Validation of specificity of antibodies for immunohistochemistry: the case of ROR2.

The Wnt signalling receptor receptor tyrosine kinase-like orphan receptor 2 (ROR2) is implicated in numerous human cancers. However, there have been conflicting reports regarding ROR2 expression, some studies showing upregulation and others downregulation of ROR2 in the same cancer type. The majority of these studies used immunohistochemistry (IHC) to detect ROR2 protein, without validation of the used antibodies. There appears to be currently no consensus on the antibody best suited for ROR2 detection or how ROR2 expression changes in various cancer types. We examined three commercially available ROR2 antibodies and found that only one bound specifically to ROR2. Another antibody cross-reacted with other proteins, and the third failed to detect ROR2 at all. ROR2 detection by IHC on 107 patient samples using the ROR2 specific antibody showed that the majority of colorectal cancers show loss of ROR2 protein. We found no association between ROR2 staining and poor patient survival, as had been previously reported. These results question the previously reported association between ROR2 and poor patient survival in colorectal cancer. Future studies should use fully validated antibodies when detecting ROR2 protein, as non-specific staining can lead to irrelevant observations and misinterpretations.

ROR2 is epigenetically inactivated in the early stages of colorectal neoplasia and is associated with proliferation and migration.

BACKGROUND: Colorectal cancer (CRC) is closely linked to Wnt signalling, with 94 % of cases exhibiting a Wnt related mutation. ROR2 is a receptor tyrosine kinase that is thought to repress ß-catenin dependent Wnt signalling. Our study aims to determine if ROR2 is epigenetically silenced in CRC and determine if in vitro silencing of ROR2 potentiates Wnt signalling, and alters the proliferative, migratory or invasive potential of cells. METHODS: ROR2 expression was examined in CRC cell lines and patient adenomas using qRT-PCR, while COBRA and bisulphite sequencing was used to analyse ROR2 promoter methylation. 258 patient primary tumour samples from publicly available databases were also examined for ROR2 expression and methylation. In addition, the functional effects of ROR2 modulation were investigated in HCT116 cells following ROR2 siRNA knockdown and in RKO and SW620 cells following ectopic ROR2 expression. RESULTS: Reduced ROR2 expression was found to correlate with ROR2 promoter hypermethylation in colorectal cancer cell lines, carcinomas and adenomas. ROR2 expression was downregulated in 76.7 % (23/30) of CRC cell lines with increasing ROR2 promoter hypermethylation correlating with progressively lower expression. Analysis of 239 primary tumour samples from a publicly available cohort also found a significant correlation between reduced ROR2 expression and increased promoter methylation. Methylation analysis of 88 adenomas and 47 normal mucosa samples found greater percentage of adenoma samples to be methylated. Additional analysis also revealed that adenoma samples with reduced ROR2 expression also possessed ROR2 promoter hypermethylation. ROR2 knockdown in the CRC cell line HCT116 significantly decreased expression of the ß-catenin independent Wnt targets genes JNK and NFATC1, increased cellular proliferation and migration but decreased invasion. When ROR2 was ectopically expressed in RKO and SW620 cells, there was no significant change to either cellular proliferation or migration. CONCLUSION: ROR2 is frequently epigenetically inactivated by promoter hypermethylation in the early stages of colorectal neoplasia and this may contribute to colorectal cancer progression by increasing cellular proliferation and migration.