ERK-Dependent Downregulation of Skp2 Reduces Myc Activity with HGF, Leading to Inhibition of Cell Proliferation through a Decrease in Id1 Expression

Abstract

Hepatocyte growth factor (HGF) has an inhibitory effect on human HepG2 hepatoma cell proliferation. Previously, it was shown that HGF treatment downregulated Id1 and upregulated p16 INK4a in an ERK-dependent manner, leading to the inhibition of cellular proliferation. Here, new insight suggests that Skp2, an SCF complex component and potential prognosticator in cancer, is downregulated by injection of HGF into established HepG2 xenograft tumors. The downregulation was evident at both the mRNA and protein level and in an ERK-dependent manner. Critically, high expression of Skp2 restored HGF-inhibited cell proliferation, indicating that the inhibitory effect of HGF required the downregulation of Skp2. However, downregulation was not involved in the HGFinduced upregulation of a CDK inhibitor, p27 Kip1 , a known SCF-Skp2 target. Instead, data revealed that Skp2 regulated Myc activity, which has oncogenic potential in the generation of hepatocellular carcinoma. Elevated expression of Skp2 or a mutant that is unable to associate with the SCF complex was capable of activating Myc, suggesting that Skp2 does not act on Myc as a component of the SCF complex, and thus functions as an activator of Myc independent of its role in ubiquitination. Furthermore, Skp2 regulated Id1 expression by regulating Myc activity, and the regulation of Skp2 is involved in the activity of p16 promoter through regulation of Id1 expression. Overall, these mechanistic findings provide the first evidence that ERK-dependent downregulation of Skp2 reduced Myc activity, leading to HGF-induced inhibition of cell proliferation through decreased Id1 expression.

Selective targeting of IRF4 by synthetic microRNA-125b-5p mimics induces anti-multiple myeloma activity in vitro and in vivo

“… 3 In this regard, we found that exogenous interleukin-6 (IL-6) or insulin-like growth-factor-1 (IGF-1) or hepatocyte growth-factor (HGF) significantly reduced miR-125b-5p expression in all MM cell lines except U266 cells ( Figure 6a ), which express L-Myc instead of c-Myc. Since c-Myc suppresses miR-125b transcription 39 , 40 and is upregulated by IL-6, IGF-1 and HGF, 40 , 41 , 42 we investigated whether these factors downregulate miR-125b in MM cells through c-Myc induction. Specifically, we treated c-Myc-expressing SK-MM-1 and c-Myc-defective U266 cells with the 10058-F4 small molecule inhibitor of Myc–Max heterodimerization 38 and with the JQ1 BET-bromodomain inhibitor, which is reported to inhibit c-Myc transcription.…”

Antineoplastic Activity of Monocrotaline Against Hepatocellular Carcinoma

“…Molecular docking predicts the best interaction of proteinligand complexes virtually and determines the appropriate orientation of the inhibitor when bound to a protein [36]. The crystal structure of p53 tumor suppressor protein PDB_ID: 1TSR_B with resolution 2.20Å; crystal structure Hepatocytes Growth Factor PDB_ID: 3HN4_A with resolution of 2.60Å and the crystal structure of TREM1 PDB_ID: 1Q8M_A with resolution of 2.60Å are retrieved from protein data bank.…”

Acetaminophen‐induced hepatotoxicity of cultured hepatocytes depends on timing of isolation from light‐cycle controlled mice

“…Equal amounts of protein in the precleared cell extracts (30 μg of total protein) were resolved by sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE) on 10% gel after heat denaturation. Immunoblotting was carried out following standard procedures as previously described (Li et al, ). Antibodies used for immunoblotting were as follows: anti‐CYP2e1 antibody (AB1252) from Merck Millipore, anti‐β‐actin antibody from Sigma‐Aldrich, and anti‐Bmal1 antibody (ab93806) and anti‐Per2 antibody (ab180655) from Abcam.…”