Dual-Specificity Phosphatase 1 Ubiquitination in Extracellular Signal-Regulated Kinase–Mediated Control of Growth in Human Hepatocellular Carcinoma

Abstract

Sustained activation of extracellular signal-regulated kinase (ERK) has been detected previously in numerous tumors in the absence of RAS-activating mutations. However, the molecular mechanisms responsible for ERK-unrestrained activity independent of RAS mutations remain unknown. Here, we evaluated the effects of the functional interactions of ERK proteins with dual-specificity phosphatase 1 (DUSP1), a specific inhibitor of ERK, and S-phase kinase-associated protein 2 (SKP2)/ CDC28 protein kinase 1b (CKS1) ubiquitin ligase complex in human hepatocellular carcinoma (HCC). Levels of DUSP1, as assessed by real-time reverse transcription-PCR and Western blot analysis, were significantly higher in tumors with better prognosis (as defined by the length of patients' survival) when compared with both normal and nontumorous surrounding livers, whereas DUSP1 protein expression sharply declined in all HCC with poorer prognosis. In the latter HCC subtype, DUSP1 inactivation was due to either ERK/SKP2/CKS1-dependent ubiquitination or promoter hypermethylation associated with loss of heterozygosity at the DUSP1 locus. Noticeably, expression levels of DUSP1 inversely correlated with those of activated ERK, as well as with proliferation index and microvessel density, and directly with apoptosis and survival rate. Subsequent functional studies revealed that DUSP1 reactivation led to suppression of ERK, CKS1, and SKP2 activity, inhibition of proliferation and induction of apoptosis in human hepatoma cell lines. Taken together, the present data indicate that ERK achieves unrestrained activity during HCC progression by triggering ubiquitin-mediated proteolysis of its specific inhibitor DUSP1. Thus, DUSP1 may represent a valuable prognostic marker and ERK, CKS1, or SKP2 potential therapeutic targets for human HCC.

Role of DUSP1/MKP1 in tumorigenesis, tumor progression and therapy

“…Downregulating DUSP1 allows for proliferation and increased tumor mass in the more advanced stages of tumorigenesis by enhancing ERK/MAPK signaling pathway. DUSP1 expression was also found to be significantly lower in HCC patients with poor prognosis than the patients with better prognosis [36,37]. However, Calvisi [36] found DUSP1 was not the main causative event responsible for phosphorylated ERK (p-ERK) up-regulation in human HCC.…”

“…DUSP1 expression was also found to be significantly lower in HCC patients with poor prognosis than the patients with better prognosis [36,37]. However, Calvisi [36] found DUSP1 was not the main causative event responsible for phosphorylated ERK (p-ERK) up-regulation in human HCC. Besides, degradation of DUSP1 was detected in HCC via the ubiquitination proteasomal pathway caused by ERK2 activation [36,38].…”

“…However, Calvisi [36] found DUSP1 was not the main causative event responsible for phosphorylated ERK (p-ERK) up-regulation in human HCC. Besides, degradation of DUSP1 was detected in HCC via the ubiquitination proteasomal pathway caused by ERK2 activation [36,38]. The degradation of DUSP1 may then further strengthen the promotive effect on HCC growth by prolonging the half-life of active ERK.…”

Regulation of ERK and AKT Pathways by Hepatitis B Virus X Protein via Notch1 Pathway in Hepatocellular Carcinoma

“…Real-time PCR primers are listed in Table II Transient RNA interference. Small interfering RNA (siRNA) duplexes targeting human HBx, Hes1, DUSP1, and PTEN sequences and a scrambled siRNA were designed as described previously (5,(21)(22)(23). All siRNAs were synthesized by Ribobio (Guangzhou, China).…”

Interaction of major genes predisposing to hepatocellular carcinoma with genes encoding signal transduction pathways influences tumor phenotype and prognosis

“…Genetic control of signaling pathways in liver cancer positivity for DUSP1 in human HCC is associated with longer patients' survival [91] . The interactions of DUSP1 with CKS1-SKP2 ubiquitin ligase have been recently evaluated in human HCC subtypes with different survival times, in the attempt to correlate the effects of DUSP1 molecular interactions with tumor growth and patients' survival, and explore DUSP1 prognostic role [92] . It was found that the levels of DUSP1 are significantly higher in HCCB when compared with both normal and nontumorous surrounding livers, whereas DUSP1 protein expression sharply declines in HCCP [92] .…”