Tackling EGFR signaling with TACE antagonists: a rational target for metalloprotease inhibitors in cancer

ADAM17 inhibition enhances platinum efficiency in ovarian cancer

Chemotherapeutic resistance evolves in about 70 % of ovarian cancer patients and is a major cause of death in this tumor entity. Novel approaches to overcome these therapeutic limitations are therefore highly warranted. A disintegrin and metalloprotease 17 (ADAM17) is highly expressed in ovarian cancer and required for releasing epidermal growth factor receptor (EGFR) ligands like amphiregulin (AREG). This factor has recently been detected in ascites of advanced stage ovarian cancer patients. However, it is not well understood, whether and how ADAM17 might contribute to chemo resistance of ovarian cancer.

In this study, we identified ADAM17 as an essential upstream regulator of AREG release under chemotherapeutic treatment in ovarian cancer cell lines and patient derived cells. In the majority of ovarian cancer cells cisplatin treatment resulted in enhanced ADAM17 activity, as shown by an increased shedding of AREG. Moreover, both mRNA and the protein content of AREG were dose-dependently increased by cisplatin exposure. Consequently, cisplatin strongly induced phosphorylation of ADAM17-downstream mediators, the EGFR and extracellular signal-regulated kinases (ERK). Phorbol 12-myristate 13-acetate (PMA), similarly to cisplatin, mediated AREG shedding and membrane fading of surface ADAM17.

Inhibition of ADAM17 with either GW280264X or the anti-ADAM17 antibody D1 (A12) as well as silencing of ADAM17 by siRNA selectively reduced AREG release. Thus, ADAM17 inhibition sensitized cancer cells to cisplatin-induced apoptosis, and significantly reduced cell viability.

Based on these findings, we propose that targeting of ADAM17 in parallel to chemotherapeutic treatment suppresses survival pathways and potentially diminish evolving secondary chemo resistance mechanisms.

Role of ADAM17 in invasion and migration of CD133-expressing liver cancer stem cells after irradiation

We investigated the biological role of CD133-expressing liver cancer stem cells (CSCs) enriched after irradiation of Huh7 cells in cell invasion and migration. We also explored whether a disintegrin and metalloproteinase-17 (ADAM17) influences the metastatic potential of CSC-enriched hepatocellular carcinoma (HCC) cells after irradiation. A CD133-expressing Huh7 cell subpopulation showed greater resistance to sublethal irradiation and specifically enhanced cell invasion and migration capabilities. We also demonstrated that the radiation-induced MMP-2 and MMP-9 enzyme activities as well as the secretion of vascular endothelial growth factor were increased more predominantly in Huh7^CD133+ cell subpopulations than Huh7^CD133− cell subpopulations. Furthermore, we showed that silencing ADAM17 significantly inhibited the migration and invasiveness of enriched Huh7^CD133+ cells after irradiation; moreover, Notch signaling was significantly reduced in irradiated CD133-expressing liver CSCs following stable knockdown of the ADAM17 gene. In conclusion, our findings indicate that CD133-expressing liver CSCs have considerable metastatic capabilities after irradiation of HCC cells, and their metastatic capabilities might be maintained by ADAM17. Therefore, suppression of ADAM17 shows promise for improving the efficiency of current radiotherapies and reducing the metastatic potential of liver CSCs during HCC treatment.

Role of ADAM17 in invasion and migration of CD133-expressing liver cancer stem cells after irradiation

We investigated the biological role of CD133-expressing liver cancer stem cells (CSCs) enriched after irradiation of Huh7 cells in cell invasion and migration. We also explored whether a disintegrin and metalloproteinase-17 (ADAM17) influences the metastatic potential of CSC-enriched hepatocellular carcinoma (HCC) cells after irradiation. A CD133-expressing Huh7 cell subpopulation showed greater resistance to sublethal irradiation and specifically enhanced cell invasion and migration capabilities. We also demonstrated that the radiation-induced MMP-2 and MMP-9 enzyme activities as well as the secretion of vascular endothelial growth factor were increased more predominantly in Huh7CD133+ cell subpopulations than Huh7CD133- cell subpopulations. Furthermore, we showed that silencing ADAM17 significantly inhibited the migration and invasiveness of enriched Huh7CD133+ cells after irradiation; moreover, Notch signaling was significantly reduced in irradiated CD133-expressing liver CSCs following stable knockdown of the ADAM17 gene. In conclusion, our findings indicate that CD133-expressing liver CSCs have considerable metastatic capabilities after irradiation of HCC cells, and their metastatic capabilities might be maintained by ADAM17. Therefore, suppression of ADAM17 shows promise for improving the efficiency of current radiotherapies and reducing the metastatic potential of liver CSCs during HCC treatment.

Soluble TNF Regulates TACE via AP-2α Transcription Factor in Mouse Dendritic Cells

Dendritic cells (DCs), the essential immunoregulatory and APCs, are major producers of the central mediator of inflammation, soluble TNF-α (sTNF). sTNF is generated by TNF-α converting enzyme (TACE) proteolytic release of the transmembrane TNF (tmTNF) ectodomain. The mechanisms of TACE and sTNF regulation in DCs remain elusive. This study newly defines that sTNF regulates TACE in mouse DCs by engaging the AP-2α transcription factor. We found that the expression of AP-2α was higher, whereas the expression and activity of TACE were lower, in wild-type DCs (wtDCs) than in TNF knockout (TNFko) DCs. Exogenous sTNF rapidly and simultaneously induced increases of AP-2α expression and decreases of TACE expression and activity in wtDCs and TNFko DCs, indicating that AP-2α and TACE are inversely dependent on sTNF and are functionally associated. To define this functional association, we identified an AP-2α binding site in TACE promoter and demonstrated, using EMSAs and chromatin immunoprecipitation assays, that AP-2α could bind to TACE promoter in a TNF-dependent manner. Additionally, sTNF simultaneously enhanced AP-2α expression and decreased TACE promoter luciferase activity in DCs. Similarly, transfection of AP-2α cDNA decreased TACE promoter luciferase activity, TACE expression, and TACE enzymatic activity in wtDCs or TNFko DCs. In contrast, transfection of AP-2α small interfering RNA increased TACE promoter luciferase activity, TACE expression, and TACE enzymatic activity in wtDCs. These results show that TACE is a target of, and is downregulated by, sTNF-induced AP-2α transcription factor in DCs.

Targeted elimination of activated hepatic stellate cells by an anti-epidermal growth factor-receptor single chain fragment variable antibody-tumor necrosis factor-related apoptosis-inducing ligand (scFv425-sTRAIL)

BACKGROUND

Progressive liver fibrosis is the result of chronic liver injury and is characterized by the excessive accumulation of extracellular matrix that may result in liver failure. Activated hepatic stellate cells are known to play a central role in this process and their elimination is a crucial step towards the resolution and reversion of liver fibrosis. In the present study, we investigated the potential application of an anti-epidermal growth factor receptor single chain fragment variable antibody-tumor necrosis factor-related apoptosis-inducing ligand (scFv425-sTRAIL) fusion protein in the targeted elimination of activated hepatic stellate cells.

METHODS

Activated hepatic stellate cells (LX2 cells) were treated by adenovirus-derived scFv425-sTRAIL to evaluate its effect on the viability and extracellular matrix production of this type of cells.

RESULTS

In vitro treatment of activated hepatic stellate cells with scFv425-sTRAIL induced a significant reduction in viability (up to 100% reduction) and extracellular matrix production (60% reduction), yet no significant effect was observed on hepatic parenchymal cells. Blockage of the epidermal growth factor receptor (EGFR) by a monoclonal antibody significantly reduced the effectiveness of scFv425-sTRAIL in activated hepatic stellate cells, whereas a reduced effectivity was also observed after inhibition of the caspase pathway.

CONCLUSIONS

Evidence is presented for the successful application of the scFv425-sTRAIL fusion protein in the targeted elimination of activated hepatic stellate cells via EGFR and simultaneous activation of the caspase pathway. scFv425-sTRAIL may thus represent a new therapeutic compound against liver fibrosis.

Targeting the sheddase activity of ADAM17 by an anti-ADAM17 antibody D1(A12) inhibits head and neck squamous cell carcinoma cell proliferation and motility via blockage of bradykinin induced HERs transactivation

A disintegrin and metalloproteinase 17 (ADAM17) regulates key cellular processes including proliferation and migration through the shedding of a diverse array of substrates such as epidermal growth factor receptor (EGFR) ligands. ADAM17 is implicated in the pathogenesis of many diseases including rheumatoid arthritis and cancers such as head and neck squamous cell carcinoma (HNSCC). As a central mediator of cellular events, overexpressed EGFR is a validated molecular target in HNSCC. However, EGFR inhibition constantly leads to tumour resistance. One possible mechanism of resistance is the activation of alternative EGFR family receptors and downstream pathways via the release of their ligands. Here, we report that treating human HNSCC cells in vitro with a human anti-ADAM17 inhibitory antibody, D1(A12), suppresses proliferation and motility in the absence or presence of the EGFR tyrosine kinase inhibitor (TKI) gefitinib. Treatment with D1(A12) decreases both the endogenous and the bradykinin (BK)-stimulated shedding of HER ligands, accompanied by a reduction in the phosphorylation of HER receptors and downstream signalling pathways including STAT3, AKT and ERK. Knockdown of ADAM17, but not ADAM10, also suppresses HNSCC cell proliferation and migration. Furthermore, we show that heregulin (HRG) and heparin-binding epidermal growth factor like growth factor (HB-EGF) predominantly participate in proliferation and migration, respectively. Taken together, these results demonstrate that D1(A12)-mediated inhibition of cell proliferation, motility, phosphorylation of HER receptors and downstream signalling is achieved via reduced shedding of ADAM17 ligands. These findings underscore the importance of ADAM17 and suggest that D1(A12) might be an effective targeted agent for treating EGFR TKI-resistant HNSCC.

Evaluation of serum Amphiregulin levels in breast cancer patients and cancer-free controls

Background

Expression of the Epidermal Growth Factor Receptor ligand, Amphiregulin, has been associated with estrogen receptor positive breast cancer. As Amphiregulin is proteolytically released from the surface of breast cancer cells, we investigated the levels of Amphiregulin in the serum of breast cancer patients and cancer-free women to evaluate its potential utility as a breast cancer biomarker.

Findings

Serum Amphiregulin levels were quantified by ELISA from 125 cancer-free women and 114 breast cancer patients. No significant association between serum Amphiregulin levels and breast cancer status was detected at two cut-points evaluated.

Conclusions

Measurement of serum Amphiregulin levels lacks the necessary sensitivity and specificity for breast cancer screening in the general population.

Association of epidermal growth factor and epidermal growth factor receptor polymorphisms with the risk of hepatitis B virus-related hepatocellular carcinoma in the population of North China

BACKGROUND

Hepatocellular carcinoma (HCC) is a common solid malignant tumor occurring worldwide that leads to the third largest cause of death compared to other cancers. Genetic and environmental factors are involved in the pathogenesis of HCC. Epidermal growth factor (EGF) and epidermal growth factor receptor (EGFR) can stimulate the proliferation of epidermal and epithelial cells. The EGF signal pathway has a relationship with the growth of the embryo, tissue repairing, and tumorigenesis.

METHODS

In this study, 416 patients with hepatitis B virus infection (HBV)-related HCC and 645 individuals who had never been infected with HBV of the Chinese Han population were enrolled. Eight single-nucleotide polymorphisms (SNPs), whose minor allele frequency >20% in the EGF and EGFR genes, were genotyped to examine their associations with hepatocarcinogenesis. Genotyping experiments were carried out using TaqMan.

RESULTS

There were significant differences in genotype distributions (p=0.005) and allele frequencies (p=0.001, odds ratio [OR]=1.43, 95% confidence interval [CI]=1.15-1.79) of rs11569017 in the EGF gene between the HCC and control groups. After binary logistic regression to determine independent factors for susceptibility to HCC under an additive model, rs11569017 was still independently associated with the susceptibility to HCC (p=0.021, OR=1.48, 95% CI=1.06-2.07), but no significant differences in other SNPs were found. Additionally, the haplotype T-G constructed by rs11569017 and rs4444903 of the EGF gene might increase the risk of HBV-related HCC (p=0.002, OR=1.44, 95% CI=1.15-1.82).

CONCLUSION

The rs11569017 T allele was associated with susceptibility to HBV-related HCC.

Blockade of tumor necrosis factor-α converting enzyme (TACE) enhances IL-1β and IFN-γ via caspase-1 activation: a probable cause for loss of efficacy of TACE inhibitors in humans?

TNF-α converting enzyme (TACE) is a member of the ADAM (a disintegrin and metalloproteinase) family and is known as ADAM17, which processes precursor TNF-α in order to release soluble TNF-α (sTNF-α). Inhibition of TACE has been effective as a strategy to inhibit arthritis in animal models; however, it has not been translated in the clinic due to lack of efficacy or toxicity. We hypothesized that inhibition of TACE may activate a different pro-inflammatory pathway in human. To investigate this, we studied the effect of TACE inhibitor DPC-333 on cytokine levels in concanavalin A (Con A) activated human peripheral blood mononuclear cells (hPBMC). We have also studied the effects of DPC-333 on Con A induced cytokine levels in mice in vivo or in vitro in whole blood assay. DPC-333 treatment significantly up-regulated IL-1β and IFN-γ in Con A activated hPBMC. In contrast, pre-treatment with DPC-333 effectively suppressed IL-1β and IFN-γ in mice in vivo or in vitro. Interestingly, DPC-333 was found to up-regulate mRNA expression of caspase-1 in hPBMC in a dose dependent fashion and selective caspase-1 inhibitor completely restored DPC-333 induced IL-1β and IFN-γ. Furthermore, selective IL-1β receptor antagonist (anakinra) prevented DPC-333 induced IFN-γ. In conclusion, our data demonstrates that blockade of TACE enhances IL-1β in a caspase-1 dependent manner in vitro in hPBMC and the elevation of IFN-γ is secondarily mediated via IL-1β. This novel finding might explain the possible cause behind the loss of efficacy of TACE inhibitors in human.

Tumor selective cytotoxic action of a thiomorpholin hydroxamate inhibitor (TMI-1) in breast cancer

Background

Targeted therapies, associated with standard chemotherapies, have improved breast cancer care. However, primary and acquired resistances are frequently observed and the development of new concepts is needed. High-throughput approaches to identify new active and safe molecules with or without an “a priori” are currently developed. Also, repositioning already-approved drugs in cancer therapy is of growing interest. The thiomorpholine hydroxamate compound TMI-1 has been previously designed to inhibit metalloproteinase activity for the treatment of rheumatoid arthritis. We present here the repositioning of TMI-1 drug in breast cancer.

Methodology/Principal Findings

We tested the effect of TMI-1 on luminal, basal and ERBB2-overexpressing breast tumor cell lines and on MMTV-ERBB2/neu tumor evolution. We measured the effects on i) cell survival, ii) cell cycle, iii) extrinsic and intrinsic apoptotic pathways, iv) association with doxorubicin, docetaxel and lapatinib, v) cancer stem cells compartment. In contrast with conventional cytotoxic drugs, TMI-1 was highly selective for tumor cells and cancer stem cells at submicromolar range. All non-malignant cells tested were resistant even at high concentration. TMI-1 was active on triple negative (TN) and ERBB2-overexpressing breast tumor cell lines, and was also highly efficient on human and murine “primary” ERBB2-overexpressing cells. Treatment of transgenic MMTV-ERBB2/neu mice with 100 mg/kg/day TMI-1 alone induced tumor apoptosis, inhibiting mammary gland tumor occurrence and development. No adverse effects were noticed during the treatment. This compound had a strong synergistic effect in association with docetaxel, doxorubicin and lapatinib. We showed that TMI-1 mediates its selective effects by caspase-dependent apoptosis. TMI-1 was efficient in 34/40 tumor cell lines of various origins (ED50: 0.6 µM to 12.5 µM).

Conclusions/Significance

This is the first demonstration of the tumor selective cytotoxic action of a thiomorpholin hydroxamate compound. TMI-1 is a novel repositionable drug not only for the treatment of adverse prognosis breast cancers but also for other neoplasms.

ADAM17 regulates prostate cancer cell proliferation through mediating cell cycle progression by EGFR/PI3K/AKT pathway

A disintegrin and metalloprotease 17 (ADAM17) is a transmembrane protein that can cleave membrane anchored proteins to release soluble factors and regulate important biological phenomena in cancers. In the present study, we evaluated the effects of ADAM17 on the proliferation and on the cell cycle distribution of human prostate cancer cells. Experiments were also performed to gain insights into the possible mechanism of action of ADAM17. We used over-expression and RNAi strategy to investigate the function of ADAM17 in human prostate cancer cells. Changes in rate of proliferation and cell cycle profile were measured by growth curve, Cell Counting Kit-8 (CCK-8) assay, bromodeoxyuridine (BrdU) incorporation assay and cell cycle analysis. In addition, changes in expression of associated genes and proteins were studied by semiquantitative RT-PCR, western blotting and ELISA analysis. Ectopic over-expression of ADAM17 resulted in increased cell proliferation. We also showed that ADAM17 promoted G1 to S phase transition concomitantly with upregulation of cyclin E, CDK2 and downregulation of p21 and p27 proteins. ADAM17 over-expression cells showed that more TGF-α released to the supernatant and activated the EGFR/PI3K/AKT pathway. Conversely, silencing ADAM17 led to the opposite effect. Both siRNAs knockdown of ADAM17 and blocking the EGFR/PI3K/AKT pathway using specific inhibitor caused downregulation of cyclin E, CDK2, and upregulation of p21 and p27 in prostate cancer cells. Collectively, this study demonstrates that over-expression of ADAM17 might target cyclin E, CDK2, p21, and p27 to promote prostate cancer cell proliferation through activation of the EGFR/PI3K/AKT pathway.

G protein-coupled receptors: novel targets for drug discovery in cancer

G protein-coupled receptors (GPCRs) belong to a superfamily of cell surface signalling proteins that have a pivotal role in many physiological functions and in multiple diseases, including the development of cancer and cancer metastasis. Current drugs that target GPCRs - many of which have excellent therapeutic benefits - are directed towards only a few GPCR members. Therefore, huge efforts are currently underway to develop new GPCR-based drugs, particularly for cancer. We review recent findings that present unexpected opportunities to interfere with major tumorigenic signals by manipulating GPCR-mediated pathways. We also discuss current data regarding novel GPCR targets that may provide promising opportunities for drug discovery in cancer prevention and treatment.

2-(2-Aminothiazol-4-yl)pyrrolidine-based tartrate diamides as potent, selective and orally bioavailable TACE inhibitors

TNF-α converting enzyme (TACE) inhibitors are promising agents to treat inflammatory disorders and cancer. We have investigated novel tartrate diamide TACE inhibitors where the tartrate core binds to zinc in a unique tridentate fashion. Incorporating (R)-2-(2-N-alkylaminothiazol-4-yl)pyrrolidines into the left hand side amide of the tartrate scaffold led to the discovery of potent and selective TACE inhibitors, some of which exhibited good rat oral bioavailability.

Novel TACE inhibitors in drug discovery: a review of patented compounds

TNF-alpha converting enzyme (TACE), a pro-inflammatory cytokine, catalyzes the formation of TNF-alpha from membrane bound TNF-alpha precursor protein. TNF-alpha is believed to play pathophysiological roles in inflammation, anorexia, cachexia, septic shock, viral replication and so on. TNF-alpha is a key player in inflammation and joint damage in rheumatoid arthritis. While a variety of TACE inhibitors have been reported in the literature, a vast majority of these compounds are peptidic and peptide-like compounds that are expected to have bioavailability and pharmacokinetic problems, common to such compounds, limiting their clinical effectiveness. Low molecular mass, long acting, orally bioavailable inhibitors of TACE are, therefore, highly desirable for the treatment of potential chronic diseases mentioned above. A review of patented compounds as TACE inhibitors in drug discovery is given. A selection of interesting patents recorded from 2001 to 2009 is presented. Various novel TACE inhibitors developed by different companies have been discussed.

Reconstitution of amphiregulin-epidermal growth factor receptor signaling in lung squamous cell carcinomas activates PTHrP gene expression and contributes to cancer-mediated diseases of the bone

Parathyroid hormone-related protein (PTHrP) is the causative factor of the paraneoplastic syndrome humoral hypercalcemia of malignancy (HHM) and it also contributes to osteolytic metastases, both of which are common complications of squamous carcinomas of the lung. Inhibition of autocrine epidermal growth factor receptor (EGFR) signaling has been shown to reduce plasma calcium and PTHrP concentrations in two lung squamous cell carcinoma xenograft models of HHM. The purpose of this study was to investigate the mechanism by which EGFR is activated and stimulates PTHrP gene expression in lung squamous carcinoma cell lines. Amphiregulin (AREG) was the only EGFR ligand that could be consistently detected in conditioned media from the SCC lines, and reduction of its expression either by siRNA or by precipitating antibody reduced PTHrP mRNA expression as effectively as EGFR-targeted inhibition. Using siRNA knockdown or inhibitors to upstream regulators of AREG shedding including TACE, Src/Lck, and G(i/o), also reduced PTHrP mRNA expression. We determined that blockade of autocrine AREG-EGFR signaling does not affect PTHrP mRNA stability. Of the three PTHrP promoters (P1, P2, and P3), P1 mRNA could be reduced by nearly 100% with an EGFR inhibitor, and both epidermal growth factor and AREG stimulated P1 mRNA by approximately 5-fold. Finally, ectopic expression of EGFR in a receptor-low but AREG-expressing cell line increased PTHrP mRNA levels in vitro, and induced the capability to cause HHM and rapid osteolytic growth in vivo. Taken together, we provide evidence that AREG stimulation of EGFR results in high levels of PTHrP gene expression, contributing to cancer-associated bone pathology.

Tumorigenicity of cortical astrocyte cell line induced by the protease ADAM17

The metalloprotease ADAM17 (a.k.a. TACE) plays a pivotal role in the cleavage and activation of membrane-anchored receptor ligands. More recently, it has been revealed that ADAM17 is a potent sheddase of the epidermal growth factor (EGF) family of ligands and regulates epidermal growth factor receptor (EGFR) activity in a variety of tumors. EGFR is a key component of autonomous growth signaling in several tumors, and correlates with the malignancy grade of astrocytoma. In this study, we tested the hypothesis that over-expression of ADAM17 in cortical astrocytes derived from normal brain would induce a progression towards a malignant phenotype. Over-expression of human ADAM17 (hADAM17) in the CTX-TNA2 cortical astrocyte cell line resulted in non-adherent growth, increased proliferation, invasiveness, production of angiogenic factors, and expression of genes associated with immature and/or neoplastic cells. hADAM17 up-regulated EGFR and AKT phosphorylation, and increased proliferation and cell invasion were significantly dependent upon EGFR activity. When implanted in the nude mouse brain, CTX-TNA2 cells induced low histological grade, benign intraventricular gliomas. In contrast, the same astrocytes with hADAM17 formed large malignant gliomas. Taken together, these findings suggest that unregulated ADAM17 activity induces functional changes in astrocytes that significantly advance the malignant phenotype.

The epidermal growth factor receptor: a link between inflammation and liver cancer

Epidemiological studies have established that many tumours occur in association with persistent inflammation. One clear example of inflammation-related cancer is hepatocellular carcinoma (HCC). HCC slowly unfolds on a background of chronic inflammation triggered by exposure to infectious agents (hepatotropic viruses), toxic compounds (ethanol), or metabolic impairment. The molecular links that connect inflammation and cancer are not completely known, but evidence gathered over the past few years is beginning to define the precise mechanisms. A central role for cytokines such as interleukin-6 (IL-6) and IL-1 (alpha and beta) in liver cancer has been established in experimental models. Besides these inflammatory mediators, mounting evidence points to the dysregulation of specific growth and survival-related pathways in HCC development. Among them is the pathway governed by the epidermal growth factor receptor (EGFR), which can be bound and activated by a broad family of ligands. Of special relevance is the fact that the EGFR engages in extensive crosstalk with other signaling pathways, serving as a "signaling hub" for an increasing list of growth factors, cytokines, and inflammatory mediators. In this review, we summarize the most recent evidences supporting a role for the EGFR system in inflammation-related cell signaling, with special emphasis in liver inflammation and HCC. The molecular dissection of the pathways connecting the inflammatory reaction and neoplasia will facilitate the development of novel and more effective antitumor strategies.

Studies on novel 2-imidazolidinones and tetrahydropyrimidin-2(1H)-ones as potential TACE inhibitors: design, synthesis, molecular modeling, and preliminary biological evaluation

Compounds belonging to the class of 2-imidazolidinones and tetrahydropyrimidin-2(1H)-ones were synthesized and evaluated for their TACE inhibitory activity. Most of the compounds showed very good TACE inhibitory activity. Docking study clearly indicates importance of the P1' group of the inhibitor for the TACE inhibitory activity. This work proves that these two classes of molecules could be used as potential leads for the development of TACE inhibitors.

Expression, purification and insights into structure and folding of the ADAM22 pro domain

The ADAMs (a disintegrin and metalloproteases) are an important class of enzymes in the regulation of human disease. The pro domains of ADAMs are responsible for the latency and secretion of mature enzymes. Unlike other metzincins, ADAM pro domains remain bound to the mature enzyme after secretion. To understand the functions of human ADAM pro domains and to determine three-dimensional structures, we have screened promising targets for expression and purification properties when using Escherichia coli as the host. The pro domain of ADAM22 (ADAM22-P) expressed in E. coli was folded, as determined by CD and NMR spectroscopy. An ADAM22-P fragment encoding residues 26-199 could be expressed in high amounts, remained soluble above 1 mM, and was suitable for structural studies by NMR spectroscopy. CD spectroscopy and predictions suggest that the secondary structure in ADAM22-P consists of beta-strands. Furthermore, our data indicate that the pro domains of ADAMs are expressed as two subdomains. The most N-terminal subdomain (ADAM22-P(N)) was found to be susceptible to proteolysis and was required for folding stability of the second subdomain (ADAM22-P(C)).

Roles of transforming growth factor-alpha in mammary development and disease

Transforming growth factor-alpha (TGFalpha) is a member of the epidermal growth factor (EGF) family. Expression of TGFalpha is highly regulated in response to exogenous cellular signals including cytokines and other growth factors. The growth factor has been found to be indispensable for proper development of many tissues and organs. TGFalpha has also been implicated in numerous disease states including forms of breast cancer. This minireview summarizes the basic biology of TGFalpha and its actions during normal and pathogenic development of the mammary epithelium.