The yeast G-protein homolog is involved in the mating pheromone signal transduction system

LINC01526 Promotes Proliferation and Metastasis of Gastric Cancer by Interacting with TARBP2 to Induce GNG7 mRNA Decay

Simple Summary

Many long noncoding RNAs play an important role in gastric cancer progression. In this study, we focused on LINC01526. Through expression and functional analyses, we obtained a preliminary understanding of the pro-cancer role of LINC01526 in gastric cancer. Furthermore, RNA pull-down and RNA immunoprecipitation chip assays demonstrated that LINC01526 interacts with TARBP2, an RNA-binding protein controlling mRNA stability. Moreover, TARBP2 could bind and destabilize GNG7 transcripts. Finally, the rescue assay disclosed that LINC01526 promoted gastric cancer progression by interacting with TARBP2, leading to the degradation of GNG7 mRNA.

Abstract

Gastric cancer is the most common malignancy of the human digestive system. Long noncoding RNAs (lncRNAs) influence the occurrence and development of gastric cancer in multiple ways. However, the function and mechanism of LINC01526 in gastric cancer remain unknown. Herein, we investigated the function of LINC01526 with respect to the malignant progression of gastric cancer. We found that LINC01526 was upregulated in gastric cancer cells and tissues. The function experiments in vitro and the Xenograft mouse model in vivo proved that LINC01526 could promote gastric cancer cell proliferation and migration. Furthermore, LINC01526 interacted with TAR (HIV-1) RNA-binding protein 2 (TARBP2) and decreased the mRNA stability of G protein gamma 7 (GNG7) through TARBP2. Finally, the rescue assay showed that downregulating GNG7 partially rescued the cell proliferation inhibited by LINC01526 or TARBP2 silencing. In summary, LINC01526 promoted gastric cancer progression by interacting with TARBP2, which subsequently degraded GNG7 mRNA. This study not only explores the role of LINC01526 in gastric cancer, but also provides a laboratory basis for its use as a new biomarker for diagnosis and therapeutic targets.

Loss of protein expression and recurrent DNA hypermethylation of the GNG7 gene in squamous cell carcinoma of the head and neck

Although down-regulation of GNG7 in cancer was reported before, its role in carcinogenesis is poorly understood. It belongs to a family of large G-proteins that may be involved in cell-contact-induced growth arrest and function in tumor suppression. In the present study, we stained immunohistochemically 188 tumors derived from larynx or floor of the mouth for GNG7 protein and confronted it with clinicopathologic data. Moreover, we performed bisulfite pyrosequencing to analyze GNG7 promoter methylation. We identified recurrent loss of GNG7 protein expression in 68/188 (36%) cases and promoter hypermethylation in (42/98; 43%) primary tumors, predominantly in young patients (p < 0.001). Loss of GNG7 expression correlated with hypermethylation of GNG7 promoter region (p < 0.001). Moreover, loss of GNG7 protein expression correlated with tumor size (p = 0.012) and lack of cervical metastasis (p = 0.02) whereas sustained expression correlated with keratinization (p = 0.008). Taken together, loss of GNG7 protein expression is a frequent event in head and neck cancer. Moreover, our data suggest that hypermethylation of the promoter region of GNG7 is probably the mechanism of the observed inactivation.

Identification of the mgc1 mutation which affects mating-pheromone-induced morphogenesis in the yeast Saccharomyces cerevisiae

Cells of the yeast Saccharomyces cerevisiae undergo morphogenesis in response to the mating pheromones a- and alpha-factors. The 'shmoo' morphology involves localized cell surface projection formation and cytoskeleton protein synthesis. This polarization is presumed to be a prelude to mating between mating partners with opposite mating types, a and alpha. To identify genes involved in pheromone-induced morphogenesis, a system in which a gpa1 fus3 double mutant was used as a parent strain was developed, and mutants which showed altered morphogenesis in response to mating pheromone were identified. The mutation was designated mgc1 for morphogenesis control by mating pheromones. The mgc1 mutant arrested cell division in response to alpha-factor and mated with cells of the opposite mating type, but did not form a typical projection in response to pheromones.

Block of the cell cycle of the yeast Saccharomyces cerevisiae by tyrphostin, an inhibitor of protein tyrosine kinase

Tyrphostins are inhibitors of the epidermal growth factor receptor tyrosine kinase. To elucidate the biological function of protein tyrosine kinases in yeast cells, a mutant hypersensitive to tyrphostin was isolated and investigated for its response to the drug. The mutation was recessive and was designated tpt1 for tyrphostin hypersensitive. A tpt1 strain cannot grow in the presence of tyrphostin, implying that a biological process sensitive to tyrphostin is essential for cell growth. Microscopic observation indicated that large-budded cells were accumulated in the presence of the inhibitor. The results suggest the involvement of protein tyrosine phosphorylation in the cell cycle progression of Saccharomyces cerevisiae.

Characterization of the basal and pheromone-stimulated phosphorylation states of Ste12p

The Saccharomyces cerevisiae transcription factor Ste12p is required for basal and activated expression of pheromone-responsive genes, and for invasive growth in haploid cells. In diploid yeast, Ste12p is implicated in pseudohyphal development. The ability of Ste12p to effect these various responses in three different cell types must require stringent regulation of its transcriptional activation function and interaction with additional transcription factors. We have examined the phosphorylation state of Ste12p in untreated and pheromone-treated haploid cells, and found eight constitutively phosphorylated peptides. Phosphorylation at the constitutive sites does not require the protein kinases of the pheromone-response pathway. Treatment of haploid yeast with mating pheromone causes the appearance of novel relatively minor phosphorylations on Ste12p. Brief [35S]methionine labeling reveals novel pheromone-dependent, electrophoretically slower migrating Ste12p species. Similarly, the sole difference we observe in tryptic phosphopeptides generated from Ste12p from pheromone-treated and untreated cells is the transient appearance of two novel minor hydrophobic phosphopeptides. The pheromone-dependent phosphorylation of Ste12p requires an intact pheromone-response pathway and localization of Ste12p to the nucleus, but does not require the Ste12p DNA-binding domain. We conclude from these experiments that the pheromone-response pathway induces the formation of specific hyperphosphorylation on Ste12p, which can only be detected as apparently minor modifications in vivo. We argue that, if Ste12p is regulated by direct pheromone-responsive phosphorylation, then that phosphorylation must be represented by the two novel phosphopeptides. However, we cannot exclude the possibility that pheromone-responsive transcription is controlled by direct phosphorylation of a target other than Ste12p.

Identification and characterization of FAR3, a gene required for pheromone-mediated G1 arrest in Saccharomyces cerevisiae

In haploid Saccharomyces cerevisiae cells, mating pheromones activate a signal transduction pathway that leads to cell cycle arrest in the G1 phase and to transcription induction of genes that promote conjugation. To identify genes that link the signal transduction pathway and the cell cycle machinery, we developed a selection strategy to isolate yeast mutants specifically defective for G1 arrest. Several of these mutants identified previously known genes, including CLN3, FUS3, and FAR1. In addition, a new gene, FAR3, was identified and characterized. FAR3 encodes a novel protein of 204 amino acid residues that is dispensable for viability. Northern blot experiments indicated that FAR3 expression is constitutive with respect to cell type, pheromone treatment, and cell cycle position. As a first step toward elucidating the mechanism by which Far3 promotes pheromone-mediated G1 arrest, we performed genetic and molecular experiments to test the possibility that Far3 participates in one of the heretofore characterized mechanisms, namely Fus3/Far1-mediated inhibition of Cdc28-Cln kinase activity, G1 cyclin gene repression, and G1 cyclin protein turnover. Our data indicate that Far3 effects G1 arrest by a mechanism distinct from those previously known.

The immunosuppressant leflunomide blocks the yeast Saccharomyces cerevisiae cell cycle at the G1 phase

Leflunomide is a novel immunomodulatory drug representing a new small molecule class of substances which are structurally unrelated to previously described immunomodulatory/immunosuppressive compounds. The effect of leflunomide on the cell cycle of Saccharomyces cerevisiae was investigated to elucidate the molecular mechanism of its action in eukaryotic organisms. When yeast cells were treated with leflunomide, unbudded cells were accumulated, suggesting that leflunomide may arrest the cell cycle in the G1 phase. When leflunomide-treated cells were subjected to heat shock treatment, the cells became resistant to heat shock treatment, implying that leflunomide-mediated block to cell division results in entry from the proliferative cycle into the alternative developmental G0 phase.

Saccharomyces cerevisiae MATa mutant cells defective in pointed projection formation in response to alpha-factor at high concentrations

We have isolated Saccharomyces cerevisiae MATa mutant cells that do not form a pointed projection but elongate in response to alpha-factor at high concentrations. Complementation tests defined three genes, PPF1, PPF2, and PPF3 (for pointed projection formation), necessary for pointed projection formation. Allelism tests with genes known to be needed for projection formation revealed that PPF1 is identical to SPA2, while PPF2 and PPF3 are not allelic to SST2, STE2, SPA2, BEM1 or SLK1/SSP31/BCK1. The morphology of MATa ppf mutants treated with high concentrations of alpha-factor is similar to that of MATa PPF cells treated with alpha-factor at low concentrations. Quantitative mating tests showed that PPF2 and PPF3 are not essential for mating in either MATa or MAT alpha background. Monitoring of division arrest and expression of an alpha-factor-inducible gene revealed that mutations in the PPF genes do not affect the responses of MATa cells to low concentrations of alpha-factor. Unlike wild-type cells, the ppf mutants exhibited early recovery from alpha-factor-induced division arrest. Furthermore, vegetatively growing ppf3-1 cells are slightly defective in cell separation of mother and daughter cells and in selection of the correct bud sites in all cell types. These results indicate that PPF2 and PPF3 are involved in the response to alpha-factor at high concentrations and that PPF3 is also required for proper establishment of polarity in vegetative growth.

Genetic mapping of STE20 to the left arm of chromosome VIII

STE20 is a newly-discovered element of the Saccharomyces cerevisiae pheromone response pathway. We have isolated a recessive ste20 mutation and have used it to map the gene to the left arm of chromosome VIII, establishing the gene order STE20-CEN8-GPA1-ARG4.

Molecular cloning of the DAC2/FUS3 gene essential for pheromone-induced G1-arrest of the cell cycle in Saccharomyces cerevisiae

Mating pheromones, known as a and alpha-factors, arrest the division of cells of opposite mating types, alpha and a respectively, in Saccharomyces cerevisiae. I have cloned the DAC2 gene, which is required for both pheromone-induced division-arrest and cell-fusion during conjugation. The constructed dac2::LEU2 null mutation leads to defects in both pheromone-induced division-arrest and cell-fusion during conjugation; it also suppresses the growth defect caused by the gpa1 mutation (a mutation in the alpha subunit of the S. cerevisiae G protein). These results indicate that DAC2 may be the same gene as FUS3, which was recently isolated by Elion et al. (1990) as a gene essential for cell-fusion during conjugation. The dac2::LEU2 null mutant also showed morphological alterations in response to mating pheromones. I show here that the DAC2 product plays an essential role in both the division-arrest signalling pathway of the yeast pheromone response and in cell-fusion during conjugation.