The clinical relevance of epithelial-mesenchymal transition and its correlations with tumorigenic immune infiltrates in hepatocellular carcinoma.

Hepatocellular carcinoma (HCC) is a cancer with extremely high mortality. Epithelial-mesenchymal transition (EMT) may play an important role in the occurrence, invasion and prognosis of HCC; however, its relationship with immunity in HCC has not yet been studied. Therefore, we investigated the diagnostic and prognostic values of EMT and explored its potential connections with tumorigenic immune infiltrates in HCC. We first proposed a quantitative metric of EMT activity, the EMT score. After applying this metric to 20 datasets from the Integrative Molecular Database of Hepatocellular Carcinoma, the Cancer Genome Atlas, and the Gene Expression Omnibus, we explored the ability of the EMT score to stratify across sample types. We then applied the EMT score for survival analysis and to differentiate patients with/without vascular invasion to test its prognostic value. We also collected and calculated data on the abundance of immune cells and immune cell markers in HCC and investigated their correlations with EMT scores. Finally, we synthesized and analyzed 20 datasets and constructed an EMT-gene-immune linkage network. The results showed higher EMT scores in HCC samples than in cirrhotic and normal livers. The cases with higher EMT scores also showed poorer performance in terms of prognostic factors such as vascular invasion and overall survival time. Our research demonstrated a broad correlation between EMT and the tumor immune microenvironment, and we uncovered multiple potential linkers associated with both EMT and immunity. Studying EMT has clinical relevance and high diagnostic and prognostic value for HCC.

Dual roles of Atg8-PE deconjugation by Atg4 in autophagy.

Modification of target molecules by ubiquitin or ubiquitin-like (Ubl) proteins is generally reversible. Little is known, however, about the physiological function of the reverse reaction, deconjugation. Atg8 is a unique Ubl protein whose conjugation target is the lipid phosphatidylethanolamine (PE). Atg8 functions in the formation of double-membrane autophagosomes, a central step in the well-conserved intracellular degradation pathway of macroautophagy (hereafter autophagy). Here we show that the deconjugation of Atg8-PE by the cysteine protease Atg4 plays dual roles in the formation of autophagosomes. During the early stage of autophagosome formation, deconjugation releases Atg8 from non-autophagosomal membranes to maintain a proper supply of Atg8. At a later stage, the release of Atg8 from intermediate autophagosomal membranes facilitates the maturation of these structures into fusion-capable autophagosomes. These results provide new insights into the functions of Atg8-PE and its deconjugation.

Function and molecular mechanism of acetylation in autophagy regulation.

Protein acetylation emerged as a key regulatory mechanism for many cellular processes. We used genetic analysis of Saccharomyces cerevisiae to identify Esa1 as a histone acetyltransferase required for autophagy. We further identified the autophagy signaling component Atg3 as a substrate for Esa1. Specifically, acetylation of K19 and K48 of Atg3 regulated autophagy by controlling Atg3 and Atg8 interaction and lipidation of Atg8. Starvation induced transient K19-K48 acetylation through spatial and temporal regulation of the localization of acetylase Esa1 and the deacetylase Rpd3 on pre-autophagosomal structures (PASs) and their interaction with Atg3. Attenuation of K19-K48 acetylation was associated with attenuation of autophagy. Increased K19-K48 acetylation after deletion of the deacetylase Rpd3 caused increased autophagy. Thus, protein acetylation contributes to control of autophagy.

Deficiency of hepatocystin induces autophagy through an mTOR-dependent pathway.

Mutations in the gene encoding hepatocystin/80K-H (PRKCSH) cause autosomal-dominant polycystic liver disease (ADPLD). Hepatocystin functions in the processing of nascent glycoproteins as the noncatalytic beta subunit of glucosidase II (Glu II) and regulates calcium release from endoplasmic reticulum (ER) through the inositol 1,4,5-trisphosphate receptor (IP3R). Little is known, however, on how cells respond to a deficiency of hepatocystin. In this study, we demonstrate that knockdown of hepatocystin induces autophagy, the major intracellular degradation pathway essential for cellular health. Ectopic expression of wild-type hepatocystin, but not pathogenic mutants, rescues the siRNA-induced effect. Our data indicate that the induction of autophagy by hepatocystin deficiency is mediated through mammalian target of rapamycin (mTOR). Despite the resulting severe reduction in Glu II activity, the unfolded protein response (UPR) pathway is not disturbed. Furthermore, the inhibition of IP3R-mediated transient calcium flux is not required for the induction of autophagy. These results provide new insights into the function of hepatocysin and the regulation of autophagy.