RASSF7 negatively regulates pro-apoptotic JNK signaling by inhibiting the activity of phosphorylated-MKK7

Abstract

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 ...

RASSF tumor suppressor gene family: Biological functions and regulation

“…During initial stress, RASSF7 associates with N-Ras, inhibiting MKK7/JNK signaling pathway and inducing cell growth [104]. However, the anti-apoptotic property of RASSF7 is soon lost following prolonged exposure of UV radiation, due to degradation of RASSF7 through ubiquitination [104]. Thus, the mounting evidence so far argues a tumor suppressor function for this RASSF protein.…”

“…A recent study illustrated the role of RASSF7 in cell survival during periods of stress. During initial stress, RASSF7 associates with N-Ras, inhibiting MKK7/JNK signaling pathway and inducing cell growth [104]. However, the anti-apoptotic property of RASSF7 is soon lost following prolonged exposure of UV radiation, due to degradation of RASSF7 through ubiquitination [104].…”

A Systems Biology Approach Using Transcriptomic Data Reveals Genes and Pathways in Porcine Skeletal Muscle Affected by Dietary Lysine

“…Lysine deficiency also decreased the expression of RASSF7 (Ras association domain family member 7), which is a member of the N-terminal Ras association domain family. RASSF7 negatively regulates pro-apoptotic JNK signaling [57], which is a member of an evolutionarily conserved sub-family of mitogen-activated protein (MAP) kinases and important as both positive and negative modulators of apoptosis [58]. Knocking down of RASSF7 has been shown to inhibit cell growth [59].…”

MAP Kinase-Mediated and MLCK-Independent Phosphorylation of MLC20 in Smooth Muscle Cells

“…The concentration ranges used by most previous researchers are 10-30 µM (Renlund et al, 2008). The recently used concentration is 20 µM (Takahashi et al, 2011). The ERK inhibitors include the PD98059, ERK Inhibitor II (C18H13N7), U0126, and inhibitory peptide.…”