Abstract
BackgroundGranulin-epithelin precursor (GEP) is a secretory growth factor, which has been demonstrated to control cancer growth, invasion, drug resistance and immune escape. Our previous studies and others also demonstrated its potential in targeted therapy. Comprehensive characterization of GEP partner on cancer cells are warranted. We have previously shown that GEP interacted with heparan sulfate on the surface of liver cancer cells and the interaction is crucial for GEP-mediated signaling transduction. This study aims to characterize GEP protein partner at the cell membrane with the co-immunoprecipitation and mass spectrometry approach.MethodsThe membrane fraction from liver cancer model Hep3B was used for capturing binding partner with the specific monoclonal antibody against GEP. The precipitated proteins were analyzed by mass spectrometry. After identifying the GEP binding partner, this specific interaction was validated in additional liver cancer cell line HepG2 by co-immunoprecipitation using GRP78 and GEP antibodies, respectively, as the bait. GRP78 transcript levels in hepatocellular carcinoma (HCC) clinical samples (n = 77 pairs) were examined by real-time quantitative RT-PCR. GEP and GRP78 protein expressions were investigated by immunohistochemistry on paraffin sections.ResultsWe identified the GEP-binding protein as 78-kDa glucose-regulated protein (GRP78, also named heat shock 70-kDa protein 5, HSPA5). This interaction was validated in independent HCC cell lines. Increased GRP78 mRNA levels were demonstrated in liver cancer tissues compared with the paralleled liver tissues (t-test, P = 0.002). GRP78 and GEP transcript levels were significantly correlated (Spearman’s correlation, P = 0.001), and the proteins were also detectable in the cytoplasm of liver cancer cells by immunohistochemical staining.ConclusionsGRP78 and GEP are interacting protein partners in liver cancer cells and may play a role in GEP-mediated cancer progression in HCC.
Highlights
Granulin-epithelin precursor (GEP) is a secretory growth factor, which has been demonstrated to control cancer growth, invasion, drug resistance and immune escape
We previously showed that GEP was over-expressed in over 70% of human hepatocellular carcinoma (HCC) samples [7]
We have previously shown that heparan sulfate (HS) might act as the co-receptor, which is essential in the cell surface binding and the signaling transduction of GEP [19]
Summary
Granulin-epithelin precursor (GEP) is a secretory growth factor, which has been demonstrated to control cancer growth, invasion, drug resistance and immune escape. The secretory growth factor granulin-epithelin precursor (GEP) is known as progranulin or PC cell-derived growth factor. It constitutes of seven and half cysteine rich granulin subunits, which are known to regulate inflammation [1]. Yip et al BMC Cancer (2017) 17:409 patients with less than 20% survival rates in five years [11]. Current technologies in HCC prognosis are unsatisfactory, a thorough understanding of the mechanisms of HCC is essential for developing diagnostic approaches and for seeking alternative or supportive therapies to manage liver malignancy. A detailed understanding of the mechanisms of GEP-mediated tumorigenesis in HCC is urgently needed
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