Chicago EYES on Cancer: Fostering Diversity in Biomedicine through Cancer Research Training for Students and Teachers.

The National Cancer Institute's Youth Enjoy Science Research Education Program (YES) supports cancer-based research experiences, curriculum development and outreach activities to foster diversity in the biomedical workforce. The University of Chicago Medicine Comprehensive Cancer Center was among the first recipients of the YES award in 2017, launching the Chicago EYES (Educators and Youth Enjoy Science) on Cancer program for high school and college students. The EYES team also introduced immersive research experiences and mentored curriculum development for high school science teachers, a potentially powerful means to extend science enrichment and career exposure to schools across Chicago. Ongoing evaluation of the EYES program suggests positive outcomes in terms of trainees' research skill development and their knowledge about, and positive attitudes towards, careers in biomedicine. Teacher research fellows reported that the program inspired new insights about science learning and practice that not only strengthened their skills as science educators, but also improved their ability to relate to their pupils. These findings contribute to the broader effort to establish best practices among cancer research training programs, particularly those with a shared mission to empower youth from diverse backgrounds to contribute to a field deeply in need of their talents and perspectives.

Adapting Pathway Programs to the Virtual World: Insights from the Chicago EYES on Cancer Response to COVID-19-Related Disruptions to Training.

Since spring 2020, the COVID-19 pandemic has disrupted development of the next generation of cancer researchers and physicians, forcing pathway programs across the nation to cancel, postpone or reinvent education and training activities. Accordingly, the University of Chicago's Chicago EYES on Cancer program was converted to a fully-online format, which prioritized flexibility for the 26 high school and undergraduate trainees, from underrepresented backgrounds, who were eligible to participate. Evaluation data suggest that the program's redesign successfully preserved trainees' access to intellectual, social and financial support despite the pandemic, with 88% of trainees meeting, and most exceeding, program requirements. Data also suggest positive outcomes for trainees, particularly with regard to their understanding of careers in biomedicine, their commitment to and confidence in planning for a research career, and their readiness and self-confidence as researchers. In the immediate term, our experiences offer practical insights for our colleagues similarly challenged to provide high-quality cancer research training within the context of COVID. In the long term, the success of our online programming can be leveraged to extend enrichment opportunities to program alumni, partner schools and other priority groups as a permanent component of the Comprehensive Cancer Center's broad cancer education strategy.

Cohort profile: the ChicagO Multiethnic Prevention and Surveillance Study (COMPASS).

PURPOSE: The ChicagO Multiethnic Prevention and Surveillance Study or 'COMPASS' is a population-based cohort study with a goal to examine the risk and determinants of cancer and chronic disease. COMPASS aims to address factors causing and/or exacerbating health disparities using a precision health approach by recruiting diverse participants in Chicago, with an emphasis on those historically underrepresented in biomedical research. PARTICIPANTS: Nearly 8000 participants have been recruited from 72 of the 77 Chicago community areas. Enrolment entails the completion of a 1-hour long survey, consenting for past and future medical records from all sources, the collection of clinical and physical measurement data and the on-site collection of biological samples including blood, urine and saliva. Indoor air monitoring data and stool samples are being collected from a subset of participants. On collection, all biological samples are processed and aliquoted within 24 hours before long-term storage and subsequent analysis. FINDINGS TO DATE: The cohort reported an average age of 53.7 years, while 80.5% identified as African-American, 5.7% as Hispanic and 47.8% as men. Over 50% reported earning less than US$15 000 yearly, 35% were obese and 47.8% were current smokers. Moreover, 38% self-reported having had a diagnosis of hypertension, while 66.4% were measured as hypertensive at enrolment. FUTURE PLANS: We plan to expand recruitment up to 100 000 participants from the Chicago metropolitan area in the next decade using a hybrid community and clinic-based recruitment framework that incorporates data collection through mobile medical units. Follow-up data collection from current cohort members will include serial samples, as well as longitudinal health, lifestyle and behavioural assessment. We will supplement self-reported data with electronic medical records, expand the collection of biometrics and biosamples to facilitate increasing digital epidemiological study designs and link to state and/or national level databases to ascertain outcomes. The results and findings will inform potential opportunities for precision disease prevention and mitigation in Chicago and other urban areas with a diverse population. REGISTRATION: NA.

Racial disparities in omission of oncotype DX but no racial disparities in chemotherapy receipt following completed oncotype DX test results.

PURPOSE: To examine racial/ethnic disparities in Oncotype DX (ODX) testing among patients with node-negative, estrogen receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)-negative breast cancers and possible racial/ethnic disparities in chemotherapy receipt following ODX testing within Recurrence Score (RS) category (Not Done, Low, Intermediate, High), as well as chemotherapy receipt time trends within RS categories. METHODS: A retrospective cohort list of 125,288 women who were potentially indicated for ODX testing from 2010 to 2014 was obtained using the National Cancer Database. We fit multivariate logistic regression predicting chemotherapy receipt, adjusting for clinical factors, patient demographic factors, and hospital-level factors, separately by RS category, and calculated odds ratios (OR) and 95% confidence intervals (CI), as well as time trends. RESULTS: Overall, ODX testing was completed for 46.1% of Non-Hispanic (NH) Whites, 43.9% of NH Blacks, and 41.7% of Hispanics. Among patients who did not receive ODX testing, NH Black and Hispanic women both experienced statistically significant increases in chemotherapy receipt relative to NH White women (NH Black OR 1.23; 95% CI 1.11-1.37; Hispanic OR 1.23; 95% CI 1.07-1.42). However, among patients with ODX results, no statistically significant racial/ethnic differences in chemotherapy receipt were observed within strata of RS category. Trend analyses demonstrated increasing adherence to national guidelines for ODX testing. CONCLUSIONS: We identified racial disparities in omission of ODX testing but no differences in chemotherapy receipt if ODX test results were obtained, suggesting increasing access to ODX testing may improve racial equality in efficacious use of adjuvant chemotherapy for ER-positive HER2-negative breast cancer.

A p53-regulated apoptotic gene signature predicts treatment response and outcome in pediatric acute lymphoblastic leukemia.

Gene signatures have been associated with outcome in pediatric acute lymphoblastic leukemia (ALL) and other malignancies. However, determining the molecular drivers of these expression changes remains challenging. In ALL blasts, the p53 tumor suppressor is the primary regulator of the apoptotic response to genotoxic chemotherapy, which is predictive of outcome. Consequently, we hypothesized that the normal p53-regulated apoptotic response to DNA damage would be altered in ALL and that this alteration would influence drug response and treatment outcome. To test this, we first used global expression profiling in related human B-lineage lymphoblastoid cell lines with either wild type or mutant TP53 to characterize the normal p53-mediated transcriptional response to ionizing radiation (IR) and identified 747 p53-regulated apoptotic target genes. We then sorted these genes into six temporal expression clusters (TECs) based upon differences over time in their IR-induced p53-regulated gene expression patterns, and found that one cluster (TEC1) was associated with multidrug resistance in leukemic blasts in one cohort of children with ALL and was an independent predictor of survival in two others. Therefore, by investigating p53-mediated apoptosis in vitro, we identified a gene signature significantly associated with drug resistance and treatment outcome in ALL. These results suggest that intersecting pathway-derived and clinically derived expression data may be a powerful method to discover driver gene signatures with functional and clinical implications in pediatric ALL and perhaps other cancers as well.

Hsp70 exerts oncogenic activity in the Apc mutant Min mouse model.

Colorectal cancer (CRC) develops from colonic epithelial cells that lose expression of key tumor suppressor genes and/or gain expression of proproliferative and antiapoptotic genes like heat shock protein 70 (Hsp70). Heat shock protein 70 is overexpressed in CRC, but it is not known whether this is in response to the proteotoxic stress induced by transformation, or if it contributes to the process of transformation itself. Here, using the Apc (Min/+) mouse model of CRC, we show that Hsp70 regulates mitogenic signaling in intestinal epithelial cells through stabilization of proteins involved in the receptor tyrosine kinase (RTK) and WNT signaling pathways. Loss of Hsp70 reduced tumor size with decreased proliferation and increased tumor cell death. Hsp70 loss also led to decreased expression of ErbB2, Akt, ERK and ß-catenin along with decreased ß-catenin transcriptional activity as measured by c-myc and axin2 expression. Upregulation of RTK or WNT signals are frequent oncogenic events in CRC and many other cancers. Thus, in addition to the role of Hsp70 in cell-survival after transformation, Hsp70 stabilization of ß-catenin, Akt, ERK and ErbB2 are predicted to contribute to transformation. This has important implications not only for understanding the pathophysiology of these cancers, but also for treatment since anti-EGFR antibodies are in clinical use for CRC and EGFR is a major ErbB2 heterodimeric partner. Targeting Hsp70, therefore, might provide an alternative or complementary strategy for achieving better outcomes for CRC and other related cancer types.

ß-catenin regulates c-Myc and CDKN1A expression in breast cancer cells.

We previously reported that the Wnt pathway is preferentially activated in basal-like breast cancer. However, the mechanisms by which the Wnt pathway regulates down-stream targets in basal-like breast cancer, and the biological significance of this regulation, are poorly understood. In this study, we found that c-Myc is highly expressed in the basal-like subtype by microarray analyses and immunohistochemical staining. After silencing ß-catenin using siRNA, c-Myc expression was decreased in non-basal-like breast cancer cells. In contrast, c-Myc mRNA and protein expression were up-regulated in the basal-like breast cancer cell lines. Decreased c-Myc promoter activity was observed after inhibiting ß-catenin by siRNA in non-basal-like breast cancer cells; however, inhibition of ß-catenin or over-expression of dominant-negative LEF1 had no effect on c-Myc promoter activity in basal-like breast cancer cell lines. In addition, CDKN1A mRNA and p21 protein expression were significantly increased in all breast cancer cell lines upon ß-catenin silencing. Interestingly, inhibiting ß-catenin expression alone did not induce apoptosis in breast cancer cell lines despite c-Myc regulation, but we observed a modest increase of cells in the G1 phase of the cell cycle and decrease of cells in S phase upon ß-catenin silencing. Our findings suggest that the regulation of c-Myc in breast cancer cells is dependent on the molecular subtype, and that ß-catenin-mediated regulation of c-Myc and p21 may control the balance of cell death and proliferation in breast cancer.

ß-Catenin is required for the tumorigenic behavior of triple-negative breast cancer cells.

Our previous data illustrated that activation of the canonical Wnt signaling pathway was enriched in triple-negative breast cancer and associated with reduced overall survival in all patients. To determine whether Wnt signaling may be a promising therapeutic target for triple-negative breast cancer, we investigated whether ß-catenin was necessary for tumorigenic behaviors in vivo and in vitro. ß-catenin expression level was significantly reduced in two human triple-negative breast cancer cell lines, MDA-MB-231 and HCC38, using lentiviral delivery of ß-catenin-specific small hairpin RNAs (shRNAs). Upon implantation of the cells in the mammary fat pad of immunocompromised mice, we found that ß-catenin shRNA HCC38 cells formed markedly smaller tumors than control cells and grew much more slowly. In in vitro assays, ß-catenin silencing significantly reduced the percentage of Aldefluor-positive cells, a read-out of the stem-like cell population, as well as the expression of stem cell-related target genes including Bmi-1 and c-Myc. ß-catenin-knockdown cells were also significantly impaired in their ability to migrate in wound-filling assays and form anchorage-independent colonies in soft agar. ß-catenin-knockdown cells were more sensitive to chemotherapeutic agents doxorubicin and cisplatin. Collectively, these data suggest that ß-catenin is required for triple-negative breast cancer development by controlling numerous tumor-associated properties, such as migration, stemness, anchorage-independent growth and chemosensitivity.

The APC tumor suppressor is required for epithelial cell polarization and three-dimensional morphogenesis.

The Adenomatous Polyposis Coli (APC) tumor suppressor has been previously implicated in the control of apical-basal polarity; yet, the consequence of APC loss-of-function in epithelial polarization and morphogenesis has not been characterized. To test the hypothesis that APC is required for the establishment of normal epithelial polarity and morphogenesis programs, we generated APC-knockdown epithelial cell lines. APC depletion resulted in loss of polarity and multi-layering on permeable supports, and enlarged, filled spheroids with disrupted polarity in 3D culture. Importantly, these effects of APC knockdown were independent of Wnt/ß-catenin signaling, but were rescued with either full-length or a carboxy (c)-terminal segment of APC. Moreover, we identified a gene expression signature associated with APC knockdown that points to several candidates known to regulate cell-cell and cell-matrix communication. Analysis of epithelial tissues from mice and humans carrying heterozygous APC mutations further supports the importance of APC as a regulator of epithelial behavior and tissue architecture. These data also suggest that the initiation of epithelial-derived tumors as a result of APC mutation or gene silencing may be driven by loss of polarity and dysmorphogenesis.

Exploiting APC function as a novel cancer therapy.

The Adenomatous Polyposis Coli (APC) tumor suppressor is most commonly mutated in colorectal cancers such as familial adenomatous polyposis (FAP); as well as many other epithelial cancers like breast, pancreatic, and lung cancer. APC mutations usually result in a truncated form of the protein lacking the carboxy-terminal region resulting in loss of function. Mutations in APC have been identified in early stages of cancer development making it a gatekeeper of tumor progression and therefore an ideal therapeutic target. APC is best known for its role as a negative regulator of the Wnt/ß -catenin pathway. However, APC also mediates several other normal cell functions independently of Wnt/ß-catenin signaling such as apical-basal polarity, microtubule networks, cell cycle, DNA replication and repair, apoptosis, and cell migration. Given the vast cellular processes involving APC, the loss of these "normal" functions due to mutation can contribute to chemotherapeutic resistance. Several therapeutic treatments have been explored to restore APC function including the reintroduction of APC into mutant cells, inhibiting pathways activated by the loss of APC, and targeting APCmutant cells for apoptosis. This review will discuss the normal functions of APC as they relate to potential treatments for patients, the role of APC loss in several types of epithelial cancers, and an overview of therapeutic options targeting both the Wnt-dependent and -independent functions of APC.

Regulation of Tcf7l1 DNA binding and protein stability as principal mechanisms of Wnt/ß-catenin signaling.

Wnt/ß-catenin signal transduction requires direct binding of ß-catenin to Tcf/Lef proteins, an event that is classically associated with stimulating transcription by recruiting coactivators. This molecular cascade plays critical roles throughout embryonic development and normal postnatal life by affecting stem cell characteristics and tumor formation. Here, we show that this pathway utilizes a fundamentally different mechanism to regulate Tcf7l1 (formerly named Tcf3) activity. ß-catenin inactivates Tcf7l1 without a switch to a coactivator complex by removing it from DNA, which leads to Tcf7l1 protein degradation. Mouse genetic experiments demonstrate that Tcf7l1 inactivation is the only required effect of the Tcf7l1-ß-catenin interaction. Given the expression of Tcf7l1 in pluripotent embryonic and adult stem cells, as well as in poorly differentiated breast cancer, these findings provide mechanistic insights into the regulation of pluripotency and the role of Wnt/ß-catenin in breast cancer.

APC/ß-catenin-rich complexes at membrane protrusions regulate mammary tumor cell migration and mesenchymal morphology.

BACKGROUND: The APC tumor suppressor is mutated or downregulated in many tumor types, and is prominently localized to punctate clusters at protrusion tips in migratory cells, such as in astrocytes where it has been implicated in directed cell motility. Although APC loss is considered an initiating event in colorectal cancer, for example, it is less clear what role APC plays in tumor cell motility and whether loss of APC might be an important promoter of tumor progression in addition to initiation. METHODS: The localization of APC and ß-catenin was analyzed in multiple cell lines, including non-transformed epithelial lines treated with a proteasome inhibitor or TGFß to induce an epithelial-to-mesenchymal transition (EMT), as well as several breast cancer lines, by immunofluorescence. APC expression was knocked down in 4T07 mammary tumor cells using lentiviral-mediated delivery of APC-specific short-hairpin (sh) RNAs, and assessed using quantitative (q) reverse-transcriptase (RT)-PCR and western blotting. Tumor cell motility was analyzed by performing wound-filling assays, and morphology via immunofluorescence (IF) and phase-contrast microscopy. Additionally, proliferation was measured using BrdU incorporation, and TCF reporter assays were performed to determine ß-catenin/TCF-mediated transcriptional activity. RESULTS: APC/ß-catenin-rich complexes were observed at protrusion ends of migratory epithelial cells treated with a proteasome inhibitor or when EMT has been induced and in tumor cells with a mesenchymal, spindle-like morphology. 4T07 tumor cells with reduced APC levels were significantly less motile and had a more rounded morphology; yet, they did not differ significantly in proliferation or ß-catenin/TCF transcriptional activity. Furthermore, we found that APC/ß-catenin-rich complexes at protrusion ends were dependent upon an intact microtubule cytoskeleton. CONCLUSIONS: These findings indicate that membrane protrusions with APC/ß-catenin-containing puncta control the migratory potential and mesenchymal morphology of mammary tumor cells and suggest that APC loss during later stages of tumor progression might impact tumor cell dissemination or colonization.

Apc mutation enhances PyMT-induced mammary tumorigenesis.

The Adenomatous Polyposis Coli (APC) tumor suppressor gene is silenced by hypermethylation or mutated in up to 70% of human breast cancers. In mouse models, Apc mutation disrupts normal mammary development and predisposes to mammary tumor formation; however, the cooperation between APC and other mutations in breast tumorigenesis has not been studied. To test the hypothesis that loss of one copy of APC promotes oncogene-mediated mammary tumorigenesis, Apc(Min/+) mice were crossed with the mouse mammary tumor virus (MMTV)-Polyoma virus middle T antigen (PyMT) or MMTV-c-Neu transgenic mice. In the PyMT tumor model, the Apc(Min/+) mutation significantly decreased survival and tumor latency, promoted a squamous adenocarcinoma phenotype, and enhanced tumor cell proliferation. In tumor-derived cell lines, the proliferative advantage was a result of increased FAK, Src and JNK signaling. These effects were specific to the PyMT model, as no changes were observed in MMTV-c-Neu mice carrying the Apc(Min/+) mutation. Our data indicate that heterozygosity of Apc enhances tumor development in an oncogene-specific manner, providing evidence that APC-dependent pathways may be valuable therapeutic targets in breast cancer. Moreover, these preclinical model systems offer a platform for dissection of the molecular mechanisms by which APC mutation enhances breast carcinogenesis, such as altered FAK/Src/JNK signaling.

A Wnt-ow of opportunity: targeting the Wnt/beta-catenin pathway in breast cancer.

Aberrant activation of the Wnt/beta-catenin signaling pathway is a hallmark of many tumors, including breast cancer. In the normal breast, tightly regulated expression of Wnt/beta-catenin pathway components, including Wnts and the APC tumor suppressor, dictates its role in balancing stem cell self-renewal, maintenance and differentiation during embryonic and postnatal development. Therefore, not surprisingly, dysregulation of Wnt/beta-catenin signaling through overexpression of pathway activators, such as Wnts or stabilized beta-catenin, or targeted disruption of inhibitors, such as APC, leads to mammary tumorigenesis in several genetically engineered mouse (GEM) models. These models are powerful tools to dissect the importance of Wnt/beta-catenin signaling in human breast cancer because they recapitulate some of the histological features of human breast cancers that demonstrate pathway dysregulation. Over the last decade, numerous approaches have been developed to target the Wnt/beta-catenin pathway in tumor cells, from antagonizing Wnt ligand secretion or binding to promoting beta-catenin degradation to specifically blocking beta-catenin-mediated transcriptional activity. Despite sizeable hurdles because of gaps in our knowledge of most efficacious ways to inhibit the pathway, the breast cancer subtypes to target and how pathway antagonists might be used in combination therapy, crippling Wnt/beta-catenin signaling offers a tremendous opportunity to impact breast cancer pathogenesis. This review will provide an overview of the current understanding of Wnt/beta-catenin pathway involvement in regulating normal breast development and morphogenesis, the generation of Wnt/beta-catenin-dependent GEM models of human breast cancer, upregulation of signaling in human breast cancers and the compelling therapeutic strategies aimed at targeting the Wnt/beta-catenin pathway that show promising anti-tumor activity.

Wnt/beta-catenin pathway activation is enriched in basal-like breast cancers and predicts poor outcome.

Although Wnt/beta-catenin pathway activation has been implicated in mouse models of breast cancer, there is contradictory evidence regarding its importance in human breast cancer. In this study, invasive and in situ breast cancer tissue microarrays containing luminal A, luminal B, human epidermal growth factor receptor 2 (HER2)(+)/ER(-) and basal-like breast cancers were analyzed for beta-catenin subcellular localization. We demonstrate that nuclear and cytosolic accumulation of beta-catenin, a read-out of Wnt pathway activation, was enriched in basal-like breast cancers. In contrast, membrane-associated beta-catenin was observed in all breast cancer subtypes, and its expression decreased with tumor progression. Moreover, nuclear and cytosolic localization of beta-catenin was associated with other markers of the basal-like phenotype, including nuclear hormone receptor and HER2 negativity, cytokeratin 5/6 and vimentin expression, and stem cell enrichment. Importantly, this subcellular localization of beta-catenin was associated with a poor outcome and is more frequently observed in tumors from black patients. In addition, beta-catenin accumulation was more often observed in basal-like in situ carcinomas than other in situ subtypes, suggesting that activation of this pathway might be an early event in basal-like tumor development. Collectively, these data indicate that Wnt/beta-catenin activation is an important feature of basal-like breast cancers and is predictive of worse overall survival, suggesting that it may be an attractive pharmacological target for this aggressive breast cancer subtype.

The Ron receptor tyrosine kinase is not required for adenoma formation in Apc(Min/+) mice.

The Ron receptor tyrosine kinase is overexpressed in approximately half of all human colon cancers. Increased Ron expression positively correlates with tumor progression, and reduction of Ron levels in human colon adenocarcinoma cells reverses their tumorigenic properties. Nearly all colon tumors demonstrate loss of the adenomatous polyposis coli (APC) tumor suppressor, an early initiating event, subsequently leading to beta-catenin stabilization. To understand the role of Ron in early stage intestinal tumorigenesis, we generated Apc-mutant (Apc(Min/+)) mice with and without Ron signaling. Interestingly, we report here that significantly more Apc(Min/+) Ron-deficient mice developed higher tumor burden than Apc(Min/+) mice with wild-type Ron. Even though baseline levels of intestinal crypt proliferation were increased in the Apc(Min/+) Ron-deficient mice, loss of Ron did not influence tumor size or histological appearance of the Apc(Min/+) adenomas, nor was beta-catenin localization changed compared to Apc(Min/+) mice with Ron. Together, these data suggest that Ron may be important in normal intestinal tissue homeostasis, but that the expression of this receptor is not required for the formation and growth of adenomas in Apc(Min/+) mice.

The APC tumor suppressor is required for epithelial integrity in the mouse mammary gland.

Inactivation of the adenomatous polyposis coli (APC) tumor suppressor has been associated with mammary tumorigenesis in mouse models and through epidemiological studies of human breast cancers, but the normal role for APC in mammary development has not been thoroughly characterized. We report here that Apc(Min/+) mice containing one functional allele of Apc have severely disrupted lobuloalveolar development during pregnancy and lactation, time points at which Apc gene expression is at its highest levels in normal mice. This phenotype was accompanied by altered proliferation during pregnancy and involution, increased apoptosis throughout lactation, the formation of preneoplastic lesions and changes in specific genes associated with each of these processes. Neither modifications in beta-catenin localization, nor the expression of beta-catenin transcriptional target genes, were observed in Apc(Min/+) mammary tissues; however, tissues from lactating Apc(Min/+) mice had a significantly altered epithelial architecture, including disrupted localization of junctional proteins and polarization. Consistent with these findings, APC knockdown in non-transformed mouse mammary epithelial cells in vitro resulted in altered monolayer formation and proliferation without changes in beta-catenin-mediated transcription. These results suggest that APC expression is tightly regulated during mammary gland development and is required for normal mammary homeostasis and tumor suppression primarily through maintaining epithelial integrity.

Strain-specific of alachlor on murine olfactory mucosal responses.

Chloracetanilide herbicides are multisite carcinogens in rodents. Progression of alachlor-induced olfactory tumors in rats is accompanied by cytoplasmic accumulation and nuclear localization of beta-catenin, suggesting activation of Wint signaling. Female CD-1 mice were resistant to alachlor-induced olfactory carcinogenesis. The current studies were performed to determine whether Apc(Min/+) mice, which have activated Wnt signaling due to mutation of the second allele of Apc, would be susceptible to alachlor olfactory carcinogenesis. Female and male Apc(Min/+) mice, as well as Apc(+/+) littermates received alachlor in the diet (260 mg/kg/d) for up to 3 months. Female A/J and C57BL/6J wild-type mice were also treated (for 10 and 14 months, respectively), as these strains vary in sensitivity to many respiratory tract insults. No olfactory mucosal tumors were observed in any of the mice, although alachlor-treated Apc(Min/+) mice developed histological changes similar to those in alachlor-treated rats. Alachlor-treated A/J mice developed pronounced intracellular accumulation of amorphous eosinophilic material in the olfactory mucosa, foci of respiratory-like metaplasia,and hyperplasia of nasal mucus glands. A similar but less intense response was seen in C57BL/6J mice. Mice and rats had equivalent levels of the putative bioactivating enzyme (CYP2A) in olfactory mucosa. and mice had induced hepatic CYP3A and CYP2B enzymes with alachlor treatment, which may increase alachlor elimination. These studies extend previous observations by describing alachlor-induced olfactory mucosal changes in mice and suggest that hepatic metabolic enzyme induction may be responsible for resistance of mice to alachlor-induced olfactory carcinogenesis.

Alternative splicing of the APC gene in the neural retina and retinal pigment epithelium.

PURPOSE: Hypertrophy and hyperplasia of the retinal pigment epithelium (RPE) is associated with an inherited predisposition to human familial adenomatous polyposis coli, suggesting that expression of the adenomatous polyposis coli (APC) tumor suppressor may regulate RPE proliferation/differentiation. Distinctive APC isoforms exist in different cell types due to alternative splicing of the APC transcripts. We hypothesize that differences in expression patterns of APC protein isoforms are critical to RPE proliferation/differentiation. METHODS: To investigate these relationships, APC gene expression was characterized in the retinas and RPE from fetal and adult human and mouse, and in the epiretinal membranes (ERM) from 5 patients with proliferative vitreoretinopathy (PVR). Expression patterns of alternative splice-forms of APC transcripts were evaluated by comparative quantitative RT-PCR. Exon 1 of APC encodes a heptad repeat that confers the ability of APC to homodimerize. APC protein isoforms containing or lacking this heptad were characterized by western blot analysis and immunohistochemistry. RESULTS: Comparative quantitative RT-PCR demonstrated a predominant exon 1 containing, conventional APC splice-form in the early developing fetal RPE and retina, and in all the tested ERM samples from patients with PVR. This method also demonstrated an increased level of exon 1 lacking APC splice-form in the mature RPE and retina. Western blot analysis and immunofluorescence microscopy demonstrated the conventional APC only in the RPE, and the APC isoform without the first heptad repeat in both the retina and RPE. Immunofluorescence microscopy also demonstrated only the conventional APC in the ERM samples tested. CONCLUSIONS: These results suggest that alternative splicing of APC leads to differential APC expression with potentially unique functions. APC isoform without the first heptad repeat may play a role in cell cycle cessation in the adult retina and RPE, and the down regulation of this APC isoform may contribute to the potential of RPE to migrate and proliferate.