Epigenetic inactivation of RASSF1A in lung and breast cancers and malignant phenotype suppression.

BACKGROUND: The recently identified RASSF1 locus is located within a 120-kilobase region of chromosome 3p21.3 that frequently undergoes allele loss in lung and breast cancers. We explored the hypothesis that RASSF1 encodes a tumor suppressor gene for lung and breast cancers. METHODS: We assessed expression of two RASSF1 gene products, RASSF1A and RASSF1C, and the methylation status of their respective promoters in 27 non-small-cell lung cancer (NSCLC) cell lines, in 107 resected NSCLCs, in 47 small-cell lung cancer (SCLC) cell lines, in 22 breast cancer cell lines, in 39 resected breast cancers, in 104 nonmalignant lung samples, and in three breast and lung epithelial cultures. We also transfected a lung cancer cell line that lacks RASSF1A expression with vectors containing RASSF1A complementary DNA to determine whether exogenous expression of RASSF1A would affect in vitro growth and in vivo tumorigenicity of this cell line. All statistical tests were two-sided. RESULTS: RASSF1A messenger RNA was expressed in nonmalignant epithelial cultures but not in 100% of the SCLC, in 65% of the NSCLC, or in 60% of the breast cancer lines. By contrast, RASSF1C was expressed in all nonmalignant cell cultures and in nearly all cancer cell lines. RASSF1A promoter hypermethylation was detected in 100% of SCLC, in 63% of NSCLC, in 64% of breast cancer lines, in 30% of primary NSCLCs, and in 49% of primary breast tumors but in none of the nonmalignant lung tissues. RASSF1A promoter hypermethylation in resected NSCLCs was associated with impaired patient survival (P =.046). Exogenous expression of RASSF1A in a cell line lacking expression decreased in vitro colony formation and in vivo tumorigenicity. CONCLUSION: RASSF1A is a potential tumor suppressor gene that undergoes epigenetic inactivation in lung and breast cancers through hypermethylation of its promoter region.

Role of SHIP in FcgammaRIIb-mediated inhibition of Ras activation in B cells.

Previous studies by our lab and others established that co-crosslinking sIg and IgG receptor FcgammaRIIb in B cells in a feedback suppression model (negative signaling) promoted tyrosine phosphorylation of the inositol 5-phosphatase SHIP and its interaction with Shc and that these events were associated with inhibition of the Ras pathway. We therefore hypothesized a competition model in which the SH2 domain of SHIP competes with that of Grb2 for binding to phospho-Shc to inhibit the Ras pathway. Here, we provide evidence consistent with this hypothesis. First, FcgammaRIIb-deficient B cells, which do not undergo SHIP tyrosine phosphorylation nor interaction with Shc, displayed an active Ras pathway under negative signaling conditions; reconstitution of FcgammaRIIb expression restored the block in Ras. Second, under conditions of negative signaling leading to SHIP-Shc interaction in wild-type B cells, we observed a profound reduction in the activation-induced association of Grb2 to Sos. Experiments reported here and elsewhere revealed the Grb2-Sos interaction required the engagement of the Grb2 SH2 domain by phospho-Shc. Third, we demonstrated that phospho-Shc cannot concomitantly bind Grb2 and SHIP, indicating that the two proteins competed for the same phospho-tyrosine residue on Shc. These data are consistent with the proposed competition model, and further indicate that the activation induced Grb2-Sos association is rate limiting for Ras activation.

SODs, DNA binding and cleavage studies of new Mn(III) complexes with 2-((3-(benzyloxy)pyridin-2-ylimino)methyl)phenol.

Newly synthesized ligand [2-((3-(benzyloxy)pyridin-2-ylimino)methyl)phenol] (Bpmp) react with manganese(II) to form mononuclear complexes [Mn(phen)(Bpmp)(CH3COO)(H2O)]·4H2O (1), (phen=1,10-phenanthroline) and [Mn(Bpmp)2(CH3COO)(H2O)]·5H2O (2). These complexes were characterized by elemental analysis, IR, (1)H NMR, Mass, UV-vis spectral studies. Molar conductance and thermogravimetric analysis of these complexes were also recorded. The in vitro SOD mimic activity of Mn(III) complexes were carried out and obtained with good result. The DNA-binding properties of the complexes 1 and 2 were investigated by UV-spectroscopy, fluorescence spectroscopy and viscosity measurements. The spectral results suggest that the complexes 1 and 2 can bind to Calf thymus DNA by intercalation mode. The cleavage properties of these complexes with super coiled pUC19 have been studied using the gel electrophoresis method, wherein both complexes 1 and 2 displayed chemical nuclease activity in the absence and presence of H2O2 via an oxidative mechanism. All the complexes inhibit the growth of both Gram positive and Gram negative bacteria to competent level. The MIC was determined by microtiter method.

Contribution of the ERK5/MEK5 pathway to Ras/Raf signaling and growth control.

The activity of the catalytic domain of the orphan MAP kinase ERK5 is increased by Ras but not Raf-1 in cells, which suggests that ERK5 might mediate Raf-independent signaling by Ras. We found that Raf-1 does contribute to Ras activation of ERK5 but in a manner that does not correlate with Raf-1 catalytic activity. A clue to the mechanism of action of Raf-1 on ERK5 comes from the observation that endogenous Raf-1 binds to endogenous ERK5, suggesting the involvement of regulatory protein-protein interactions. This interaction is specific because Raf-1 binds only to ERK5 and not ERK2 or SAPK. Finally, we demonstrate the ERK5/MEK5 pathway is required for Raf-dependent cellular transformation and that a constitutively active form of MEK5, MEK5DD, synergizes with Raf to transform NIH 3T3 cells. These observations suggest that ERK5 plays a large role in Raf-1-mediated signal transduction.