Differential gene expression of tight-junction proteins and their correlation with PRSS8 and prognosis in colorectal cancer.

Authors: Wancai Yang, Yongchen Guo, Jim Lu, Yonghua Bao

Affiliations: GoPath Laboratories LLC; University of Illinois at Chicago, Chicago, IL; Institute of Precision Medicine, Jining Medical University, Jining, China; GoPath Laboratories, LLC, Buffalo Grove, IL

BACKGROUND: Intestinal epithelia cells are made up of tight junctions, adheren junctions and desmosomes. As integral membrane proteins, the tight junction proteins (TJPs) claudins (CLDNs) and occludin (OCLN) are the most important TJPs that play a major role in maintaining the integrity of the intestinal epithelia and regulate several key signaling pathways in cancers. Dysregulation of tight junction and adheren junction has been shown to be associated with disruption of mucosa barriers, chronic colitis, early onset of colorectal carcinogenesis, epithelial mesenchymal transition and cancer metastasis. Our recent studies have shown that intestinal conditional knockout of the Press8 (protease serine 8) gene causes disruption of intestinal epithelial homeostasis, spontaneous inflammation and tumorigenesis in mouse intestine. Whether these pathogeneses are resulted from TJPs alterations and their correlation with PRSS8 are largely unknown.

METHODS: PRSS8 overexpression plasmid was transfected into colon cancer cell line HCT116 cells and proteomics was conducted. The Cancer Genome Atlas colorectal cancer (CRC) data set was deeply mined, and the correlation between TJPs’ alterations, PRSS8 and prognosis was analyzed. 

RESULTS: In vitro proteomics assay showed that increasing expression of PRSS8 led to differential expression of cellular TJPs and adheren proteins, including upregulation of E-cadherin, TJP1 (ZO-1) and OCLN, and downregulation of RAC1, CDC42, RHOA, CLDND1, ARHGAP1, CTNNB1 and CTNNBL1. TCGA data mining showed differential gene expression of tight junction proteins. For instance, similar as PRSS8, most colonic mucosal TJPs, such as TJP1 (ZO-1), TJP3, OLCN, CLDN7, CLDN8 and PTPRJ, were significantly decreased in CRC tissues (n = 215), compared to normal mucosa (n = 22). Moreover, these reduced expression of TJPs were positively correlated with the reduction of PRSS8 and were inversely associated with prognosis. In contrast, another group of TJPs, such as TJP2, CLDN1, CLDN2 and CLDN12, was significantly increased in CRC tissues in comparison with the normal mucosa. These increases of expression were negatively correlated with PRSS8 expression and poor outcomes. More interestingly, the PTPRJ, a newly identified tumor suppressor, was dramatically reduced in metastatic CRC, compared to the primary CRC. Furthermore, the reduced expression of PTPRJ was linked to poor prognosis in the CRC patients.

The underlying mechanisms of regulatory interaction between PRSS8 and TJPs are under investigation.  

CONCLUSION: TJPs are differentially expressed in CRC and the alterations were well correlated with PRSS8 and prognosis. Therefore, these two opposite groups of TJPs could be used as biomarkers for the monitoring of early onset colorectal carcinogenesis, progression and for the prediction of prognosis.

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