High EPHB2 mutation rate in gastric but not endometrial tumors with microsatellite instability.

The EPH/EFN family of receptor tyrosine kinases regulates cell adhesion and migration and has an important role in controlling cell positioning in the normal intestinal epithelium. Inactivation of EPHB2 has recently been shown to accelerate tumorigenesis in the colon and rectum, and we have previously demonstrated frequent frameshift mutations (41%) in an A9 coding microsatellite repeat in exon 17 of EPHB2 in colorectal tumors with microsatellite instability (MSI). In this study, we extended these analyses to extracolonic MSI cancers, and found frameshift EPHB2 mutations in 39% (25/64) of gastric tumors and 14% (8/56) of endometrial tumors. Regression analysis of these EPHB2 mutation data on the basis of our previously proposed statistical model identified EPHB2 as a selective target of frameshift mutations in MSI gastric cancers but not in MSI endometrial carcinomas. These results suggest a functional role for EPHB2 in gastric tumor progression, and emphasize the differences between the tumorigenic processes in MSI gastrointestinal and endometrial cancer.

Detection of high-risk cervical intraepithelial neoplasia and cervical cancer by amplification of transcripts derived from integrated papillomavirus oncogenes.

Cervical cancer emerges from cervical intraepithelial neoplasia (CIN) induced by high-risk HPV (HR-HPV) infections. However, the vast majority of CIN lesions regresses spontaneously, and only a few lesions persist or progress to invasive carcinoma. On the basis of morphological criteria, it is not possible to differentiate high-grade lesions that will regress or persist from those that inevitably will progress to invasive cancers. In most cervical carcinomas, human papillomavirus (HPV) genomes are integrated into host cell chromosomes and transcribed into mRNAs encompassing viral and cellular sequences. In contrast, in early preneoplastic lesions, HPV genomes persist as episomes, and derived transcripts contain exclusively viral sequences. Thus, detection of HPV transcripts derived from integrated HPV genomes may specifically indicate both CIN lesions at high risk for progression as well as invasive cervical cancers. Here, we established a protocol for the amplification of papillomavirus oncogene transcripts (APOT) from cervical specimens that allows us to distinguish episome- from integrate-derived HPV mRNAs. Cervical swab and biopsy samples from 549 patients attending outpatient clinics for cervical dysplasia were screened for the presence of HPV DNA, and 155 samples that were positive for either HPV type 16 (n = 143) or 18 (n = 12) were subjected to the APOT assay. In samples derived from normal cervical epithelia (n = 19) or low-grade cervical lesions (CIN I, n = 10), no integrate-derived HPV transcripts were found. In contrast, in 1 (5%) of 22 samples derived from CIN II lesions, in 10 (16%) of 64 samples from patients with CIN III lesions, and in 35 (88%) of 40 samples from patients with cervical cancer, integrate-derived HPV transcripts were detected. Thus, detection of integrate-derived HPV transcripts in cervical swabs or biopsy specimens by the APOT assay points to advanced dysplasia or invasive cervical cancer.

Expression of CD44 splice variants in normal respiratory epithelium and bronchial carcinomas: no evidence for altered CD44 splicing in metastasis.

Expression of alternatively spliced CD44 adhesion molecules has been implicated in metastatic spread of various rodent and human tumors. To determine whether specific CD44 splice variants contribute to metastatic spread of bronchial cancers, we compared the expression of CD44 splice variants in normal bronchial epithelium and bronchial cancers, including tumors which already spread to regional lymph nodes or distant organs. Variant CD44 expression was analysed by immunohistochemistry using variant exon-specific monoclonal antibodies. The precise composition of CD44 transcripts was delineated by exon-specific RT-PCR. The concurring data obtained by both methods revealed that high levels of standard CD44 and variants v5 and v6 as well as low levels of variants v7 and v10 are expressed both in normal bronchial epithelium and squamous cell lung cancers. No CD44 expression was observed in the highly metastatic small cell lung cancers and adenocarcinomas with the exception of bronchioalveolar cancers showing weak expression of standard CD44. These data suggest that expression of alternatively spliced CD44 molecules in the bronchial tract is related to the distinct differentiation of the respiratory epithelium. No correlation between expression of specific CD44 splice variants and metastasis of bronchial cancers was observed.

Expression of CD44 splice variants in normal, dysplastic, and neoplastic cervical epithelium.

Expression of splice variants of the CD44 adhesion molecule has been implicated in metastatic spread of various human tumor cells, including malignant lymphomas and colon, mammary, and gastric carcinomas, and has been correlated to a poor prognosis for the respective patients. To determine whether variant CD44 molecules might also contribute to the metastatic spread of cervical cancer, we analyzed the CD44 expression pattern in normal cervical epithelium and in low- and high-grade cervical dysplasia and compared it with invasive and metastasizing cervical cancers, including cell lines derived thereof by immunofluorescence and exon-specific PCR amplification of reverse-transcribed CD44 transcripts. We observed that normal cervical epithelium and dysplastic lesions express high levels of standard CD44 in the basal and spinous epithelial layers. CD44 molecules encompassing variant exons v5 and v6 are strongly expressed throughout the epithelium. Low levels of variants encompassing exon v7 are expressed in basal and spinous layers, with particular strength in the suprabasal layer. Low levels of epitopes encoded by v8 and v10 are expressed in the basal and spinous layers. In cervical cancers, including lymph node metastasis, we observed strong expression of v5 and v6, but almost no expression of v7, v8, and v10. Expression of the CD44 standard form appeared to be down-regulated in some cancers when compared to normal cervical epithelium. Thus, expression of variant CD44 molecules is related to distinct differentiation of mucosal squamous epithelia in the female genital tract. No correlation of the expression of variant CD44 isoforms, including the v7-v8 fusion epitope with tumor progression or lymphatic spread, was observed.

Sensitive detection of rare cancer cells in sputum and peripheral blood samples of patients with lung cancer by preproGRP-specific RT-PCR.

RT-PCR-based amplification of transcripts expressed in cancer but not in normal non-neoplastic cells is increasingly used for the sensitive detection of rare disseminated or exfoliated cancer cells to improve cancer staging and early detection protocols. However, these assays are frequently hampered by false-positive test results due to low-level transcription of the marker genes in normal cells. To overcome these limitations, target transcripts have to be identified that are tightly suppressed in normal non-neoplastic tissues, whereas they should be actively transcribed in the respective cancer cells. Here, we tested RT-PCR assays for 7 neuroendocrine marker transcripts including NCAM, PGP 9.5, gastrin, gastrin receptor, synaptophysin, preprogastrin-releasing peptide (preproGRP) and GRP-receptor to detect rare exfoliated tumor cells in peripheral venous blood and sputum samples from patients with lung cancer. Among these preproGRP RT-PCR was the only assay with which illegitimate transcription in blood or sputum samples from healthy donors or patients with unrelated diseases did not interfere. However, it reproducibly detected up to 10 small-cell lung cancer cells diluted in either 10 ml blood or 5 ml sputum samples. Single blood and sputum samples were collected directly before diagnostic bronchoscopy from 175 patients suspected to have lung cancer. Twenty-six of these had small-cell lung cancer (SCLC). Thereof, 13 patients (50%) tested positive in the blood sample and 5 of 23 patients (22%) tested positive in the sputum sample. Moreover, among 92 patients with non-small-cell lung cancer (NSCLC) 25 patients (27%) had disseminated cancer cells in peripheral blood. Amplification of preproGRP transcripts from clinical samples is a sensitive and specific assay to detect disseminated or exfoliated lung cancer cells either in peripheral blood or sputum samples.

Systematic identification of genes with coding microsatellites mutated in DNA mismatch repair-deficient cancer cells.

Microsatellite instability (MSI) caused by deficient DNA mismatch-repair functions is a hallmark of cancers associated with the hereditary nonpolyposis colorectal cancer (HNPCC) syndrome but is also found in about 15% of all sporadic tumors. Most affected microsatellites reside in untranslated intergenic or intronic sequences. However, recently few genes with coding microsatellites were also shown to be mutational targets in MSI-positive cancers and might represent important mutation targets in their pathogenesis. The systematic identification of such genes and the analysis of their mutation frequency in MSI-positive cancers might thus reveal major clues to their functional role in MSI-associated carcinogenesis. We therefore initiated a systematic database search in 33,595 distinctly annotated human genes and identified 17,654 potentially coding mononucleotide repeats (cMNRs) and 2,028 coding dinucleotide repeats (cDNRs), which consist of n > or = 6 and n > or = 4 repeat units, respectively. Expression pattern and mutation frequency of 19 of these genes with the longest repeats were compared between DNA mismatch repair-deficient (MSI(+)) and proficient (MSS) cancer cells. Instability frequencies in these coding microsatellite genes ranged from 10% to 100% in MSI-H tumor cells, whereas MSS cancer cells did not show mutations. RT-PCR analysis further showed that most of the affected genes (10/15) were highly expressed in tumor cells. The approach outlined here identified a new set of genes frequently affected by mutations in MSI-positive tumor cells. It will lead to novel and highly specific diagnostic and therapeutic targets for microsatellite unstable cancers.