadmium.

Cell type-specific autoregulation of the Caudal-related homeobox gene Cdx-2/3

The caudal-related homeobox gene Cdx-2/3 is a critical "master" control gene in embryogenesis. Mice heterozygous for a null mutation in Cdx-2/3 exhibit multiple malfunctions including tail abnormalities, stunted growth, a homeotic shift in vertebrae, and the development of multiple intestinal adenomatous polyps, indicating that Cdx-2/3 is haplo-insufficient. In vitro studies have identified more than a half-dozen downstream target genes expressed in pancreatic and intestinal cells for this transcription factor. We have examined the transcriptional properties of the mouse Cdx-2/3 promoter. This promoter could be autoregulated in pancreatic and intestinal cells that express endogenous Cdx-2/3. In contrast, Cdx-2/3 transfection represses the Cdx-2/3 promoter in fibroblasts, which do not express endogenous Cdx-2/3. Since Cdx-2/3 activates proglucagon gene promoter in both pancreatic and intestinal cells and in fibroblasts, we suggest that some, yet to be identified, cell type-specific components are required for activating selected target gene promoters of Cdx-2/3, including the Cdx-2/3 promoter itself. Cdx-2/3 binds to the TATA box and another AT-rich motif, designated as DBS, within an evolutionarily conserved proximal element of the Cdx-2/3 promoter. The DBS motif is critical for the autoregulation, whereas the TATA box may act as an attenuating element for the autoregulatory loop. Finally, overexpression of Cdx-2/3 in a pancreatic cell line activated the expression of the endogenous Cdx-2/3. Taken together, our results indicate that the dose-dependent phenotype of Cdx-2/3 expression on its downstream targets in vivo could be regulated initially via a transcriptional network involving cell type-specific autoregulation of the Cdx-2/3 promoter.

Nucleotide sequence of a 5892 base pairs fragment of the LsMNPV genome and phylogenetic analysis of LsMNPV

A 5892 bp fragment of Leucania separata multiple nuclear polyhederosis virus (LsMNPV) containing gp37, 39 k genes and another four ORFs was sequenced in this article. According to regulatory elements on 5' uncoding sequences, the ORF4 and ORF1 are probably two novel baculovirus genes, and the ORF4 probably also is a new early-late gene. The possible functions about GP37 and 39 K proteins were explored. The homology of GP37 protein among LsMNPV and 8 other insect virus was compared. The evolutional position of LsMNPV is also estimated based on the homology of gp37 genes. The structure and its homology of several genes in LsMNPV prove that LsMNPV is far related with other baculovirus and has an exceptional genome organization.

Proteasomal degradation and N-terminal protease resistance of the codon 145 mutant prion protein

An amber mutation at codon 145 (Y145stop) of the prion protein gene results in a variant of an inherited human prion disease named Gerstmann-Sträussler-Scheinker syndrome. The characteristic features of this disorder include amyloid deposits of prion protein in cerebral parenchyma and vessels. We have studied the biosynthesis and processing of the prion protein containing the Y145stop mutation (PrP(145)) in transfected human neuroblastoma cells in an attempt to clarify the effect of the mutation on the metabolism of PrP(145) and to gain insight into the underlying pathogenetic mechanism. Our results demonstrate that 1) a significant proportion of PrP(145) is not processed post-translationally and retains the N-terminal signal peptide, 2) most PrP(145) is degraded very rapidly by the proteasome-mediated pathway, 3) blockage of proteasomal degradation results in intracellular accumulation of PrP(145), 4) most of the accumulated PrP(145) is detergent-insoluble, and both the detergent-soluble and -insoluble fractions are resistant to mild proteinase K (PK) treatment, suggesting that PK resistance is not simply because of aggregation. The present study demonstrates for the first time that a mutant prion protein is degraded through the proteasomal pathway and acquires PK-resistance if degradation is impaired.

Urinary N-acetyl-beta-D-glucosaminidase isoenzymes as biomarker of renal dysfunction caused by cadmium in a general population

N-Acetyl-beta-D-glucosaminidase (NAG) and its isoenzymes in urine have been studied in a population group residing in a polluted area in China. The area studied was contaminated by industrial wastewater from a nearby smelter that discharged cadmium-polluted wastewater into a river used for the irrigation of rice fields. Cadmium concentrations in rice were 3.70, 0.51, and 0.07 mg/kg for the highly and moderately polluted areas and the control area, respectively. Cadmium concentrations in urine exceeded 5 microgram/liter in the majority of subjects in the most highly polluted area. There was a marked dose-dependent increase in NAG and NAG B content of urine related both to urinary cadmium and to the calculated cadmium uptake. It is concluded that urinary NAG and its isoenzymes could serve as a sensitive biomarker of renal dysfunction in cadmium-exposed populations. The mechanisms underlying the increase in NAG and its isoenzymes after cadmium exposure need to be studied further.

Apoptosis and p53 gene expression in male reproductive tissues of cadmium exposed rats

Reverse transcription (RT) PCR technique was used to investigate the mechanism of apoptosis induced by Cd and the change of its related genes in testes and prostate of rats. Adult male rats were given a single (s.c.) injection of CdCl2 0, 2.5, 5.0, 10 mumol/kg. 48 h and 72 h after administration of Cd, animals were sacrificed. The results indicated that Cd can induce apoptosis in testes via p53-independent pathway. No apoptosis occurred in prostate in any of the Cd-exposed groups. There was a clearly negative relationship in testes between p53 gene expression and Cd exposure and this dose-response relationship was observed both at 48 h and 72 h. There was a very small increase of this gene expression in the dorsolateral lobe of the prostate in Cd exposed groups. The other apoptosis related gene, bcl-x, was not detectable in either control or Cd-exposed group in testes and dorsal prostate. Although the MT-I gene was expressed in testes or dorsal prostate both in control and exposed groups, no overexpression of MT-I gene was found after administration of Cd. The expression of MT-I in the ventral prostate was not detected in the control group, but a weak expression was found after Cd exposure. Since p53 is a tumor suppressor gene which can inhibit tumorigenesis, the consequence of a Cd-induced decrease of p53 in testes may have a relation to the known risk of Cd tumorigenesis in this tissue.

Persistent tolerance induced after portal venous injection of allogeneic cells plus cyclophosphamide treatment

The injection of allogeneic cells via the portal vein (p.v.) is known to reduce responses to donor-alloantigens. In the present study, we have obtained persistent tolerance across Mls and multiple minor histocompatibility complexes by p.v. preimmunization followed by the administration of cyclophosphamide (CY). A hundred percent survival of (BALB/c x DBA/2)F1 (CDF1) skin grafts for more than 200 days was observed when BALB/c mice were preimmunized with spleen cells of CDF1 (3 x 10(7)) via the p.v. and administered 300 mg/Kg CY 2 days after the p.v. injection. Comparable survival of the skin graft was observed when bone marrow cells instead of spleen cells were p.v. preimmunized. However, the survival rate was significantly decreased when LPS-stimulated blastic cells were p.v. preimmunized. Microchimerism has been observed in the liver, thymus, bone marrow and peripheral blood of recipients. V beta 6+ cells decreased in CD4+ cells of recipients of the p.v. preimmunization plus CY treatment. However, there was no difference in the decrease in V beta 6+ cells between recipients accepting the CDF1 skin grafts and recipients that had rejected the skin grafts. Furthermore, no intrathymic depletion of the V beta 6+ cells was observed. From these results, it is suggested that, rather than clonal deletion, other mechanisms such as clonal anergy or suppression may be involved in the induction of persistent tolerance after the p.v. preimmunization plus CY treatment.

c-kit<low Pluripotent hemopoietic stem cells form CFU-S on day 16

Using Ly5 congenic mice, we characterized the early differentiation step of pluripotent hemopoietic stem cells. Lineage- (Lin-)/CD71- cells in the bone marrow cells were separated into major histocompatibility complex (MHC) class I(high)/c-kit(low) and MHC class I(high)/c-kit<low populations from C57BL/6 Ly5.1 male mice. These two populations (1,000 cells) were transplanted into lethally irradiated (5.5 Gy x 2) C57BL/6 Ly5.2 female mice. Colony-forming unit in spleen (CFU-S) assays were carried out on days 10, 12, 14, 16, and 20. In the mice that received c-kit(low) cells, CFU-S were first detected on day 12, and the CFU-S counts gradually increased. In contrast, no visible colony was detected until day 14 in the mice that received c-kit<low cells; CFU-S were first observed on day 16. Donor-derived (Ly5.1+) cells, such as B cells, T cells, and myeloid cells, were detected by fluorescence-activated cell sorter analyses, and donor-derived erythroid cells were detected by polymerase chain reaction analyses using Y-chromosome-specific primers. Donor-derived cells in the recipients of c-kit(low) cells were detected in the spleen, bone marrow, and peripheral blood on day 12 after transplantation, while they were detected on day 16 in the mice that received c-kit<low cells. Therefore, c-kit<low cells have the capacity not only to form CFU-S on day 16 but also to reconstitute the recipients with donor-derived hematolymphoid cells 16 days after transplantation.

Mechanical properties of several nickel-titanium alloy wires in three-point bending tests

The purpose of this study was to clarify the mechanical properties of 42 brands of nickel-titanium alloy orthodontic wires from 9 manufacturers by conducting three-point bending tests under uniform testing conditions. Manufacturers included A-Company, Hoya Medical, Lancer, Ormco, Rocky Mountain, Sankin, Tomy (GAC), TP, and 3M/Unitek. Cobalt-chrome, and titanium-molybdenum alloy wires were also tested as a reference for comparison of force levels. All reported data were recorded during the unloading process to simulate the force that a wire exerts on a tooth as it is moved into the dental arch from a position of malocclusion. The following results were obtained for the nickel-titanium wires tested. (1) Among the 0.016 inch round wires tested under a maximum deflection of 1.5 mm, the difference between the smallest (Copper nickel-titanium 35) and the largest (Aline) load values was 136 g. For the 0.016 x 0.022 inch rectangular wires tested, the difference between the smallest (Copper nickel-titanium 40) and the largest (Aline) load values was 337 g. (2) The change in load between 1.5 and 0.5 mm of deflection was examined to clarify the superelastic properties of the wires tested. For the 0.016 inch wires, 17 wire brands produced a load difference of less than 100 g, and two brands produced a difference of at least 100 g (Aline and Titanal = 100 g). For the 0.016 x 0.022 inch wires, 15 brands produced a load difference of less than 100 g, and eight brands produced a difference of over 100 g. The smallest and largest load differences were 3 g (Copper nickel-titanium 35) and 200 g (Aline). (3) The majority of the samples with a smaller load difference between deflections of 1.5 mm and 0.5 mm in the unloading process were found among super-elastic wires, while samples with a larger load difference were predominantly found among work-hardened wires. Compared with cobalt-chrome and TMA wires, nickel-titanium alloy wires exert significantly less force. However, the amount of force varies greatly from brand to brand. Consequently, when using nickel-titanium alloy wires, brands must be selected carefully by taking into consideration the severity of the malocclusion and the stage of orthodontic treatment in each case. It is the intent of this study to offer clinicians an unbiased guide for the selection of appropriate nickel-titanium alloy wires.

[The relation between alpha1-antichymotrypsin gene polymorphism and epsilon4 allele of apolipoprotein E gene in Alzheimer disease in Chinese]

OBJECTIVE

To detect the relation between alpha1-antichymotrpsin(AACT)gene polymorphism and epsilon4 allele of apolipoprotein E (ApoE) gene in Alzheimer disease (AD) in Chinese.

METHODS

The gene polymorphisms of ApoE and AACT were genotyped in 125 AD cases and 140 controls with PCR methods and RFLP typing. Then the association between AACT polymorphism and ApoE epsilon4 was analysed.

RESULTS

There was no association between AD and any allele or genotype of AACT polymorphism; AACT polymorphism was not associated with AD ApoE epsilon4 or without ApoE epsilon4. In AACT*AT and AACT*TT genotypes, ApoE epsilon4 allele was associated with AD, but no association was observed in AACT*AA genotype.

CONCLUSION

AACT may not be associated with AD in Chinese, and this effect can not be influenced by ApoE epsilon4, but AACT gene polymorphism may affect the association between ApoE epsilon4 allele and AD.

Examination of POU homeobox gene expression in human breast cancer cells

Abnormal expression of homeobox genes may lead to the development of leukemias, lymphomas, and solid tumors. Expression of homeobox genes in mammary glands, however, has not been studied actively until recently. We have examined the expression of POU homeobox genes in human breast cancer cell lines and human breast tissue samples. Using a pair of degenerate primers for reverse transcription-polymerase chain reaction (RT-PCR) followed by DNA sequencing, we found that the human breast cancer cell line, MCF7, expresses at least 4 POU gene products: OCT1, OCT2, OCT3 and OCT11 (Skn-1a/i, Epoc-1). The expression of OCT1 and OCT2 in other human breast epithelial cell lines was further determined by Western blot analyses and electrophoretic mobility shift assay. We were unable to detect OCT11 in human breast cancer cell lines using the anti rat Skn-1a/i antibody, although the expression of this gene in both human breast cancer cell lines and human primary breast tumors was detected by RT-PCR. OCT3 is an embryonic transcription factor. We found that this gene is also expressed in human breast cancer cell lines and all human primary breast carcinomas examined, but not in normal human breast tissue. Taken together, we have shown that several POU genes are expressed in human breast epithelial cells. As OCT3 expression was detected only in the breast cancerous cells, this embryonic transcription factor could play an important role in mammary gland carcinogenesis.

Identification of domains mediating transcriptional activation and cytoplasmic export in the caudal homeobox protein Cdx-3

The caudal genes have important functions in embryonic development and cell differentiation. The caudal-related protein Cdx-2/3 (the protein designated Cdx-2 in the mouse and Cdx-3 in the hamster) is expressed in the gastrointestinal epithelium and in islet and enteroendocrine cells, where it activates proglucagon gene transcription. We show here that Cdx-3 sequences amino-terminal to the homeodomain (amino acids 1-180) function as a heterologous transcriptional activation domain when fused to the LexA DNA binding domain. A Cdx-3-Pit-1 fusion protein containing only the first 83 amino acids of Cdx-3 linked to the POU domain of Pit-1 markedly stimulated the transcriptional activity of a Pit-1-responsive promoter. Analysis of the transcriptional properties of Cdx-3 mutants in fibroblasts and islet cells revealed distinct amino-terminal subdomains that function in a cell-specific manner. Point mutations within the amino-terminal A domain were associated with reduced transcriptional activity. Furthermore, internal deletions and selected point mutations within domain A, but not the B or C domains, resulted in accumulation of mutant Cdx-3 in the cytoplasm. Unexpectedly, mutation of an Asp-Lys-Asp motif within domain A identified a putative cytoplasmic membrane-associated export signal that mediates Cdx-3 compartmentalization. These experiments delineate unique activities for specific amino-terminal sequences that are functionally important for Cdx-3 biological activity.