A Lactobacillus rhamnosus GG-derived soluble protein, p40, stimulates ligand release from intestinal epithelial cells to transactivate epidermal growth factor receptor

p40, a Lactobacillus rhamnosus GG (LGG)-derived soluble protein, ameliorates intestinal injury and colitis, reduces apoptosis, and preserves barrier function by transactivation of the EGF receptor (EGFR) in intestinal epithelial cells. The aim of this study is to determine the mechanisms by which p40 transactivates the EGFR in intestinal epithelial cells. Here we show that p40-conditioned medium activates EGFR in young adult mouse colon epithelial cells and human colonic epithelial cell line, T84 cells. p40 up-regulates a disintegrin and metalloproteinase domain-containing protein 17 (ADAM17) catalytic activity, and broad spectrum metalloproteinase inhibitors block EGFR transactivation by p40 in these two cell lines. In ADAM17-deficient mouse colonic epithelial (ADAM17(-/-) MCE) cells, p40 transactivation of EGFR is blocked, but can be rescued by re-expression with WT ADAM17. Furthermore, p40 stimulates release of heparin binding (HB)-EGF, but not transforming growth factor (TGF)α or amphiregulin, in young adult mouse colon cells and ADAM17(-/-) MCE cells overexpressing WT ADAM17. Knockdown of HB-EGF expression by siRNA suppresses p40 effects on transactivating EGFR and Akt, preventing apoptosis, and preserving tight junction function. The effects of p40 on HB-EGF release and ADAM17 activation in vivo are examined after administration of p40-containing pectin/zein hydrogel beads to mice. p40 stimulates ADAM17 activity and EGFR activation in colonic epithelial cells and increases HB-EGF levels in blood from WT mice, but not from mice with intestinal epithelial cell-specific ADAM17 deletion. Thus, these data define a mechanism of a probiotic-derived soluble protein in modulating intestinal epithelial cell homeostasis through ADAM17-mediated HB-EGF release, leading to transactivation of EGFR.

Notch signaling modulates proliferation and differentiation of intestinal crypt base columnar stem cells

Notch signaling is known to regulate the proliferation and differentiation of intestinal stem and progenitor cells; however, direct cellular targets and specific functions of Notch signals had not been identified. We show here in mice that Notch directly targets the crypt base columnar (CBC) cell to maintain stem cell activity. Notch inhibition induced rapid CBC cell loss, with reduced proliferation, apoptotic cell death and reduced efficiency of organoid initiation. Furthermore, expression of the CBC stem cell-specific marker Olfm4 was directly dependent on Notch signaling, with transcription activated through RBP-Jκ binding sites in the promoter. Notch inhibition also led to precocious differentiation of epithelial progenitors into secretory cell types, including large numbers of cells that expressed both Paneth and goblet cell markers. Analysis of Notch function in Atoh1-deficient intestine demonstrated that the cellular changes were dependent on Atoh1, whereas Notch regulation of Olfm4 gene expression was Atoh1 independent. Our findings suggest that Notch targets distinct progenitor cell populations to maintain adult intestinal stem cells and to regulate cell fate choice to control epithelial cell homeostasis.

TNF-α converting enzyme-mediated ErbB4 transactivation by TNF promotes colonic epithelial cell survival

Disruption of intestinal epithelial homeostasis, including enhanced apoptosis, is a hallmark of inflammatory bowel disease (IBD). We have recently shown that tumor necrosis factor (TNF) increases the kinase activity of ErbB4, a member of the epidermal growth factor receptor family that is elevated in mucosa of IBD patients and that promotes colon epithelial cell survival. In this study, we tested the hypothesis that TNF transactivates ErbB4 through TNF-α converting enzyme (TACE)-mediated ligand release and that this transactivation is necessary to protect colonic epithelial cells from cytokine-induced apoptosis. Using neutralizing antibodies, we show that heparin-binding EGF-like growth factor (HB-EGF) is required for ErbB4 phosphorylation in response to TNF. Pharmacological or genetic inhibition of the metalloprotease TACE, which mediates HB-EGF release from cells, blocked TNF-induced ErbB4 activation. MEK, but not Src or p38, was also required for transactivation. TACE activity and ligand binding were required for ErbB4-mediated antiapoptotic signaling; whereas mouse colon epithelial cells expressing ErbB4 were resistant to TNF-induced apoptosis, TACE inhibition or blockade of ErbB4 ligand binding reversed the survival advantage. We conclude that TNF transactivates ErbB4 through TACE-dependent HB-EGF release, thus protecting colon epithelial cells from cytokine-induced apoptosis. These findings have important implications for understanding how ErbB4 protects the colon from apoptosis-induced tissue injury in inflammatory conditions such as IBD.

Conditional gene targeting in mouse pancreatic ß-Cells: analysis of ectopic Cre transgene expression in the brain

OBJECTIVE

Conditional gene targeting has been extensively used for in vivo analysis of gene function in β-cell biology. The objective of this study was to examine whether mouse transgenic Cre lines, used to mediate β-cell- or pancreas-specific recombination, also drive Cre expression in the brain.

RESEARCH DESIGN AND METHODS

Transgenic Cre lines driven by Ins1, Ins2, and Pdx1 promoters were bred to R26R reporter strains. Cre activity was assessed by β-galactosidase or yellow fluorescent protein expression in the pancreas and the brain. Endogenous Pdx1 gene expression was monitored using Pdx1(tm1Cvw) lacZ knock-in mice. Cre expression in β-cells and co-localization of Cre activity with orexin-expressing and leptin-responsive neurons within the brain was assessed by immunohistochemistry.

RESULTS

All transgenic Cre lines examined that used the Ins2 promoter to drive Cre expression showed widespread Cre activity in the brain, whereas Cre lines that used Pdx1 promoter fragments showed more restricted Cre activity primarily within the hypothalamus. Immunohistochemical analysis of the hypothalamus from Tg(Pdx1-cre)(89.1Dam) mice revealed Cre activity in neurons expressing orexin and in neurons activated by leptin. Tg(Ins1-Cre/ERT)(1Lphi) mice were the only line that lacked Cre activity in the brain.

CONCLUSIONS

Cre-mediated gene manipulation using transgenic lines that express Cre under the control of the Ins2 and Pdx1 promoters are likely to alter gene expression in nutrient-sensing neurons. Therefore, data arising from the use of these transgenic Cre lines must be interpreted carefully to assess whether the resultant phenotype is solely attributable to alterations in the islet β-cells.

The need for breast cancer screening in women undergoing elective breast surgery: an assessment of risk and risk factors for breast cancer in young women

BACKGROUND

Given the 11% lifetime risk of breast cancer and increasing popularity of elective breast surgery, the role of preoperative screening begs further investigation. There are currently no guidelines that indicate which women younger than 40 years of age should be screened preoperatively.

OBJECTIVES

A meta-analysis of studies regarding the odds ratio (OR) and relative risk ratio for breast cancer risk factors in women younger than 40 was completed.

METHODS

Of a total of 240 results in the PubMed database for articles referencing breast cancer risk factors in young women, eight were selected for review. A total of 5381 patients were included in the studies in this meta-analysis; 26 risk factors were identified. A meta-analysis was performed to determine the OR of each specific risk factor, with a 95% confidence interval.

RESULTS

The most significant risk factors were having a sister with breast cancer (OR, 11.66), having a first-degree relative with breast cancer (OR, 2.66), having a mother with breast cancer (OR, 2.31), never having breastfed (OR, 1.77), and having undergone a breast biopsy (OR, 1.66). From these data, the authors developed a clinical questionnaire to estimate the risk of breast cancer in young women. In addition, an algorithm was developed for preoperative breast cancer screening for women of all ages undergoing elective breast procedures.

CONCLUSIONS

For women younger than 40, the preoperative risk assessment involves two steps. First, the possibility of existing breast cancer should be evaluated with a preoperative screening survey. Second, the patient's risk for future development of cancer should be assessed, with a focus on genetic mutations. Women older than 40 years of age should be stratified to receive either a preoperative mammogram or MRI. The clinical questionnaire and preoperative screening algorithm provide an evidence-based guideline on which to base the discussion with patients regarding preoperative breast cancer screening.

Sequential and gamma-secretase-dependent processing of the betacellulin precursor generates a palmitoylated intracellular-domain fragment that inhibits cell growth

Betacellulin (BTC) belongs to the family of epidermal growth factor (EGF)-like growth factors that are expressed as transmembrane precursors and undergo proteolytic ectodomain shedding to release soluble mature ligands. BTC is a dual-specificity ligand for ErbB1 and ErbB4 receptors, and can activate unique signal-transduction pathways that are beneficial for the function, survival and regeneration of pancreatic beta-cells. We have previously shown that BTC precursor (proBTC) is cleaved by ADAM10 to generate soluble ligand and a stable, transmembrane remnant (BTC-CTF). In this study, we analyzed the fate of the BTC-CTF in greater detail. We demonstrated that proBTC is cleaved by ADAM10 to produce BTC-CTF, which then undergoes intramembrane processing by presenilin-1- and/or presenilin-2-dependent gamma-secretase to generate an intracellular-domain fragment (BTC-ICD). We found that the proBTC cytoplasmic domain is palmitoylated and that palmitoylation is not required for ADAM10-dependent cleavage but is necessary for the stability and gamma-secretase-dependent processing of BTC-CTF to generate BTC-ICD. Additionally, palmitoylation is required for nuclear-membrane localization of BTC-ICD, as demonstrated by the redistribution of non-palmitoylated BTC-ICD mutant to the nucleoplasm. Importantly, a novel receptor-independent role for BTC-ICD signaling is suggested by the ability of BTC-ICD to inhibit cell growth in vitro.

Fluorescent substrates useful as high-throughput screening tools for ADAM9

Fluorescence resonance energy transfer substrates were designed and tested as substrates for ADAM9. The donor/quencher pair used were 5-carboxy fluorescein (Fam) and 4-(4-dimethyl-aminophenylazo)benzoyl (Dabcyl) since they have been well studied sensitive fluorescent probes. The peptides based on precursor TNF-alpha, Dabcyl-Ser-Pro-Leu-Ala-Gln-Ala-Val-Arg-Ser-Ser-Lys(Fam)- NH2 and Dabcyl-Leu-Ala-Gln-Ala-HomoPhe-Arg-Ser-Lys(Fam)- NH2, and C-terminal TGF-alpha, Dabcyl-Glu-His-Ala-Asp-Leu-Leu-Ala-Val-Val-Ala-Ala-Lys(Fam)- NH2 cleavage sites were effectively processed by ADAM9 with turnover numbers of 100 +/- 20 x 10(-2) min(-1), 20 +/- 10 x 10(-2) min(-1), and 10 +/- 3 x 10(-2) min(-1). In addition, a peptide based on the 33 kDa cleavage site of the low affinity receptor for IgE, CD23, Dabcyl-Leu-Arg-Ala-Glu-Gln-Gln-Arg-Leu-Lys-Ser-Lys(Fam)- NH2 was processed as well but with less efficiency. A more selective substrate for ADAM9 was found based on the betacellulin cleavage site. However, the valine containing precursor TNF-alpha based substrate was used to measure IC50 values of metalloproteinase inhibitors against ADAM9 since it was processed the most efficiently. The tightest binding inhibitor was the Wyeth Aerst compound, TMI-1, with an IC50 of 2.1 +/- 0.3 nM. In addition, GI254023, previously identified as a selective inhibitor of ADAM10, also inhibited ADAM9 with an IC50 of 280 +/- 110 nM. These results demonstrate that sensitive substrates for ADAM9 can be developed that are useful in high-throughput screening assays for ADAM9.

ADAM10 is essential for Notch2-dependent marginal zone B cell development and CD23 cleavage in vivo

The proteolytic activity of a disintegrin and metalloproteinase 10 (ADAM10) regulates cell-fate decisions in Drosophila and mouse embryos. However, in utero lethality of ADAM10^−/− mice has prevented examination of ADAM10 cleavage events in lymphocytes. To investigate their role in B cell development, we generated B cell–specific ADAM10 knockout mice. Intriguingly, deletion of ADAM10 prevented development of the entire marginal zone B cell (MZB) lineage. Additionally, cleavage of the low affinity IgE receptor, CD23, was profoundly impaired, but subsequent experiments demonstrated that ADAM10 regulates CD23 cleavage and MZB development by independent mechanisms. Development of MZBs is dependent on Notch2 signaling, which requires proteolysis of the Notch2 receptor by a previously unidentified proteinase. Further experiments revealed that Notch2 signaling is severely impaired in ADAM10-null B cells. Thus, ADAM10 critically regulates MZB development by initiating Notch2 signaling. This study identifies ADAM10 as the in vivo CD23 sheddase and an important regulator of B cell development. Moreover, it has important implications for the treatment of numerous CD23- and Notch-mediated pathologies, ranging from allergy to cancer.

ADAM10 as a therapeutic target for cancer and inflammation

Both cancer and chronic inflammatory diseases are often marked by homeostatic signal transduction pathways run amok. Cleavage of membrane-bound substrates by extracellular metalloproteinases is frequently the rate limiting step in activating many of these pathways, resulting either in liberation of active ligands (shedding) or initiating further processing into bioactive cytoplasmic domains (regulated intramembrane proteolysis or RIP). ADAM10 is a member of the ADAM (A Disintegrin And Metalloproteinase) family of transmembrane metalloproteinases implicated in the RIPing and shedding of dozens of substrates that drive cancer progression and inflammatory disease, including Notch, E-cadherin, EGF, ErbB2 and inflammatory cytokines. ADAM10's emerging role as a significant contributor to these pathologies has led to intense interest in it as a potential drug target for disease treatment. Here we discuss some of the established functions of ADAM10 and the implications of its inhibition in disease progression.

Epidermal growth factor receptor activation protects gastric epithelial cells from Helicobacter pylori-induced apoptosis

BACKGROUND & AIMS

Helicobacter pylori infection disrupts the balance between gastric epithelial cell proliferation and apoptosis, which is likely to lower the threshold for the development of gastric adenocarcinoma. H pylori infection is associated with epidermal growth factor (EGF) receptor (EGFR) activation through metalloproteinase-dependent release of EGFR ligands in gastric epithelial cells. Because EGFR signaling regulates cell survival, we investigated whether activation of EGFR following H pylori infection promotes gastric epithelial survival.

METHODS

Mouse conditionally immortalized stomach epithelial cells (ImSt) and a human gastric epithelial cell line, AGS cells, as well as wild-type and kinase-defective EGFR (EGFRwa2) mice, were infected with the H pylori cag+ strain 7.13. Apoptosis, caspase activity, EGFR activation (phosphorylation), and EGFR downstream targets were analyzed.

RESULTS

Inhibiting EGFR kinase activity or decreasing EGFR expression significantly increased H pylori-induced apoptosis in ImSt. Blocking H pylori-induced EGFR activation with a heparin-binding (HB)-EGF neutralizing antibody or abrogating a disintegrin and matrix metalloproteinase-17 (ADAM-17) expression increased apoptosis of H pylori-infected AGS and ImSt, respectively. Conversely, pretreatment of ImSt with HB-EGF completely blocked H pylori-induced apoptosis. H pylori infection stimulated gastric epithelial cell apoptosis in EGFRwa2 but not in wild-type mice. Furthermore, H pylori-induced EGFR phosphorylation stimulated phosphotidylinositol-3'-kinase-dependent activation of the antiapoptotic factor Akt, increased expression of the antiapoptotic factor Bcl-2, and decreased expression of the proapoptotic factor Bax.

CONCLUSIONS

EGFR activation by H pylori infection has an antiapoptotic effect in gastric epithelial cells that appears to involve Akt signaling and Bcl family members. These findings provide important insights into the mechanisms of H pylori-associated tumorigenesis.

Deficiency of TNFalpha converting enzyme (TACE/ADAM17) causes a lean, hypermetabolic phenotype in mice

Energy homeostasis involves central nervous system integration of afferent inputs that coordinately regulate food intake and energy expenditure. Here, we report that adult homozygous TNFalpha converting enzyme (TACE)-deficient mice exhibit one of the most dramatic examples of hypermetabolism yet reported in a rodent system. Because this effect is not matched by increased food intake, mice lacking TACE exhibit a lean phenotype. In the hypothalamus of these mice, neurons in the arcuate nucleus exhibit intact responses to reduced fat mass and low circulating leptin levels, suggesting that defects in other components of the energy homeostasis system explain the phenotype of Tace(DeltaZn/DeltaZn) mice. Elevated levels of uncoupling protein-1 in brown adipose tissue from Tace(DeltaZn/DeltaZn) mice when compared with weight-matched controls suggest that deficient TACE activity is linked to increased sympathetic outflow. These findings collectively identify a novel and potentially important role for TACE in energy homeostasis.

Generation of novel, secreted epidermal growth factor receptor (EGFR/ErbB1) isoforms via metalloprotease-dependent ectodomain shedding and exosome secretion

Exosomes are small membrane vesicles derived from intracellular multivescicular bodies (MVBs) that can undergo constitutive and regulated secretion from cells. Exosomes can also secrete soluble proteins through metalloprotease-dependent ectodomain shedding. In this study, we sought to determine whether ErbB1 receptors are present within exosomes isolated from the human keratinocyte cell line, HaCaT, and whether exosome-associated ErbB1 receptors can undergo further proteolytic processing. We show that full-length transmembrane ErbB1 is secreted in HaCaT exosomes. EGF treatment and calcium flux stimulated the release of phosphorylated ErbB1 in exosomes but only ligand-stimulated release was blocked by the ErbB1 kinase inhibitor, AG1478, indicating that ligand-dependent ErbB1 receptor activation can initiate ErbB1 secretion into exosomes. In addition, other immunoreactive but truncated ErbB1 isoforms were detected in exosomes suggestive of additional proteolytic processing. We demonstrate that cellular and exosomal ErbB1 receptors can undergo ectodomain shedding to generate soluble N-terminal ectodomains and membrane-associated C-terminal remnant fragments (CTFs). ErbB1 shedding was activated by calcium flux and the metalloprotease activator APMA (4-aminophenylmercuric acetate) and was blocked by a metalloprotease inhibitor (GM6001). Soluble ErbB1 ectodomains shed into conditioned medium retained the ability to bind exogenous ligand. Our results provide new insights into the proteolysis, trafficking and fate of ErbB1 receptors and suggest that the novel ErbB1 isoforms may have functions distinct from the plasma membrane receptor.

TACE/ADAM-17: a component of the epidermal growth factor receptor axis and a promising therapeutic target in colorectal cancer

PURPOSE

Activation of the epidermal growth factor receptor (EGFR) requires cell surface cleavage of EGFR ligands, uptake of soluble ligand by the receptor, and initiation of EGFR tyrosine kinase activity. We define these collective events as the EGFR axis. Transforming growth factor-alpha (TGF-alpha) and amphiregulin are two EGFR ligands that are delivered preferentially to the basolateral surface of polarized epithelial cells where the EGFR resides. TACE/ADAM-17 (tumor necrosis factor-alpha converting enzyme/a disintegrin and metalloprotease) has been implicated in ectodomain cleavage of TGF-alpha and amphiregulin.

EXPERIMENTAL DESIGN

Using a human polarizing colorectal cancer (CRC) cell line, HCA-7, and a tissue array of normal colonic mucosa and primary and metastatic CRC, we determined the intracellular localization of TACE and the effects of EGFR axis inhibition in CRC.

RESULTS

Herein, we show that TACE is localized to the basolateral plasma membrane of polarized HCA-7 cells. TACE is overexpressed in primary and metastatic CRC tumors compared with normal colonic mucosa; the intensity of its immunoreactivity is inversely correlated with that of TGF-alpha and amphiregulin. Pharmacologic blockade of HCA-7 cells with an EGFR monoclonal antibody, a selective EGFR tyrosine kinase inhibitor, and a selective TACE inhibitor results in concentration-dependent decreases in cell proliferation and active, phosphorylated mitogen-activated protein kinase. Combining suboptimal concentrations of these agents results in cooperative growth inhibition, increased apoptosis, and reduced mitogen-activated protein kinase pathway activation. Furthermore, an EGFR tyrosine kinase-resistant clone of HCA-7 cells is growth-inhibited by combined monoclonal antibody and TACE inhibition.

CONCLUSION

These results implicate TACE as a promising target of EGFR axis inhibition in CRC.

Results of a survey on digital screening mammography: prevalence, efficiency, and use of ancillary diagnostic AIDS

OBJECTIVE

As the use of full-field digital screening mammography grows rapidly, this study was conducted to determine the time required to interpret digital soft-copy (filmless) mammography compared with conventional film-screen screening mammography and to evaluate radiologists' use of ancillary diagnostic aids when interpreting digital mammography (DM) and conventional film-screen mammography (FSM).

MATERIALS AND METHODS

An 18-question survey was sent to 1,703 members of the Society of Breast Imaging, whose e-mail addresses were provided by the society. After subtracting those from whom out-of-office e-mail responses were received and three who wrote back to exclude themselves, there were 1,659 potential participants. Data from the respondents were collected and analyzed by tabulation and cross-tabulation.

RESULTS

In total, 396 members of the Society of Breast Imaging completed and returned surveys, for a 23.9% response rate. Of the respondents, 49.0% said that they had access to and interpreted DM. Their estimated average time to read a single digital mammographic study was 2.6 minutes, compared with 2.0 minutes for reading a single film-screen mammographic study. Therefore, the perceived time difference was 0.6 minutes. Magnification was the main ancillary diagnostic aid used in interpreting both DM and FSM: 74.2% of respondents used computer-based magnification at least half the time in interpreting DM, and 90.9% used optical magnification at least half the time in interpreting FSM. Optical magnification was also used by 28.5% of respondents at least half the time in interpreting DM. The respondents also used computer-aided detection frequently: 91.0% and 76.3% of those who had computer-aided detection available said that they used it at least 75% of the time in interpreting DM and FSM, respectively.

CONCLUSION

Digital mammography takes longer to interpret than FSM. Radiologists use various ancillary diagnostic aids, but magnification and computer-aided detection are the two most commonly used aids.

ADAM10 as a target for anti-cancer therapy

There is a great unmet medical need in the area of cancer treatment. A potential therapeutic target for intervention in cancer is ADAM10. ADAM10 is a disintegrin-metalloproteinase that processes membrane bound proteins from the cell surface to yield soluble forms. Pharmaceutical companies are actively seeking out inhibitors of ADAM10 for treatments in cancer as the enzyme is known to release the ErbB receptor, HER2/ErbB2 from the cell membrane, an event that is necessary for HER2 positive tumor cells to proliferate. ADAM10 is also capable of processing betacellulin indicating that an inhibitor could be used against EGFR/ErbB1 and/or HER4/ErbB4 receptor positive tumor cells that are betacellulin-dependent. ADAM10 is the principle sheddase for several other molecules associated with cancer proliferation, differentiation, adhesion and migration such as Notch, E-cadherin, CD44 and L1 adhesion molecule indicating that targeting ADAM10 with specific inhibitors could be beneficial.

Novel role of protein kinase C-delta Tyr 311 phosphorylation in vascular smooth muscle cell hypertrophy by angiotensin II

We have shown previously that activation of protein kinase C-delta (PKC delta) is required for angiotensin II (Ang II)-induced migration of vascular smooth muscle cells (VSMCs). Here, we have hypothesized that PKC delta phosphorylation at Tyr(311) plays a critical role in VSMC hypertrophy induced by Ang II. Immunoblotting was used to monitor PKC delta phosphorylation at Tyr(311), and cell size and protein measurements were used to detect hypertrophy in VSMCs. PKC delta was rapidly (0.5 to 10.0 minutes) phosphorylated at Tyr(311) by Ang II. This phosphorylation was markedly blocked by an Src family kinase inhibitor and dominant-negative Src but not by an epidermal growth factor receptor kinase inhibitor. Ang II-induced Akt phosphorylation and hypertrophic responses were significantly enhanced in VSMCs expressing PKC delta wild-type compared with VSMCs expressing control vector, whereas the enhancements were markedly diminished in VSMCs expressing a PKC delta Y311F mutant. Also, these responses were significantly inhibited in VSMCs expressing kinase-inactive PKC delta K376A compared with VSMCs expressing control vector. From these data, we conclude that not only PKC delta kinase activation but also the Src-dependent Tyr(311) phosphorylation contributes to Akt activation and subsequent VSMC hypertrophy induced by Ang II, thus signifying a novel molecular mechanism for enhancement of cardiovascular diseases induced by Ang II.

Diagnostic Breast Ultrasound: Current Status and Future Directions

This summary of breast ultrasound reviews the current indications for its use, discusses the potential technical and human pitfalls in its performance, and briefly examines possible future applications that currently are works in progress. It also contains an in-depth discussion of the use and interpretation of color Doppler and power Doppler imaging, techniques that do not seem to be understood or used fully in daily practice.

Metalloproteases regulate T-cell proliferation and effector function via LAG-3

Tight control of T-cell proliferation and effector function is essential to ensure an effective but appropriate immune response. Here, we reveal that this is controlled by the metalloprotease-mediated cleavage of LAG-3, a negative regulatory protein expressed by all activated T cells. We show that LAG-3 cleavage is mediated by two transmembrane metalloproteases, ADAM10 and ADAM17, with the activity of both modulated by two distinct T-cell receptor (TCR) signaling-dependent mechanisms. ADAM10 mediates constitutive LAG-3 cleavage but increases approximately 12-fold following T-cell activation, whereas LAG-3 shedding by ADAM17 is induced by TCR signaling in a PKCtheta-dependent manner. LAG-3 must be cleaved from the cell surface to allow for normal T-cell activation as noncleavable LAG-3 mutants prevented proliferation and cytokine production. Lastly, ADAM10 knockdown reduced wild-type but not LAG-3(-/-) T-cell proliferation. These data demonstrate that LAG-3 must be cleaved to allow efficient T-cell proliferation and cytokine production and establish a novel paradigm in which T-cell expansion and function are regulated by metalloprotease cleavage with LAG-3 as its sole molecular target.

Non-Cell Autonomous Expression of TNF-α-Converting Enzyme ADAM17 Is Required for Normal Lymphocyte Development

TNF-alpha converting enzyme (TACE; ADAM17), a member of the ADAM (a disintegrin and metalloprotease) family of metalloproteases, has been shown to cleave a wide variety of cell surface proteins of immunological importance. Due to the broad expression of TACE and the early postnatal lethality of TACE-deficient mice, it has been difficult to assess the role of TACE in lymphocyte development. Indeed, it is not known whether hemopoietic and/or nonhemopoietic expression of TACE is required for normal lymphocyte development. In the current study, we analyzed the lymphoid system of tace(DeltaZn/DeltaZn) mice and tace(DeltaZn/DeltaZn) bone marrow RAG1(-/-) recipients. Our results clearly show that nonlymphocyte expression of TACE is required for normal lymphocyte development and lymphoid organ structure. Lack of TACE function resulted in a partial block in T cell development at the double-negative 4:double-positive transition in the thymus, a loss of B cell development/maturation in the spleen, and a lack of B cell follicle and germinal center formation in the spleen. Thus, TACE serves as a lymphocyte extrinsic factor that is essential for normal T development and peripheral B cell maturation.

Comparison of full-field digital mammography and screen-film mammography for detection and characterization of simulated small masses

OBJECTIVE

The two objectives of this study were to create an ex vivo phantom model that closely mimics human breast cancer for detection tasks and to compare the performance of full-field digital mammography with screen-film mammography in detecting and characterizing small breast masses in a phantom with a spectrum of complex tissue backgrounds.

MATERIALS AND METHODS

Sixteen phantom breast masses of varying sizes (0.3-1.2 cm), shapes (round and irregular), and densities (high and low) were created from shaved tumor specimens and imaged using both full-field digital and screen-film mammography techniques. We created 408 detection tasks that were captured on 68 films. On each radiograph, six detection tasks were partially obscured by areas of varying breast-pattern complexity, including low (predominantly fatty), mixed (scattered fibroglandular densities and heterogeneously dense), and high (extremely dense) density patterns. Each detection task was scored using a five-point confidence scale by three mammographers. Receiver operating characteristic (ROC) curve analysis was performed to analyze differences in detection of masses between the two imaging systems, and sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were computed.

RESULTS

Full-field digital mammography showed higher area under the ROC curve than screen-film mammography for detecting masses in each breast background and performed significantly better than screen-film mammography in mixed (p = 0.010), dense (p = 0.029), and all breast backgrounds combined (p = 0.004). Full-field digital mammography was superior to screen-film mammography for characterizing round and irregular masses and low- and high-density masses.

CONCLUSION

Full-field digital mammography was significantly superior to screen-film technique for detecting and characterizing small masses in mixed and dense breast backgrounds in a phantom model.

Hydrogen peroxide and endothelin-1 are novel activators of betacellulin ectodomain shedding

The betacellulin precursor (pro-BTC) is a novel substrate for ADAM10-mediated ectodomain shedding. In this report, we investigated the ability of novel physiologically relevant stimuli, including G-protein coupled receptor (GPCR) agonists and reactive oxygen species (ROS), to stimulate pro-BTC shedding. We found that in breast adenocarcinoma MCF7 cells overexpressing pro-BTC, hydrogen peroxide (H2O2) was a powerful stimulator of ectodomain shedding. The stimulation of pro-BTC shedding by H2O2 was blocked by the broad-spectrum metalloprotease inhibitor TAPI-0 but was still functional in ADAM17 (TACE)-deficient stomach epithelial cells indicating the involvement of a distinct metalloprotease. H2O2-induced pro-BTC shedding was blocked by co-culturing cells in the anti-oxidant N-acetyl-L-cysteine but was unaffected by culture in calcium-deficient media. By contrast, calcium ionophore, which is a previously characterized activator of pro-BTC shedding, was sensitive to calcium depletion but was unaffected by co-culture with the anti-oxidant, identifying a clear distinction between these stimuli. We found that in vascular smooth muscle cells overexpressing pro-BTC, the GPCR agonist endothelin-1 (ET-1) was a strong inducer of ectodomain shedding. This was blocked by a metalloprotease inhibitor and by overexpression of catalytically inactive E385A ADAM10. However, overexpression of wild-type ADAM10 or ADAM17 led to an increase in ET-1-induced pro-BTC shedding providing evidence for an involvement of both enzymes in this process. This study identifies ROS and ET-1 as two novel inducers of pro-BTC shedding and lends support to the notion of activated shedding occurring under the control of physiologically relevant stimuli.