Down-regulation of the expression of RB18A/MED1, a cofactor of transcription, triggers strong tumorigenic phenotype of human melanoma cells.
The RB18A/MED1 human gene, also named TRAP220, DRIP205 and PBP, encodes for a single 205 kDa component, which interacts with nuclear receptors and transcription factors. RB18A/MED1 chromosome localization on locus 17q12-q21.1 suggests its involvement in human cancers. We herein analyzed RB18A/MED1 expression in human melanoma cell lines. We found that RB18A/MED1 is either highly or weakly expressed in melanoma cells, depending on their respectively non or highly-tumorigenic phenotype. We therefore investigated the possible existence of a relationship between the RB18A/MED1 expression level and melanoma cell phenotype. For this purpose, we down-regulated RB18A/MED1 expression by transfecting melanoma cells with a RB18A/MED1 small interfering RNA (siRNA), specific to the 3'-untranslated region of native RB18A/MED1 RNA, already demonstrated to inhibit specifically RB18A/MED1 protein expression. A nonspecific (scrambled) siRNA was used as control. This RB18A/MED1 siRNA did not modify the expression of cathepsin L forms or lamin A/C, nor the secretion of procathepsin L and MMP2 in transfected cells. Analysis using a microarray membrane with 113 cancer-related genes, western blot and specific tests, demonstrated that RB18A/MED1 knockdown significantly inhibits tissue inhibitor of metalloproteinase-3 expression, and increases uPAR expression, two genes well known to be involved in melanoma cell invasion, through modifications of the tumor microenvironment. Indeed, RB18A/MED1 knockdown in melanoma cells in vitro increased their invasive properties, without modification of cell proliferation. Furthermore, RB18A/MED1 knockdown in vivo switched melanoma phenotype from non to strongly-tumorigenic in nude mice. Our data thus demonstrated for the first time that a decrease of RB18A/MED1 expression in human melanoma cells increases their tumorigenic phenotype.
Ndong
Jean de La Croix
Jde L
INSERM U.672, Immunochemistry of Cell Regulations and Viral Interactions, EVRY Cedex, France.
Jean
Didier
D
Rousselet
Nathalie
N
Frade
Raymond
R
D000818:Animals; D045744:Cell Line, Tumor; D015536:Down-Regulation; D006801:Humans; D008297:Male; D056913:Mediator Complex Subunit 1; D008545:Melanoma / Q000473:pathology*; D051379:Mice; D008807:Mice, Inbred BALB C; D009361:Neoplasm Invasiveness; D010641:Phenotype; D034741:RNA, Small Interfering / Q000235:genetics; D055293:Receptors, Urokinase Plasminogen Activator / Q000235:genetics; D019717:Tissue Inhibitor of Metalloproteinase-3 / Q000235:genetics; D014157:Transcription Factors / Q000032:analysis / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*
C538855:MED1 protein, human; C538856:Med1 protein, mouse; D056913:Mediator Complex Subunit 1; D034741:RNA, Small Interfering; D055293:Receptors, Urokinase Plasminogen Activator; D019717:Tissue Inhibitor of Metalloproteinase-3; D014157:Transcription Factors