Somatic Mutations and Altered Expression of the Candidate Tumor Suppressors CSNK1ε , DLG1 , and EDD/hHYD in Mammary Ductal Carcinoma

Abstract

We report somatic mutations in three genes (CSNK1⑀, encoding the Ser/Thr kinase casein kinase I ⑀; DLG1, encoding a membrane-associated putative scaffolding protein; and EDD/hHYD, encoding a progestin induced putative ubiquitin-protein ligase) in mammary ductal carcinoma. These genes were suspected of playing a role in cancer because loss-offunction mutations in their Drosophila homologues cause excess tissue growth. Using DNA from 82 laser-microdissected tumor samples, followed by microsatellite analysis, denaturing HPLC and direct sequencing, we found multiple somatic point mutations in all three genes, and these mutations showed significant association with loss of heterozygosity of closely linked polymorphic microsatellite markers. For CSNK1⑀ and DLG1, most of the mutations affected highly conserved residues, some were found repetitively in different patients, and no synonymous mutations were found, indicating that the observed mutations were selected in tumors and may be functionally significant. Immunohistochemical reactivity of each protein was reduced in poorly differentiated tumors, and there was a positive association between altered protein reactivity, loss of heterozygosity, and somatic mutations. There was a statistically significant association of hDlg staining with p53 and Ki67 reactivity, whereas CSK1⑀ and EDD/hHYD staining levels were associated with progesterone receptor status. The results provide strong indications for a role of all three genes in mammary ductal carcinoma. They also justify additional studies of the functional significance of the changes, as well as a search for additional changes in these and other genes identified from studies on model systems.

The E3 ubiquitin ligase EDD is an adverse prognostic factor for serous epithelial ovarian cancer and modulates cisplatin resistance in vitro

“…Although somatic mutations in the EDD gene have been reported in gastric and colorectal tumours (Mori et al, 2002) and in mammary ductal carcinoma (Fuja et al, 2004), we have not identified any deleterious EDD mutations in a number of ovarian cancer cell lines (Clancy et al, 2003), and therefore, we predict that EDD mutation would be a very rare event in ovarian cancer and hence assume that EDD is functional in ovarian cancer.…”

A whole-genome RNAi screen identifies an 8q22 gene cluster that inhibits death receptor-mediated apoptosis

“…Several reports have also demonstrated that EDD1 is overexpressed in a high percentage of cancers, consistent with a pattern that correlates with an increased copy number of the EDD1 locus (27,28). Finally, cancer-specific somatic mutations of EDD1 have been observed; however, the functional consequence of the mutations are unknown (28,29). As with EDD1, several studies have reported cancer-specific aberrations of GRHL2.…”

Epithelial polarity and proliferation control: links from the Drosophila neoplastic tumor suppressors

“…Evidence to date has been suggestive but indirect. Large-scale sequencing of nTSG homologs from mammalian tumors has not yet been performed, but a small-scale study has reported Dlg1 mutations in breast cancers (Fuja et al 2004), and microarray experiments have detected significant changes of nTSG homolog expression in several human cancers (Liu et al 2002;Boussioutas et al 2003). Immunohistochemistry has revealed a reduction of hScrib in invasive cervical cancers and Dlg1 in mammary ductal carcinoma, as well as reduction of Dlg4 in a fully defined model of mouse ovarian cancer (Huang et al 2003;Nakagawa et al 2004).…”

“…Drosophila has come into its own in particular as a system in which to identify new TSGs, and the relevance of fly TSGs to human cancer has become increasingly clear. The past few years have seen reports that TSGs first identified in the fly are mutated in human cancers and can cause tumor susceptibility in mice (e.g., St John et al 1999;Spruck et al 2002;Fuja et al 2004;Rajagopalan et al 2004). Analyses of fly TSGs have also produced substantial contributions toward understanding the basic cell biology of tumorigenesis, in particular links between cell growth, cell proliferation, and apoptosis.…”