P176 TSPAN6: a novel player in the microenvironment of primary liver cancers

IntroductionTetraspanins, a large family of membrane proteins, have been implicated in the regulation of the tumour microenvironment of a number of cancers. TSPAN6 has previously been shown to modulate the immune microenvironment in breast cancers via indirect interactions with tumour-infiltrating B cells; however, TSPAN6 has not been studied within the context of primary liver cancers, nor the human liver in general.MethodsTSPAN6 mRNA expression was quantified in normal, chronically diseased and primary liver cancer tissues. The distribution and cellular localisation of TSPAN6 protein expression was explored utilising immunohistochemistry and multi-colour immunofluorescence. In addition, hepatocellular carcinoma (HCC) tumour samples were histologically scored on intensity and proportion of positivity for TSPAN6 and Kaplan-Meier curves were generated for patients with negative/low expression vs. positive TSPAN6 tumour expression.ResultsTranscriptional expression of TSPAN6 was comparable between normal and chronically diseased liver tissues, but was increased in primary liver cancer tissues, compared to matched distal tissues. TSPAN6 was strongly expressed in biliary epithelial cells, and to a lesser degree in hepatocytes within normal tissues and showed increased expression in the diseased state. In chronically diseased tissues, a strong association with the fibrotic septa was observed and we show that TSPAN6 strongly co-localised with cytokeratin 7, a marker of intermediary cells in the ductular reaction. TSPAN6-expressing cells were also in close association with aggregates of CD20+ B cells within diseased tissues. Primary liver cancer tumours showed variable expression of TSPAN6 and preliminary analysis in HCC tumours suggested a correlation between positive tumour TSPAN6 expression and better overall patient survival, over a 5 year period.ConclusionsIn this study, we have described, for the first time, the expression of TSPAN6 in human liver tissues. Chronically diseased liver tissues showed increased protein expression of TSPAN6 compared to normal tissues, and its expression was largely associated with the fibrotic septa and was in close proximity to B cell rich areas. TSPAN6 expression was highly variable between primary liver cancer tumour tissues, but increased expression was linked to higher patient survival. Our preliminary data suggest that TSPAN6 could play a role in the tumour microenvironment of primary liver cancers and further investigation