The HMGB1-RAGE axis modulates the growth of autophagy-deficient hepatic tumors

Abstract

Autophagy is an intracellular lysosomal degradative pathway important for tumor surveillance. Autophagy deficiency can lead to tumorigenesis. Autophagy is also known to be important for the aggressive growth of tumors, yet the mechanism that sustains the growth of autophagy-deficient tumors is not known. We previously reported that progression of hepatic tumors developed in autophagy-deficient livers required high mobility group box 1 (HMGB1) that is released from autophagy-deficient hepatocytes. However, the mechanism by which HMGB1 promotes hepatic tumorigenesis is not understood. In this study we examined the pathological features of the hepatic tumors and the mechanism of HMGB1-mediated tumorigenesis using liver-specific autophagy-deficient (Atg7-/-) and Atg7-/-/Hmgb1-/- mice. We found that in Atg7-/- mice the tumors cells were still deficient in autophagy and could also release HMGB1. Histological analysis using cell-specific markers suggested that fibroblast and ductular cells were present only outside the tumor whereas macrophages were present both inside and outside the tumor. Genetic deletion of HMGB1 or one of its receptors, receptor for advanced glycated end product (Rage), retarded liver tumor development. In addition, we found that expression of RAGE was only on ductual cells and Kupffers cells but not on hepatoctyes, which suggested that HMGB1 might promote hepatic tumor growth through a paracrine mode that altered the tumor microenvironment. Furthermore, HMGB1 and RAGE enhanced the proliferation capability of the autophagy-deficient hepatocytes and tumors. Finally, RNAseq analysis of the tumors indicated that HMGB1 induced a much broad changes in tumors. In particular, genes related to mitochondrial structures or functions were enriched among those differentially expressed in tumors in the presence or absence of HMGB1, revealing a potential key role of mitochondria in sustaining the growth of autophagy-deficient liver tumors via HMGB1 stimulation.