APC Protein Expression Research Articles

The Interplay among Wnt/β-catenin Family Members in Colorectal Adenomas and Surrounding Tissues.

The colorectal adenoma undergoes neoplastic progression via the normal epithelium-adenoma-adenocarcinoma sequence as reported in the Vogelgram. The hazard of developing a tumor is deeply associated with the number and size of adenomas and their subtype. Adenomatous polyps are histologically categorized as follows: approximately 80-90% are tubular, 5-15% are villous, and 5-10% are tubular/villous. Given the higher risk of a malignant transformation observed in tubular/villous adenomas, patients diagnosed with adenomatous polyposis are at an improved risk of developing CRC. The Wnt/β-catenin pathway plays a key role in the onset of colorectal adenoma; in particular, intestinal cells first acquire loss-of-function mutations in the APC gene that induce the formation of adenomas. Wnt/β-catenin pathway APC, Wnt3a, Wnt5a, LEF1, and BCL9 genes and protein expression analyses were conducted by qRT-PCR and western blot in 68 colonic samples (polyps and adjacent mucosa) from 41 patients, of which 17 were affected by FAP. Ten normal colonic mucosal samples were collected from 10 healthy donors. In this study, both the APC gene and protein were less expressed in the colon tumor compared to the adjacent colonic mucosa. Conversely, the activated β-catenin was more expressed in polyps than in the adjacent mucosa. All results confirmed the literature data on carcinomas. A statistically significant correlation between Wnt3a and BCL9 both in polyps and in the adjacent mucosa underlines that the canonical Wnt pathway is activated in early colon carcinogenesis and that the adjacent mucosa is already altered. This is the first study analyzing the difference in expression of the Wnt/β-catenin pathway in human colorectal adenomas. Understanding the progression from adenomas to colorectal carcinomas is essential for the development of new therapeutic strategies and improving clinical outcomes with the use of APC and β-catenin as biomarkers.

Efficient Simultaneous Introduction of Premature Stop Codons in Three Tumor Suppressor Genes in PFFs via a Cytosine Base Editor.

Base editing is an efficient and precise gene-editing technique, by which a single base can be changed without introducing double-strand breaks, and it is currently widely used in studies of various species. In this study, we used hA3A-BE3-Y130F to simultaneously introduce premature stop codons (TAG, TGA, and TAA) into three tumor suppressor genes, TP53, PTEN, and APC, in large white porcine fetal fibroblasts (PFFs). Among the isolated 290 single-cell colonies, 232 (80%) had premature stop codons in all the three genes. C−to−T conversion was found in 98.6%, 92.8%, and 87.2% of these cell colonies for TP53, PTEN, and APC, respectively. High frequencies of bystander C−to−T edits were observed within the editing window (positions 3–8), and there were nine (3.01%) clones with the designed simultaneous three-gene C−to−T conversion without bystander conversion. C−to−T conversion outside the editing window was found in 9.0%, 14.1%, and 26.2% of the 290 cell colonies for TP53, PTEN, and APC, respectively. Low-frequency C−to−G or C−to−A transversion occurred in APC. The mRNA levels of the three genes showed significant declines in triple-gene-mutant (Tri-Mut) cells as expected. No PTEN and a significantly lower (p < 0.05) APC protein expression were detected in Tri-Mut cells. Interestingly, the premature stop codon introduced into the TP53 gene did not eliminate the expression of its full-length protein in the Tri-Mut cells, suggesting that stop codon read-through occurred. Tri-Mut cells showed a significantly higher (p < 0.05) proliferation rate than WT cells. Furthermore, we identified 1418 differentially expressed genes (DEGs) between the Tri-Mut and WT groups, which were mainly involved in functions such as tumor progression, cell cycle, and DNA repair. This study indicates that hA3A-BE3-Y130F can be a powerful tool to create diverse knockout cell models without double-strand breaks (DSBs), with further possibilities to produce porcine models with various purposes.

Effect of Hsa-miRNA-203a-3p on proliferation of skin squamous cell carcinoma-1 human skin squamous cell cancer cells by targeting adenomatous polyposis coli using magnetic nanoparticles

To investigate the effect of hsa-miR-203a-3p overexpression on the proliferation of human skin squamous cell carcinoma (CSCC) cells and its possible mechanism. Real-time PCR (RT-PCR) was used to detect the expression of miR-203a-3p in cell lines and clinical human CSCC samples. A luciferase reporter system was used to verify the targeted regulatory relationship of miR-203a-3p to APC, and a miR-203a-3p lentivirus overexpression vector was constructed and used to transfect CSCC SCL-1 cells. RT-PCR was used to detect changes in miR-203a-3p and APC gene expression and Western blot was used to detect differences in APC and β-catenin protein expression. MTT and clonogenic assays were used to evaluate cell growth and detect clone formation, respectively. MiR-203a-3p showed decreased expression in SCL-1 cells and CSCC samples. Results of luciferase reporter assay showed that the ratio of Renilla luciferase to Firefly luciferase was significantly decreased in SCL-1 cells of the APC 3′-UTR+miR-203a-3p (wild-type) group compared with those of the APC 3′-UTR+negative control group. After lentiviral infection of SCL-1 cells, the abundance of miR-203a-3p and phosphorylated β-catenin protein was significantly increased, whereas the abundance of APC and β-catenin protein was significantly reduced. Cell phenotyping analysis showed that miR-203a-3p decreased cell proliferation. MiR-203a-3p inhibits the proliferation of SCL-1 cells through targeted regulation of APC and may play a role as a tumor suppressor gene through the Wnt pathway. Nanotechnology has potential future research applications in gene vector transfection technology.

Immunohistochemical evaluation of potential molecular targets of desmoid-type fibromatosis

Desmoid-type fibromatosis is locally aggressive tumor rare in general population, although commonly present in patients with familial adenomatous polyposis, significantly contributing to the morbidity and mortality of patients. To optimize and individualize the management of patients it is necessary to better understand the biology of these tumors. Immunohistochemical analysis of β-catenin, VEGF, hormone receptors ERβ, ERα and PR, COX-2, APC protein, EGFR, c-kit (CD117), bcl-2 and HER2 expression, potential therapeutic targets, was carried out on 15 archival biopsy samples together with APC gene mutational screening. β-catenin expression was found in all samples, with over 73% showing high range positivity, however with no prognostic significance. Non-specific cytoplasmic localization of β-catenin was observed FAP-associated cases lacking CTNNB1 mutations. Hormone receptor status demonstrated expression of ERβ in 93% of lesions, without detectable ERα or PR. Distinct COX-2 expression of variable intensity was present in all but one desmoid-type fibromatosis case. All lesions demonstrated intense VEGF positivity. Immunoreactivity for the APC protein was found only in 4 cases associated with FAP. No EGFR, HER2, bcl-2 or c-kit expression was detected in any sample. Expression of β-catenin, VEGF, ERβ, COX-2 in high number of cases suggests a potential as future therapeutic targets in desmoid-type fibromatosis.

Immunohistochemical Study of Adenomatous Polyposis Coli Protein in Colorectal Carcinoma and its Precursor Lesions in Iraq

Globally, colorectal cancer represents the most common cancer. Its incidence was increases with advancement of age. Both men and women face a lifetime risk of 6% to get colorectal cancer. Colorectal cancer represents a major cancer-related health problem in Iraq and significant attribution to morbidity and mortality related to cancer. It ranked as the 7th most common malignant tumor in Iraq and account for about 5.4% of all cancer in this country. Inflammatory bowel disease represent a risk factor for development of colorectal carcinoma and this was related to increased severity and duration of the disease. On other hand colorectal polyp may transform to carcinoma and this risk was more with larger polyps and polyps with sever dysplasia. Adenomatous Polyposis coli gene is a tumor suppressor gene. Its inactivation represents a common genetic alteration in this tumor. This mutation in such gene occur both I sporadic as well as inherited cancers. This study was designed to clarify the role of APC gene and its protein in both colorectal cancer and its precancerous lesion and put the shadow on its possible role in disease development and progression. APC protein was reported in 33 out of 60 cases of colorectal cancer, 16 out of 50 cases of colorectal polyps, and 11 out of 50 cases taken from patients with ulcerative colitis. There was no expression of APC protein in normal looking tissues in all cases. APC expression was showed significant differences when grade and stage were considered. APC gene was altered in colorectal cancer and its precursor lesion and this alteration were correlated well with grade and stage of disease. The alteration plays a role in both disease development and progression.

Prognostic impact of the expression of Wnt-signaling proteins in cervical carcinoma FIGO stage I-IV treated with radiotherapy or chemoradiotherapy.

Wnt signaling proteins were assessed in patients with primary cervical carcinomas who received chemoradiation. The associations between three Wnt signaling proteins and prognosis were assessed. Specimens from 122 patients with cervical carcinomas (FIGO stage I-IV) were immunohistochemically (IHC) analyzed for β-catenin, APC and axin protein expression. Associations between these Wnt-protein expressions, clinicopathological factors, and clinical outcome data were examined.Positive IHC staining for the β-catenin protein (cell-membranes, cytoplasm and nuclei) was recorded in 88%, 58% and 5%, respectively. There was a strong association between β-catenin staining of the cell-membranes and prediction of recurrences and prognosis (p = 0. 002). Tumors with > 5% of nuclear β-catenin staining were associated with inferior cancer-specific survival (p = 0.048) compared with no staining. The overall recurrence rate was significantly higher in the group with increased nuclear staining (67%) compared with the group with no staining (33%). Nuclear APC staining of high intensity was associated with a significantly worse cancer-specific survival and increased overall recurrence rate compared to tumors with weak staining. Distant recurrences were recorded in 29% of cases with intense staining and in 14% of cases with low staining.The Wnt signaling pathway seems to be of importance in the process of cervical oncogenesis. A predictive and prognostic value was found for β-catenin, where strong cell-membrane staining was favorable, and > 5% positive nuclear staining was associated with poorer cancer-specific survival and overall recurrence rate. Nuclear APC staining intensity was also associated with a less favorable prognosis.

APC protein immunoexpression in colorectal adenoma and adenocarcinoma

Backgroundactivation of the Wnt pathway by mutated APC gene is considered the initial event in colorectal carcinogenesis. The identification of these mutations can improve the specific treatment of the adenocarcinoma. Objectivedetect and evaluate wild-type APC protein in tissue from colorectal adenoma, adenocarcinoma and adjacent mucosa. Methods42 patients that underwent surgery for adenocarcinoma and 53 patients with resected adenomas were studied. Tissue samples from the adenocarcinoma were obtained from the tumor and from adjacent non-neoplastic mucosa located 10cm from the proximal margin of the tumor. Adenoma tissue was obtained from representative areas. Blocks of tissue microarray (TMA) were submitted to immunohistochemistry with anti-APC, with readings of positivity and intensity of immunostaining and the score of immune expression of APC protein was obtained. Resultsthe APC protein immune expression score showed a significantly lower expression of APC protein in the adenoma when compared with the adenocarcinoma (p < 0.0001) and adjacent mucosa (p < 0.0001). The APC protein immune expression score in the colorectal mucosa and adjacent to the adenocarcinoma showed no significant difference (p = 0.24). Conclusionsthe finding of decreased expression of APC protein in adenoma tissue may indicate that the mutated APC gene may contribute to the changes in the adenoma-carcinoma process of carcinogenesis sequence. The strong expression of protein APC in tissues from the carcinoma and adjacent mucosa suggests that in most patients in this series, the mutation of the APC gene did not participate in the oncogenesis mechanism.

Methylation of multiple genes in hepatitis C virus associated hepatocellular carcinoma

We studied promoter methylation (PM) of 11 genes in Peripheral Blood Lymphocytes (PBLs) and tissues of hepatitis C virus (HCV) associated hepatocellular carcinoma (HCC) and chronic hepatitis (CH) Egyptian patients. The present study included 31 HCC with their ANT, 38 CH and 13 normal hepatic tissue (NHT) samples. In all groups, PM of APC, FHIT, p15, p73, p14, p16, DAPK1, CDH1, RARβ, RASSF1A, O6MGMT was assessed by methylation-specific PCR (MSP). APC and O6-MGMT protein expression was assessed by immunohistochemistry (IHC) in the studied HCC and CH (20 samples each) as well as in a different HCC and CH set for confirmation of MSP results. PM was associated with progression from CH to HCC. Most genes showed high methylation frequency (MF) and the methylation index (MI) increased with disease progression. MF of p14, p73, RASSF1A, CDH1 and O6MGMT was significantly higher in HCC and their ANT. MF of APC was higher in CH. We reported high concordance between MF in HCC and their ANT, MF in PBL and CH tissues as well as between PM and protein expression of APC and O6MGMT. A panel of 4 genes (APC, p73, p14, O6MGMT) classifies the cases independently into HCC and CH with high accuracy (89.9%), sensitivity (83.9%) and specificity (94.7%). HCV infection may contribute to hepatocarcinogenesis through enhancing PM of multiple genes. PM of APC occurs early in the cascade while PM of p14, p73, RASSF1A, RARB, CDH1 and O6MGMT are late changes. A panel of APC, p73, p14, O6-MGMT could be used in monitoring CH patients for early detection of HCC. Also, we found that, the methylation status is not significantly affected by whether the tissue was from the liver or PBL, indicating the possibility of use PBL as indicator to genetic profile instead of liver tissue regardless the stage of disease.

Participation of miRNA in conditioning the incidence and modification of the course of FAP

In July 2008, the report considering identification of miRNA associated with regulation of APC protein expression level was published. Two types of MIRNA; miR135a and miR-135b, which are encoded by three genes, were described. Those genes are located on chromosomes 3, 12 and 1. miR135a and miR-135b interact with sequences 3 `UTR of mRNA of gene APC on the basis of incomplete complementarity and lead to its degradation. The changes in the sequences encoding miR135a and miR-135b may lead to a change in their affinity to the 3 `UTR of mRNA of the gene APC and enhancing its degradation. It can result in a reduced number of functional APC protein. Also, changes in the sequence 3 `UTR of mRNA can change the affinity of the sites recognized by miRNA or induce new sites recognized by the miRNA and thus will induce rapid degradation of mRNA. Both these situations would provide a similar effect such as observed in case of the mutations leading to premature termination of protein translation. It could not be excluded that the mutations in the 3 `UTR and miRNA can also modify the disease course if co-occurring with mutations in the APC gene coding sequence.

Analysis of APC, α-, β-catenins, and N-cadherin protein expression in aggressive fibromatosis (desmoid tumor)

The aims of this study were to analyze the cadherin/catenin adhesion complex in cells from abdominal and extra-abdominal aggressive fibromatosis tumors, and to estimate the correlation between the expression of the tested proteins and the clinical data of the desmoid patients. Immunohistochemistry was used to examine the expression of the cadherin/catenin adhesion complex: APC protein, α-, β-catenin, and N-cadherin in archival material derived from 15 cases of extra-abdominal desmoid tumor (E-AD) and 20 cases of abdominal (AD) desmoid tumor. The tested proteins demonstrated cytoplasmic (c) staining. Furthermore, nuclear (n) or cytoplasmic and nuclear (c+n) staining was observed for β-catenin. The mean values of the percentage of positive cells for the tested proteins between E-AD vs. AD did not demonstrate any statistically significant difference except for α-catenin. In the E-AD group, in both cases of recurrent tumors, no α-catenin expression was observed but the expression of this protein was detected in primary tumors. In the groups investigated, no statistically significant correlation was found between α-catenin, β-catenin (c), (n) and (c+n) expression, and tumor size ( p>0.1). The results regarding β-catenin expression obtained in our study confirm the previous findings that nuclear accumulation of this protein plays a crucial role in the pathogenesis of aggressive fibromatosis.

APC promoter methylation and protein expression in hepatocellular carcinoma

PurposeWe investigated the impact of promoter methylation on APC protein expression in patients with hepatocellular carcinoma (HCC).Materials and methods50 patients [HCC (n=19), liver metastasis (n=19), cholangiocellular cancer (n=7), and benign liver tumors (n=5)] were studied for methylation using Methylight analysis. APC mutation was investigated by protein truncation test and direct sequencing of genomic DNA. The protein expression was evaluated by immunohistochemistry and Western blot analysis.ResultsThe APC promoter was hypermethylated in 81.8% of non-cancerous liver tissue samples. All HCC samples and ten patients with liver metastasis (52.6%) exhibited APC promoter methylation. The degree of methylation was significantly higher in samples from HCC compared to the non-cancerous liver tissue samples (63.1% vs. 24.98%; p=0.001). The level of APC protein expression was significantly reduced in HCC samples compared to that of the corresponding non-tumor liver tissue (p<0.05).ConclusionsPromoter methylation of the APC gene seems to be of significance in hepatocarcinogenesis and results in reduced protein expression in HCC. Interestingly, APC promoter methylation is also present in the vast majority of non-cancerous liver tissue whose (patho)physiological function remains unresolved.

Expression of beta-catenin and APC protein in ovarian epithelial tumor and its implication

To investigate the expression of beta-catenin, APC protein and its implication in ovarian epithelial tumor. Immunohistochemical staining with SP method was conducted to determine the expression of beta-catenin and APC protein in 48 cases of ovarian epithelial tumor. The abnormal expression rates of beta-catenin in ovarian malignant and borderline epithelial tumors were higher than that in benign epithelial tumors. The expression of APC protein in benign epithelial tumors was significantly greater than that in malignant epithelial tumors. A significant negative correlation was found between beta-catenin and APC protein in ovarian epithelial tumors. Beta-catenin and APC protein have important effect on pathogenesis and development of ovarian epithelial tumors.

Alternative splicing and nonsense-mediated mRNA decay in the regulation of a new adenomatous polyposis coli transcript

Familial adenomatous polyposis (FAP) is a rare precancerous condition caused by mutations in the adenomatous polyposis coli ( apc) gene. Alternative splicing mechanisms involving non-coding and coding exons result in multiple protein variants whose molecular weight ranges between 90 and 300 kDa. We examined the apc 5′ coding region and identified nine new transcripts generated from alternative and/or aberrant splicing. Three of these preserve the reading frame and the corresponding proteins include the catalytic domains and the sequences required for β-catenin regulation. The other six transcripts create a frameshift that produces a premature stop codon; one of these has an additional 77-nucleotide-long exon (1A) between exons 1 and 2 that leads to a frameshift and a premature stop codon in exon 2. Quantitative PCR analysis suggests that the expression of this transcript is regulated during colorectal cancer tumorigenesis and differentiation. Nonsense-mediated mRNA decay (NMD) is a eukaryotic mRNA surveillance mechanism that detects and degrades mRNAs that have premature termination codons (PTCs). Expression of splicing variants containing PTCs and their subsequent degradation via NMD seems to be a general mechanism of gene regulation. Incubation of Caco2 cell lines with cycloheximide, a chemical inhibitor of translation that is known to inhibit also NMD, indicates that the apc mRNA isoform that includes exon 1A is degraded by NMD, thereby suggesting that regulated unproductive splicing and NMD degradation could modulate APC protein expression.

Expression of mucin core proteins, trefoil factors, APC and p21 in subsets of colorectal polyps and cancers suggests a distinct pathway of pathogenesis of mucinous carcinoma of the colorectum

Mucin core proteins are expressed in a tissue and cell type specific manner in the normal gastrointestinal tract. Aberrant expression of mucin core proteins have been reported in colorectal neoplasms. To examine the relationship between subsets of colorectal polyps and non-mucinous and mucinous adenocarcinomas of the colorectum, we evaluated the frequency of the expression of cell lineage associated mucin core proteins (MUC5AC and MUC2), trefoil factors (TFF1 and TFF3), and APC and p21 in these tissues. An immunohistochemical study was performed in 10 normal rectal mucosa samples (NM) 21 hyperplastic polyps (HP), 20 serrated adenomas (SA), 25 tubular adenomas (TA), 13 tubulovillous adenomas (TVA), 7 villous adenomas (VA), 42 non-mucinous colorectal cancers (NMC), and 19 mucinous colorectal cancers (MC). A higher frequency of ectopic expression of gastric foveolar mucin, MUC5AC, and the expression of intestinal goblet cell mucins, MUC2, was observed respectively in HP (100%, 100%), SA (85%, 85%), TVA (85%, 85%), and VA (100%, 100%), compared to TA (32%, p<0.002; 36%, p<0.01). MC (68%, 100%) also showed a higher frequency of the expression of MUC5AC and MUC2 compared to NMC (31%, p=0.001; 38%, p<0.001), and TFF1 showed similar patterns of expression. APC protein and p21 were also expressed at a higher frequency in HP (100%, 100%), and SA (67%, 83%), than in TA (29%, p<0.03; 46%, p<0.05). MC (68%, 100%) showed a higher frequency of expression of APC protein and p21 than NMC (19%, p<0.001; 45%, p<0.01). Our results showed that MUC2 expression and de novo ectopic expression of MUC5AC and TFF1 are more frequent in HP, SA, TVA, VA, and MC than in TA and NMC. These results suggest that simultaneous activation of differentiation pathways of goblet cells and gastric foveolar cells may occur predominantly in the pathogenesis of HP, SA, TVA, VA, and MC, while the pathogenesis of TA and NMC are less likely to involve these processes.

Expression of the proliferating cell nuclear antigen and protein products of tumour suppressor genes in the human foetal testis

Tumour suppressor genes retinoblastoma (Rb1) and adenomatous polyposis coli (Apc) as well as the proliferating cell nuclear antigen (PCNA) are involved in embryonic development. The purpose of the present study was to investigate the expression of Rb1 protein, APC protein and PCNA during development of the human foetal testis. Qualitative analysis of their expression at the single-cell level was performed using immunohistochemistry on archive samples of the foetal testis (18-37 gestation week). Stereological parameters (volume density, absolute volume, numerical density, absolute number) were calculated for quantification of the overall expression of those proteins that were expressed frequently enough for such an analysis. PCNA was frequently expressed in nuclei of immature Sertoli cells and prospermatogonia and less frequently in surrounding peritubular (myoid) and interstitial cells. The pRb1 protein was present in nuclei of prospermatogonia and Sertoli cells but was absent from the interstitial tissue. APC protein was expressed in the cytoplasm of a very small number of prospermatogonia and interstitial (Leydig) cells. The overall expression of PCNA in all stages of development was higher than pRb1 expression.

N-Methyl-N'-nitro-N-nitrosoguanidine-induced senescence-like growth arrest in colon cancer cells is associated with loss of adenomatous polyposis coli protein, microtubule organization, and telomeric DNA

BackgroundCellular senescence is a state in which mammalian cells enter into an irreversible growth arrest and altered biological functions. The senescence response in mammalian cells can be elicited by DNA-damaging agents. In the present study we report that the DNA-damaging agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) is able to induce senescence in the HCT-116 colon cancer cell line.ResultsCells treated with lower concentrations of MNNG (0–25 microM) for 50 h showed a dose-dependent increase in G2/M phase arrest and apoptosis; however, cells treated with higher concentrations of MNNG (50–100 microM) showed a senescence-like G0/G1 phase arrest which was confirmed by increased expression of β-galactosidase, a senescence induced marker. The G2/M phase arrest and apoptosis were found to be associated with increased levels of p53 protein, but the senescence-like G0/G1 phase arrest was dissociated with p53 protein levels, since the p53 protein levels decreased in senescence-like arrested cells. We further, determined whether the decreased level of p53 was a transcriptional or a translational phenomenon. The results revealed that the decreased level of p53 protein in senescence-like arrested cells was a transcriptional phenomenon since p53 mRNA levels simultaneously decreased after treatment with higher concentrations of MNNG. We also examined the effect of MNNG treatment on other cell cycle-related proteins such as p21, p27, cyclin B1, Cdc2, c-Myc and max. The expression levels of these proteins were increased in cells treated with lower concentrations of MNNG, which supported the G2/M phase arrest. However, cells treated with higher concentrations of MNNG showed decreased levels of these proteins, and hence, may not play a role in cell cycle arrest. We then examined a possible association of the expression of APC protein and telomeric DNA signals with cellular senescence in MNNG-treated cells. We found that protein and mRNA levels of APC were drastically reduced in cells treated with higher concentrations of MNNG. The loss of APC expression might lead to chromosomal instability as well as microtubular disorganization through its dissociation with tubulin. In fact, the protein level of α-tubulin was also drastically decreased in senescence-like arrested cells treated with higher concentrations of MNNG. The levels of telomeric DNA also decreased in cells treated with higher concentrations of MNNG.ConclusionsThese results suggest that in response to DNA alkylation damage the senescence-like arrest of HCT-116 cells was associated with decreased levels of APC protein, microtubular organization, and telomeric DNA.

APC and β-catenin protein expression in adenomas of patients with familial polyposis

APC and β-catenin protein expression in adenomas of patients with familial polyposis

APC and β-catenin protein expression in adenomas of patients with familial polyposis

APC and β-catenin protein expression in adenomas of patients with familial polyposis

Allelic loss involving the tumor suppressor genes APC and MCC and expression of the APC protein in the development of dysplasia and carcinoma in Barrett esophagus.

Samples of Barrett metaplastic specialized epithelium (SE), low-grade dysplasia (LGD), high-grade dysplasia (HGD), and invasive adenocarcinoma (CA) derived from 36 esophagectomy specimens were studied for loss of heterozygosity (LOH) in APC and MCC and for expression of APC protein. Of 18 cases that were heterozygous (informative) for APC, LOH was found in none of 14 SE samples, 2 of 8 LGD samples, 3 of 11 HGD samples, and 5 of 17 CA samples. Immunohistochemically, markedly reduced expression of APC protein (< 50% positive cells) was found in 3 of 19 HGD samples and 4 of 35 CA samples but not in SE or LGD samples. Of 17 cases informative for the MCC gene, LOH was detectable in 1 of 14 SE samples, none of 7 LGD samples, none of 9 HGD samples, and 4 of 16 CA samples. Allelic loss of APC and/or loss of APC protein expression occurs earlier in the metaplasia-dysplasia-carcinoma sequence in Barrett esophagus than LOH in the MCC gene. The determination of alterations at APC or MCC would be of limited importance for the surveillance of patients with Barrett esophagus.

APC Protein Is Required for Initiation of Neuronal Differentiation in Rat Pheochromocytoma PC12 Cells

The adenomatous polyposis (APC) gene product is highly expressed in the central nervous system. To elucidate the contribution of the APC protein to neuronal differentiation, we used an inducible antisense mRNA vector to suppress APC protein expression and examined neuronal differentiation of PC12 cells induced by nerve growth factor (NGF). When antisense mRNA was induced, APC protein expression was suppressed to 20% of the noninduced level. In those cells, neurite extension induced by NGF and expression of microtubule-associated protein 2 (MAP2) was completely inhibited. However, once cells had differentiated, antisense APC mRNA expression and subsequent suppression of APC protein expression had no effect on either cell morphology or MAP2 protein expression. These results suggest that the wild type APC is critically involved only in the initiation of neuronal differentiation, but not in the maintenance of the differentiated phenotype, or that the neuronal phenotype could be maintained at lower level of APC protein.