Recurrent hyperactive ESR1 fusion proteins in endocrine therapy-resistant breast cancer

Background

Estrogen receptor-positive (ER-positive) metastatic breast cancer is often intractable due to endocrine therapy resistance. Although ESR1 promoter switching events have been associated with endocrine-therapy resistance, recurrent ESR1 fusion proteins have yet to be identified in advanced breast cancer.

Patients and methods

To identify genomic structural rearrangements (REs) including gene fusions in acquired resistance, we undertook a multimodal sequencing effort in three breast cancer patient cohorts: (i) mate-pair and/or RNAseq in 6 patient-matched primary-metastatic tumors and 51 metastases, (ii) high coverage (>500×) comprehensive genomic profiling of 287-395 cancer-related genes across 9542 solid tumors (5216 from metastatic disease), and (iii) ultra-high coverage (>5000×) genomic profiling of 62 cancer-related genes in 254 ctDNA samples. In addition to traditional gene fusion detection methods (i.e. discordant reads, split reads), ESR1 REs were detected from targeted sequencing data by applying a novel algorithm (copyshift) that identifies major copy number shifts at rearrangement hotspots.

Results

We identify 88 ESR1 REs across 83 unique patients with direct confirmation of 9 ESR1 fusion proteins (including 2 via immunoblot). ESR1 REs are highly enriched in ER-positive, metastatic disease and co-occur with known ESR1 missense alterations, suggestive of polyclonal resistance. Importantly, all fusions result from a breakpoint in or near ESR1 intron 6 and therefore lack an intact ligand binding domain (LBD). In vitro characterization of three fusions reveals ligand-independence and hyperactivity dependent upon the 3' partner gene. Our lower-bound estimate of ESR1 fusions is at least 1% of metastatic solid breast cancers, the prevalence in ctDNA is at least 10× enriched. We postulate this enrichment may represent secondary resistance to more aggressive endocrine therapies applied to patients with ESR1 LBD missense alterations.

Conclusions

Collectively, these data indicate that N-terminal ESR1 fusions involving exons 6-7 are a recurrent driver of endocrine therapy resistance and are impervious to ER-targeted therapies.

Abstract P6-07-02: The CARMA3-Bcl10-MALT1 signalosome mediates pro-angiogenic IL-6 and IL-8 paracrine signaling in GPCR+ breast cancer

Background: The overexpression of selected G-protein coupled receptors (GPCRs) has been linked to the pathogenesis of multiple cancer subtypes. We recently demonstrated that overexpression of two such GPCRs, the angiotensin II receptor type I (AGTR1) and protease-activated receptor type 1 (PAR1), occurs in a substantial fraction of luminal breast cancers and is associated with treatment resistance and poor prognosis. Further, experimental models demonstrate that overexpression of these receptors in breast cancer cell lines promotes aggressive features that include EMT, invasion, migration, and loss of ER expression. In addition to these cell intrinsic effects, we find that GPCR overexpression in breast cancer cells can impact the tumor microenvironment. Specifically, we recently reported that conditioned media from angiotensin II-stimulated AGTR1+ breast cancer cells induces endothelial chemotaxis in vitro and tumor angiogenesis in vivo. We also demonstrated that this pro-angiogenic phenotype requires the CARMA3-Bcl10-MALT1 (CBM) signalosome, a signaling complex that links upstream GPCR stimulation with downstream NF-κB activation. We hypothesized that stimulation of either AGTR1 or PAR1 induces CBM-dependent secretion of NF-κB responsive, pro-angiogenic factors from these GPCR+ breast cancer cells which then exert proangiogenic effects on neighboring endothelial cells through paracrine signaling.

Methods: To identify CBM-dependent secreted factors, we evaluated the AGTR1+ BT549 cell line, +/- Bcl10 or MALT1 siRNA knockdown, for expression of 770 genes of significance to solid tumor pathogenesis using the NanoString PanCancer Progression Panel followed by Ingenuity Pathway Analysis (IPA). RT-PCR and ELISA were used to validate hits and determine if the CBM signalosome controls expression of the same genes in the PAR1+ cell lines, MCF7-N55 and MDA-MB-231.

Results: We identified IL-6 and IL-8 signaling pathways as the two most significantly downregulated angiogenesis pathways following either Bcl10 or MALT1 knockdown. Using quantitative RT-PCR and ELISA, we confirmed that IL-6 and IL-8 gene expression and protein secretion are significantly induced in response to stimulation of BT549 cells by angiotensin II and MCF7-N55 and MDA-MB-231 cells by TRAP6, a PAR1 agonist. siRNA-mediated MALT1 knockdown in BT549 cells led to a significant reduction of IL-6 and IL-8 gene expression upon angiotensin II stimulation; similarly, CRISPR/Cas9-mediated MALT1-deletion in MCF7-N55 cells resulted in failure of these cells to secrete IL-8 upon TRAP6 stimulation.

Conclusions: The GPCR-CBM-cytokine signaling pathway provides a common druggable target to curb pro-angiogenenic paracrine signaling in GPCR+ breast cancers. Importantly, the CBM signalosome has also been shown to be required for IL-8 dependent upregulation of VEGF in endothelial cells, indicating that inhibition of the signalosome could exert complementary effects on both cancer cells and endothelial cells to effectively limit the pro-angiogenic phenotype driven by GPCR overexpression. Several small-molecule MALT1 inhibitors are now available and can be tested for their efficacy as angiogenesis inhibitors in the setting of GPCR+ breast cancer.

Citation Format: Kang H, Ekambaram P, McAllister-Lucas LM, Lucas PC. The CARMA3-Bcl10-MALT1 signalosome mediates pro-angiogenic IL-6 and IL-8 paracrine signaling in GPCR+ breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-07-02.

Abstract OT3-05-01: A randomized double-blind phase III clinical trial of neoadjuvant chemotherapy (NAC) with atezolizumab or placebo in patients (pts) with triple negative breast cancer (TNBC) followed by adjuvant atezolizumab or placebo: NSABP B-59/GBG 96-GeparDouze

Background:

TNBC is associated with higher percentages of pathological complete response (pCR) to neoadjuvant chemotherapy (NAC), and women with a pCR have a favorable prognosis. However, Liedtke (2008) and Loibl (2017) found that women with residual disease have a substantially higher risk of recurrence than women with other subtypes of breast cancer. Additionally, Adams (2017) and Schmid (2017) found that therapeutic blockade of PD-L1 binding by atezolizumab has resulted in relevant anti-tumor efficacy.

Methods:

Design

This is a phase III, double blind, placebo-control trial evaluating neoadjuvant atezolizumab with NAC followed by adjuvant atezolizumab in TNBC. Pts are stratified by region (North America; Europe), tumor size (1.1-3.0cm; >3.0cm), AC/EC schedule (q2w; q3w), and nodal status (positive; negative), then randomized 1:1 to receive atezolizumab/placebo 1200 mg IV every 3 wks concurrently with both sequential regimens of weekly paclitaxel 80 mg/m2 IV for 12 doses with every 3-wk carboplatin AUC of 5 IV for 4 doses followed by AC/EC every 2-3 wks (per investigator discretion) for 4 cycles. Following surgery, pts resume atezolizumab/placebo 1200 mg IV every 3 wks as adjuvant therapy for 6 months. Radiotherapy based on local standards is co-administered with atezolizumab/placebo.

Eligibility criteria

Centrally-confirmed ER-neg, PR-neg, HER2-neg invasive breast cancer by ASCO/CAP guidelines. Primary tumor must be stage T2 or T3 if cN0 or cN1 with negative biopsy or T1c, T2, or T3 if cN1 with positive biopsy or cN2 or cN3. LVEF >55% and no significant cardiac history.

Statistical methods

Co-primary endpoints are event-free survival (EFS) and pCR breast/nodes. Secondary endpoints include pCR breast, overall survival, distant disease-free survival, safety and toxicity. Trial is an academic collaboration between NSABP and GBG with support from Genentech/Roche.

NCT03281954

Support: Genentech/Roche

Citation Format: Geyer, Jr. CE, Loibl S, Rastogi P, Seiler S, Costantino JP, Nekljudova VN, Cortazar P, Lucas PC, Denkert C, Mamounas EP, Jackisch C, Wolmark N. A randomized double-blind phase III clinical trial of neoadjuvant chemotherapy (NAC) with atezolizumab or placebo in patients (pts) with triple negative breast cancer (TNBC) followed by adjuvant atezolizumab or placebo: NSABP B-59/GBG 96-GeparDouze [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr OT3-05-01.

Abstract P3-10-04: The fully validated NSABP/NRG 8-gene signature which predicted the degree of benefit in the adjuvant setting (B-31 and NCCTG N9831) associates with pCR in the neoadjuvant setting in NSABP clinical trial FB-7

Background: We previously described a predictive signature for trastuzumab benefit which was validated in the adjuvant setting in an independent cohort within NSABP B-31 (the 8-gene signature) (Pogue-Geile et al JNCI, 2013) and in Alliance/NCCTG N9831 (SABCs 2017). The 8-gene signature subtyped B-31 patients into three trastuzumab benefit groups: high HR=0.27, intermediate HR=0.56 and no benefit HR=1.56 based on disease free survival. The 8 gene signature was also predictive of trastuzumab benefit in N9831. HRs were 0.47, P<0.001, 0.6, P=0.02, and 1.54, P=0.375 in the predicted-high, -intermediate and -no benefit groups, respectively based on recurrence free survival (SABCS 2017). The interaction P-value was significant at 0.019 in adjusted Cox models. The RFS at 10 years for trastuzumab-treated pts was 83%, 83% and 72% in the high, intermediate and no benefit groups, respectively. Now we have tested the association of the 8-gene signature groups with pCR in FB-7 which was a 3 arm neoadjuvant study testing the pCR rate of HER2+ breast cancer patients treated with paclitaxel in combination with trastuzumab (T) or neratinib (N) or the combination (T + N).

Methods: RNA-Seq data from FB-7 pretreatment biopsies was used to predict the trastuzumab benefit groups (high, intermediate, and no) for each patient's tumor using the 8 gene signature using methods and cut-offs as previously described (Pogue-Geile et al 2013). The pCR rates (percentages) were tested for treatment interaction with a chi-square test.

Results: The pCR rates were 75%, 53%, and 22%, in the high (N=12), intermediate (N=32) and no benefit groups (N=9), respectively, when analyzed without regard to treatment arm. The pCR rates for the no benefit group and the high benefit groups were significantly different (p=0.030) and there was a significant treatment interaction with the 8-gene benefit group (intp=0.0081). The predicted low and intermediate groups were combined to test whether the 8 gene signature could identify a group of patients whose pCR rates might improve by adding N to T, and referred to it as the low benefit group. This was necessary due to the small numbers of patients in each group. The pCR rate in the low benefit group was higher in patients treated with T+N (9/15, 60%) than in the T arm (6/11, 45%) but these differences were not significant.

Conclusions: This is the first test of the 8-gene signature in the neoadjuvant setting and interpretations of these data should be interpreted cautiously due to the small numbers. However, if these results were validated in another neoadjuvant trial then the 8 gene signature could provide a rationale for selecting patients who would be appropriate for the addition of neratinib or other TKIs to trastuzumab and chemotherapy.

SUPPORT: PUMA Biotechnology, NCI U10CA180868, -180822, UG1-189867, and U24-196067; The Pennsylvania Department of Health. The Department specifically disclaims responsibility for any analysis,interpretations, or conclusions.

Citation Format: Pogue-Geile KL, Wang Y, Srinivasan A, Gavin PG, Kim RS, Song N, Feng H, Lipchik C, Costantino JP, Wolmark N, Lucas PC, Paik S, Jacobs SA. The fully validated NSABP/NRG 8-gene signature which predicted the degree of benefit in the adjuvant setting (B-31 and NCCTG N9831) associates with pCR in the neoadjuvant setting in NSABP clinical trial FB-7 [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P3-10-04.

Abstract GS2-03: Highly recurrent transcriptional remodeling events in advanced endocrine resistant ER-positive breast cancers

BACKGROUND: Although individual cancers are driven by heterogeneous processes, cancer mortality has a near universal cause—therapy resistance, recurrence and metastasis to vital organs. Characterizing more advanced tumors has borne valuable insight into cancer progression, yet studies of longitudinally collected breast cancer specimens are scarce given lengthy periods of cancer dormancy. In this study, we aimed to create the most comprehensive characterization of gene expression alterations to date between patient-matched pairs of primary and advanced ER-positive breast cancers.

MATERIALS/METHODS: Hybrid-capture RNA-sequencing was performed on 50 patient-matched pairs of primary and advanced ER-positive tumors from various recurrence sites (9 brain, 11 bone, 3 GI, 10 ovary, 17 local). Time to recurrence was up to 14.1 years with a median of 3.4 years. A shared variant analysis confirmed all paired samples were patient-matched. 1,380 cancer-related genes were analyzed for outlier expression fold-changes in matched recurrences versus primary tumors. Pair-specific, outlier fold-change thresholds were defined as Q1/Q3 +/- [1.5 X IQR]; using each pairs' fold-change values across all genes as the distribution. These discrete, longitudinal transcriptional remodeling events (LTREs) were assessed for recurrence across all sites and analyzed for enrichments within specific cohorts (Fisher's exact tests), such as locoregional vs. distant recurrences. To determine if LTREs represent acquired vulnerabilities, ex vivo and in vivo experiments targeting a recurrent, druggable LTRE gain of RET was performed.

RESULTS: The majority of advanced cancers were transcriptionally similar to patient-matched primaries with 23 of 33 distant metastases retaining PAM50 assignments of the matched primary—shifts to HER2 (n=4, 12%) or Luminal B (n=5, 15%) subtypes accounted for most metastatic discordances. Despite this intrinsic conservation, remarkably recurrent gene-level LTRE gains and losses were observed in advanced disease. Recurrent LTRE gains included NCAM1 [42%], FGFR4 [40%], IBSP [36%], ROBO2 [36%] and SPP1 [30%]. Notable LTRE losses included RELN [42%] and ESR1 [26%]. NCAM1 LTREs showed the most significant enrichments (p < 0.001) in distant disease (20 of 33, 61%) versus locoregional disease (1 of 17, 6%). A prominent LTRE enriched in brain metastasis (BrM) was RET (p-value = 0.003), expression of which showed outlier gains in 56% of ER-positive BrM. Marked anti-tumor activity was demonstrated with the RET inhibitor cabozantinib in ex vivo explant cultures of patient resected BrMs (n=3) and a BrM patient-derived xenograft.

CONCLUSIONS: Taken together, these results demonstrate profound, recurrent and metastatic site-specific LTREs in advanced breast cancers, which may be essential to our understanding of endocrine-therapy resistance and metastasis. Although current emphasis for longitudinal clinical profiling of tumors is on DNA-level alterations, these results suggest LTREs as a compelling, shared mechanism of cancer progression. Given remarkably high recurrence rates of specific LTREs across multiple cohorts, further preclinical and clinical investigations of LTREs are demanded, especially considering some (i.e. FGFR4 and RET) are readily druggable.

Citation Format: Priedigkeit N, Vareslija D, Basudan A, Watters RJ, Lucas PC, Davidson NE, Blohmer J-U, Denkert C, Machleidt A, Heppner BI, Brufsky AM, Oesterreich S, Young L, Lee AV. Highly recurrent transcriptional remodeling events in advanced endocrine resistant ER-positive breast cancers [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr GS2-03.

Abstract P6-07-07: ESR1 amplification and 5'-3' exon imbalance in metastatic breast cancer

BACKGROUND: Growing evidence indicates that base pair mutations in ESR1 are relatively uncommon in newly diagnosed, treatment-naive breast cancer, but frequently acquired in hormone-resistant metastatic breast cancer (MBC). We and others have recently identified ESR1 gene fusion and amplification in MBC, with the ESR1 fusions generally encompassing AF1 and the DNA binding domain. The genomic break required for gene fusions often results in an imbalance in the DNA copy number of exons around the break. We examined ESR1 amplification and 5' and 3' exon copy number imbalance in MBC.

MATERIALS and METHODS: We designed NanoString DNA hybridization probes against coding and non-coding exons (n=9) in ESR1 and 15 reference probes. We analyzed 128 samples consisting of 61 ER-positive and 44 ER-negative metastases, and 23 primary breast cancers. DNA copy number (CN) was determined using nSolver, with >2.7CN as copy number gain, and >10 as CN amplification. ESR1 CN was calculated by averaging the DNA copy number obtained from all coding exons. The 5'-3' copy number ratio was the average copy number of the 5' exons (3-6) divided by the 3' exons (7-10).

RESULTS: 8 (13%) ER positive metastatic breast cancers showed ESR1 amplification with 5 (8%) having >2.7CN, and 3 (5%) with >10CN. In contrast, in ER-negative metastases, we did not detect any samples with amplification >10CN, and a gain (>2.7 CN) in one case. Similarly, in ER+ primary cancers we did not detect any samples with >10 CN amplifications and 2 samples with CN gain (>2.7 CN). ESR1 showed 5'-3' CN imbalance in 1 primary (5%) and in 5 metastatic (5%) breast cancers. We are currently confirming and expanding these data in a larger dataset.

CONCLUSIONS: In addition to ESR1 mutations, ESR1 CN amplifications and 5'-3' imbalance are represent frequent occurrences in endocrine resistant breast cancer. Future studies are aimed at understanding whether the observed exon imbalances are associated with generation of fusion proteins, and whether and how ESR1 amplifications cause changes in endocrine treatment response.

Citation Format: Oesterreich S, Basudan A, Preideigkeit N, Hartmaier RJ, Bahreini A, Gyanchandani R, Leone JP, Lucas PC, Hamilton RL, Brufsky AM, Lee AV. ESR1 amplification and 5'-3' exon imbalance in metastatic breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P6-07-07.

Abstract PD1-05: Breast cancer brain metastases show limited intrinsic subtype switching, yet exhibit acquired ERBB2 amplifications and activating mutations

BACKGROUND: Metastasis is the major cause of mortality in breast cancer (BrCa) patients. Our understanding of brain metastasis (BrM) is limited, reflected by a lack of effective treatments. We aimed to (1) determine BrCa gene signature differences between primary tumors and matched BrM and (2) uncover BrM-specific alterations that may be clinically actionable.

MATERIALS and METHODS: NanoString expression profiling of 127 genes from 5 major prognostic tests (MammaPrint, EndoPredict, PAM50, OncotypeDX, MGI) was performed on 20 patient-matched primary (10 ER-neg, 10 ER-pos) and metastatic brain tumors. Subtype classification was performed using genefu. Protein changes in ER and HER2 (ERBB2) were confirmed by IHC. BrM-specific ERBB2 gains were corroborated in a publicly available dataset of 18 additional patient-matched cases (dbGAP phs000730.v1.p1). To test whether ERBB2 amplification and base pair mutation is metastasis-site specific, we further analyzed an expanded cohort of 7,884 breast tumors enriched for metastatic samples (52%) including liver (16.7%), lung (4.3%), bone (3.6%), and brain (2.0%) using comprehensive hybrid-capture sequencing of ERBB2.

RESULTS: 17/20 BrM retained the PAM50 subtype of the primary BrCa. Despite this concordance, 17/20 BrM harbored expression changes (< or > 2-fold) in clinically actionable genes including gains of FGFR4 (30%), FLT1 (20%), AURKA (10%) and loss of ESR1 expression (45%). The most recurrently upregulated gene was ERBB2, showing a >2-fold expression increase in 35% of BrM. 3 of 13 (23.3%) cases originally HER2-negative, and thus HER2-therapy naive, in the primary BrCa were IHC-positive (3+) in the paired BrM with an observed metastasis-specific amplification of the ERBB2 locus. In an independent dataset, 2 of 9 (22.2%) HER2-negative BrCa switched to HER2-positive with one BrM acquiring ERBB2 amplification and the other showing metastastic enrichment of the activating V777L ERBB2 mutation. Analysis of a large cohort of breast tumors (n=7,884) showed that across all organs ERBB2 amplification and/or base pair mutation was similar (p=0.18) between primary (13%) and metastatic disease (12%), however, a strong and significant enrichment was seen for BrM (primary 13% vs BrM 24%, p<0.0005).

CONCLUSIONS: Taken together, these results demonstrate that the majority (85%) of patient-matched BrM retain the intrinsic subtype of the primary cancer. However, despite this transcriptional similarity, alterations in clinically actionable genes are common, with BrM acquiring ERBB2 amplifications and/or base pair mutations at a frequency of ∼20%, even in HER2-therapy naive tumors. In a large cohort of primary and metastatic breast cancers, there is also a unique enrichment for ERBB2 alterations in BrM. This study provides a strong rationale to molecularly profile metastatic lesions to both better understand biological mechanisms of metastases and to perhaps refine therapeutic decision-making in advanced cancers.

Citation Format: Priedigkeit N, Hartmaier RJ, Chen Y, Vareslija D, Basudan A, Thomas R, Leone JP, Lucas PC, Bhargava R, Hamilton RL, Chmielecki J, Davidson NE, Oesterreich S, Brufsky AM, Young L, Lee AV. Breast cancer brain metastases show limited intrinsic subtype switching, yet exhibit acquired ERBB2 amplifications and activating mutations [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr PD1-05.

A dual role for the API2 moiety in API2-MALT1-dependent NF-kappaB activation: heterotypic oligomerization and TRAF2 recruitment

Mucosa-associated lymphoid tissue (MALT) lymphoma is the most common extranodal lymphoid neoplasm. Chromosomal translocation t(11;18)(q21,q21) is found in 30% of gastric MALT lymphomas and is associated with a failure to respond to standard treatment and a tendency to disseminate. This translocation generates a chimeric protein composed of N-terminal sequences of Inhibitor of Apoptosis 2 (API2, also known as BIRC3 and cIAP2) fused to C-terminal sequences of MALT1. API2-MALT1 promotes cell survival and proliferation via activation of nuclear factor-kappaB (NF-kappaB). Here, we investigate the mechanism by which the API2 moiety contributes to NF-kappaB stimulation. We find that the API2 moiety mediates oligomerization of API2-MALT1 as well as interaction with tumor necrosis factor receptor-associated factor 2 (TRAF2). Surprisingly, oligomerization does not occur via homotypic interaction; rather, the API2 moiety of one monomer interacts with the MALT1 moiety of another monomer. Further, the specific region of the API2 moiety responsible for mediating oligomerization is distinct from that mediating TRAF2 binding. Although deletion or mutation of the TRAF2 binding site does not inhibit oligomerization, it does lead to dramatically decreased NF-kappaB activation. Deletion of both TRAF2 binding and oligomerization regions results in near-complete loss of NF-kappaB activation. Thus, API2 moiety-mediated heterotypic oligomerization and TRAF2 binding both contribute to maximal API2-MALT1-dependent NF-kappaB stimulation.

Loss of CDX2 expression and microsatellite instability are prominent features of large cell minimally differentiated carcinomas of the colon

Most large bowel cancers are moderately to well-differentiated adenocarcinomas comprised chiefly or entirely of glands lined by tall columnar cells. We have identified a subset of poorly differentiated colon carcinomas with a distinctive histopathological appearance that we term large cell minimally differentiated carcinomas (LCMDCs). These tumors likely include a group of poorly differentiated carcinomas previously described by others as medullary adenocarcinomas. To better understand the pathogenesis of these uncommon neoplasms, we compared molecular features of 15 LCMDCs to those present in 25 differentiated adenocarcinomas (DACs) of the colon. Tumors were examined for alterations commonly seen in typical colorectal carcinomas, including increased p53 and beta-catenin immunoreactivity, K-ras gene mutations, microsatellite instability, and loss of heterozygosity of markers on chromosomes 5q, 17p, and 18q. In addition, tumors were evaluated by immunohistochemistry for CDX2, a homeobox protein whose expression in normal adult tissues is restricted to intestinal and colonic epithelium. Markedly reduced or absent CDX2 expression was noted in 13 of 15 (87%) LCMDCs, whereas only 1 of the 25 (4%) DACs showed reduced CDX2 expression (P < 0.001). Nine of 15 (60%) LCMDCs had the high-frequency microsatellite instability phenotype, but only 2 of 25 (8%) DACs had the high-frequency microsatellite instability phenotype (P = 0.002). Our findings provide support for the hypothesis that the molecular pathogenesis of LCMDCs is distinct from that of most DACs. CDX2 alterations and DNA mismatch repair defects have particularly prominent roles in the development of LCMDCs.

Bimp1, a MAGUK family member linking protein kinase C activation to Bcl10-mediated NF-kappaB induction

Bcl10 and MALT1, products of distinct chromosomal translocations in mucosa-associated lymphoid tissue lymphoma, cooperate in activating NF-kappaB. Mice lacking Bcl10 demonstrate severe immunodeficiency associated with failure of lymphocytes to activate nuclear factor kappaB (NF-kappaB) in response to antigen receptor stimulation and protein kinase C activation. We characterize Bimp1, a new signaling protein that binds Bcl10 and activates NF-kappaB. Bimp1-mediated NF-kappaB activation requires Bcl10 and IkappaB kinases, indicating that Bimp1 acts upstream of these mediators. Bimp1, Bcl10, and MALT1 form a ternary complex, with Bcl10 bridging the Bimp1/MALT1 interaction. A dominant negative Bimp1 mutant inhibits NF-kappaB activation by anti-CD3 ligation, phorbol ester, and protein kinase C expression. These results suggest that Bimp1 links surface receptor stimulation and protein kinase C activation to Bcl10/MALT1, thus leading to NF-kappaB induction.

Bcl10 and MALT1, independent targets of chromosomal translocation in malt lymphoma, cooperate in a novel NF-kappa B signaling pathway

At least two distinct recurrent chromosomal translocations have been implicated in the pathogenesis of MALT lymphoma. The first, t(1;14), results in the transfer of the entire Bcl10 gene to chromosome 14 wherein Bcl10 expression is inappropriately stimulated by the neighboring Ig enhancer. The second, t(11;18), results in the synthesis of a novel fusion protein, API2-MALT1. Until now, no common mechanism of action has been proposed to explain how the products of these seemingly unrelated translocations may contribute to the same malignant process. We show here that Bcl10 and MALT1 form a strong and specific complex within the cell, and that these proteins synergize in the activation of NF-kappaB. The data support a mechanism of action whereby Bcl10 mediates the oligomerization and activation of the MALT1 caspase-like domain. This subsequently activates the IKK complex through an unknown mechanism, setting in motion a cascade of events leading to NF-kappaB induction. Furthermore, the API2-MALT1 fusion protein also strongly activates NF-kappaB and shows dependence upon the same downstream signaling factors. We propose a model whereby both the Bcl10.MALT1 complex and the API2-MALT1 fusion protein activate a common downstream signaling pathway that originates with the oligomerization-dependent activation of the MALT1 caspase-like domain.

An induced proximity model for NF-kappa B activation in the Nod1/RICK and RIP signaling pathways

Nod1 is an Apaf-1-like molecule composed of a caspase-recruitment domain (CARD), nucleotide-binding domain, and leucine-rich repeats that associates with the CARD-containing kinase RICK and activates nuclear factor kappaB (NF-kappaB). We show that self-association of Nod1 mediates proximity of RICK and the interaction of RICK with the gamma subunit of the IkappaB kinase (IKKgamma). Similarly, the RICK-related kinase RIP associated via its intermediate region with IKKgamma. A mutant form of IKKgamma deficient in binding to IKKalpha and IKKbeta inhibited NF-kappaB activation induced by RICK or RIP. Enforced oligomerization of RICK or RIP as well as of IKKgamma, IKKalpha, or IKKbeta was sufficient for induction of NF-kappaB activation. Thus, the proximity of RICK, RIP, and IKK complexes may play an important role for NF-kappaB activation during Nod1 oligomerization or trimerization of the tumor necrosis factor alpha receptor.

Inhibition of adipogenesis by Wnt signaling

Wnts are secreted signaling proteins that regulate developmental processes. Here we show that Wnt signaling, likely mediated by Wnt-10b, is a molecular switch that governs adipogenesis. Wnt signaling maintains preadipocytes in an undifferentiated state through inhibition of the adipogenic transcription factors CCAAT/enhancer binding protein alpha (C/EBPalpha) and peroxisome proliferator- activated receptor gamma (PPARgamma). When Wnt signaling in preadipocytes is prevented by overexpression of Axin or dominant-negative TCF4, these cells differentiate into adipocytes. Disruption of Wnt signaling also causes transdifferentiation of myoblasts into adipocytes in vitro, highlighting the importance of this pathway not only in adipocyte differentiation but also in mesodermal cell fate determination.

Hepatic nuclear factor 3- and hormone-regulated expression of the phosphoenolpyruvate carboxykinase and insulin-like growth factor-binding protein 1 genes

The rate of transcription of the hepatic phosphoenolpyruvate carboxykinase (PEPCK) and insulin-like growth factor-binding protein 1 (IGFBP-1) genes is stimulated by glucocorticoids and inhibited by insulin. In both cases, the effect of insulin is dominant, since it suppresses both basal and glucocorticoid-stimulated PEPCK or IGFBP-1 gene transcription. Analyses of both promoters by transfection of PEPCK or IGFBP-1-chloramphenicol acetyltransferase fusion genes into rat hepatoma cells has led to the identification of insulin response sequences (IRSs) in both genes. The core IRS, T(G/A)TTTTG, is the same in both genes, but the PEPCK promoter has a single copy of this element whereas the IGFBP-1 promoter has two copies arranged as an inverted palindrome. The IGFBP-1 IRS and PEPCK IRS both bind the alpha and beta forms of hepatic nuclear factor 3 (HNF-3), although the latter does so with a sixfold-lower relative affinity. Both the PEPCK and the IGFBP-1 IRSs also function as accessory factor binding sites required for the full induction of gene transcription by glucocorticoids. A combination of transient transfection and DNA binding studies suggests that HNF-3 is the accessory factor that supports glucocorticoid-induced gene transcription. In both genes, the HNF-3 binding site overlaps the IRS core motif(s). A model in which insulin is postulated to mediate its negative effect on glucocorticoid-induced PEPCK and IGFBP-1 gene transcription indirectly by inhibiting HNF-3 action is proposed.

Potential convergence of insulin and cAMP signal transduction systems at the phosphoenolpyruvate carboxykinase (PEPCK) gene promoter through CCAAT/enhancer binding protein (C/EBP)

Adenosine 3',5'-monophosphate (cAMP) stimulates phosphoenolpyruvate carboxykinase (PEPCK) gene transcription, whereas insulin has the opposite effect. In H4IIE cells, the effect of insulin is dominant since it represses cAMP-stimulated transcription. Discrete cis-acting elements in the PEPCK promoter that serve as an insulin response sequence (IRS) and cAMP response element (CRE) have been identified. Here we show that common proteins can bind both elements, since: (i) an almost identical pattern of protein binding is seen when oligonucleotides representing either the IRS or the CRE are used as the labeled probe in a gel retardation assay and (ii) the unlabeled wild-type, but not mutated, CRE oligonucleotide competes for protein binding to the labeled IRS probe, and vice versa. Six homo- and heterodimer complexes interact with these DNA elements; the complexes are composed of three individual protein species: (a) 42-kDa C/EBP alpha, (b) 30-kDa C/EBP alpha, and (c) an unidentified 20-kDa factor termed p20- CRE/IRS Binding Protein (p20-C/IBP). These proteins have a 30-fold greater affinity for the CRE at room temperature, a difference explained by the rapid dissociation rate of protein bound to the IRS, since the association rate of protein binding to both the IRS and CRE is the same. Protease digestion experiments suggest that the proteins bind to the CRE and IRS in different conformations. The IRS and CRE both function in the context of a heterologous promoter to mediate effects of insulin and cAMP, respectively, but, although the PEPCK IRS and CRE bind common proteins, the PEPCK CRE is not a functional IRS and the PEPCK IRS is not a functional CRE.

Activation of the phosphoenolpyruvate carboxykinase gene retinoic acid response element is dependent on a retinoic acid receptor/coregulator complex

The accessory factor 1 (AF1) element is an upstream transcriptional control region that plays a role in the response of the phosphoenolpyruvate carboxykinase (PEPCK) gene to both glucocorticoids and retinoic acid. We demonstrate here that retinoic acid receptor alpha (RAR alpha) binds to a sequence within the AF1 element, TGACCT (site B), that is a consensus retinoic acid response element (RARE) half-site. A similar DNA sequence, TGGCCG (site C), located 1 bp downstream of site B, is not involved in the binding of RAR alpha monomers or dimers but is required for the constitution of a functional RARE. Site C is also required for the formation of a complex involving RAR alpha and a liver nuclear factor designated CR, for coregulator. Mutational analysis of the AF1 element shows that the RAR alpha/CR complex is the trans-acting unit that mediates the retinoic acid response of the PEPCK gene. Another member of the retinoid receptor family, retinoid X receptor alpha (RXR alpha), can also form a complex with RAR alpha and the AF1 element. Several observations, including the observation that RXR alpha antibody interacts with CR, indicate that RXR alpha and CR are identical or closely related proteins. Through RXR alpha forms a complex with RAR alpha and the AF1 element, we demonstrate that the AF1 element is functionally distinguishable from a retinoid X response element. Taken together, our results show that the AF1 element contains an RARE that mediates a retinoic acid response by binding an RAR alpha/coregulator complex; this coregulator is presumably RXR alpha.

Specificity of a retinoic acid response element in the phosphoenolpyruvate carboxykinase gene promoter: consequences of both retinoic acid and thyroid hormone receptor binding

The ability of a retinoic acid (RA) response element (RARE) in the phosphoenolpyruvate carboxykinase (PEPCK) gene promoter to mediate effects of either RA or thyroid hormone (T3) on gene expression was studied. Fusion gene constructs consisting of PEPCK promoter sequences ligated to the chloramphenicol acetyltransferase (CAT) reporter gene were used for this analysis. While T3 induced CAT expression to a small degree (about twofold) when such constructs were transiently transfected into H4IIE rat hepatoma cells, along with an expression vector encoding the alpha subtype of the T3 receptor (TR), this effect was mediated by promoter sequences distinct from the PEPCK RARE. Although TRs were capable of binding the PEPCK RARE in the form of putative monomers, dimers, and heterodimers with RA receptors (RARs), this element failed to mediate any positive effect of T3 on gene expression. In contrast, the PEPCK RARE mediated six- to eightfold induction of CAT expression by RA. When TRs were coexpressed along with RARs in transfected H4IIE cells, this RA induction was substantially blunted in a T3-independent manner. This inhibitory effect may be due to the binding of nonfunctional TRs or TR-RAR heterodimers to the PEPCK RARE. A model is proposed to explain the previously observed in vivo effects of T3 on PEPCK gene expression.

Ontogeny of two vitamin A-metabolizing enzymes and two retinol-binding proteins present in the small intestine of the rat

The patterns of expression of cellular retinol-binding protein (CRBP), cellular retinol-binding protein, type two [CRBP(II)], lecithin: retinol acyltransferase (LRAT), and microsomal retinal reductase were examined for rat small intestine during the perinatal period. CRBP was present (15 pmole per mg soluble protein) at the earliest time examined, the 16th day of gestation, declining by 70% by birth, maintained to adulthood. In contrast, CRBP(II) appeared 2-3 days before birth, rising to its highest level (500 pmole per mg soluble protein) by day 3 after birth, then declining by 50% during the late suckling period to the adult level. Immunohistochemistry revealed that CRBP(II) initially appeared in the epithelial cell layer in a patchy manner, resolving by birth into an even staining of all villus-associated enterocytes. In contrast, CRBP was evenly expressed in the epithelial cell layer at day 17/18 but was absent by birth. Intestinal LRAT activity increased rapidly in the 2 days prior to birth, then declined at weaning to the adult level. Microsomal retinal reductase was measurable in the intestine at birth, but not detected during the early suckling period, reappearing at day 21. Considerable increase was then observed coincident with weaning, when carotenes, from which retinal is derived, became an important source of vitamin A. The pattern of appearance of these elements appears to prepare the intestine for the necessary processing of vitamin A required after birth.

A retinoic acid response element is part of a pleiotropic domain in the phosphoenolpyruvate carboxykinase gene

Several hormones, including insulin, glucagon, and glucocorticoids, regulate the expression of the rate-limiting gluconeogenic enzyme, phosphoenolpyruvate carboxykinase [GTP: oxaloacetate carboxy-lyase (transphosphorylating); EC 4.1.1.32; PEPCK] in liver. In this report we demonstrate that retinoic acid (RA) also regulates PEPCK expression by inducing a 3-fold increase in the rate of transcription of the PEPCK gene. A RA response element located between -468 and -431 in the PEPCK promoter mediates a 7-fold increase in expression of a chimeric construct containing the basal PEPCK promoter ligated to the chloramphenicol acetyltransferase reporter gene. This element confers RA responsiveness through the heterologous thymidine kinase promoter and functions relatively independent of position and orientation. An 18-base-pair core sequence (-451 to -434) (i) mediates an effect of RA on PEPCK gene expression and contains motifs found in two other RA response elements; (ii) corresponds to AF1, an accessory factor element that is an integral component of the complex glucocorticoid response unit in the PEPCK gene promoter; (iii) is in a region involved in the developmental expression of the PEPCK gene; and (iv) shows homology to elements involved in the tissue-specific regulation of genes, including the hepatic apolipoprotein genes and the alpha 1-antitrypsin gene.

Regulation of phosphoenolpyruvate carboxykinase gene expression by insulin. Use of the stable transfection approach to locate an insulin responsive sequence

H4IIE rat hepatoma cells were stably transfected with various phosphoenolpyruvate carboxykinase-chloramphenicol acetyltransferase (PEPCK-CAT) expression vectors. The regulation of the transfected genes was qualitatively similar to that of the endogenous PEPCK gene. CAT expression was increased in response to cAMP and dexamethasone and insulin overrode these effects at concentrations known to be effective in suppressing transcription of the endogenous gene. The effect of insulin was dominant, as it is with the endogenous gene. A series of 5',3', and internal deletions of the PEPCK gene promoter were used to show that this insulin response requires at least two separate elements. One insulin-responsive sequence is located between -468 and -402, relative to the transcription initiation site. The other is between -271 and +69.

Identification of a sequence in the PEPCK gene that mediates a negative effect of insulin on transcription

Phosphoenolpyruvate carboxykinase (PEPCK) governs the rate-limiting step in gluconeogenesis. Glucocorticoids and adenosine 3',5'-monophosphate (cAMP) increase PEPCK gene transcription and gluconeogenesis, whereas insulin has the opposite effect. Insulin is dominant, since it prevents cAMP and glucocorticoid-stimulated transcription. Glucocorticoid and cAMP response elements have been located in the PEPCK gene and now a 15-base pair insulin-responsive sequence (IRS) is described. Evidence for a binding activity that recognizes this sequence is presented.

Micturition in the unanesthetized rat: spinal vs. peripheral pharmacology of the adrenergic system

The pharmacology of the spinal and peripheral adrenergic receptor-subtypes controlling the micturition reflex was studied in a chronic unanesthetized rat model by continuous infusion of saline in the bladder and cystometrography after intrathecal (i.t.) and i.p. injections, respectively. Due to the absence of a catheter in the urethra, the bladder contraction-sphincter relaxation coupling could be assessed very precisely. For each agent tested in this study, dose-response curves were established. Norepinephrine (i.p.), methoxamine (i.p.) and ST-91 (i.p. and i.t.) produced an increase in frequency of bladder contraction. A decrease in frequency was observed after i.p. injection of isoproterenol (30 micrograms) and terbutaline (300 micrograms). Phentolamine, yohimbine, propranolol (i.p. and i.t.), isoproterenol (i.t.) and methoxamine (i.t.) had little or no effects on frequency of contraction at the highest doses examined. In addition, norepinephrine (i.p.), isoproterenol (i.p. and i.t.), ST-91 (i.p.), terbutaline (i.p.), phentolamine (i.p.) and yohimbine (i.p.) produced some relaxation of the bladder outlet. Methoxamine (i.p.) produced an increase in tone of the outlet. Propranolol (i.p. and i.t.), methoxamine (i.t.), ST-91 (i.t.), phentolamine (i.t.) and yohimbine (i.t.) had little or no effects on the tone of the bladder outlet at the highest doses examined. Those observations suggest that peripherally, catecholamines modulate the frequency of bladder contraction (increase through alpha-1 and alpha-2 receptors; decrease through beta-2 receptors), and the tonic activity of the bladder outlet (increase in tone through alpha-1 receptors; relaxation through alpha-2 and beta-2 receptors). At the spinal level, noradrenergic systems appear to modulate the frequency of contraction and sphincter tone through alpha-2 receptors. Isoproterenol effects after i.t. injection are thought to be due to systemic distribution. However, absence of effects after i.t. injection of adrenergic antagonists suggests that spinal adrenergic systems might not be active during a normal volume-evoked micturition reflex, but might be activated in special circumstances, such as the voluntary act of retaining urine.