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 0 -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. ' 2009 Wiley-Liss, Inc.Key words: RB18A; TRAP220; DRIP205; PBP; melanoma; tumor progression; TIMP-3; uPARThe distinct names RB18A, TRAP220, DRIP205 and PBP refer to the same gene, which encodes for a single 205 kDa component. This protein acts as a cofactor of transcription and binds to nuclear hormone receptors in the presence of their cognate ligand, as a member of the transcriptional machinery. Under these different names, its first molecular properties and biological functions have been identified. Under the name RB18A, which is short for recognized by PAb1801 Antibody, an anti-p53 moAb, we discovered this new human gene from human B lymphoma cells, on the basis of its common antigenic determinants with the oncoprotein p53, 1 which interacts with the Epstein-Barr virus/C3d receptor.2 Despite the absence of any significant homology between the RB18A and p53 nucleotide sequences, both proteins shared at least 3 antigenic determinants, as recognized by 2 other anti-p53 moAbs, i.e. PAb421 and DO-1. Later, this human gene was described by others, as TRAP220, for thyroid receptor associated protein 220, 3 and DRIP205, for vitamin D receptor interacting protein 205. 4 ...
