The Role of miR-29a and miR-143 on the Anti-apoptotic MCL-1/cIAP-2 Genes Expression in EGFR Mutated Non-small Cell Lung Carcinoma Patients.

The survival rate of lung cancer is low due to the high frequency of drug resistance in patients with mutations in the driver genes. Overexpression of anti-apoptotic genes is one of the most prominent features of tumor drug resistance. EGFR signaling induces the expression of anti-apoptotic genes. Also, microRNAs (miRNAs) have a critical role in regulating biological functions such as apoptosis; a process mostly eluded in cancer progression. The mutation screening was performed on one thousand non-small cell lung carcinoma patients to enroll clinical samples in this study. Bioinformatics analysis predicted that miRNAs (miR-29a, miR-143) might regulate MCL-1 and cIAP-2 expression. We investigated the expression of MCL-1, cIAP-2, miR-29a, and miR-143 encoding genes in adenocarcinoma patients with or without EGFR mutations before treatment. The potential role of miR-29a and miR-143 on gene expression was evaluated by overexpression and luciferase assays in HEK-293T cells. EGFR mutations were found in 262 patients (26.2%) with a greater incidence in females (36.23% vs. 20.37%, P = 0.001). The expression levels of MCL-1 and cIAP-2 genes in patients with mutated EGFR were higher than those of wild-type EGFR. In contrast, compared to those of patients with wild-type EGFR, the expression levels of miR-29a and miR-143 were lower in the patients carrying EGFR mutations. In cell culture, overexpression of miR-29a and miR-143 significantly downregulated the expression of MCL-1 and cIAP-2. Dual-luciferase reporter experiments confirmed that miR-29a and miR-143 target MCL-1 and cIAP-2 mRNAs, respectively. Our results suggest that upregulation of EGFR signaling in lung cancer cells may increase anti-apoptotic MCL-1 and cIAP-2 gene expression, possibly through downregulation of miR-29a-3p and miR-143-3p.

The Canonical Wnt Signaling (Wnt/ß-Catenin Pathway): A Potential Target for Cancer Prevention and Therapy.

Precise regulation of signal transduction pathways is crucial for normal animal development and for maintaining cellular and tissue homeostasis in adults. The Wnt/Frizzled-mediated signaling includes canonical and non-canonical signal transduction pathways. Upregulation or downregulation of the canonical Wnt signaling (or the Wnt/ß-Catenin signal transduction) leads to a variety of human diseases, including cancers, neurodegenerative disorders, skin and bone diseases, and heart deficiencies. Therefore, Wnt/ß-Catenin signal transduction is a potential clinical target for the treatment of not only human cancers but also some other human chronic diseases. Here, some recent results including those from my laboratory highlighting the role of Wnt/ß-Catenin signal transduction in human cancers will be reviewed. After a brief overview on canonical Wnt signaling and introducing some critical ß-Catenin/T-cell factor-target genes, the interaction of canonical Wnt signaling with some common human cancers will be discussed. In the end, the different segments of the aforesaid signaling pathway, which have been considered as targets for clinical purposes, will be scrutinized.

Regulation of GSK-3beta and beta-Catenin by Galphaq in HEK293T cells.

Recent studies have shown that heterotrimeric G proteins are involved in the regulation of the canonical Wnt/beta-Catenin pathway. However, the mechanism(s) behind this involvement is (are) poorly understood. Our previous results have shown that activation of Galphaq in Xenopus oocytes leads to inhibition of GSK-3beta and stabilization of the beta-Catenin protein, suggesting that Galphaq might stabilize beta-Catenin via inhibition of GSK-3beta. In this study, we have observed similar results in HEK293T cells. In these cells optimal activation of endogenous Galphaq by expressing M3-muscarinic acetylcholine receptor (with or without carbachol treatment), or exposing the cells to thrombin led to an increase of 2 to 3-fold in endogenous cytoplasmic beta-Catenin protein levels. In addition, expression of the activated mutant of Galphaq (GalphaqQL) dramatically enhanced accumulation of exogenous beta-Catenin with no effect on beta-catenin (CTNNB1) gene transcription. The Galphaq-mediated cellular accumulation of beta-Catenin was blocked by expression of a minigene encoding a Galphaq specific inhibitory peptide but not by a minigene encoding a Galphas blocking peptide. Also, expression of GalphaqQL led to a significant reduction in GSK-3beta kinase activity, supporting the idea that the positive role of Galphaq signaling in inducing cellular accumulation of beta-Catenin is mediated through inhibition of GSK-3beta.

Activators of G proteins inhibit GSK-3beta and stabilize beta-Catenin in Xenopus oocytes.

Frizzled proteins, the receptors for Wnt ligands have seven hydrophobic transmembrane domains, a structural feature of G protein coupled receptors. Therefore a role for G proteins in the regulation of Wnt signaling has been proposed. Here I have used Xenopus oocytes to study the role of heterotrimeric G proteins in the regulation of GSK-3beta and beta-Catenin, two essential components of the canonical Wnt pathway. In these cells, general activators of G proteins such as GTPgamma-S and AlF4(-) increase beta-Catenin stability and decrease GSK-3beta mediated phosphorylation of the microtubule associated protein, Tau. Among several members of Galpha proteins tested, expression of a constitutively active mutant of Galphaq (GalphaqQL) led to a significant increase in accumulation of beta-Catenin. The stabilization of beta-Catenin mediated by Galphaq was reversed by a Galphaq specific inhibitor, Gp-antagonist 2A, but not by a specific blocking peptide for Galphas. Expression of GalphaqQL also inhibited GSK-3beta-mediated tau phosphorylation in Xenopus oocytes. These results support a role for the Gq class of G proteins in the regulation of Wnt/beta-Catenin signal transduction.

The adenoviral E1A induces p21WAF1/CIP1 expression in cancer cells.

The adenovirus-5 E1A gene encodes two main proteins of 289 and 243 amino acid residues from 13S and 12S mRNA, respectively. The E1A gene products function as transcriptional regulators and have anti-tumor activities. Despite the fact that E1A gene therapy has been tested in clinical trials, the molecular mechanism by which it suppresses tumor cell growth is still not completely understood. Here, we show that E1A increases the expression of the cyclin-dependent kinase (CDK) inhibitor p21(WAF1/CIP1), which inhibits cell growth. We further show that 13S E1A, but not 12S E1A, can transactivate the p21 promoter through Sp1 sites. Interestingly, the E1A-induced transactivation occurs only in cancer cells, not in normal cells. This study provides new insight into the links between E1A and the CDK inhibitor and may have important clinical implications.