Association of CDX2 loss with poor prognosis of colorectal cancer patients

다국어 초록 (Multilingual Abstract)

Caudal type homeobox 2 (CDX2) is a Drosophila caudal-related homeobox gene which encodes a transcription factor playing an essential role for the development of the intestine by inhibiting proliferation, promoting differentiation and the expression of intestine-specific genes. The expression of CDX2 in adults is restricted to the intestine from duodenum to rectum, which enables that CDX2 is regarded as a specific marker for origin of intestinal epithelial cell and utilized for identifying origin of colorectum in metastatic adenocarcinoma in the lung or liver. Besides an important role in the development and differentiation of the intestine, CDX2 has been known to exert a tumor suppressor role in colorectal cancers (CRCs). CDX2 expression is often lost in CRCs, which suggests that CDX2 might function as a tumor suppressor in colon cancer
But, although CDX2 has such a important role in maintenance of intestinal epithelium and in CRC, clinicopathologiccharacteristics and prognostic implication of CDX2 expression in CRCs are not well known. In this regard, we examined CDX2 expression in 675 CRCs with immunohistochemistry and compared it with histologic and molecular characteristics.
As a result, we found that CDX2 expression was lost in 36 (5.3%) patients and loss of CDX2 expression was associated with CpG island methylator phenotype (CIMP), microsatellite instability (MSI), and poor prognosis. CRCs could be classified into four molecular subtypes based upon combinatory statuses of CIMP and MSI, including CIMP+/MSI+, CIMP+/MSI-, CIMP-/MSI+, and CIMP-/MSI-. CDX2 loss was frequent in the CIMP+/MSI+ subtype and CIMP+/MSI- subtype.
Regarding the mechanism of CDX2 loss in CRCs, promoter CpG island hypermethylation was found to be not involved in CDX2 downregulation but loss of HNF4α seems to be involved in the downregulation of CDX2 in CRCs.
In conclusion, loss of CDX2 expression was closely associated with CIMP-H and poor differentiation and found to be an independent parameter heralding poor prognosis in CRC patients, which suggests that CDX2 loss might be utilitized as a prognostic marker for advanced CRCs.

목차 (Table of Contents)

• Abstract ⅰ
• Contents ⅲ
• List of tables ⅴ
• List of figures ⅵ
• Introduction 1
• Materials and methods 5
• 1. Tissue samples 5
• 2. Clinicopathologic analysis 5
• 3. Evaluation of CK7, CK20 and CDX2 expression 6
• 4. KRAS, BRAF mutation and MSI analysis 6
• 5. Analysis of CpG island methylator phenotype 7
• 6. Cell lines culture 7
• 7. 5-aza-2′-deoxycytidine(5-AZA), Trichostatin A(TSA) treatment 8
• 8. Reverse transcription polymerase chain reaction(RT-PCR) 8
• 9. Bisulfite modification and sequencing 9
• 10. Statistical analysis 11
• Results 12
• 1. Clinicopathologic and molecular features of CDX2 loss in CRCs 12
• 2. Prognostic implication of CDX2 loss in CRCs 18
• 3. Mechanisms for loss of CDX2 expression in colon cancer cell lines. 24
• 3.1. CDX1 versus CDX2 expression 24
• 3.2. CDX2 loss vs. CIMP-H in colon cancer cell lines 25
• 4. Changes of CDX2 expression by DNA methyltransferse inhibitor, 5-AZA. 28
• 5. Methylation of CDX2 promoter region analyzed by bisulfite sequencing 30
• 6. Association between expressions of CDX2 and HNF4α 33
• Discussion 36
• Refereneces 42
• Abstract in Korean 46