RESUMO
The RBM5/H37 gene is located at the most 'sought-after' tumor suppressor locus in lung cancer, 3p21.3. This region of most frequent chromosomal deletion found at the earliest stage in lung cancer development houses 19 genes, many of which may act together as a 'tumor suppressor group', representing one of the most promising opportunities for development of new diagnostics/prognostics and therapeutics for lung cancer as well as for many other types of cancers. For the past decade, we have demonstrated tumor suppressor function of RBM5 in vitro and in vivo involving cell cycle arrest and apoptosis, as well as loss of RBM5 mRNA and protein expression in primary lung tumors. Here we report our latest data suggesting that RBM5 may regulate inhibition of metastasis in lung cancer. We performed cDNA microarray to identify global gene expression changes caused by RBM5 gene knockdown. In order to identify "consensus" pathways consistently deregulated by RBM5 loss irrespective of genetic background, the experiments were repeated in three different lung cancer cell lines of varying RBM5 expression levels, a normal lung epithelial cell line, and a normal breast epithelial cell line. Both Gene Set Enrichment Analysis (GSEA) and individual gene analysis identified consistent, statistically significant gene expression changes common to all five cell pairs examined. Genes involved in the functions of cell adhesion, migration and motility, known to be important in the metastatic process, were upregulated with RBM5-knockdown. These genes include Rac1, ß-catenin, collagen, laminin and the overall gene set of the gene ontology group "proteinaceous extracellular matrix". Among these, we have focused on Rac1 and ß-catenin which play essential roles in cell movement downstream of Wnt signaling. We have confirmed increased protein expression of ß-catenin and increased protein activation of Rac1 with RBM5-knockdown. In addition, we found that RBM5 protein expression loss in primary lung tumors is correlated with increased lymph node metastasis in a small number of lung cancer patients. These data are corroborated by an independent report showing RBM5 as part of a 17-gene signature of metastasis in primary solid tumors. Taken together, the accumulated evidence suggests that RBM5 expression loss may increase the metastatic potential of tumors. Further study is warranted to evaluate the potential clinical utility of RBM5 in lung cancer diagnostics, prognostics and therapeutics.
Assuntos
Neoplasias da Mama/genética , Proteínas de Ciclo Celular/metabolismo , Proteínas de Ligação a DNA/metabolismo , Células Epiteliais/metabolismo , Neoplasias Pulmonares/genética , Metástase Linfática , Proteínas de Ligação a RNA/metabolismo , Proteínas Supressoras de Tumor/metabolismo , Neoplasias da Mama/metabolismo , Neoplasias da Mama/patologia , Adesão Celular/genética , Proteínas de Ciclo Celular/genética , Linhagem Celular Tumoral , Movimento Celular/genética , Cromossomos Humanos Par 3/genética , Proteínas de Ligação a DNA/genética , Células Epiteliais/patologia , Feminino , Regulação Neoplásica da Expressão Gênica , Humanos , Neoplasias Pulmonares/metabolismo , Neoplasias Pulmonares/patologia , Metástase Linfática/genética , Análise de Sequência com Séries de Oligonucleotídeos , RNA Interferente Pequeno/genética , Proteínas de Ligação a RNA/genética , Transdução de Sinais/genética , Proteínas Supressoras de Tumor/genética , Proteínas Wnt/metabolismo , beta Catenina/genética , beta Catenina/metabolismo , Proteínas rac1 de Ligação ao GTP/genética , Proteínas rac1 de Ligação ao GTP/metabolismoRESUMO
Loss of heterozygosity (LOH) at chromosome 3p21.3 is one of the most prevalent genetic disturbances occurring at the earliest stage of tumor development for a wide variety of human cancers, culminated in lung cancer. The 19 genes residing at 3p21.3 have been vigorously characterized for tumor suppressor activity and gene inactivation mechanism because of their potentially significant merits of clinical applications. Many of these 19 genes have been shown to manifest various growth inhibitory properties, however none of them are inactivated by coding mutations in their remaining allele as in the Knudson's two- hits hypothesis. Thus far the most prevailing, alternative gene inactivation mechanism known for the 3p21.3 TSGs is epigenetic silencing by promoter hypermethylation. Previously, we have focused our investigation on one of the 19 genes at 3p21.3, H37/RBM5, and demonstrated its tumor suppressor activity both in vitro and in vivo as well as its mRNA/protein expression loss from the remaining allele in a majority of the primary lung tumors examined. The current study tested our hypothesis that the H37 inactivation in primary lung tumors may, as seen in most of the other 3p21.3 TSGs, be due to hypermethylation in its promoter CpG islands. Contrary to this most plausible postulation, however, we found no evidence of epigenetic gene silencing for the H37 TSG. Here we suggest some of the possible, further- alternative means of the H37 gene expression loss in tumor, including defects in transcription and post-transcriptional/translational modifications as well as mechanisms related to haploinsufficiency.
