Downregulation of RIZ1 protein expression in left-sided versus right-sided primary colorectal carcinomas and their distant metastases and the association with NF-B activation

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e15112 Background: Activation of NF- B leads to enhanced proliferation and the expression of anti-apoptotic proteins, which are cancer phenotypes. RIZ1 inactivation through various molecular events was linked to increased proliferation, migration induction and apoptosis inhibition in human cancer. RIZ1 frameshift mutations were recently reported to be confined to MSI-H colorectal tumors and proximal tumor origin, while its hypermethylation was not limited to MSI-H tumors. However, RIZ1 protein expression has not been evaluated in colorectal carcinoma. Methods: TMAs included 28 left-sided and 12 right-sided primary colorectal adenocarcinomas, their matched normal mucosa and their respective distant metastases. Left-sided tumors were compared to right-sided tumors for expression of RIZ1 protein and NF- B activation. RIZ1 immunostaining was scored semiquantitatively (0–3+). NF- B activation was determined by IHC detecting nuclear translocation of its p65 subunit in more than 30% tumor nuclei. Discrepant results were defined as score difference of 2. Results: RIZ1 was less expressed in tumors than in benign mucosa (p<0.0001, r=- 0.377, Chi-Square). The difference between primary vs. metastatic carcinoma was not significant. Low RIZ1 was associated with NF- B activation (p<0.0001, Linear-by-Linear). Left-sided primary tumors showed less RIZ1 protein expression than right-sided (p=0.03, Chi-Square). NF- B activation was more frequent in left-sided primary tumors and their respective metastases (35% in right vs. 67% in left; p=0.002, Chi-Square Test). RIZ1 expression and NF- B activation were almost identical in primary and their respective metastatic tumors with only 3 discrepant results for NF- B status and 2 discrepant results in RIZ1 expression. Conclusions: While RIZ1 downregulation in colorectal adenocarcinoma due to RIZ1 mutations appears to be associated with MSI-H and proximal origin, its protein expression appears to be downregulated more often in distal tumors. NF- B activation is strongly associated with lower RIZ1 protein expression in colorectal adenocarcinoma. No significant financial relationships to disclose.