The HtrA1 serine protease is down-regulated during human melanoma progression and represses growth of metastatic melanoma cells

Identification of tubulins as substrates of serine protease HtrA1 by mixture-based oriented peptide library screening

Serine protease HtrA1 belongs to a family of chymotrypsin-like proteases that were first identified in bacteria and later in mammalian systems. These proteases were identified as components of protein quality control in prokaryotic systems and as regulators of diverse signaling pathways in mammalian systems. In particular, HtrA1 is implicated in trophoblast cell migration and invasion, tumor progression, chemotherapy-induced cytotoxicity, osteoarthritis, age-related macular degeneration, and pathogenesis of Alzheimer's disease. However, systematic analysis of its potential substrates in biological system is still lacking. Therefore, we performed a mixture-based oriented peptide library screening to identify putative substrates of HtrA1. We identified [AEGR]-[LAGR]-[IAMLR]-[TVIAL] as consensus residues for P1 to P4 sites. We identified several putative substrates of HtrA1 involved in the pathogenesis of various diseases. In this study, we report on the identification of tubulins as potential substrates of HtrA1, and validated tubulins as in vitro and intracellular substrates of HtrA1. These results provide initial insights into substrate identification and functional characterization of HtrA1 in pathogenesis of various diseases.

Peptidic small molecule activators of the stress sensor DegS

Bacterial DegS is a regulatory protease that acts as a molecular stress sensor and initiates a periplasmic stress response pathway. Upon binding of misfolded proteins to its PDZ domain, the protease domain of DegS is allosterically activated, thereby initiating a signal cascade that results in the elevated expression of protein quality control factors. Although the structural basis of this activation mode has been elucidated previously, it is not yet fully understood if binding to the PDZ domain is sufficient for protease domain activation or if secondary interactions with the protease domain are required. Here, we demonstrate that tripeptidic small molecule activators which only bind to the PDZ domain are sufficient to trigger DegS activation. Furthermore, we show that the hydrophobicity of the peptidic small molecule activators is a critical determinant for efficient activation.

Expression patterns of two serine protease HtrA1 forms in human placentas complicated by preeclampsia with and without intrauterine growth restriction

Preeclampsia (PE) and intrauterine growth restriction (IUGR) are pregnancy-specific disorders that have in common abnormal placental implantation, a marked proliferation of villous cytotrophoblastic cells and focal necrosis of the syncytiotrophoblast. Several studies show an ischemic placenta with a high-resistance vasculature, which cannot deliver an adequate blood supply to the feto-placental unit. The cause of PE is a matter of debate, but recently studies in mice suggest that the primary feto-placental lesions are sufficient to initiate the disease. HtrA1, a member of the family of HtrA proteins, is a secreted multidomain protein with serine protease activity. It is expressed in first and third trimester of gestation. In specimens from the first trimester of gestation, immunostaining for HtrA1 is generally found in both layers of villous trophoblast, syncytiotrophoblast and cytotrophoblast. Cytoplasm of extravillous trophoblast and extracellular matrix of cell islands and cell columns are labeled for HtrA1. Specimens from third trimester of gestation show a more intense positivity for HtrA1 in the syncytiotrophoblast than in cytotrophoblast. The extravillous trophoblast and the decidual cells, is positive for HtrA1. The purpose of this study is to investigate the expression pattern of HtrA1 in placentas from PE without IUGR (maternal PE) and with IUGR (fetal PE) by quantitative western blotting and immunohistochemistry. By quantitative western blotting analysis we observed a significant upregulation of approximately 30 kDa HtrA1 form in PE. Differently, we detected a significant total HtrA1 down-regulation in PE-IUGR. Moreover, immunostaining for HtrA1 was positive in the villous trophoblast, in the syncytial knots and irregularly in the fetal vessel walls in PE placentas while immunostaining for HtrA1was present particularly in the syncytial knots in PE-IUGR placentas. In conclusion, we suggest that the approximately 30 kDa HtrA1 form can be correlated to maternal PE while that the significant down-regulation of total HtrA1 can be correlated to placental PE. These HtrA1 alterations could be considered as possible markers to discriminate placental PE from maternal PE.

Expression and regulation of HTRA1 during chick and early mouse development

HTRA1, a member of the high temperature requirement factor A family, is a secreted serine protease that can bind to and inactivate members of the transforming growth factor-beta (TGFbeta) family, modulate insulin-like growth factor signaling and stimulate long range fibroblast growth factor (FGF) signaling in Xenopus. In vertebrates, so far homologues from mouse, human, and Xenopus have been cloned and studied. Here we report the cloning of the chicken HTRA1 homologue from a screen for FGF8 inducible genes in chick facial mesenchyme. We characterize its expression pattern from gastrulation (Hamburger and Hamilton stage 4) to day 4 of development, and in forming inner organs and limbs. We show that chick HTRA1 has a dynamic expression pattern that differs significantly from the expression of its mouse homolog. We, furthermore, demonstrate that FGF signaling is necessary and sufficient for HTRA1 expression in chick facial and forelimb mesenchyme, but is not required for HTRA1 expression in HH11 embryos.

Elevated expression of serine protease HtrA1 in preeclampsia and its role in trophoblast cell migration and invasion

OBJECTIVE

Aberrant expression of developmentally regulated genes during placental development could affect fetal growth and contribute to preeclampsia. Expression of serine protease HtrA1 is developmentally regulated with the highest expression in decidua capsularis, compared with ectoplacental cone, and with the highest expression during later stages of pregnancy, compared with early stages. This study was designed to determine the expression of HtrA1 in placental tissues from control and preeclamptic pregnancies and to determine the effect of HtrA1 expression in trophoblast cell migration and invasion.

STUDY DESIGN

HtrA1 expression was assessed by immunohistochemistry in placentas from gestational age-matched preeclamptic and control pregnancies. HtrA1 expression in extravillous trophoblast cells, HTR-8/SVneo, was assessed by immunoblotting and immunofluorescence microscopy. Finally, the effect of ectopic expression of HtrA1 on cell migration and invasion was determined in HTR-8/SVneo cells.

RESULTS

Higher expression of HtrA1 was detected in placental tissues collected from patients with early-onset preeclampsia, compared with those from gestational age-matched control samples. Moreover, ectopic expression of HtrA1 significantly attenuates HTR-8/SVneo cell migration and invasion.

CONCLUSION

Higher expression of HtrA1 is associated with early-onset preeclampsia and may affect trophoblast cell migration and invasion.

The yeast HtrA orthologue Ynm3 is a protease with chaperone activity that aids survival under heat stress

Ynm3 is the only budding yeast protein possessing a combination of serine protease and postsynaptic density 95/disc-large/zona occludens domains, a defining feature of the high temperature requirement A (HtrA) protein family. The bacterial HtrA/DegP is involved in protective stress response to aid survival at higher temperatures. The role of mammalian mitochondrial HtrA2/Omi in protein quality control is unclear, although loss of its protease activity results in susceptibility toward Parkinson's disease, in which mitochondrial dysfunction and impairment of protein folding and degradation are key pathogenetic features. We studied the role of the budding yeast HtrA, Ynm3, with respect to unfolding stresses. Similar to Escherichia coli DegP, we find that Ynm3 is a dual chaperone-protease. Its proteolytic activity is crucial for cell survival at higher temperature. Ynm3 also exhibits strong general chaperone activity, a novel finding for a eukaryotic HtrA member. We propose that the chaperone activity of Ynm3 may be important to improve the efficiency of proteolysis of aberrant proteins by averting the formation of nonproductive toxic aggregates and presenting them in a soluble state to its protease domain. Suppression studies with Deltaynm3 led to the discovery of chaperone activity in a nucleolar peptidyl-prolyl cis-trans isomerase, Fpr3, which could partly relieve the heat sensitivity of Deltaynm3.

Intracellular localization of the tumor suppressor HtrA1/Prss11 and its association with HPV16 E6 and E7 proteins

We have a long-standing interest in a nuclear protease which appears to be involved in carcinogenesis. We recently identified the protease as high temperature requirement factor A 1 (HtrA1), also known as Prss11, which is member of an oxidative stress-response family of proteases. HtrA1 has been classified as a secreted protease involved in TGFbeta signaling, but recent work has shown HtrA1 to be a tumor suppressor. Here we show that processed forms of HtrA1 are found intracellularly and intranuclearly, and the active intranuclear form of HtrA1 shows an approximately Mr 29,000. Further, expression of HPV E6/E7 proteins is associated with a post-transcriptional up-regulation of HtrA1 (most notably the nuclear form), and HtrA1 is found associated with both HPV E6 and E7 proteins.

The serine protease HtrA1 is a novel prognostic factor for human mesothelioma

AIMS

The objective of our study was to analyze the potential prognostic value of the expression of the serine protease HtrA1 and of EGFR in 70 malignant mesotheliomas.

MATERIALS & METHODS

Immunohistochemistry was used to determine the expression of HtrA1 and EGFR. Univariate and multivariate analyses were used to correlate expression of these molecular factors in combination with available clinicopathologic data to patient survival.

RESULTS

A positive, statistically significant relationship has been recorded between HtrA1 expression level and survival (p < 0.0001). By contrast, a negative relationship has been identified between EGFR expression and survival (p = 0.02). Moreover, extension of the tumor (T) and involvement of lymph nodes (N) advanced status (p = 0.001 and 0.002, respectively), as well as the sarcomatoid histotype (p = 0.005), correlated significantly with poor survival. Finally, by a multivariate Cox regression analysis, the only immunohistochemical parameter that resulted to influence overall survival was HtrA1 (p = 0.0001). Interestingly, the prognostic value of HtrA1 expression was completely independent from EGFR expression (p < 0.0001).

CONCLUSION

This is the first study of the relationship between HtrA1 expression and survival of mesothelioma patients. The data obtained strongly indicate the utilization of HtrA1 expression as a prognostic parameter for mesothelioma and suggest this serine protease as a possible molecular target for the treatment of malignant mesotheliomas.

Changes in mRNA and protein levels of human HtrA1, HtrA2 and HtrA3 in ovarian cancer

OBJECTIVES

Expression of human HtrA1, HtrA2, HtrA3 and TGF-beta1 genes was examined in ovarian tissue specimens including 19 normal ovaries, 20 benign tumors, 7 borderline tumors, 44 cancers and 8 Krukenberg tumors.

DESIGN AND METHODS

mRNA and protein levels were evaluated by semi-quantitative RT-PCR and Western-blotting methods, respectively.

RESULTS

A statistically significant decrease of HtrA1 and HtrA3 expression in ovarian tumors comparing to normal tissues was observed. A dramatic decrease of HtrA3 mRNA and protein levels in all tumor tissue groups, and a loss of HtrA3 protein in 30% malignant tumors were found. A significant decrease of HtrA1 mRNA, and of HtrA3 mRNA and protein in malignant tumors compared to benign tumors was revealed. HtrA2 expression in tumor tissues was slightly decreased. Expression of TGF-beta1 in tumor tissues was not significantly different compared to control tissues.

CONCLUSIONS

Our results show downregulation of HtrA1 and HtrA3 genes' expression in different types of ovarian tumors and give additional evidence that these genes may function as tumor suppressors.

HtrA1 inhibits mineral deposition by osteoblasts: requirement for the protease and PDZ domains

HtrA1 is a secreted multidomain protein with serine protease activity. In light of increasing evidence implicating this protein in the regulation of skeletal development and pathology, we investigated the role of HtrA1 in osteoblast mineralization and identified domains essential for this activity. We demonstrate increased HtrA1 expression in differentiating 2T3 osteoblasts prior to the appearance of mineralization. HtrA1 is subsequently down-regulated in fully mineralized cultures. The functional role of HtrA1 in matrix calcification was investigated using three complementary approaches. First, we transfected a full-length HtrA1 expression plasmid into 2T3 cells and showed that overexpression of HtrA1 delayed mineralization, reduced expression of Cbfa1 and collagen type I mRNA, and prevented BMP-2-induced mineralization. Second, knocking down HtrA1 expression using short interfering RNA induced mineral deposition by 2T3 cells. Third, by expressing a series of recombinant HtrA1 proteins, we demonstrated that the protease domain and the PDZ domain are essential for the inhibitory effect of HtrA1 on osteoblast mineralization. Finally, we tested whether HtrA1 cleaves specific matrix proteins that are known to regulate osteoblast differentiation, mineralization, and/or BMP-2 activity. Full-length recombinant HtrA1 cleaved recombinant decorin, fibronectin, and matrix Gla protein. Both the protease domain and the PDZ domain were necessary for the cleavage of matrix Gla protein, whereas the PDZ domain was not required for the cleavage of decorin or fibronectin. Type I collagen was not cleaved by recombinant HtrA1. These results suggest that HtrA1 may regulate matrix calcification via the inhibition of BMP-2 signaling, modulating osteoblast gene expression, and/or via the degradation of specific matrix proteins.

The mitochondrial serine protease HtrA2/Omi: an overview

The HtrA family refers to a group of related oligomeric serine proteases that combine a trypsin-like protease domain with at least one PDZ interaction domain. Mammals encode four HtrA proteases, named HtrA1-4. The protease activity of the HtrA member HtrA2/Omi is required for mitochondrial homeostasis in mice and humans and inactivating mutations associated with neurodegenerative disorders such as Parkinson's disease. Moreover, HtrA2/Omi is released in the cytosol, where it contributes to apoptosis through both caspase-dependent and -independent pathways. Here, we review the current knowledge of HtrA2/Omi biology and discuss the signaling pathways that underlie its mitochondrial and apoptotic functions from an evolutionary perspective.

Structural and functional analysis of the PDZ domains of human HtrA1 and HtrA3

High-temperature requirement A (HtrA) and its homologs contain a serine protease domain followed by one or two PDZ domains. Bacterial HtrA proteins and the mitochondrial protein HtrA2/Omi maintain cell function by acting as both molecular chaperones and proteases to manage misfolded proteins. The biological roles of the mammalian family members HtrA1 and HtrA3 are less clear. We report a detailed structural and functional analysis of the PDZ domains of human HtrA1 and HtrA3 using peptide libraries and affinity assays to define specificity, structural studies to view the molecular details of ligand recognition, and alanine scanning mutagenesis to investigate the energetic contributions of individual residues to ligand binding. In common with HtrA2/Omi, we show that the PDZ domains of HtrA1 and HtrA3 recognize hydrophobic polypeptides, and while C-terminal sequences are preferred, internal sequences are also recognized. However, the details of the interactions differ, as different domains rely on interactions with different residues within the ligand to achieve high affinity binding. The results suggest that mammalian HtrA PDZ domains interact with a broad range of hydrophobic binding partners. This promiscuous specificity resembles that of bacterial HtrA family members and suggests a similar function for recognizing misfolded polypeptides with exposed hydrophobic sequences. Our results support a common activation mechanism for the HtrA family, whereby hydrophobic peptides bind to the PDZ domain and induce conformational changes that activate the protease. Such a mechanism is well suited to proteases evolved for the recognition and degradation of misfolded proteins.

The secreted serine protease xHtrA1 stimulates long-range FGF signaling in the early Xenopus embryo

We found that the secreted serine protease xHtrA1, expressed in the early embryo and transcriptionally activated by FGF signals, promotes posterior development in mRNA-injected Xenopus embryos. xHtrA1 mRNA led to the induction of secondary tail-like structures, expansion of mesoderm, and formation of ectopic neurons in an FGF-dependent manner. An antisense morpholino oligonucleotide or a neutralizing antibody against xHtrA1 had the opposite effects. xHtrA1 activates FGF/ERK signaling and the transcription of FGF genes. We show that Xenopus Biglycan, Syndecan-4, and Glypican-4 are proteolytic targets of xHtrA1 and that heparan sulfate and dermatan sulfate trigger posteriorization, mesoderm induction, and neuronal differentiation via the FGF signaling pathway. The results are consistent with a mechanism by which xHtrA1, through cleaving proteoglycans, releases cell-surface-bound FGF ligands and stimulates long-range FGF signaling.

The chloromethylketone protease inhibitor AAPF(CMK) also targets ATP-dependent helicases and SAP-domain proteins

We have been studying a nuclear protease, which appears to be involved in cellular transformation, as well as in infections with high-risk human papillomaviruses (HPVs). This protease has a chymotrypsin-like substrate specificity and the chloromethylketone inhibitor AAPF(CMK) is a potent (and relatively selective) inhibitor of it. Recently, we have observed that AAPF(CMK) has potent effects in some model systems which appear not to be mediated by decreases in the nuclear protease. Here we show that AAPF(CMK) selectively reacts with ATP-dependent helicases as well as a limited spectrum of proteins in other DNA repair/chromatin remodeling nuclear complexes, including for example Cohesin complex components and proteins containing SAP-domains. In vitro, AAPF(CMK) selectively reacts with SV40 large T antigen, and inhibits its helicase activity.

Expression profiling of vitamin D treated primary human keratinocytes

Vitamin D has attracted much attention by its ability to stop cell proliferation and induce differentiation, which became of particular interest for the treatment of cancer and psoriasis. We performed an expression profile of 12 hours and 24 hours 1alpha,25-dihydroxyvitamin D(3) (1alpha,25(OH)(2)D(3)) treated primary human keratinocytes, to determine the changes in gene expression induced by the steroid in order to improve our understanding of the biological activity of 1alpha,25(OH)(2)D(3). This we expect to be useful for establishing a test system for vitamin D analogs or might open new therapeutic targets or uses for the hormone. For the filter array experiments a non-redundant set of 2135 sequence verified EST clones was used. The normalized raw data of 2 filters per time point were combined and subjected to SAM analysis to further increase the statistical significance. 86 positive and 50 negative genes were identified after 12 h. The numbers went down to 43 positive and 1 negative gene after 24 h of treatment. Fifteen genes are up-regulated over a longer period of time (12 h and 24 h). Results were verified by real-time PCR and/or Northern blots. Targets identified are involved in intracellular signaling, transcription, cell cycle, metabolism, cellular growth, constitution of the extracellular matrix or the cytoskeleton and apoptosis, immune responses, and DNA repair, respectively. Expression profiles showed an initial stop of proliferation and induction of differentiation, and resumed proliferation after prolonged incubation, most likely due to degradation of the hormone.

Progression-associated genes in astrocytoma identified by novel microarray gene expression data reanalysis

Astrocytoma is graded as pilocytic (WHO grade I), diffuse (WHO grade II), anaplastic (WHO grade III), and glioblastoma multiforme (WHO grade IV). The progression from low- to high-grade astrocytoma is associated with distinct molecular changes that vary with patient age, yet the prognosis of high-grade tumors in children and adults is equally dismal. Whether specific gene expression changes are consistently associated with all high-grade astrocytomas, independent of patient age, is not known. To address this question, we reanalyzed the microarray datasets comprising astrocytomas from children and adults, respectively. We identified nine genes consistently dysregulated in high-grade tumors, using four novel tests for identifying differentially expressed genes. Four genes encoding ribosomal proteins (RPS2, RPS8, RPS18, RPL37A) were upregulated, and five genes (APOD, SORL1, SPOCK2, PRSS11, ID3) were downregulated in high-grade by all tests. Expression results were validated using a third astrocytoma dataset. APOD, the most differentially expressed gene, has been shown to inhibit tumor cell and vascular smooth muscle cell proliferation. This suggests that dysregulation of APOD may be critical for malignant astrocytoma formation, and thus a possible novel universal target for therapeutic intervention. Further investigation is needed to evaluate the role of APOD, as well as the other genes identified, in malignant astrocytoma development.

Piroxicam and cisplatin in a mouse model of peritoneal mesothelioma

PURPOSE

The aim of the present study was to evaluate the effects of piroxicam, a widely used nonsteroidal anti-inflammatory drug, alone and in combination with cisplatin (CDDP), on cell growth of mesothelioma cells.

EXPERIMENTAL DESIGN

Cell proliferation, cell cycle analysis, and microarray technology were done on MSTO-211H and NCI-H2452 cells treated with piroxicam. Moreover, the effects of piroxicam and CDDP on tumor growth and survival of mouse xenograft models of mesothelioma were determined.

RESULTS

Piroxicam treatment of MSTO-211H and NCI-H2452 cells resulted in a significant inhibition of proliferation. Cell cycle analysis revealed that there was an increase in the rate of apoptosis in MSTO-211H cells and an increase in the cells accumulating in G2-M in NCI-H2452. Moreover, a marked tumor growth inhibition and an extended survival of mice treated with a combination of piroxicam and CDDP in MSTO-211H cell-induced peritoneal mesotheliomas was observed. Last, GeneChip array analysis of MSTO-211H mesothelioma cell line revealed that piroxicam treatment caused up-regulation of metabolic pathway-associated genes and down-regulation of genes related to RNA processing apparatus. Of note, epidermal growth factor receptor, one of the new biological targets of chemotherapy for mesothelioma, was down-regulated and HtrA1, a serine protease recently shown to be an endogenous mediator of CDDP cytotoxicity, was up-regulated following piroxicam treatment both in vitro and in vivo.

CONCLUSION

These data suggest that piroxicam sensitizes mesothelioma cells to CDDP-induced cytotoxicity by modulating the expression of several target genes. Therefore, piroxicam in combination with CDDP might potentially be useful in the treatment of patients with mesothelioma.

Serine proteases HTRA1 and HTRA3 are down-regulated with increasing grades of human endometrial cancer

OBJECTIVE

The high temperature requirement factor A (HTRA) family consists of serine proteases with domains homologous to those of bacterial HTRA. Four human HTRA members have been described: HTRA1-4. HTRA1 and HTRA3 share a high degree of domain homologies and may therefore share a functional similarity. HTRA1 mRNA and protein is reported to be down-regulated in SV40-transformed cells, a malignant melanoma cell line, ovarian tumors, and ovarian cancer cell lines, suggesting a progressive loss of HTRA1 and the protein in cancer. This raises the possibility that HTRA3 may likewise be involved in cancer. This study examined the expression of mRNA and protein levels of HTRA1 and HTRA3 in human endometrial cancer (EC).

METHODS

Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis was performed in normal endometrium (n = 4) and in three grades of EC (n = 5 for each EC grade). Immunohistochemistry was used to determine the protein expression and the cellular localization of HTRA1 and HTRA3 in normal endometrium tissue (n = 6) and in three grades of EC (n = 8-10 for each EC grade).

RESULTS

RT-PCR analysis showed a significant reduction of HTRA1 and HTRA3 mRNA in endometrial cancer compared to normal endometrium. HTRA1 and HTRA3 protein showed a similar pattern of expression in EC tissue. Positive immunostaining, scored semiquantitatively, revealed a significant decrease of HTRA1 and 3 protein expression with increasing grades of EC.

CONCLUSION

These data suggest that HTRA1 and HTRA3 mRNA and protein levels decrease with increasing grades of EC.

Negative and positive regulation of gene expression by mouse histone deacetylase 1

Histone deacetylases (HDACs) catalyze the removal of acetyl groups from core histones. Because of their capacity to induce local condensation of chromatin, HDACs are generally considered repressors of transcription. In this report, we analyzed the role of the class I histone deacetylase HDAC1 as a transcriptional regulator by comparing the expression profiles of wild-type and HDAC1-deficient embryonic stem cells. A specific subset of mouse genes (7%) was deregulated in the absence of HDAC1. We identified several putative tumor suppressors (JunB, Prss11, and Plagl1) and imprinted genes (Igf2, H19, and p57) as novel HDAC1 targets. The majority of HDAC1 target genes showed reduced expression accompanied by recruitment of HDAC1 and local reduction in histone acetylation at regulatory regions. At some target genes, the related deacetylase HDAC2 partially masks the loss of HDAC1. A second group of genes was found to be downregulated in HDAC1-deficient cells, predominantly by additional recruitment of HDAC2 in the absence of HDAC1. Finally, a small set of genes (Gja1, Irf1, and Gbp2) was found to require HDAC activity and recruitment of HDAC1 for their transcriptional activation. Our study reveals a regulatory cross talk between HDAC1 and HDAC2 and a novel function for HDAC1 as a transcriptional coactivator.

Serine protease HtrA1 modulates chemotherapy-induced cytotoxicity

Resistance to chemotherapy presents a serious challenge in the successful treatment of various cancers and is mainly responsible for mortality associated with disseminated cancers. Here we show that expression of HtrA1, which is frequently downregulated in ovarian cancer, influences tumor response to chemotherapy by modulating chemotherapy-induced cytotoxicity. Downregulation of HtrA1 attenuated cisplatin- and paclitaxel-induced cytotoxicity, while forced expression of HtrA1 enhanced cisplatin- and paclitaxel-induced cytotoxicity. HtrA1 expression was upregulated by both cisplatin and paclitaxel treatment. This upregulation resulted in limited autoproteolysis and activation of HtrA1. Active HtrA1 induces cell death in a serine protease-dependent manner. The potential role of HtrA1 as a predictive factor of clinical response to chemotherapy was assessed in both ovarian and gastric cancer patients receiving cisplatin-based regimens. Patients with ovarian or gastric tumors expressing higher levels of HtrA1 showed a higher response rate compared with those with lower levels of HtrA1 expression. These findings uncover what we believe to be a novel pathway by which serine protease HtrA1 mediates paclitaxel- and cisplatin-induced cytotoxicity and suggest that loss of HtrA1 in ovarian and gastric cancers may contribute to in vivo chemoresistance.

Evaluation of Antitumoral Properties of the Protease Inhibitor Indinavir in a Murine Model of Hepatocarcinoma

PURPOSE

Accumulating evidences show a higher incidence of hepatic neoplasm in HIV/hepatitis C virus (HCV)-coinfected individuals compared with HCV-monoinfected patients. Treatment with HIV-1 protease inhibitors inhibited cancer-promoted angiogenesis in HIV-infected patients affected by Kaposi sarcoma. We aimed to evaluate the antineoplastic potential activities of the protease inhibitor indinavir (Crixivan) in in vitro and in vivo hepatocarcinoma models.

EXPERIMENTAL DESIGN

We analyzed effects of indinavir on cell growth and invasiveness in Huh7 and SK-HEP-1 hepatocarcinoma cell lines and on in vivo tumor growth of the same cells in nude mice. Morphologic and molecular analyses on explanted tumors were carried out to evaluate vascularization and apoptosis.

RESULTS

We observed a reduced ability to invade an in vitro extracellular matrix for both cell lines treated with indinavir compared with controls (P = 0,001). Moreover, indinavir treatment was able to inhibit matrix metalloproteinase-2 proteolytic activation, whereas there was no effect on cell proliferation. The drug was also able to delay in vivo tumor growth. The inhibition of tumor growth was statistically significant from days 6 to 21 (P = 0.004 and P = 0.003, respectively). Moreover, the drug showed antiangiogenic and proapoptotic actions, as revealed by vessel count and apoptotic index by terminal deoxynucleotide transferase-mediated nick end labeling in explanted tumors. Finally, treatment with indinavir did not block the production of vascular endothelial growth factor in the tumors.

CONCLUSION

Indinavir could be helpful to prevent the development of hepatocarcinomas in HIV/HCV-coinfected individuals. In view of the current trend to substitute protease inhibitors with other antiretroviral agents, this information may have clinical implications.

Prediction of individual response to platinum/paclitaxel combination using novel marker genes in ovarian cancers

We attempted to identify potent marker genes using a new statistical analysis and developed a prediction system for individual response to platinum/paclitaxel combination chemotherapy in ovarian cancer patients based on the hypothesis that expression analysis of a set of the key drug sensitivity genes for platinum and paclitaxel could allow us to predict therapeutic response to the combination. From 10 human ovarian cancer cell lines, genes correlative in the expression levels with cytotoxicities of cisplatin (CDDP) and paclitaxel were chosen. We first selected five reliable prediction markers for the two drugs from 22 genes already known as sensitivity determinants and then identified another 8 novel genes through a two-dimensional mixed normal model using oligomicroarray expression data. Using expression data of genes quantified by real-time reverse transcription-PCR, we fixed the best linear model, which converted the quantified expression data into an IC(50) of each drug. Multiple regression analysis of the selected genes yielded three prediction formulae for in vitro activity of CDDP and paclitaxel. In the same way, using the same genes selected in vitro, we then attempted to develop prediction formulae for progression-free survival to the platinum/paclitaxel combination. We therefore constructed possible formulae using different sets of 13 selected marker genes (5 known and 8 novel genes): Utility confirmation analyses using another nine test samples seemed to show that the formulae using a set of 8 novel marker genes alone could accurately predict progression-free survival (r = 0.683; P = 0.042).

The role of human HtrA1 in arthritic disease

Human HtrA1 belongs to a widely conserved family of serine proteases involved in various aspects of protein quality control and cell fate. Although HtrA1 has been implicated in the pathology of several diseases, its precise biological functions remain to be established. Through identification of potential HtrA1 targets, studies presented herein propose that within the context of arthritis pathology HtrA1 contributes to cartilage degradation. Elevated synovial HtrA1 levels were detected in fluids obtained from rheumatoid and osteoarthritis patients, with synovial fibroblasts identified as a major source of secreted HtrA1. Mass spectrometry analysis of potential HtrA1 substrates within synovial fluids identified fibronectin as a candidate target, and treatment of fibronectin with recombinant HtrA1 led to the generation of fibronectin-degradation products that may be involved in cartilage catabolism. Consistently, treatment of synovial fibroblasts with HtrA1 or HtrA1-generated fibronectin fragments resulted in the specific induction of matrix metalloprotease 1 and matrix metalloprotease 3 expression, suggesting that HtrA1 contributes to the destruction of extracellular matrix through both direct and indirect mechanisms.

Gene expression profile associated with response to doxorubicin-based therapy in breast cancer

PURPOSE

This study was designed to identify genes that could predict response to doxorubicin-based primary chemotherapy in breast cancer patients.

EXPERIMENTAL DESIGN

Biopsy samples were obtained before primary treatment with doxorubicin and cyclophosphamide. RNA was extracted and amplified and gene expression was analyzed using cDNA microarrays.

RESULTS

Response to chemotherapy was evaluated in 51 patients, and based on Response Evaluation Criteria in Solid Tumors guidelines, 42 patients, who presented at least a partial response (> or =30% reduction in tumor dimension), were classified as responsive. Gene profile of samples, divided into training set (n = 38) and independent validation set (n = 13), were at first analyzed against a cDNA microarray platform containing 692 genes. Unsupervised clustering could not separate responders from nonresponders. A classifier was identified comprising EMILIN1, FAM14B, and PBEF, which however could not correctly classify samples included in the validation set. Our next step was to analyze gene profile in a more comprehensive cDNA microarray platform, containing 4,608 open reading frame expressed sequence tags. Seven samples of the initial training set (all responder patients) could not be analyzed. Unsupervised clustering could correctly group all the resistant samples as well as at least 85% of the sensitive samples. Additionally, a classifier, including PRSS11, MTSS1, and CLPTM1, could correctly distinguish 95.4% of the 44 samples analyzed, with only two misclassifications, one sensitive sample and one resistant tumor. The robustness of this classifier is 2.5 greater than the first one.

CONCLUSION

A trio of genes might potentially distinguish doxorubicin-responsive from nonresponsive tumors, but further validation by a larger number of samples is still needed.

The future of dermatopathology

Of the major issues that dermatopathology will face in the immediate future, two powerful challenges loom large. The first is the application of novel nondestructive imaging technologies to in vivo diagnosis in humans. The second is the application of molecular technologies to a diagnostic arena which formerly belonged exclusively to the light microscopist. The first to be considered in this context is the application of near infrared spectroscopy to the noninvasive in vivo diagnosis of neoplastic skin disease. The second will be a discussion of application, methodology and the current state of the art in microarray technologies as they apply to neoplastic dermatopathology and, in particular, the diagnosis and prognostication of melanoma.

The inflammatory and normal transcriptome of mouse bladder detrusor and mucosa

Background

An organ such as the bladder consists of complex, interacting set of tissues and cells. Inflammation has been implicated in every major disease of the bladder, including cancer, interstitial cystitis, and infection. However, scanty is the information about individual detrusor and urothelium transcriptomes in response to inflammation. Here, we used suppression subtractive hybridizations (SSH) to determine bladder tissue- and disease-specific genes and transcriptional regulatory elements (TRE)s. Unique TREs and genes were assembled into putative networks.

Results

It was found that the control bladder mucosa presented regulatory elements driving genes such as myosin light chain phosphatase and calponin 1 that influence the smooth muscle phenotype. In the control detrusor network the Pax-3 TRE was significantly over-represented. During development, the Pax-3 transcription factor (TF) maintains progenitor cells in an undifferentiated state whereas, during inflammation, Pax-3 was suppressed and genes involved in neuronal development (synapsin I) were up-regulated. Therefore, during inflammation, an increased maturation of neural progenitor cells in the muscle may underlie detrusor instability. NF-κB was specifically over-represented in the inflamed mucosa regulatory network. When the inflamed detrusor was compared to control, two major pathways were found, one encoding synapsin I, a neuron-specific phosphoprotein, and the other an important apoptotic protein, siva. In response to LPS-induced inflammation, the liver X receptor was over-represented in both mucosa and detrusor regulatory networks confirming a role for this nuclear receptor in LPS-induced gene expression.

Conclusion

A new approach for understanding bladder muscle-urothelium interaction was developed by assembling SSH, real time PCR, and TRE analysis results into regulatory networks. Interestingly, some of the TREs and their downstream transcripts originally involved in organogenesis and oncogenesis were also activated during inflammation. The latter represents an additional link between inflammation and cancer. The regulatory networks represent key targets for development of novel drugs targeting bladder diseases.

Expression of mouse HtrA1 serine protease in normal bone and cartilage and its upregulation in joint cartilage damaged by experimental arthritis

Levels of HtrA1 protein in cartilage have been reported to elevate in joints of human osteoarthritis patients. To understand roles of HtrA1 in normal osteogenesis as well as in pathogenesis of arthritis, we examine HtrA1 expression pattern during bone and cartilage development and in articular cartilage affected by experimental arthritis. HtrA1 is not expressed in mesenchymal or cartilage condensations before initiation of ossification. When ossification begins in the condensations, the expression of HtrA1 starts in chondrocytes undergoing hypertrophic differentiation near the ossification center. Hypertrophic chondrocytes found in adult articular cartilage and epiphyseal growth plates also express HtrA1. When arthritis is induced by injection of anti-collagen antibodies and lipopolysaccharide, resting chondrocytes proceed to terminal hypertrophic differentiation and start expressing HtrA1. These data suggest that hypertrophic change induces HtrA1 expression in chondrocytes both in normal and pathological conditions. HtrA1 has been reported to inhibit TGF-beta signaling. We show that HtrA1 digests major components of cartilage, such as aggrecan, decorin, fibromodulin, and soluble type II collagen. HtrA1 may, therefore, promote degeneration of cartilage by inducing terminal hypertrophic chondrocyte differentiation and by digesting cartilage matrix though its TGF-beta inhibitory activity and protease activity, respectively. In bone, active cuboidal osteoblasts barely express HtrA1, but osteoblasts which flatten and adhere to the bone matrix and osteocytes embedded in bone are strongly positive for HtrA1 production. The bone matrix shows a high level of HtrA1 protein deposition akin to that of TGF-beta, suggesting a close functional interaction between TGF-beta and HtrA1.

Tumor suppressor and growth regulatory genes are overexpressed in severe early-onset preeclampsia--an array study on case-specific human preeclamptic placental tissue

BACKGROUND

Preeclampsia is an important clinical condition with unknown etiology. We used DNA array technique to compare placental gene expression profile in severe early-onset preeclampsia from 25 to 27 gestational weeks with strictly non-affected placental samples from similar gestational weeks.

METHOD

DNA arrays were validated by showing the up-regulation of several genes typical for preeclampsia such as chorionic gonadotrophin beta-chain, tissue factor pathway inhibitor, and intercellular adhesion molecule-1. In DNA array, 5% of genes displayed less than or equal to twofold increase in expression level and only 0.2% of genes showed < or =0.5-fold decrease in expression in preeclampsia versus control. Signs of immunological factors, hypoxia, apoptosis, oxidative stress and altered thrombosis, coagulation as well as endothelial injury were seen in the gene expression profile.

RESULTS

As a new finding, we identified a group of 13 genes with a function in tumor suppression and growth regulation which were significantly up-regulated in preeclampsia. Three out of the five most highly up-regulated genes belonged to this group which included genes, such as protein phosphatase 2, phospholipid scramblase 1, transcription elongation factor, melanoma adhesion molecule, retinoic acid receptor responder 3, and RANTES.

CONCLUSIONS

It is concluded that up-regulation of tumor suppressor and growth regulatory genes may play an important role in the pathogenesis of severe early-onset preeclampsia.

Genomic deletions in cell lines derived from primitive neuroectodermal tumors of the central nervous system

Extensive genomic deletions affecting a variety of chromosomes are a common finding in primitive neuroectodermal tumors of the central nervous system (CNS-PNETs), implicating the loss of multiple tumor suppressor genes in the pathogenesis of these tumors. We have used representational difference analysis, microsatellite mapping, and quantitative polymerase chain reaction to identify and verify the presence of genomic deletions on a number of chromosomes in CNS-PNET cell lines. This systematic approach has confirmed the importance of deletions at 10q, 16q, and 17p in PNET pathology and has revealed other regions of deletion not commonly described (e.g., Xq, 1p, 7p, and 13q). These data highlight the prevalence of hemizygous loss in CNS-PNET cells, suggesting that haploinsufficiency affecting multiple tumor suppressor genes may play a fundamental role in CNS-PNET pathogenesis. The identification of specific genes and signaling pathways that are compromised in CNS-PNET cells is crucial for development of more efficacious and less invasive treatments, as are urgently needed.

Transcriptional profiling of keratinocytes reveals a vitamin D-regulated epidermal differentiation network

1alpha,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] regulates mineral homeostasis and exhibits potent anti-proliferative, prodifferentiative, and immunomodulatory activities. It mediates these effects by binding to the vitamin D receptor (VDR), which belongs to the superfamily of steroid/thyroid hormone nuclear receptors. As a result of keratinocyte differentiation and anti-proliferation activities, 1,25(OH)(2)D(3) and its synthetic analogs are therapeutically effective in psoriasis and show promise for the treatment of actinic keratosis and squamous cell carcinoma. To elucidate the VDR signaling pathway in keratinocytes, we examined the gene expression profile with 1,25(OH)(2)D(3) treatment using oligonucleotide microarrays. Out of the 12,600 genes investigated, 82 were upregulated and 16 were downregulated and many of these were involved in differentiation, proliferation, and immune response. We have identified three vitamin D-responsive chromosomal loci (1p36, 19q13, and 6p25) and show the induction of various class II tumor suppressor/growth-regulatory genes in response to 1,25(OH)(2)D(3). Finally, quantitative differences in gene expression revealed a vitamin D-regulated differentiation network and identified peptidylarginine deiminases, kallikreins, serine proteinase inhibitor family members, Kruppel-like factor 4, and c-fos as vitamin D-responsive genes, whose protein products may play an important role in epidermal differentiation in normal and diseased state.

DNA microarrays: from structural genomics to functional genomics. The applications of gene chips in dermatology and dermatopathology

The human genome project was successful in sequencing the entire human genome and ended earlier than expected. The vast genetic information now available will have far-reaching consequences for medicine in the twenty-first century. The knowledge gained from the mapping and sequencing of human genes on a genome-wide scale--commonly referred to as structural genomics--is prerequisite for studies that focus on the functional aspects of genes. A recently invented technique, known as gene chip, or DNA microarray, technology, allows the study of the function of thousands of genes at once, thereby opening the door to the new field of functional genomics. At its core, the DNA microarray utilizes a unique feature of DNA known as complementary hybridization. As such, it is not different from Southern (DNA) blot or northern (RNA) blot hybridizations, or the polymerase chain reaction, with the exception that it allows expression profiling of the entire human genome in a single hybridization experiment. The article highlights the principles, technology, and applications of DNA microarrays as they pertain to the field of dermatology and dermatopathology. The most important applications are the gene expression profiling of skin cancer, especially of melanoma. Other potential applications include gene expression profiling of inflammatory skin diseases, the mutational analysis of genodermatoses, and polymorphism screening, as well as drug development and chemosensitivity prediction. cDNA microarrays will shape the diagnostic approach of the dermatology and the dermatopathology of the future and may lead to new therapeutic options.

Implications of the serine protease HtrA1 in amyloid precursor protein processing

The defining features of the widely conserved HtrA (high temperature requirement) family of serine proteases are the combination of a catalytic protease domain with one or more C-terminal PDZ domains and reversible zymogen activation. Even though HtrAs have previously been implicated in protein quality control and various diseases, including cancer, arthritis, and neuromuscular disorder, the biology of the human family members is not well understood. Our data suggest that HtrA1 is directly involved in the beta-amyloid pathway as it degrades various fragments of amyloid precursor protein while an HtrA1 inhibitor causes accumulation of Abeta in astrocyte cell culture supernatants. Furthermore, HtrA1 colocalizes with beta-amyloid deposits in human brain samples. Potential implications in Alzheimer's disease are discussed.

Omi/HtrA2 protease mediates cisplatin-induced cell death in renal cells

Omi/HtrA2 is a mitochondrial proapoptotic serine protease that is able to induce both caspase-dependent and caspase-independent cell death. After apoptotic stimuli, Omi is released to the cytoplasm where it binds and cleaves inhibitor of apoptosis proteins. In this report, we investigated the role of Omi in renal cell death following cisplatin treatment. Using primary mouse proximal tubule cells, as well as established renal cell lines, we show that the level of Omi protein is upregulated after treatment with cisplatin. This upregulation is followed by the release of Omi from mitochondria to the cytoplasm and degradation of XIAP. Reducing the endogenous level of Omi protein using RNA interference renders renal cells resistant to cisplatin-induced cell death. Furthermore, we show that the proteolytic activity of Omi is necessary and essential for cisplatin-induced cell death in this system. When renal cells are treated with Omi's specific inhibitor, ucf-101, they become significantly resistant to cisplatin-induced cell death. Ucf-101 was also able to minimize cisplatin-induced nephrotoxic injury in animals. Our results demonstrate that Omi is a major mediator of cisplatin-induced cell death in renal cells and suggest a way to limit renal injury by specifically inhibiting its proteolytic activity.

Serine protease HtrA1 is developmentally regulated in trophoblast and uterine decidual cells during placental formation in the mouse

Development of a hemochorial placenta involves trophoblast proliferation, differentiation, and invasion into the uterus to promote blood flow to the embryo. Trophoblast invasion is tightly controlled by expression of specific proteases in the trophoblast and highly coordinated activities in the uterus. One uterine event essential for placentation is the developmentally regulated formation and regression of the decidua. In mice, decidual regression takes place in a temporal- and spatial-specific manner that is coordinated with placental development. In this study, we identified that the serine protease HtrA1 (high temperature requirement factor A1) was specifically expressed in differentiated trophoblast cells, especially the giant cells, during the early stages of placental development. A high level of HtrA1 expression was also detected in decidua capsularis specifically at the decidual-trophoblast interface where active involution occurs. Thus, we have identified a previously unknown role for HtrA1 as a protease potentially important for trophoblast differentiation/invasion and uterine decidual regression during placental development.

Pattern of expression of HtrA1 during mouse development

The human HtrA family of proteases consists of four members: HtrA1, HtrA2, HtrA3, and HtrA4. In humans the four HtrA homologues appear to be involved in several important functions such as cell growth, apoptosis, and inflammatory reactions, and they control cell fate via regulated protein metabolism. In previous studies it was shown that the expression of HtrA1 was ubiquitous in normal adult human tissues. Here we examined the expression of HtrA1 protein and its corresponding mRNA during mouse embryogenesis using Northern blotting hybridization, RT-PCR, and immunohistochemical staining analyses. Our results indicate that HtrA1 is expressed in a variety of tissues in mouse embryos. Furthermore, this expression is regulated in a spatial and temporal manner. Relatively low levels of HtrA1 mRNA are detected in embryos at the beginning of organogenesis (E8), and the levels of expression increase during late organogenesis (E14-E19). Our results show that HtrA1 was expressed during embryonic development in specific areas where signaling by TGFbeta family proteins plays important regulatory roles. The expression of HtrA1, documented both at mRNA and protein levels by RT-PCR and immunohistochemistry in the developing nervous system, is consistent with a possible role of this protein both in dividing and postmitotic neurons, possibly via its documented inhibitory effects on TGFbeta proteins. An exhaustive knowledge of the different cell- and tissue-specific patterns of expression of HtrA1 in normal mouse embryos is essential for a critical evaluation of the exact role played by this protein during development.

Developmentally regulated expression of mouse HtrA3 and its role as an inhibitor of TGF-beta signaling

The expression of mouse HtrA1 is developmentally regulated and restricted in embryo tissues which depend largely on TGF-beta signaling for their differentiation. We examined whether mouse HtrA3, another HtrA family member very close to HtrA1, shows similar expression patterns. HtrA3 and -1 were expressed mostly in the same embryonic organs but exhibited complementary patterns in various tissues; the lens epithelial cells in day 12.5 embryo expressed HtrA3 whereas the ciliary body and pigment retina expressed HtrA1. In the vertebrae of day 14.5 embryo, HtrA3 was expressed in the tail region, but HtrA1 was predominantly expressed in the thoracic and lumbar regions. Similar to HtrA1, HtrA3 bound to various TGF-beta proteins and inhibited the signaling of BMP-4, -2 and TGF-beta 1. HtrA3 did not inhibit signaling originated from a constitutively active BMP receptor, indicating that the inhibition occurred upstream of the cell surface receptor. HtrA3 also showed proteolytic activities indistinguishable from those of HtrA1 toward beta-casein and some extracellular matrix (ECM) proteoglycans. The protease activity was absolutely required for the TGF-beta signal inhibition activity. All these data suggest that HtrA3 and -1 have the overlapping biological activities but can function in complementary fashion in certain types of tissues.

Binding of proteins to the PDZ domain regulates proteolytic activity of HtrA1 serine protease

HtrA1, a member of the mammalian HtrA (high temperature requirement A) serine protease family, has a highly conserved protease domain followed by a PDZ domain. Accumulating evidence has indicated that PDZ domains regulate protease activity of HtrA proteins. We searched for binding partners of the PDZ domain of mouse HtrA1 by yeast two-hybrid screening, and isolated proteins that were recognized by the HtrA1 PDZ domain through their C-terminal ends with a core consensus Phi-X-Phi-[V/L/F/A]-COOH sequence (where Phi is a hydrophobic/non-polar amino acid). C-propeptides of fibrillar collagens were most frequently isolated. Type III procollagen alpha1 C-propeptide, which was used as a model protein, was digested by HtrA1. HtrA1 cleavage of the collagen C-propeptide was enhanced by reductive denaturation of the C-propeptide and partly inhibited by removal of the C-terminal four amino acids from the C-propeptide, suggesting that the substrate recognition was facilitated by the binding of the free C-terminal ends of substrates to the PDZ domain of HtrA1. The synthetic oligopeptide (GM130Pep) that fitted the consensus recognition sequence bound to HtrA1 with a high affinity (K(d)=6.0 nM). GM130Pep stimulated HtrA1 protease activity 3- to 4-fold, but did not efficiently stimulate the activity of an HtrA1 mutant lacking the PDZ domain, supporting the notion that the PDZ domain enhances protease activity upon ligand binding. The peptide derived from Type III collagen alpha1 C-propeptide specifically stimulated protease activity of HtrA1, but did not stimulate nor significantly bind to HtrA2, suggesting that the collagen C-propeptide is a specific physiological regulator of HtrA1.

The serine protease HtrA1 is upregulated in the human placenta during pregnancy

The placenta has a dynamic and continuous capacity for self-renewal. The molecular mechanisms responsible for controlling trophoblast proliferation are still unclear. It is generally accepted that the simultaneous activity of proteins involved in cell proliferation, apoptosis, and extracellular matrix degradation plays an important role in correct placental development. We investigated in depth the expression of the serine protease HtrA1 during pregnancy in human placenta by in situ hybridization and immunohistochemistry, we demonstrated that HtrA1 displayed a low level of expression in the first trimester of gestation and a strong increase of HtrA1 expression in the third trimester. Finally, by electron microscopy, we demonstrated that HtrA1 was localized either in the cytoplasm of placental cells, especially close to microvilli that characterized the plasma membrane of syncytiotrophoblast cells, or in the extracytoplasmic space of the stroma of placental villi, particularly in the spaces between collagen fibers and on collagen fibers themselves. The expression pattern of HtrA1 in human placentas strongly suggests a role for this protein in placental development and function. Moreover, on the basis of its subcellular distribution it can be postulated that HtrA1 acts on different targets, such as intracellular growth factors or extracellular matrix proteins, to favor the correct formation/function of the placenta.

Crystal Structure of the DegS Stress Sensor

Gram-negative bacteria respond to misfolded proteins in the cell envelope with the sigmaE-driven expression of periplasmic proteases/chaperones. Activation of sigmaE is controlled by a proteolytic cascade that is initiated by the DegS protease. DegS senses misfolded protein in the periplasm, undergoes autoactivation, and cleaves the antisigma factor RseA. Here, we present the crystal structures of three distinct states of DegS from E. coli. DegS alone exists in a catalytically inactive form. Binding of stress-signaling peptides to its PDZ domain induces a series of conformational changes that activates protease function. Backsoaking of crystals containing the DegS-activator complex revealed the presence of an active/inactive hybrid structure and demonstrated the reversibility of activation. Taken together, the structural data illustrate in molecular detail how DegS acts as a periplasmic stress sensor. Our results suggest a novel regulatory role for PDZ domains and unveil a novel mechanism of reversible protease activation.

Regulators of G-protein signaling 3 and 4 (RGS3, RGS4) are associated with glioma cell motility

Diffuse brain invasion is a major reason for poor prognosis of glioma patients. The molecular mechanisms underlying infiltration are different from those of other cancer types. To detect genes associated with glioma invasion, highly migratory clones were selected from U373MG glioma cells and from primary glioblastoma cells, and the gene expression pattern of these "fast" cells was compared with that of the original ("slow") cells using oligonucleotide microarrays comprising 12,625 genes. A total of 28 genes were differently expressed in both primary and established cell populations, including 19 genes that were upregulated and 9 that were downregulated in fast cells. Most of these genes have not been linked to glioma invasion so far. Specifically, differentially expressed genes included those encoding extracellular matrix components (COL16A1, DPT), proteases (CATD, PRSS11), cytokines (MDK, IL8), transport proteins (SLC1A3, ATP10B), cytoskeleton constituents (ACTA2, ACTSG, NEFL), DNA repair enzymes (WRN, ADPRTL2), and G-protein signaling components (GNA12, RGS3, RGS4). RGS3 and RGS4, which are homologs of the Drosophila glia gene loco, were further functionally analyzed. U373MG glioma cell clones overexpressing RGS3 or RGS4 showed an increase of both adhesion and migration. These findings expand the spectrum of possible molecular pathways underlying the invasion of neoplastic astrocytes. Specifically, they suggest that RGS proteins and G-protein-mediated signal transduction are evolutionary conserved functional players.

Normal cells control the growth of neighboring transformed cells independent of gap junctional communication and SRC activity

The growth of many types of cancer cells can be controlled by surrounding normal cells. However, mechanisms underlying this phenomenon have not been defined. We used a layered culture system to investigate how nontransformed cells suppress the growth of neighboring transformed cells. Direct physical contact between transformed and nontransformed cells was required for growth suppression of transformed cells in this system; communication by diffusible factors was not sufficient. However, significant gap junctional communication was not required, indicating that other intercellular junctions mediated this growth regulatory response. We also report that the Src kinase activity in transformed cells was not directly inhibited by contact with nontransformed cells. Instead, nontransformed cells increased the expression of serum deprivation-response protein and the transcription factor four and a half LIM domain 1 in tumor cells. In addition, these results suggest mechanisms by which normal cells may block Wnt signaling, inhibit insulin-like growth factor activity, and promote host recognition of neighboring tumor cells.

HtrA1 serine protease inhibits signaling mediated by Tgfβ family proteins

HtrA1, a member of the mammalian HtrA serine protease family, has a highly conserved protease domain followed by a PDZ domain. Because HtrA1 is a secretory protein and has another functional domain with homology to follistatin, we examined whether HtrA1 functions as an antagonist of Tgfβfamily proteins. During embryo development, mouse HtrA1 was expressed in specific areas where signaling by Tgfβ family proteins plays important regulatory roles. The GST-pulldown assay showed that HtrA1 binds to a broad range of Tgfβ family proteins, including Bmp4, Gdf5, Tgfβs and activin. HtrA1 inhibited signaling by Bmp4, Bmp2, and Tgfβ1 in C2C12 cells, presumably by preventing receptor activation. Experiments using a series of deletion mutants indicated that the binding activity of HtrA1 required the protease domain and a small linker region preceding it, and that inhibition of Tgfβ signaling is dependent on the proteolytic activity of HtrA1. Misexpression of HtrA1 near the developing chick eye led to suppression of eye development that was indistinguishable from the effects of noggin. Taken together, these data indicate that HtrA1 protease is a novel inhibitor of Tgfβ family members.

A candidate tumor suppressor HtrA1 is downregulated in ovarian cancer

We report here that HtrA1, a candidate tumor suppressor, is downregulated in ovarian cancer. Expression of HtrA1 is downregulated in five of seven ovarian cancer cell lines. In total, 59% of primary ovarian tumors have either a complete absence or markedly reduced levels of HtrA1 expression compared to the brushings of ovarian surface epithelium. Primary ovarian tumors show high frequencies of loss of an allele at microsatellite markers near htrA1 locus on 10q26. Downregulation of HtrA1 in SKOV3 by antisense transfection promotes anchorage-independent growth, while exogenous expression of HtrA1 in OV202 induces cell death. HtrA1-induced cell death is not inhibited by the broad caspase inhibitor, zVAD(OMe)fmk, but instead reflects serine protease activity associated with HtrA1. These observations raise the possibility of HtrA1 as a candidate tumor suppressor involved in promoting serine-protease-mediated cell death and that downregulation of HtrA1 in ovarian cancer may contribute to malignant phenotype.

Distribution of the serine protease HtrA1 in normal human tissues

The human HtrA family of proteases consists of three members: HtrA1, HtrA2, and HtrA3. In bacteria, the chief role of HtrA is recognition and degradation of misfolded proteins in the periplasm, combining a dual activity of chaperone and protease. In humans, the three HtrA homologues appear to be involved in diverse functions such as cell growth, apoptosis, allergic reactions, fertilization, control of blood pressure, and blood clotting. Previous studies using RNA blot hybridization have shown that the expression of HtrA1 is ubiquitous in normal human tissues. Here we show by immunohistochemistry (IHC) that HtrA1 is widely expressed, although different tissue distributions and/or levels of expression were detected in the different tissues examined. In particular, high to medium HtrA1 expression was detected in mature layers of epidermis, in secretory breast epithelium, in liver, and in kidney tubules of cortex, in concordance with its secretory properties. Furthermore, we show a higher protein expression level in the epithelium of proliferative endometrium, in contrast to epithelium of secretory endometrium, which is almost completely negative for this protein. This suggests a possible role for HtrA1 in the modulation of tissue activity in this organ. The various expression levels in human tissues indicate several possible roles for HtrA1 in different cell types.

cDNA array technology in melanoma: an overview

Genetic aberrations, mostly resulting in changes in gene expression, are critical events in cancer onset and progression. The advent of the cDNA array technology allows the screening and the efficient measurement of expression of thousands genes simultaneously in a wide spectrum of experimental and clinical models. This genomic scale approach is being currently used to obtain global views of human cancer gene expression and to identify genetic markers that might be important for diagnosis, prognosis, and therapy. This review discusses some recent findings obtained by means of cDNA arrays investigating the human melanoma.

The N-terminal region of HtrA heat shock protease from Escherichia coli is essential for stabilization of HtrA primary structure and maintaining of its oligomeric structure

HtrA heat shock protease is highly conserved in evolution, and in Escherichia coli, it protects the cell by degradation of proteins denatured by heat and oxidative stress, and also degrades misfolded proteins with reduced disulfide bonds. The mature, 48-kDa HtrA undergoes partial autocleavage with formation of two approximately 43 kDa truncated polypeptides. We showed that under reducing conditions, the HtrA level in cells was increased and efficient autocleavage occurred, while heat shock and oxidative shock caused the increase of HtrA level, but not the autocleavage. Purified HtrA cleaved itself during proteolysis of substrates but only under reducing conditions. These results indicate that the autocleavage is triggered specifically by proteolysis under reducing conditions, and is a physiological process occurring in cells. Conformations of reduced and oxidized forms of HtrA differed as judged by SDS-PAGE, indicating presence of a disulfide bridge in native protein. HtrA mutant protein lacking Cys57 and Cys69 was autocleaved even without the reducing agents, which indicates that the cysteines present in the N-terminal region are necessary for stabilization of HtrA peptide. Autocleavage caused the native, hexameric HtrA molecules dissociate into monomers that were still proteolytically active. This shows that the N-terminal part of HtrA is essential for maintaining quaternary structure of HtrA.

Identification of genes down-regulated during melanoma progression: a cDNA array study

In order to identify genes relevant for melanoma development, we carried out cDNA array experiments employing an in vitro model of human melanoma progression, consisting of two cell lines: one, LP, derived from a primary melanoma and the other, LM, from its metastatic supraclavicular lymph node. Basic cDNA array data identified 26 genes as down-regulated in the LM cell line. Northern blot analysis confirmed an effective transcriptional down-regulation for five out of 13 genes analyzed. The products of these five genes belong to different functional protein types, such as transcription and translation regulators (Edg-2, eIF-3 p110, and RNPL/RBM3), extracellular communicators (PRSS11) and members of the major histocompatibility complex (beta2-microglobulin). Some previously described differences in expression patterns, such as loss of HLA I, were confirmed by our array data. In addition, we identified and validated for the first time the reduced expression level of several genes during melanoma progression. In particular, reduced Edg-2 gene product expression was also confirmed in a group of 50 primary melanomas and unrelated metastases. In conclusion, comparative hybridization by means of cDNA arrays assisted in identifying a series of novel progression-associated changes in gene expression, confirming, at the same time, a number of previously described results.