ABSTRACT
'Cancer stem cells' (CSCs) are tumor cells with stem cell properties hypothesized to be responsible for tumorigenesis, metastatis, and resistance to treatment, and have been identified in different tumors including cutaneous melanoma, using stem cell markers such as CD133. This study explored expression of CD133 and other putative stem cell markers in uveal melanoma. Eight uveal melanoma cell lines were subjected to flow-cytometric (fluorescence-activated cell sorting) analysis of CD133 and other stem cell markers. Eight paraffin-embedded tumors were analyzed by immunohistochemistry for CD133, Pax6, Musashi, nestin, Sox2, ABCB5, and CD68 expressions. Ocular, uveal melanoma, and hematopoietic stem cell distributions of C-terminal and N-terminal CD133 mRNA splice variants were compared by reverse-transcription PCR. Fluorescence-activated cell sorting analysis revealed a population of CD133-positive/nestin-positive cells in cell lines Mel270, OMM 2.3, and OMM2.5. All cell lines studied were positive for nestin, CXCR-4, CD44, and c-kit. Immunohistochemistry identified cells positive for CD133, Pax6, Musashi, nestin, Sox2, ABCB5, and CD68 predominantly at the invading tumor front. C-terminal primers interacting with CD133 splice variant s2 detected a novel variant lacking exon 27. Differential expression of CD133 splice variants was found in iris, ciliary body, retina, and retinal pigment epithelium/choroid as well as in uveal melanoma cell lines. mRNA for nestin, Sox2, and Musashi was present in all studied cell lines. Uveal melanoma such as cutaneous melanoma may therefore contain CSCs. Further experiments are needed to isolate stem cell marker-positive cells, to evaluate their functional properties and to explore therapeutical approaches to these putative CSCs in uveal melanoma.
Subject(s)
Antigens, CD/biosynthesis , Glycoproteins/biosynthesis , Melanoma/metabolism , Neoplastic Stem Cells/metabolism , Uveal Neoplasms/metabolism , AC133 Antigen , Adult , Aged , Aged, 80 and over , Animals , Antigens, CD/genetics , Biomarkers, Tumor/biosynthesis , Biomarkers, Tumor/genetics , Female , Glycoproteins/genetics , Humans , Immunohistochemistry , Intermediate Filament Proteins/biosynthesis , Male , Melanoma/genetics , Melanoma/pathology , Mice , Middle Aged , Neoplastic Stem Cells/pathology , Nerve Tissue Proteins/biosynthesis , Nestin , Peptides/genetics , RNA, Messenger/biosynthesis , RNA, Messenger/genetics , Uveal Neoplasms/genetics , Uveal Neoplasms/pathologyABSTRACT
BACKGROUND/AIMS: Hepatocellular carcinomas (HCC) often show resistance to the effects of transforming growth factor-beta (TGF-beta). This study focuses on molecular mechanisms of this resistance to explore ways to overcome it. METHODS: Transcription and protein expression of TGF-beta type I and type II receptors (TGF-betaRI/RII) were analyzed in clinical HCCs and the human hepatoma cell lines HuH-7 and HepG2. HuH-7 cells were transiently and stably transfected with a constitutively active TGF-betaRI mutant (CA TGF-betaRI). Resulting growth kinetics, integrin expression, invasiveness, TGF-beta-mediated activation of human plasminogen activator inhibitor type-1 (PAI-1) promoter and Smad expression were determined. RESULTS: In clinical HCCs, there was less TGF-betaRII (6/10 cases) and more TGF-betaRI (8/10 cases) protein expression detectable in tumor compared to adjacent liver tissue. In HuH-7 cells, TGF-betaRII expression was likewise decreased. Cells transiently transfected with CA TGF-betaRI exhibited strong TGF-beta-related PAI-1 promoter activation. Stably transfected cells showed an attenuated response of the PAI-1 promoter, but increased Smad7 expression. Proliferation of stable clones was decreased. There was no change in integrin expression or invasiveness. CONCLUSIONS: Decreased TGF-betaRII protein expression might cause TGF-beta resistance in a subset of clinical HCCs. Stable transfection with CA TGF-betaRI reverses this in HuH-7 cells without increasing invasiveness.
