Small GTPase proteins such as Ras are key regulators of cellular proliferation and are activated by guanine nucleotide exchange/releasing factors (GEFs/GRFs). Three classes of Ras GRFs have been identified to date, represented by Sos1/2, Ras-GRF1/2 and Ras-GRP. Here, we describe a novel candidate Ras activator, cyclic nucleotide rasGEF (CNrasGEF), which contains CDC25, Ras exchange motif (REM), Ras-association (RA), PDZ and cNMP (cAMP/cGMP) binding (cNMP-BD) domains, two PY motifs and a carboxy-terminal SxV sequence. CNrasGEF can activate Ras in vitro, and it binds cAMP directly via its cNMP-BD. In cells, CNrasGEF activates Ras in response to elevation of intracellular cAMP or cGMP, or treatment with their analogues 8-Br-cAMP or 8-Br-cGMP, independently of protein kinases A and G (PKA and PKG). This activation is prevented in CNrasGEF lacking its CDC25 domain or cNMP-BD. CNrasGEF can also activate the small GTPase Rap1 in cells, but this activation is constitutive and independent of cAMP. CNrasGEF is expressed mainly in the brain and is localized at the plasma membrane, a localization dependent on the presence of intact PDZ domain but not the SxV sequence. These results suggest that CNrasGEF may directly connect cAMP-generating pathways or cGMP-generating pathways to Ras.

Integrins control a variety of signal transduction pathways central to cell survival, proliferation, and differentiation and their functions and expression levels are altered in many types of cancer. Although alpha5beta1 is one of the most studied integrins in cancer, its functions in different aspects of this disease have not been completely elucidated. In particular, controversial data exist on its role in tumor invasion and metastasis. In order to establish mechanisms underlying involvement of alpha5beta1 integrin in invasion, we depleted its expression in MCF-7Dox human breast carcinoma cells via siRNA. We demonstrated that concomitant to alpha5beta1 integrin depletion, was a sharp decrease in MMP-2 collagenase expression and inhibition of the invasiveness of these cells in vitro. Similar reduction of invasion potential was observed upon siRNA-mediated silencing of the MMP-2 gene. Down-regulation of alpha5beta1 integrin was accompanied by a substantial decrease in the amounts of active (phosphorylated) forms of Akt, Erk1/2 kinases and c-Jun oncoprotein. Moreover, in MCF-7Dox cells, blocking the activity of above kinases by specific inhibitors strongly reduced expression of MMP-2 and c-Jun, and suppressed invasion of the cells in vitro. Similar results were observed upon siRNA-mediated silencing of c-Jun expression. Co-immunoprecipitation experiments demonstrated that alpha5beta1 integrin interacts with MMP-2 collagenase on the surface of MCF-7Dox breast carcinoma and SKMel-147 human melanoma cells. Our data suggest that alpha5beta1 integrin controls invasion of the studied cells via regulation of MMP-2 collagenase expression which can occur either through signaling pathways involving PI-3K, Akt, and Erk protein kinases and the c-Jun or via direct recruitment of MMP-2 to the cell surface.

Intracerebral and intraperitoneal inoculation with β-amyloid-rich brain extracts originating from patients with Alzheimer's disease as well as intracerebral injection of aggregates composed of synthetic Aβ can induce cerebral β-amyloidosis, and associated cognitive dysfunctions in susceptible animal hosts. We have found that repetitive intravenous administration of 100 μg of synthetic peptide corresponding to isoAsp7-containing Aβ(1-42), an abundant age-dependent Aβ isoform present both in the pathological brain and in synthetic Aβ preparations, robustly accelerates formation of classic dense-core congophilic amyloid plaques in the brain of β-amyloid precursor protein transgenic mice. Our findings indicate this peptide as an inductive agent of cerebral β-amyloidosis in vivo.