A positive feedback loop between PIM2 and TNFα contributes to hepatocellular carcinoma tumorigenesis and progression

Abstract

Liver cancer is one of the most common human malignancies. Ranks as the third leading cause of cancer-related mortality and fifth commonest human malignancy worldwide, hepatocellular carcinoma (HCC) is the major form (more than 80%) of primary liver cancer. The pathogenesis of HCC is a complicated long-term process that involves the activation of oncogenes and inactivation of tumor suppressor genes caused by genetic and epigenetic alterations. Thus, a better understanding of the genetic and epigenetic alterations during the development and progression of HCC is of great importance for early diagnosis and treatment. Epidemiological studies found that chronic HBV and/or HCV infection, alcohol consumption and aflatoxin B intake are the most common risk factors for HCC incidence. Chronic inflammation is an important factor in the incidence and progression of many human malignancies, up to 20% of human cancers are developed from chronic inflammation, and HCC is the case. Comparison of transcriptomic and proteomic profiles is a powerful strategy to study oncogenic targets during disease progression in cancer research. Previously, a RNA sequencing (RNA-Seq) of 3 paired HCC tumor and non-tumor tissues was carried out in the Laboratory of Cancer Genetics at The University of Hong Kong to identify genetic alterations of HCC. According to the RNA sequencing result, up-regulation of PIM2was observed in HCC tumor tissues compared with paired non-tumor tissues. PIM2 belongs to PIM serine/threonine kinase family, which consists of three members, PIM1, PIM2 and PIM3. Up-regulation of PIM2 was found in many human malignancies, such as leukemia, lymphoma, prostate cancer and ovarian cancer. This study aims to characterize the roles of PIM2 in the pathogenesis and progression of HCC. In this study, up-regulation of PIM2was frequently observed in HCC patients, and following clinical pathological study showed that HCC patients with higher PIM2 expression level had a higher recurrence rate (P = 0.031) and poorer prognosis (P = 0.001). Functional studies showed that PIM2 overexpression could promote HCC cell proliferation, resistance to chemotherapy, tumorigenesis and metastasis in nude mice; and PIM2 knockdown by shRNA could effectively inhibit these phenotypes. Mechanistic studies revealed that PIM2 overexpression could activate NF-κB signaling pathway through or partly through up-regulating phosphorylation level of RIPK2, a well-known potent activator of NF-κB signaling. Furthermore, I found TNFα, a pro-inflammatory cytokine, could stimulate the expression of PIM2in HCC cells and PIM2 overexpression in HCC cells could in turn up-regulate the expression level of TNFα. In addition, the mRNA levels of PIM2 and TNFα in HCC patients are closely correlated (Pearson r = 0.5332, P < 0.0001). I also found that PIM kinase inhibitor AZD1208 treatment could effectively attenuate HCC cells’ tumorigenic ability both in vitro and in vivo. Collectively, my study revealed a positive feedback loop between an inflammatory factor and a proto-oncogene that contributed to the tumorigenesis and progression of HCC, and PIM kinases may serve as a therapeutic target in the treatment of HCC.