The Wilms' tumor gene product WT1 mediates the down-regulation of the rat epidermal growth factor receptor by nerve growth factor in PC12 cells

Wilms' tumor gene 1 (WT1) silencing inhibits proliferation of malignant peripheral nerve sheath tumor sNF96.2 cell line

Wilms’ tumor gene 1 (WT1) plays complex roles in tumorigenesis, acting as tumor suppressor gene or an oncogene depending on the cellular context. WT1 expression has been variably reported in both benign and malignant peripheral nerve sheath tumors (MPNSTs) by means of immunohistochemistry. The aim of the present study was to characterize its potential pathogenetic role in these relatively uncommon malignant tumors. Firstly, immunohistochemical analyses in MPNST sNF96.2 cell line showed strong WT1 staining in nuclear and perinuclear areas of neoplastic cells. Thus, we investigated the effects of silencing WT1 by RNA interference. Through Western Blot analysis and proliferation assay we found that WT1 knockdown leads to the reduction of cell growth in a time- and dose-dependent manner. siWT1 inhibited proliferation of sNF96.2 cell lines likely by influencing cell cycle progression through a decrease in the protein levels of cyclin D1 and inhibition of Akt phosphorylation compared to the control cells. These results indicate that WT1 knockdown attenuates the biological behavior of MPNST cells by decreasing Akt activity, demonstrating that WT1 is involved in the development and progression of MPNSTs. Thus, WT1 is suggested to serve as a potential therapeutic target for MPNSTs.

Mechanisms of transcriptional regulation by WT1 (Wilms' tumour 1)

The WT1 (Wilms' tumour 1) gene encodes a zinc finger transcription factor and RNA-binding protein that direct the development of several organs and tissues. WT1 manifests both tumour suppressor and oncogenic activities, but the reasons behind these opposing functions are still not clear. As a transcriptional regulator, WT1 can either activate or repress numerous target genes resulting in disparate biological effects such as growth, differentiation and apoptosis. The complex nature of WT1 is exemplified by a plethora of isoforms, post-translational modifications and multiple binding partners. How WT1 achieves specificity to regulate a large number of target genes involved in diverse physiological processes is the focus of the present review. We discuss the wealth of the growing molecular information that defines our current understanding of the versatility and utility of WT1 as a master regulator of organ development, a tumour suppressor and an oncogene.

Loss of WT1 expression in the endometrium of infertile PCOS patients: a hyperandrogenic effect?

CONTEXT

In fertile patients the endometrial Wilms tumor suppressor gene (WT1) is expressed during the window of implantation. Polycystic ovary syndrome (PCOS) patients suffer from hyperandrogenemia and infertility and have elevated endometrial androgen receptor (AR) expression. WT1 is known to be down-regulated by AR. Therefore, the expression of WT1 and its targets may be altered in PCOS endometrium.

OBJECTIVE

The objective of the study was to assess the expression and regulation of WT1 and selected downstream targets in secretory endometrium from ovulatory PCOS (ovPCOS) and fertile women.

DESIGN AND PATIENTS

Endometrial samples were obtained from 25 ovPCOS and 25 fertile patients.

MAIN OUTCOME MEASURE

Endometrial expression of WT1 and selected downstream targets were assessed by immunohistochemistry and RT-PCR. The androgen effect on WT1 expression was determined in vitro by immunoblots and RT-PCR. The expression of WT1 and its targets was quantified in fertile and ovPCOS stromal cells in the presence of androgens by RT-PCR. Caspase-3/7 activity was measured to evaluate sensitivity to drug-induced apoptosis.

RESULTS

WT1 expression was down-regulated in secretory-phase ovPCOS endometrium. Stromal expression of Bcl-2 and p27 was higher, and epidermal growth factor receptor was lower in ovPCOS than in fertile patients. Endometrial stromal expression of WT1, Bcl-2, Bcl-2-associated X protein, and β-catenin was regulated by androgens. Apoptosis levels were reduced in ovPCOS samples and androgen-treated fertile samples.

CONCLUSION

WT1 expression is down-regulated in ovPCOS endometrium during the window of implantation. Androgens regulate the expression of WT1 and its targets during endometrial decidualization. The altered balance between WT1 and AR in the endometrium of PCOS patients may jeopardize the success of decidualization and endometrial receptivity.

Opposite regulation of estrogen receptor-α and its variant ER-α36 by the Wilms' tumor suppressor WT1

The genomic and non-genomic signaling pathways are well-known estrogen signaling pathways. The 66-kDa estrogen receptor-α (ER-α66) is a typical ligand-inducible transcription factor that mainly mediates genomic estrogen signaling. Recently, we identified and cloned a 36-kDa variant of ER-α66, known as ER-α36. This variant lacks intrinsic transcription activity and predominantly mediates non-genomic estrogen signaling. Thus, the expression of ER-α66 and ER-α36 should be firmly regulated and carefully correlated to maintain a balance between genomic and non-genomic estrogen signaling. However, the molecular mechanisms underlying this correlation remain poorly understood. The Wilms' tumor suppressor gene, wt1, encodes a zinc-finger protein WT1 that functions as a dual transcription regulator to activate or suppress gene transcription. High levels of WT1 expression are associated with breast cancer malignancy. In the present study, high-passage ER-positive breast cancer MCF7 cells were found to express ER-α66 and WT1 at higher levels and ER-α36 at a very low level. Using the small hairpin RNA method, stable MCF7 cells were established that expressed knocked-down levels of WT1. The cells expressed a reduced level of ER-α66 but an increased level of ER-α36, suggesting that WT1 regulates the expression of ER-α66 and ER-α36 oppositely. Further co-transfection assays showed that all isoforms of WT1 directly activated the promoter activity of the ER-α66 gene while suppressing ER-α36 promoter activity. Our results therefore indicate that WT1 acts as a dual transcription factor that regulates the promoter activity of ER-α66 and ER-α36 oppositely, implicating WT1 as one of the coordinators that orchestrate genomic and non-genomic estrogen signaling.

Wilms' tumor 1 silencing decreases the viability and chemoresistance of glioblastoma cells in vitro: a potential role for IGF-1R de-repression

Wilms' tumor 1 (WT1) is a transcription factor with a multitude of downstream targets that have wide-ranging effects in non-glioma cell lines. Though its expression in glioblastomas is now well-documented, the role of WT1 in these tumors remains poorly defined. We hypothesized that WT1 functions as an oncogene to enhance glioblastoma viability and chemoresistance. WT1's role was examined by studying the effect of WT1 silencing and overexpression on DNA damage, apoptosis and cell viability. Results indicated that WT1 silencing adversely affected glioblastoma viability, at times, in synergy with 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and cisplatin. To investigate other mechanisms through which WT1 could affect viability, we measured cell cycle distribution, senescence, and autophagy. WT1 silencing had no effect on these processes. Lastly, we examined WT1 regulation of IGF-1R expression. Counterintuitively, upregulation of IGF-1R was evident after WT1 silencing. In conclusion, WT1 functions as a survival factor in glioblastomas, possibly through inhibition of IGF-1R expression.

The Wilms' tumor suppressor WT1 induces estrogen-independent growth and anti-estrogen insensitivity in ER-positive breast cancer MCF7 cells

A switch from estrogen-dependent to estrogen-independent growth is a critical step in malignant progression of breast cancer and is a major problem in endocrine therapy. However, the molecular mechanisms underlying this switch remain poorly understood. The Wilms' tumor suppressor gene, wt1, encodes a zinc finger protein WT1 that functions as a transcription regulator. High levels of the WT1 expression have been associated with malignancy of breast cancer. The goal of this study was to investigate the function of WT1 in malignant progression of breast cancer. We found that the high passage ER-positive breast cancer MCF7H cells expressed EGFR, HER2 and WT1 at higher levels compared to the low passage MCF7L cells. MCF7H cells responded weakly to estrogen stimulation, grew rapidly in the absence of estrogen and were insensitive to anti-estrogens such as ICI 182,780 and 4-hydroxy-tamoxifen (4OH-TAM). We also established stable cell lines from the low passage MCF7L cells to constitutively express exogenous WT1 and found elevated levels of EGFR and HER2 expression, estrogen-independent growth and anti-estrogen insensitivity in WT1-transfected MCF7L cells. These results suggested WT1 promotes estrogen-independent growth and anti-estrogen resistance in ER-positive breast cancer cells presumably through activation of the signaling pathways mediated by the members of EGFR family.

Effect of WT1 gene silencing on the tumorigenicity of human glioblastoma multiforme cells

OBJECT

Wilms tumor 1 (WT1) is overexpressed in many human cancers, including glioblastoma multiforme (GBM). In another study, the authors showed that transient WT1 silencing increases the radiosensitivity of glioma cells. Studies of nonglioma cell lines have demonstrated that WT1 promotes cell proliferation and survival; however, this ability has not been rigorously analyzed in human GBM.

METHODS

The authors tested the efficacy of 2 sequences of short hairpin RNA (shRNA) directed against WT1 in U251MG human GBM cells and found that 1 sequence was capable of stably silencing WT1 expression. They then evaluated the effect of WT1 silencing on cellular proliferation, invasion, and in vivo tumor formation.

RESULTS

Stable WT1-shRNA expression significantly decreased the proliferation of U251MG cells in vitro as demonstrated by both an adenosine 5'-triphosphate-based viability assay and tritiated thymidine uptake. Furthermore, stable WT1 silencing caused significantly slower growth after the subcutaneous inoculation of tumor cells in the flanks of athymic nude mice and was associated with an increased latency period.

CONCLUSIONS

Data in this study provide proof of the principle that downregulation of WT1 causes decreased tumorigenicity of a GBM cell line in vitro and in vivo and suggest that WT1 is a promising target for novel molecular GBM therapies, perhaps in combination with standard treatment modalities.

NEAP causes down-regulation of EGFR, subsequently induces the suppression of NGF-induced differentiation in PC12 cells

Neuroendocrine-associated phosphatase (NEAP), an atypical dual specificity phosphatase is preferentially expressed in neuroendocrine cells. In this study we found that NEAP, but not NEAP-(C152S) mutant, evidently reduced epidermal growth factor (EGF) receptor (EGFR) downstream signaling, and impaired cell growth in response to EGF stimulation in PC12 cells. These phenomena were associated with NEAP-mediated down-regulation of EGFR mRNA and protein. NEAP had no significant effect on ErbB2/3 expression and phosphorylation levels in response to heregulin, indicating that the negative effect of NEAP on EGFR was selective. We showed that NEAP suppressed EGFR expression via decreasing the EGFR promoter activity and this was mediated through down-regulations of the Akt pathway and Wilms' tumor gene product (WT1). Consistent with these results, expression of WT1 reversed the suppressive effect of NEAP on EGFR promoter activity. Additionally, NEAP knockdown by RNA interference enhanced EGFR protein expression and nerve growth factor-induced differentiation, and an EGFR-specific inhibitor could reverse the later event. Taken together, our study indicated that NEAP modulates PC12 differentiation via suppression of EGFR expression and signaling.

WT1 induction of mitogen-activated protein kinase phosphatase 3 represents a novel mechanism of growth suppression

In its role as a tumor suppressor, WT1 transactivates several genes that are regulators of cell growth and differentiation pathways. For instance, WT1 induces the expression of the cell cycle regulator p21, the growth-regulating glycoprotein amphiregulin, the proapoptotic gene Bak, and the Ras/mitogen-activated protein kinase (MAPK) inhibitor Sprouty1. Here, we show that WT1 transactivates another important negative regulator of the Ras/MAPK pathway, MAPK phosphatase 3 (MKP3). In a WT1-inducible cell line that exhibits decreased cell growth and increased apoptosis on expression of WT1, microarray analysis showed that MKP3 is the most highly induced gene. This was confirmed by real-time PCR where MKP3 and other members of the fibroblast growth factor 8 syn expression group, which includes Sprouty 1 and the Ets family of transcription factors, were induced rapidly following WT1 expression. WT1 induction was associated with a block in the phosphorylation of extracellular signal-regulated kinase in response to epidermal growth factor stimulation, an effect mediated by MKP3. In the presence of a dominant-negative MKP3, WT1 could no longer block phosphorylation of extracellular signal-regulated kinase. Lastly, when MKP3 expression is down-regulated by short hairpin RNA, WT1 is less able to block Ras-mediated transformation of 3T3 cells.

Regulation of Wilms' tumor gene expression by nerve growth factor and follicle-stimulating hormone in the immature mouse ovary

This study investigated the regulation of Wilms' tumor gene (WT1) in the ovary by nerve growth factor and FSH to better understand signals that initiate early follicular growth. Nerve growth factor showed a direct stimulatory effect on endogenous expression of WT1, whereas FSH attenuated basal and nerve growth factor-stimulated WT1 protein expression, which most likely depended on FSH responsiveness according to the follicle growth stage.

Characterization of the insulin-like growth factor axis and Wilms' tumour suppressor gene in hyperparathyroidism

Background

Genetic mutations and upregulation of growth factors are implicated in the pathogenesis of hyperparathyroidism. The aim of this study was to evaluate the role of Wilms' tumour suppressor gene (WT-1) and the insulin-like growth factor (IGF) axis in hyperparathyroidism.

Methods

The expression of WT-1 and IGF components was examined by immunohistochemistry, reverse transcriptase–polymerase chain reaction and western immunoblotting in a panel of parathyroid specimens from both primary and secondary hyperparathyroidism. A human parathyroid cell culture model was established to examine the parathyroid response to IGF stimulation.

Results

There was a significantly lower level of WT-1 expression in parathyroid tumours than in normal parathyroid glands. Most tumours expressed IGF-I and IGF-II receptors and responded to IGF stimulation. Only IGF-I was present in normal parathyroid glands, whereas IGF-II was expressed exclusively in parathyroid tumours.

Conclusion

Abnormal expression of WT-1 and the IGF axis may play a role in the pathogenesis of hyperparathyroidism.

The role of the Wilms tumour gene (WT1) in normal and malignant haematopoiesis

In addition to its loss playing a pivotal role in the development of a childhood kidney malignancy, the Wilms tumour 1 gene (WT1) has emerged as an important factor in normal and malignant haematopoiesis. Preferentially expressed in CD34+ haematopoietic progenitors and down-regulated in more-differentiated cells, the WT1 transcription factor has been implicated in regulation of apoptosis, proliferation and differentiation. Putative target genes, such as BCL2, MYC, A1 and cyclin E, may cooperate with WT1 to modulate cell growth. However, the effects of WT1 on target gene expression appear to be isoform-specific. Certain WT1 isoforms are over-represented in leukaemia, but the exact mechanisms underlying the role of WT1 in transformation remain unclear. The ubiquity of WT1 in haematological malignancies has led to efforts to exploit it as a marker for minimal residual disease and as a prognostic factor, with conflicting results. In vitro killing of tumour cells by WT1-specific CD8+ cytotoxic T lymphocytes facilitated design of Phase I vaccine trials that showed clinical regression of WT1-positive tumours. Alternative methods employing WT1-specific immunotherapy are being investigated and might ultimately be used to optimise multimodal therapy of haematological malignancies.

Down-regulation of Wilms’ tumor 1 expression in glioblastoma cells increases radiosensitivity independently of p53

The Wilms' tumor 1 (WT1) gene is overexpressed in human glioblastoma and correlates with wild-type p53 status. In other cell types, WT1 inhibits p53-mediated apoptosis in response to DNA damaging agents. However, neither this interaction nor the relationship between WT1 and radiosensitivity has been studied in glioblastoma. To study this interaction, we generated LN-229 glioma cell lines (p53 mutant) stably expressing WT1 isoforms and induced apoptosis by transfecting with different doses of wild-type p53 plasmid expression vector. Constitutive expression of WT1 did not protect against exogenous p53-mediated apoptosis. Likewise, WT1 expression did not protect against endogenous p53-mediated cell death induced by radiotherapy in U87MG cells, which contain functional wild-type p53. We then tested the efficacy of WT1 siRNA in inhibiting WT1 expression and its effect on radiosensitivity. In T98G and LN-18 glioma cells, which possess p53 mutations, WT1 siRNA decreased WT1 protein to almost undetectable levels by 96-h post-transfection. Furthermore, WT1 siRNA transfection caused a significantly larger decrease in viability following irradiation than was seen in untransfected cells in both cell lines after treatment with ED50 of ionizing radiation. In conclusion, WT1 overexpression did not protect against p53-mediated apoptosis or ionizing radiation induced cell death. WT1 siRNA increased the radiosensitivity of two human glioma cell lines independently of p53. Anti-WT1 strategies may, therefore, prove useful in improving the response of glioblastoma to radiotherapy, thus potentially improving patient survival.

The WT1 Wilms' tumor suppressor gene is a downstream target for insulin-like growth factor-I (IGF-I) action in PC12 cells

The biological actions of the insulin-like growth factors, IGF-I and IGF-II, are mediated by the ligand-induced activation of the IGF-I receptor (IGF-IR), a transmembrane heterotetramer linked to the ras-raf-mitogen-activated protein kinase (MAPK) and phosphatidyl inositol 3 kinase (PI3K)-protein kinase B (PKB)/Akt signal transduction cascades. The Wilms' tumor suppressor gene (wt1) encodes a zinc finger transcription factor, WT1, which has been implicated in various cellular processes including proliferation, differentiation and apoptosis. In the present study we demonstrated that IGF-I modulates the WT1 gene expression in neurally derived PC12 cells in a dose- and time-dependent manner. This effect was mediated through both the MAPK and PI3-kinase signaling pathways, as shown by the ability of the specific inhibitors UO126 and LY294002 to abrogate IGF-I action. Moreover, using RT-PCR and transient transfection assays, we demonstrated that the IGF-I effect was associated with corresponding changes in WT1 mRNA levels and WT1 promoter activity. In addition, the results of the present study revealed that high WT1 levels were associated with the induction of apoptosis, whereas low WT1 levels were correlated with the inhibition of apoptosis, as demonstrated by poly ADP ribose polymerase (PARP) cleavage, Bax expression, Annexin V-FITC staining, and by the use of antisense oligonucleotides against WT1. In summary, our results show that the wt1 gene is a novel target for IGF-I action in neurally derived cells.

Pigment epithelium-derived factor targets endothelial and epithelial cells in Wilms' tumor

PURPOSE

Loss of pigment epithelium-derived factor (PEDF), a potent inhibitor of angiogenesis, has been linked to progression of angiogenesis-dependent diseases. We postulated that decreased levels of endogenous PEDF in the kidney creates a tumor permissive environment for Wilms' tumor.

METHODS

Fresh and frozen Wilms' tumor (n = 28), adjacent (n = 3), and normal kidney (n = 8) were immunostained and graded. The Wilms' tumor cells (SK-NEP-1), renal epithelial cells (NRK-52), and fresh tumor samples were grown in culture. Condition media were collected and analyzed by an in vitro angiogenesis assay and Western blot. The SK-NEP-1 cells were treated with PEDF and cell viability assessed.

RESULTS

Wilms' tumors expressed less PEDF than normal and adjacent kidney. Pigment epithelium-derived factor protein secretion was abundant in NRK-52 cells but significantly decreased in Wilms' tumor. Pigment epithelium-derived factor acted as blockade to angiogenesis and it had a dose-dependent cytotoxic effect on Wilms' tumor epithelial cells.

CONCLUSION

Renal tubular epithelial cells are a rich source of PEDF in the normal kidney. Reduced levels of PEDF in Wilms' tumor remove a critical endogenous renal barrier to angiogenesis and tumor cell survival. Therapeutic replacement of PEDF may prove to be an effective strategy to combat Wilms' tumor progression.

The effects of retinoic acid on the insulin-like growth factor axis in primary tissue culture from hyperparathyroidism

BACKGROUND

The importance of the IGF system in HPT has been previously demonstrated. Additionally, the role of vitamin A in HPT has been reported. Retinoic acid (RA), a derivative of vitamin A, is a ligand for the IGF II receptor (IGF2R). We have evaluated the interactions of RA with the IGF system in a primary parathyroid cell culture model.

MATERIALS AND METHODS

Primary cell cultures were prepared from nine patients. Following adhesion, the cells were transferred to serum-free medium and dosed once with growth factors +/- RA for 96 hours. Proliferation was assessed by measuring tritiated thymidine incorporation.

RESULTS

Compared with the control group (100%), both IGF I and II increased DNA synthesis significantly. Retinoic acid significantly reduced the basal DNA synthesis to 82.2% +/- 4.2% compared with control (P < 0.05). Retinoic acid x10(-5) M completely abrogated the proliferative actions of IGF II (70.2% +/- 9.7%, P < 0.05) but had no significant effect on the IGF I response (P > 0.05). To evaluate the role of IGF2R or IGFBPs in mediating the actions of RA, the IGF II analogs [Leu27]IGF II (10-20-fold reduced IGF I receptor affinity) and des(1-6) IGF II (lower IGFBP binding affinity) were used. The IGF II inhibitory effect of RA was enhanced in the presence of analogs [Leu27]IGF II (P = 0.052) but not with des(1-6)IGF II (P > 0.05), compared with wild-type IGF II.

CONCLUSIONS

These data implicate a novel antiproliferative role for RA in enhancing the pericellular clearance of IGF II via the IGF2R preventing ligand activation of the IGF I receptor. This may have broader implications for RA effects in other tumors.

Expression of the Wilms' tumor gene product WT1 in glioblastomas and medulloblastomas

The Wilms' tumor gene WT1 was first identified as the gene responsible for a childhood renal tumor, Wilms' tumor. This gene encodes for a zinc finger-containing transcription factor. Although originally identified as a tumor suppressor gene, WT1 is overexpressed in a variety of hematologic malignancies and solid tumors. Recently, WT1 protein has been considered as a new molecular target of cancer immunotherapy for several solid tumors. In the present study, we investigated the expression of WT1 protein and WT1 mRNA in glioblastomas and medulloblastomas. Forty-eight of 51 glioblastoma samples (94%) showed immunohistochemically positive staining of WT1 protein, whereas all 10 medulloblastomas examined were negative. According to the immunohistochemical expression of WT1 protein, WT1 mRNA was also highly expressed in the same glioblastoma tissue. Our results suggest that the WT1 gene may play an important role in the tumorigenesis of glioblastoma, in contrast to medulloblastoma, and be integral in the development of the immunotherapy targeting WT1 protein in patients with glioblastoma.

Human cytotoxic T lymphocytes specific for Wilms' tumor antigen-1 inhibit engraftment of leukemia-initiating stem cells in non-obese diabetic-severe combined immunodeficient recipients

Leukemia is a disease characterized by the malignant transformation of hematopoietic stem cells. Previous studies have shown that the Wilms' tumor antigen-1 (WT1) transcription factor is expressed at elevated levels in hematopoietic stem cells of leukemia patients compared with normal stem cells. In the past, we have generated cytotoxic T lymphocytes (CTL) specific for WT1, and we have shown that they killed WT1-expressing leukemia cell lines and inhibited the in vitro colony-forming activity of leukemia cells of patients. We used a xenotransplantation model to address whether WT1-specific CTL can selectively inhibit engraftment of malignant but not normal stem cells. CD34+ hematopoietic cells isolated from individuals with chronic myeloid leukemia or normal hematopoiesis were treated with WT1-specific CTL and injected into immunodeficient non-obese diabetic-severe combined immunodeficient mice. After 5 to 8 weeks, engraftment of leukemic or normal human cells was analyzed using immunohistology, flow cytometry, and polymerase chain reaction amplification of human sequences. The data showed that exposure of chronic myeloid leukemia CD34+ cells to WT1-specifc CTL completely prevented the development of leukemia in the recipient mice, whereas CTL treatment did not inhibit engraftment of normal CD34+ stem cells. The experiments indicate that WT1-specific CTL can discriminate between stem cells that give raise to leukemia and normal hematopoiesis in the xenogenic transplantation model. This supports the use of CTL with this specificity for treatment of leukemia patients undergoing stem-cell transplantation.

Non-coding ribonucleic acids--a class of their own?

Non-coding ribonucleic acids (RNAs) do not contain a peptide-encoding open reading frame and are therefore not translated into proteins. They are expressed in all phyla, and in eukaryotic cells they are found in the nucleus, cytoplasm, and mitochondria. Non-coding RNAs either can exert structural functions, as do transfer and ribosomal RNAs, or they can regulate gene expression. Non-coding RNAs with regulatory functions differ in size ranging from a few nucleotides to over 100 kb and have diverse cell- or development-specific functions. Some of the non-coding RNAs associate with human diseases. This chapter summarizes the current knowledge about regulatory non-coding RNAs.

Neuronal apoptosis induced by endoplasmic reticulum stress

Apoptosis is a conserved active cellular mechanism occurring under a range of physiological and pathological conditions. In the nervous system, apoptosis plays crucial roles in normal development and neuronal degenerating diseases. Various deleterious conditions, including accumulation of the mutant proteins in the endoplasmic reticulum (ER) and inhibition of ER to Golgi transport of proteins, may result in apoptosis. In this study, we examined the downstream events of apoptosis in differentiated PC 12 cells under ER stress induced by brefeldin A, an inhibitor of ER to Golgi protein transport. Activation of NF-kappaB and degradation of I-kappaB were observed within 2 hours, followed by up-regulation of GRP78 protein level in treated cells. Caspase-12 only appeared around 24 hours after brefeldin A treatment, coincident with cell nuclei fragmentation. These results suggest that neuronal apoptosis may be induced by ER stress through a NF-kappaB and caspase related pathway.

Downregulation of Wilms' tumor 1 protein inhibits breast cancer proliferation

High levels of Wilms' Tumor 1 (WT1) mRNA have been correlated with poor prognosis in breast cancer patients. However, the function of WT1 protein in breast cancer is not known. We observed that the levels of WT1 protein correlated with the proliferation of breast cancer cells. When the proliferation of breast cancer cells was stimulated by 17beta-estradiol, WT1 protein expression increased. But when the proliferation of breast cancer cells was inhibited by tamoxifen or all-trans retinoic acid (ATRA), WT1 protein expression decreased. We hypothesize that WT1 protein plays a role in regulating breast cancer cell proliferation. Using liposome-incorporated WT1 antisense oligodeoxynucleotides, we found that downregulation of WT1 protein expression led to breast cancer growth inhibition and reduced cyclin D1 protein levels. These results indicate that WT1 protein contributes to breast cancer progression by promoting breast cancer cell proliferation.

Growth and death in the developing mammalian kidney: signals, receptors and conversations

Because the kidney (metanephros) starts to function before completing development, its patterning and morphogenesis need to be closely integrated with its growth. This is achieved by blast cells at the kidney periphery generating new nephrons that link up to the extending collecting-duct arborisation, while earlier-formed and more internal nephrons are maturing and beginning to filter serum. This pattern of development requires that cell division and apoptosis be co-ordinated in the various kidney compartments (collecting-ducts, blast cells, metanephric mesenchyme, nephrons and vascular system). The underlying regulatory networks for cell proliferation are beginning to be unravelled, mainly through expression studies, mutation analysis and experimentation in vitro. This article summarises current knowledge of kidney growth and apoptosis, and analyses some of the 80 or so ligand-receptor pairings that seem to sustain development and growth. It also points to some unanswered questions, the most intriguing being what role does apoptosis play during normal kidney development?

WT1 proteins: functions in growth and differentiation

The Wilms' tumor 1 gene (WT1) has been identified as a tumor suppressor gene involved in the etiology of Wilms' tumor. Approximately 10% of all Wilms' tumors carry mutations in the WT1 gene. Alterations in the WT1 gene have also been observed in other tumor types, such as leukemia, mesothelioma and desmoplastic small round cell tumor. Dependent on the tumor type, WT1 proteins might either function as tumor suppressor proteins or as survival factors. Mutations in the WT1 gene can also result in congenital abnormalities as observed in Denys-Drash and Frasier syndrome patients. Mouse models have proven the critical importance of WT1 expression for the development of several organs, including the kidneys, the gonads and the spleen. The WT1 proteins seem to perform two main functions. They regulate the transcription of a variety of target genes and may be involved in post-transcriptional processing of RNA. The WT1 gene encodes at least 24 protein forms. These isoforms have partially distinct biological functions and effects, which in many cases are also specific for the model system in which WT1 is studied. This review discusses the molecular mechanisms by which the various WT1 isoforms exert their functions in normal development and how alterations in WT1 may lead to developmental abnormalities and tumor growth.