Members of the Ras-association domain family (RASSF) of proteins influence apoptosis and cell cycling but little is known about the mechanisms. Here, we show that RASSF7 interacts with N-Ras and mitogen-activated protein kinase kinase 7 (MKK7) to negatively regulate c-Jun N-terminal kinase (JNK) signaling. Stress-induced JNK activation and apoptosis were markedly enhanced in cells depleted of RASSF7 or N-Ras by RNAi knockdown. An interaction with RASSF7 promoted the phosphorylated state of MKK7 but inhibited this kinase's ability to activate JNK. RASSF7 required its RA domain for both interaction with GTP-bound N-Ras and the anti-apoptotic response to stress stimuli. Following prolonged stress, however, RASSF7's antiapoptotic effect was eliminated because of degradation of RASSF7 protein via the ubiquitin-proteasome pathway. Our results indicate that RASSF7 acts in concert with N-Ras to constitute a stress-sensitive temporary mechanism of apoptotic regulation. With initial stress, RASSF7/N-Ras promotes cell survival by inhibiting the MKK7/JNK pathway. However, with prolonged stress, RASSF7 protein undergoes degradation that allows cell death signaling to proceed. Our findings may account for the association of elevated RASSF7 with tumorigenesis. Members of the Ras-association domain family (RASSF) share a conserved motif called the RalGDS/AF6-type Ras association (RA) domain. 1-3 The vertebrate RASSF comprises the classical RASSF members, RASSF1-6, and the more recently identified N-terminal (NT) RASSF members, RASSF7-10. 1-3 Epigenetic silencing of most of RASSF genes has been observed at high frequencies in various tumor types. 1,2 In contrast, upregulation of RASSF7 has been noted in pancreatic, endometrial and ovarian cancers, 4-8 although no direct evidence exists indicating that RASSF7 promotes tumorigenesis.RASSF7 was originally identified as HRAS cluster 1 (HRC1), located within a cluster of genes situated about 32-kb upstream of HRAS1 on human chromosome 11p15. In Xenopus, knockdown of the RASSF7 homolog prevented cells from completing mitosis and caused a striking loss of tissue architecture in the neural tube. 9 However, the physiological functions of RASSF7 in mammals are unknown, and the signaling pathways in which RASSF7 participates remain a mystery.The c-Jun N-terminal kinase (JNK) enzymes function primarily in stress-activated signaling and are important as both positive and negative modulators of apoptosis, depending on the cellular context. 10,11 In response to cell stresses, such as heat shock, ultraviolet (UV) irradiation, hyperosmolarity and ischemia/reperfusion injury, MAP kinase kinase kinases (MAPKKKs) are activated. These enzymes then activate MAP kinase kinase 4 (MKK4; also known as SEK1) and/or MKK7, which in turn activate JNKs. 12,13 The extent and specificity of JNK activation serve as important signals for promoting the stabilization and transcriptional activity of JNK substrates, which then mediate cell survival and/or apoptosis. Although phosphatases capable of dephosphorylating ...

Cytoplasmic ribonucleoprotein granules, known as processing bodies (P-bodies), contain a common set of conserved RNA-processing enzymes, and mRNAs with AU-rich elements (AREs) are delivered to P-bodies for translational silencing. Although the dynamics of P-bodies is physically linked to cytoskeletal network, it is unclear how small GTPases are involved in the P-body regulation and the ARE-mRNA metabolism. We found here that glucose depletion activates RhoA GTPase and alters the P-body dynamics in HeLa cells. These glucose-depleted effects are reproduced by the overexpression of the RhoA-subfamily GTPases and conversely abolished by the inhibition of RhoA activation. Interestingly, both RhoA activation and glucose depletion inhibit the mRNA accumulation and degradation. These findings indicate that RhoA participates in the stress-induced rearrangement of P-bodies and the release of nucleated ARE-mRNAs for their stabilization.

Background: Di-Ras2 is a poorly characterized Ras-family GTPase specifically expressed in brain. Results: Di-Ras2 co-purifies with SmgGDS from cytosol, and the affinity of Di-Ras2 for guanine-nucleotides is reduced when complexed with SmgGDS. Conclusion: Di-Ras2 exits as a complex with SmgGDS in cytosol with lowered affinity for guanine nucleotides. Significance: Di-Ras2 activity may be atypically regulated by complex formation with SmgGDS.