Exosomes are secreted vesicles of endosomal origin involved in signaling processes. We recently showed that the syndecan heparan sulfate proteoglycans control the biogenesis of exosomes through their interaction with syntenin-1 and the endosomal-sorting complex required for transport accessory component ALIX. Here we investigated the role of heparanase, the only mammalian enzyme able to cleave heparan sulfate internally, in the syndecan-syntenin-ALIX exosome biogenesis pathway. We show that heparanase stimulates the exosomal secretion of syntenin-1, syndecan and certain other exosomal cargo, such as CD63, in a concentration-dependent manner. In contrast, exosomal CD9, CD81 and flotillin-1 are not affected. Conversely, reduction of endogenous heparanase reduces the secretion of syntenin-1-containing exosomes. The ability of heparanase to stimulate exosome production depends on syntenin-1 and ALIX. Syndecans, but not glypicans, support exosome biogenesis in heparanase-exposed cells. Finally, heparanase stimulates intraluminal budding of syndecan and syntenin-1 in endosomes, depending on the syntenin-ALIX interaction. Taken together, our findings identify heparanase as a modulator of the syndecan-syntenin-ALIX pathway, fostering endosomal membrane budding and the biogenesis of exosomes by trimming the heparan sulfate chains on syndecans. In addition, our data suggest that this mechanism controls the selection of specific cargo to exosomes.

Signaling through the AKT and ERK pathways controls cell proliferation. However, the integrated regulation of this multistep process, involving signal processing, cell growth and cell cycle progression, is poorly understood. Here, we study different hematopoietic cell types, in which AKT and ERK signaling is triggered by erythropoietin (Epo). Although these cell types share the molecular network topology for pro‐proliferative Epo signaling, they exhibit distinct proliferative responses. Iterating quantitative experiments and mathematical modeling, we identify two molecular sources for cell type‐specific proliferation. First, cell type‐specific protein abundance patterns cause differential signal flow along the AKT and ERK pathways. Second, downstream regulators of both pathways have differential effects on proliferation, suggesting that protein synthesis is rate‐limiting for faster cycling cells while slower cell cycles are controlled at the G1‐S progression. The integrated mathematical model of Epo‐driven proliferation explains cell type‐specific effects of targeted AKT and ERK inhibitors and faithfully predicts, based on the protein abundance, anti‐proliferative effects of inhibitors in primary human erythroid progenitor cells. Our findings suggest that the effectiveness of targeted cancer therapy might become predictable from protein abundance.

Emerging evidence has shown that microRNA-126 (miR-126) is aberrantly downregulated and plays a vital role in carcinogenesis in various cancers, including HCC. However, the underlying biological mechanisms of miR-126 in HCC are still largely unknown. In present study, we found that miR-126 was downregulated both in HCC tissues and cell lines. Low expression level of miR-126 was associated with poor overall survival (OS), late TNM stage and the presence of recurrence. Overexpression of miR-126 significantly decreased cell proliferation, metastasis and promoted apoptosis in vitro. Additional, high miR-126 expression reduced the tumor growth in vivo. Further we discovered that PLK (polo-like kinases)-4, a critical regulator in cell cycle, was a target of miR-126. PLK-4 overexpression could rescue the inhibitory effects of miR-126 on cell proliferation and invasion. Moreover, PLK-4 mRNA and protein levels were significantly upregulated in HCC tissues and positively associated with malignancies and poor OS. Knockdown PLK-4 significantly inhibited cell proliferation, invasion and promoted cell apoptosis in vitro whereas decreased tumor growth in vivo. More importantly, bioinformatics analysis combined with validation experiments in vitro and in vivo showed that activation of the ATR/CHEK1 pathway was involved in the oncogenic functions of PLK4 in HCC. We also validated that PLK4 could directly interact with ATR through CoIP assay. Taken together, we demonstrate that miRNA-126/PLK-4 axis is critical for tumorigenesis and progression of HCC, and the newly identified PLK-4/ATR/CHEK1 pathway may be a potential therapeutic target for HCC treatment.

These results demonstrated a novel role for miR-139-5p/PKM2 in GBC progression and provided potential prognostic predictors for GBC patients.

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