Frequent overexpression of CADM1/IGSF4 in lung adenocarcinoma

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Abstract

We reported comprehensive screening for antigens (Ags) overexpressed on various carcinomas via isolation of human monoclonal antibodies (mAbs) that may be therapeutic in a previous paper (Proc. Natl. Acad. Sci. USA 105, 7287-7292, 2008). Twenty-one distinct Ags highly expressed on several carcinomas were identified and 356 mAbs with unique sequences turned out to bind to one of the 21 Ags. Among them CADM1/IGSF4 which had been originally referred to as tumor suppressor lung cancer 1 (TSLC1) was included. Therefore we examined the expression of CADM1 in lung cancers in this study. Eight different anti CADM1 mAbs were used for immunohistochemical analysis of 29 fresh lung cancer specimens. Staining patterns were categorized to six groups based on the extent of positive staining and the localization of stained portions. While overexpression of CADM1 was observed on the cell surface of adenocarcinomas at a high frequency, around 60%, positive stainings were rarely observed on that of other lung carcinomas including squamous cell carcinomas. Moreover, some clones among the eight mAbs gave different staining patterns from those by the other clones against the same fresh specimen, suggesting presence of variant forms of CADM1 differentiated by mAbs.

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Materials and methods

Cells and mAbs. HepG2 [10], Caco-2 [11] and SKOv3 [11] were obtained from Riken Bioresource Center, ATCC and Dr. H. Shiku in Mie University School of medicine, respectively. mAbs used in this study were isolated in the previous study [4].

Flow cytometry (FCM). scFv-CL molecules fused with a truncated cp3 (scFv-CL-cp3) form of Ab was used for FCM analysis without purification. 5 × 105 cells were suspended in 500 μl to 1 ml of 2.5% normal goat serum/2.5% BSA/0.05% NaN3/PBS and stood for 30 min on ice.

Isolation of human mAbs against CADM1/IGSF4

As reported in a previous paper, 23 distinct anti CADM1 human mAbs have been isolated [4]. Table 1 summarized the results of screening showing how they had been isolated. Since the same clones were isolated from different screenings, 34 mAbs consisting of 23 distinct clones were listed in Table 1. Of those 34 mAbs 24 were isolated from screenings against hepatocarcinomas, five against colonic cancer, four against ovarian carcinoma and one against pancreatic carcinoma. Furthermore, 19 distinct

Discussion

In the previous work we identified 21 distinct Ags that are highly expressed on various carcinomas. Among them CADM1 that had been originally identified to be a tumor suppressor of human non-small cell lung cancer was included [4]. Many reports showed hypermethylation of the promoter region of CADM1 gene in various cancers including lung cancer, pancreatic carcinoma and breast cancer [13], [14]. Tumor suppressor activity mediated by CADM1/TSLC1 was shown by functional complementation experiment

Acknowledgments

This study was supported in part by a grant-in-aid for the 21st Century Center of Excellence (COE) Program of Fujita Health University from the Ministry of Education, Culture, Sports, Science, and Technology and by a grant from the New Energy and Industrial Technology Development Organization (NEDO) to Y.K.

References (22)

  • G. Kurosawa et al.

    Comprehensive screening for antigens overexpressed on carcinomas via isolation of human mAbs that may be therapeutic

    Proc. Natl. Acad. Sci. USA

    (2008)
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