Hepatocyte growth factor in physiology and infectious diseases
Hepatocyte growth factor (HGF) is a pleiotropic cytokine composed of an α-chain and a β-chain, and these chains contain four kringle domains and a serine protease-like structure, respectively. The receptor for HGF was identified as the c-met proto-oncogene product of transmembrane receptor tyrosine kinase. HGF-induced signaling through the receptor Met provokes dynamic biological responses that support morphogenesis, regeneration, and the survival of various cells and tissues, which includes hepatocytes, renal tubular cells, and neurons. Characterization of tissue-specific Met knockout mice has further indicated that the HGF–Met system modulates immune cell functions and also plays an inhibitory role in the progression of chronic inflammation and fibrosis. However, the biological actions that are driven by the HGF–Met pathway all play a role in the acquisition of the malignant characteristics in tumor cells, such as invasion, metastasis, and drug resistance in the tumor microenvironment. Even though oncogenic Met signaling remains the major research focus, the HGF–Met axis has also been implicated in infectious diseases. Many pathogens try to utilize host HGF–Met system to establish comfortable environment for infection. Their strategies are not only simply change the expression level of HGF or Met, but also actively hijack HGF–Met system and deregulating Met signaling using their pathogenic factors. Consequently, the monitoring of HGF and Met expression, along with real-time detection of Met activation, can be a beneficial biomarker of these infectious diseases. Preclinical studies designed to address the therapeutic significance of HGF have been performed on injury/disease models, including acute tissue injury, chronic fibrosis, and cardiovascular and neurodegenerative diseases. Likewise, manipulating the HGF–Met system with complete control will lead to a tailor made treatment for those infectious diseases.