Dual-specificity phosphatase 1 ubiquitination in extracellular signal-regulated kinase-mediated control of growth in human hepatocellular carcinoma.
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.
Calvisi
Diego F
DF
Department of Biomedical Sciences, Division of Experimental Pathology and Oncology, University of Sassari, 07100 Sassari, Italy.
Pinna
Federico
F
Meloni
Floriana
F
Ladu
Sara
S
Pellegrino
Rossella
R
Sini
Marcella
M
Daino
Lucia
L
Simile
Maria M
MM
De Miglio
Maria R
MR
Virdis
Patrizia
P
Frau
Maddalena
M
Tomasi
Maria L
ML
Seddaiu
Maria A
MA
Muroni
Maria R
MR
Feo
Francesco
F
Pascale
Rosa M
RM
D015153:Blotting, Western; D006528:Carcinoma, Hepatocellular / Q000201:enzymology / Q000473:pathology*; D002455:Cell Division; D054638:Dual Specificity Phosphatase 1 / Q000378:metabolism*; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D006801:Humans; D047468:Immunoprecipitation; D008113:Liver Neoplasms / Q000201:enzymology / Q000473:pathology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D025801:Ubiquitin / Q000378:metabolism*
D025801:Ubiquitin; D048049:Extracellular Signal-Regulated MAP Kinases; C517019:DUSP1 protein, human; D054638:Dual Specificity Phosphatase 1