Heterogeneous expression and functional relevance of the ubiquitin carboxyl-terminal hydrolase L1 in melanoma

Abstract

The expression of ubiquitin carboxyl-terminal hydrolase 1 (UCHL1) is deregulated in human cancer cells with tumor inhibiting or promoting functions. Due to less knowledge on the role of UCHL1 in melanoma progression, the expression pattern and function of UCHL1 as well as the deregulated signaling pathways were characterized. A large number of melanoma cell lines, tissue microarrays of melanoma lesions and control tissues were analyzed for UCHL1 expression using PCR, Western blot and/ or immunohistochemistry. The analysis revealed that melanocyte cultures, 24 of 331 melanoma lesions, two of 18 short-term cultures and two of 19 melanoma cell lines tested, respectively, heterogeneously expressed UCHL1. The low frequency of UCHL1 expression in melanoma cells was due to gene silencing by promoter DNA hypermethylation. Using different transfection models an enzyme activity-dependent growth promoting function of UCHL1 via the activation of the mitogen-activated protein kinase signaling pathway was found in melanoma cells. Under oxygen stress a dose-dependent effect of UCHL1 was detected, which was mediated by a dynamic modification of the PI3K-Akt signaling. Thus, the aberrant UCHL1 expression in melanoma cells is linked to dynamic changes in growth properties and signal transduction cascades suggesting that UCHL1 provides a novel marker and/or therapeutic target at least for a subset of melanoma patients.Ubiquitination plays a key role in the post-translational modification of proteins and regulates in combination with phosphorylation and other post-translational alterations a number of cellular processes such as differentiation, proliferation, apoptosis and neoplastic transformation. The ubiquitination of proteins is controlled by so called deubiquitinating enzymes (DUB), which revert the binding between ubiquitin (ub) and their substrates, 1 protect proteins from proteasomal degradation and recycle ub-molecules of poly-ub chains. The DUB family is categorized into five different groups: (i) the ubiquitin carboxyl-terminal hydrolases (UCH), (ii) the ubiquitinspecific proteases (USP), (iii) the ovarial tumor proteases, (iv) the protein domain proteases of the Machado-Josef-disease and (v) the Jab1/MPN domain associated metalloproteinases. 2 The UCH family member UCHL1, also known as PGP9.5, GAD or PARK5, is a cysteine protease with a molecular weight of approximately 25 kDa. Next to its hydrolase activity UCHL1 also possesses ligase activity, 3,4 thereby the protein repertoire is multivalent regulated by its involvement in the cellular protein degradation and stabilization processes as well as in the homeostasis of the ub balance. Although UCHL1 is mainly expressed in neuronal and neuroendocrine tissues and represents about 2% of the total protein content of the brain, 3 it is also found in the tubule epithelium of the kidney, 5,6 in ovary 7 as well as in testis. 8 In neurodegenerative diseases such as Alzheimer's (AD) or Parkinson's disease (PD), an altered expression of UCHL1 could be indicated 9,10 suggesting that...

The de-ubiquitinase UCHL1 promotes gastric cancer metastasis via the Akt and Erk1/2 pathways

“…In melanoma, UCHL1 promotes cell proliferation via Erk1/2 activation [11]. Microarray data revealed that inhibition of UCHL1 suppresses expression of genes involved in proliferation and migration pathways, and p-Akt is downregulated in UCHL1 siRNA-expressing 293T cells [26].…”

“…Xiang et al have reported that UCHL1 induces G0/G1 cell cycle arrest and apoptosis through stabilizing p53 in breast cancer [6]. On the other hand, UCHL1 is also considered as an oncogene in cancers including non-small lung cancer, lymphoma, prostate cancer, colorectal cancer, melanoma, as well as osteosarcoma [7][8][9][10][11][12]. Meanwhile, Lien et al also demonstrated that high expression of UCHL1 in metaplastic carcinomas of the breast is related to epithelial-mesenchymal transition (EMT) [13].…”

Proteomic identification of proteins differentially expressed following overexpression of hTERT (human telomerase reverse transcriptase) in cancer cells

“…It is a cysteine protease belongs to the UCH proteases family and has also acquired E3 ubiquitin-protein ligase activity and stabilizes ubiquitin monomers in vivo [37]. This protein has heterogeneous expression in cancer cells and performs both tumor inhibition and promoting functions [38]. Down regulation of this protein in U2OS cells after hTERT overexpression indicates that hTERT modulates the expression of this deubiquitinating enzyme to avoid proteosomal degradation of itself.…”

Reprogramming human A375 amelanotic melanoma cells by catalase overexpression: Upregulation of antioxidant genes correlates with regression of melanoma malignancy and with malignant progression when downregulated

“…Besides, primary lesions present higher UCHL1 expression than metastatic lesions [21]. Suppression of UCHL1 was postulated as an early step of melanoma development, given that melanocytes present high levels of UCHL1, while benign nevi lack this protein [34]. Moreover, high levels of MTSS1, an actin-binding protein, inhibited migration in fibroblasts [35] and in glioblastoma cells inhibited cell growth, colony formation, migration and invasion [36].…”