The loss of the CBX7 gene expression represents an adverse prognostic marker for survival of colon carcinoma patients
Introduction
Colorectal carcinoma (CRC) is the third most common cancer in the USA,1 with survival estimates at 5 years of 64%.1 The molecular events underlying the genesis of CRC, both familiar and sporadic, have been well determined.2, 3, 4 Approximately 85% of CRCs arise through the so-called chromosomal instability (CIN) pathway, characterised by microsatellite stability (MSS).5 The remaining tumours are characterised by microsatellite instability (MSI) due to inactivation of mismatch repair (MMR) genes.5 There are, however, several unknown events that regulate the invasiveness of CRC and might influence the survival of the patients.6 The knowledge of these events may help to identify subgroups with more aggressive disease, thereby, leading to more individualised treatment protocols.7
CBX7 is a chromobox family protein and a member of the Polycomb repressive complex 1 (PRC1), which together with the PRC2, maintains developmental regulatory genes in a silenced state.8, 9, 10 Mouse Cbx7 associates with facultative heterochromatin and inactive X chromosome, suggesting a role of the Cbx7 protein in the repression of gene transcription.11, 12 Our group has previously reported that CBX7 gene is drastically downregulated in thyroid carcinomas and its expression progressively decreases with malignant grade and neoplastic stage.13 Indeed, CBX7 protein levels decreased in an increasing percentage of cases going from benign adenomas to papillary, follicular and anaplastic thyroid carcinomas. Very recently the loss of CBX7 expression has been shown to be related to progression of urothelial carcinoma of the bladder.14 These data suggest that the loss of CBX7 expression may be strictly correlated with the acquisition of invasiveness accompanied by the loss of the epithelial features and the gain of a mesenchymal phenotype, a process known as epithelial-mesenchymal transition (EMT). Consistent with this hypothesis, we have recently demonstrated that the CBX7 is able to positively regulate E-cadherin expression that plays a critical role in maintaining normal epithelial cell morphology, by interacting with histone deacetylase 2 and inhibiting its activity on the E-cadherin promoter thereby accounting for the correlation between the loss of CBX7 expression and a highly malignant phenotype.15
Therefore, CBX7 could be involved in cancerogenesis and may be a candidate to predict the prognosis also of other cancer types. Hence, the aim of this study was to investigate a possible prognostic role of CBX7 detection in CRC.
Section snippets
Human colorectal tissue samples
Human neoplastic colorectal tissues and normal mucosa tissues were obtained from surgical specimens and immediately frozen in liquid nitrogen at the Department of Pathology, University of Basel, Switzerland. The tumour samples were stored at –70 °C.
Tissue microarray (TMA) and immunohistochemistry (IHC)
TMA of 1420 unselected, non-consecutive CRC from 1985 to 1998 was constructed as previously described.16, 17, 18, 19, 20, 21 Normal colonic mucosa samples (n = 9, as normal controls) and colonic adenomas (n = 45 mild dysplasia, n = 48 moderate dysplasia and
Immunohistochemical analysis of CBX7 expression
A TMA including 1420 cases was analysed by IHC using polyclonal antibodies raised against the C-terminal region of human CBX7 protein. IHC results are summarised in Table 1, Table 2. 1273 cases were evaluable (89.7%): 1042 (81.9%) cases showed at least some degree of positivity. Some representative results of the immunohistochemical analyses are shown in Fig. 1 (Fig. 1A–G). The specificity of the reaction was confirmed by the lack of tissue immunoreactivity after pre-incubation of the antibody
Discussion
In this study we have identified, by using TMA technology, IHC and FISH, CBX7 as a prognostic marker for patients with CRC. By IHC performed on normal colonic mucosa, colonic adenomas (moderate, mild and severe dysplasia) and CRC samples, we found that the loss of CBX7 expression is strongly related with the colon cancer phenotype. In fact, we also found that the loss of CBX7 expression is positively correlated with the progression of the dysplasia, as we observed in colonic adenomas. Therefore
Conflict of interest statement
None declared.
Acknowledgements
This work was supported by grants from the Associazione Italiana per la Ricerca sul Cancro (AIRC), Progetto Strategico Oncologia Consiglio Nazionale delle Ricerche, the Ministero dell’Università e della Ricerca Scientifica e Tecnologica (MIUR). This work was supported from NOGEC-Naples Oncogenomic Center. We thank the Associazione Partenopea per le Ricerche Oncologiche (APRO) for its support.
References (34)
- et al.
Lessons from hereditary colorectal cancer
Cell
(1996) - et al.
Genome regulation by polycomb and trithorax proteins
Cell
(2007) - et al.
Understanding the words of chromatin regulation
Cell
(2009) - et al.
Polycomb complexes and silencing mechanisms
Curr Opin Cell Biol
(2004) - et al.
Role of the mitogen-activated protein kinase and phosphoinositide 3-kinase/AKT pathways downstream molecules, phosphorylated extracellular signal-regulated kinase, and phosphorylated AKT in colorectal cancer-a tissue microarray-based approach
Hum Pathol
(2006) - et al.
Hereditary colorectal cancer
N Engl J Med
(2003) - et al.
Cancer genes and the pathways they control
Nat Med
(2004) - et al.
Systematic review of microsatellite instability and colorectal cancer prognosis
J Clin Oncol
(2005) - et al.
Reduced hGC-1 protein expression is associated with malignant progression of colon carcinoma
Clin Cancer Res
(2008)