Ras-association domain family 1C protein promotes breast cancer cell migration and attenuates apoptosis.

BACKGROUND: The Ras association domain family 1 (RASSF1) gene is a Ras effector encoding two major mRNA forms, RASSF1A and RASSF1C, derived by alternative promoter selection and alternative mRNA splicing. RASSF1A is a tumor suppressor gene. However, very little is known about the function of RASSF1C both in normal and transformed cells. METHODS: Gene silencing and over-expression techniques were used to modulate RASSF1C expression in human breast cancer cells. Affymetrix-microarray analysis was performed using T47D cells over-expressing RASSF1C to identify RASSF1C target genes. RT-PCR and western blot techniques were used to validate target gene expression. Cell invasion and apoptosis assays were also performed. RESULTS: In this article, we report the effects of altering RASSF1C expression in human breast cancer cells. We found that silencing RASSF1C mRNA in breast cancer cell lines (MDA-MB231 and T47D) caused a small but significant decrease in cell proliferation. Conversely, inducible over-expression of RASSF1C in breast cancer cells (MDA-MB231 and T47D) resulted in a small increase in cell proliferation. We also report on the identification of novel RASSF1C target genes. RASSF1C down-regulates several pro-apoptotic and tumor suppressor genes and up-regulates several growth promoting genes in breast cancer cells. We further show that down-regulation of caspase 3 via overexpression of RASSF1C reduces breast cancer cells' sensitivity to the apoptosis inducing agent, etoposide. Furthermore, we found that RASSF1C over-expression enhances T47D cell invasion/migration in vitro. CONCLUSION: Together, our findings suggest that RASSF1C, unlike RASSF1A, is not a tumor suppressor, but instead may play a role in stimulating metastasis and survival in breast cancer cells.

RASSF1C modulates the expression of a stem cell renewal gene, PIWIL1.

BACKGROUND: RASSF1A and RASSF1C are two major isoforms encoded by the Ras association domain family 1 (RASSF1) gene through alternative promoter selection and mRNA splicing. RASSF1A is a well established tumor suppressor gene. Unlike RASSF1A, RASSF1C appears to have growth promoting actions in lung cancer. In this article, we report on the identification of novel RASSF1C target genes in non small cell lung cancer (NSCLC). METHODS: Over-expression and siRNA techniques were used to alter RASSF1C expression in human lung cancer cells, and Affymetrix-microarray study was conducted using NCI-H1299 cells over-expressing RASSF1C to identify RASSF1C target genes. RESULTS: The microarray study intriguingly shows that RASSF1C modulates the expression of a number of genes that are involved in cancer development, cell growth and proliferation, cell death, and cell cycle. We have validated the expression of some target genes using qRT-PCR. We demonstrate that RASSF1C over-expression increases, and silencing of RASSF1C decreases, the expression of PIWIL1 gene in NSCLC cells using qRT-PCR, immunostaining, and Western blot analysis. We also show that RASSF1C over-expression induces phosphorylation of ERK1/2 in lung cancer cells, and inhibition of the MEK-ERK1/2 pathway suppresses the expression of PIWIL1 gene expression, suggesting that RASSF1C may exert its activities on some target genes such as PIWIL1 through the activation of the MEK-ERK1/2 pathway. Also, PIWIL1 expression is elevated in lung cancer cell lines compared to normal lung epithelial cells. CONCLUSIONS: Taken together, our findings provide significant data to propose a model for investigating the role of RASSF1C/PIWIL1 proteins in initiation and progression of lung cancer.

The yeast SUMO isopeptidase Smt4/Ulp2 and the polo kinase Cdc5 act in an opposing fashion to regulate sumoylation in mitosis and cohesion at centromeres.

Post-translation modification through the SUMO pathway is cell cycle regulated, with specific SUMO conjugates accumulating in mitotic cells. The basis for this regulation, however, and its functional significance remain poorly understood. We present evidence that in budding yeast sumoylation during mitosis may be controlled through the SUMO deconjugating enzyme Smt4/Ulp2. We isolated the polo kinase Cdc5 as an Ulp2-interacting protein, and find a C-terminal region of Ulp2 is phosphorylated during mitosis in a Cdc5-dependent manner. cdc5 mutants display reduced levels of mitotic SUMO conjugates, suggesting Cdc5 may negatively regulate Ulp2 to promote sumoylation. Previously, we found one phenotype associated with ulp2 mutants is an inability to maintain chromatid cohesion at centromere-proximal chromosomal regions. We now show this defect is rescued by inactivating Cdc5, indicating Ulp2 maintains cohesion by counter-acting Cdc5 activity. The cohesinregulator Pds5 is a likely target of this pathway, as Cdc5 overproduction forces Pds5 dissociation from chromosomes and Pds5 overproduction restores cohesion in ulp2 mutants. Overall, these observations reveal Cdc5 is a novel regulator of the SUMO pathway and suggest the outlines of a broader circuitry in which Ulp2 and Cdc5 act in a mutually antagonistic fashion to modulate maintenance and dissolution of cohesion at centromeres.