NIPBL, a Cohesion Loading Factor, Is Somatically Mutated in Gastric and Colorectal Cancers with High Microsatellite Instability

Abstract

Timely segregation of sister chromatids during the cell cycle is essential for maintaining euploidy [1]. Aberrant segregation into daughter cells promotes aneuploidy and chromosome instability, which are features of many tumors [1]. Chromatid cohesion, a physical linkage of replicated sister chromatids, is mediated by a multiprotein complex called cohesin [1]. NIPBL is a cohesion loading factor that is required for cohesin to interact with chromosomes [2, 3]. NIPBL mutations (missense, nonsense, frameshift and deletion mutations) account for approximately 60 % of Cornelia de Lange syndrome, a congenital disorder with multisystem developmental abnormalities [3]. In Cornelia de Lange syndrome, mutated NIPBL interferes with its interaction with its partners in the cohesion complex [3]. Components in the cohesin complex and cohesin regulatory proteins are frequently altered at expression and mutation levels in human cancers [1]. For example, cohesin protector SGOL1 down-regulation leads to chromosomal instability in colorectal cancers (CRC) [4]. Somatic mutations of cohesion regulatory factor PDS5B have been identified in prostate cancers [5]. These data suggest that cohesin-related genes could be considered potential tumor suppressor genes (TSG) [1]. Somatic mutations of the NIPBL gene have been found in CRC with stable miscrosatellite instability (MSI) that may underlie chromosomal instability in CRC [6]. Together, these data suggest a possibility that NIPBL is a candidate TSG. In a public genome database (http://genome.cse.ucsc. edu/), we found that the human NIPBL gene had mononucleotide repeats in its coding sequences that could be targets for frameshift mutation in cancers with high MSI (MSI-H) [7]. To data, however, the data on NIPBL somatic mutation in gastric (GC) and CRC with MSI-H are lacking. To see whether the mononucleotide repeats in the NIPBL gene are mutated in GC and CRC, we analyzed two A7 and one A8 repeats in NIPBL exon 10 by polymerase chain reaction (PCR)-based single strand conformation polymorphism (SSCP) assay with three primer pairs. For this, we used 32 GC with MSI-H, 59 GC with MSS, 47 CRC with MSI-H and 53 CRC with MSS in methacarnfixed tissues. All of the patients of the cancers were Koreans. In cancer tissues, malignant cells and normal cells were selectively procured from hematoxylin and eosinstained slides by microdissection [8]. Radioisotope ([P]dCTP) was incorporated into the PCR products for detection by autoradiogram. The PCR products were subsequently displayed in SSCP gels. After SSCP, direct DNA sequencing reactions were performed in the cancers with mobility shifts in the SSCP. On the SSCP, we observed aberrant bands of the NIPBL gene in 11 cancers (Fig. 1). DNA from normal tissue Min Sung Kim and Chang Hyeok An contributed equally to this study.