Blockade of v-Src-stimulated tumor formation by the Src homology 3 domain of Crk-associated substrate (Cas)

miR-3174 Contributes to Apoptosis and Autophagic Cell Death Defects in Gastric Cancer Cells by Targeting ARHGAP10

Gastric cancer (GC) is a major health problem worldwide because of its high morbidity and mortality. Considering the well-established roles of miRNA in the regulation of GC carcinogenesis and progression, we screened differentially expressed microRNAs (miRNAs) by using The Cancer Genome Atlas (TCGA) and the GEO databases. We found that miR-3174 was the most significantly differentially expressed miRNA in GC. Ectopic miR-3174 expression was also detected in clinical GC patient samples and cell lines and associated with poor patient prognosis. Apoptosis and autophagic cell death are two types of programmed cell death, whereas both are deficient in gastric cancer. Our functional analyses demonstrated that miR-3174 inhibited mitochondria-dependent apoptosis and autophagic cell death in GC. Moreover, high expression of miR-3174 also resulted in Cisplatin resistance in GC cells. Using bioinformatics analyses combined with in vitro and in vivo experiments, we determined that miR-3174 directly targets ARHGAP10. Notably, ARHGAP10 promoted mitochondria-dependent apoptosis by enhancing p53 expression, which was followed by Bax trans-activation and caspase cleavage. ARHGAP10 also facilitated autophagic cell death by suppressing mammalian target of rapamycin complex 1 (mTOC1) activity. Our results reveal a potential miRNA-based clinical therapeutic target that may also serve as a predictive marker for GC.

Overexpression of CASS4 promotes invasion in non-small cell lung cancer by activating the AKT signaling pathway and inhibiting E-cadherin expression

The role of Crk-associated substrate (CAS) family members in regulating invasion and metastasis has been described in several cancers. As the fourth member of the CAS family, CASS4 is also related with positive lymph node metastasis and poor prognosis in lung cancer. However, the underlying mechanisms and downstream effectors of CASS4 in the development and progression of non-small cell lung cancer (NSCLC) remain unclear. In this study, CASS4 overexpression inhibited E-cadherin expression and enhanced invasion in NSCLC cell line transfected with CASS4 plasmid, while CASS4 depletion upregulated E-cadherin expression and inhibited invasion in NSCLC cell line transfected with CASS4 siRNA. The effect of CASS4 overexpression in facilitating invasion of NSCLC cells was reversed by restoring E-cadherin expression, which indicates that CASS4 may promote invasion by inhibiting E-cadherin expression. Subsequent immunohistochemistry results confirmed that CASS4 overexpression correlated with loss of E-cadherin expression. We next investigated the phosphorylation levels of focal adhesion kinase (FAK), p38, extracellular signal-related kinase (ERK), and AKT after CASS4 plasmid or CASS4 siRNA transfection. CASS4 facilitated AKT (Ser473) phosphorylation. Treatment with an AKT phosphorylation inhibitor reversed the increased invasive capacity and downregulation of E-cadherin protein induced by CASS4 overexpression. Taken together, the present results indicate that CASS4 may promote NSCLC invasion by activating the AKT signaling pathway, thereby inhibiting E-cadherin expression.

RRIG1 mediates effects of retinoic acid receptor beta2 on tumor cell growth and gene expression through binding to and inhibition of RhoA

The expression of retinoic acid receptor beta2 (RAR-beta2) is frequently lost in various cancers and their premalignant lesions. However, the restoration of RAR-beta2 expression inhibits tumor cell growth and suppresses cancer development. To understand the molecular mechanisms responsible for this RAR-beta2-mediated antitumor activity, we did restriction fragment differential display-PCR and cloned a novel retinoid receptor-induced gene 1 (RRIG1), which is differentially expressed in RAR-beta2-positive and RAR-beta2-negative tumor cells. RRIG1 cDNA contains 2,851 bp and encodes a protein with 276 amino acids; the gene is localized at chromosome 9q34. Expressed in a broad range of normal tissues, RRIG1 is also lost in various cancer specimens. RRIG1 mediates the effect of RAR-beta2 on cell growth and gene expression (e.g., extracellular signal-regulated kinase 1/2 and cyclooxygenase-2). The RRIG1 protein is expressed in the cell membrane and binds to and inhibits the activity of a small GTPase RhoA. Whereas induction of RRIG1 expression inhibits RhoA activation and f-actin formation and consequently reduces colony formation, invasion, and proliferation of esophageal cancer cells, antisense RRIG1 increases RhoA activity and f-actin formation and thus induces the colony formation, invasion, and proliferation of these cells. Our findings therefore show a novel molecular pathway involving RAR-beta2 regulation of RRIG1 expression and RRIG1-RhoA interaction. An understanding of this pathway may translate into better control of human cancer.

Differential Effect of the Focal Adhesion Kinase Y397F Mutant on v-Src-Stimulated Cell Invasion and Tumor Growth

Upon cell adhesion to extracellular matrix proteins, focal adhesion kinase (FAK) rapidly undergoes autophosphorylation on its Tyr-397 which consequently serves as a binding site for the Src homology 2 domains of the Src family protein kinases and several other intracellular signaling molecules. In this study, we have attempted to examine the effect of the FAK Y397F mutant on v-Src-stimulated cell transformation by establishing an inducible expression of the Y397F mutant in v-Src-transformed FAK-null (FAK(-/-)) mouse embryo fibroblasts. We found that the FAK Y397F mutant had both positive and negative effects on v-Src-stimulated cell transformation; it promoted v-Src-stimulated invasion, but on the other hand it inhibited the v-Src-stimulated anchorage-independent cell growth in vitro and tumor formation in vivo . The positive effect of the Y397F mutant on v-Src-stimulated invasion was correlated with an increased expression of matrix metalloproteinase-2, both of which were inhibited by the specific phosphatidylinositol 3-kinase inhibitor wortmannin or a dominant negative mutant of AKT, suggesting a critical role for the phosphatidylinositol 3-kinase/AKT pathway in both events. However, the expression of the Y397F mutant rendered v-Src-transformed FAK(-/-) cells susceptible to anoikis, correlated with suppression on v-Src-stimulated activation of ERK and AKT. In addition, under anoikis stress, the induction of the Y397F mutant in v-Src-transformed FAK(-/-) cells selectively led to a decrease in the level of p130(Cas), but not other focal adhesion proteins such as talin, vinculin, and paxillin. These results suggest that FAK may increase the susceptibility of v-Src-transformed cells to anoikis by modulating the level of p130(Cas).