Unconventional protein secretion of La/SSB in liver cancer

The La nucleoprotein/Sjögren syndrome type B antigen (La/SSB) is an RNA-binding factor in the nucleus that is associated with autoimmune diseases. In this study, we show that La/SSB is a biomarker for liver cancer. We detected full-length La/SSB in several liver cancer cell lines, but not in colorectal cancer cell lines. Importantly, serological analysis using a hepatocellular carcinoma (HCC) mouse model and human samples demonstrated that extracellular detection of La/SSB is specific for HCC. Furthermore, we found that the addition of exogenous La/SSB extract induces extracellular signal-regulated kinase (ERK) activation, which leads to accelerated cell growth. This study suggests that the La/SSB is a novel biomarker for HCC, and in the microenvironment, it may act as a growth factor in the progression of liver cancer.