Activation state-dependent interaction between Gαq subunits and the Fhit tumor suppressor

Effects of FHIT gene on proliferation and apoptosis of osteosarcoma cells

Regulatory effects of fragile histidine triad (FHIT) gene on proliferation and apoptosis of osteosarcoma cells were studied. The hFOB1.19 and Saos2 cells were routinely cultured, pcDNA3.1-FHIT overexpression vectors carrying FHIT gene fragments and blank pcDNA3.1 vectors were transfected into Saos2 cells, respectively, and the cells were divided into hFOB, Saos2, transfection and no-load transfection groups. After transfection for 48 h, the cells were collected and analyzed. The expression of FHIT messenger ribonucleic acid (mRNA) was detected by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). The expression of FHIT protein was detected by western blot analysis. Cell Counting Kit 8 (CCK8) was used to detect cell proliferation, and flow cytometry was used to detect apoptosis. The expression of FHIT mRNA was significantly decreased in Saos2 group compared with that in hFOB group, and the difference was statistically significant (P<0.05). The expression of FHIT mRNA was significantly increased in transfection group compared with that in Saos2 group, and the difference was statistically significant (P<0.05). The expression of FHIT protein was obviously decreased in Saos2 group compared with that in hFOB group, and there was a statistically significant difference (P<0.05). The expression of FHIT protein was obviously increased in transfection group compared with that in Saos2 group, and the difference was statistically significant (P<0.05). Compared with that in the hFOB group, the cell proliferation rate was remarkably increased in Saos2 group, while the apoptosis rate was remarkably decreased, showing statistically significant differences (P<0.05). Compared with those in Saos2 group, the cell proliferation rate was significantly decreased in transfection group, while the apoptosis rate was significantly increased, and the differences were statistically significant (P<0.05). In conclusion, FHIT gene regulates the proliferation and apoptosis of Saos2 osteosarcoma cells, inhibits the proliferation and promotes apoptosis of Saos2 osteosarcoma cells.

FHIT down-regulation was inversely linked to aggressive behaviors and adverse prognosis of gastric cancer: a meta- and bioinformatics analysis

FHIT (fragile histine triad) acts as diadenosine P1, P3-bis (5'-adenosyl)-triphosphate adenylohydrolase involved in purine metabolism, and induces apoptosis as a tumor suppressor. We performed a systematic meta- and bioinformatics analysis through multiple online databases up to March 14, 2017. The down-regulated FHIT expression was found in gastric cancer, compared with normal mucosa and dysplasia (p < 0.05). FHIT expression was negatively with depth of invasion, lymph node metastasis, distant metastasis, TNM staging and dedifferentiation of gastric cancer (p < 0.05). A positive association between FHIT expression and favorable overall survival was found in patients with gastric cancer (p < 0.05). According to Kaplan-Meier plotter, we found that a higher FHIT expression was negatively correlated with overall and progression-free survival rates of all cancer patients, even stratified by aggressive parameters (p < 0.05). These findings indicated that FHIT expression might be employed as a potential marker to indicate gastric carcinogenesis and subsequent progression, even prognosis.

Association of activated Gαq to the tumor suppressor Fhit is enhanced by phospholipase Cβ

BACKGROUND

G proteins are known to modulate various growth signals and are implicated in the regulation of tumorigenesis. The tumor suppressor Fhit is a newly identified interaction partner of Gq proteins that typically stimulate the phospholipase C pathway. Activated Gαq subunits have been shown to interact directly with Fhit, up-regulate Fhit expression and enhance its suppressive effect on cell growth and migration. Other signaling molecules may be involved in modulating Gαq/Fhit interaction.

METHODS

To test the relationship of PLCβ with the interaction between Gαq and Fhit, co-immunoprecipication assay was performed on HEK293 cells co-transfected with different combinations of Flag-Fhit, Gα16, Gα16QL, pcDNA3 vector, and PLCβ isoforms. Possible associations of Fhit with other effectors of Gαq were also demonstrated by co-immunoprecipitation. The regions of Gαq for Fhit interaction and PLCβ stimulation were further evaluated by inositol phosphates accumulation assay using a series of Gα16/z chimeras with discrete regions of Gα16 replaced by those of Gαz.

RESULTS

PLCβ1, 2 and 3 interacted with Fhit regardless of the expression of Gαq. Expression of PLCβ increased the affinities of Fhit for both wild-type and activated Gαq. Swapping of the Fhit-interacting α2-β4 region of Gαq with Gαi eliminated the association of Gαq with Fhit without affecting the ability of the mutant to stimulate PLCβ. Other effectors of Gαq including RGS2 and p63RhoGEF were unable to interact with Fhit.

CONCLUSIONS

PLCβ may participate in the regulation of Fhit by Gq in a unique way. PLCβ interacts with Fhit and increases the interaction between Gαq and Fhit. The Gαq/PLCβ/Fhit complex formation points to a novel signaling pathway that may negatively regulate tumor cell growth.

Elimination of cap structures generated by mRNA decay involves the new scavenger mRNA decapping enzyme Aph1/FHIT together with DcpS

Eukaryotic 5' mRNA cap structures participate to the post-transcriptional control of gene expression before being released by the two main mRNA decay pathways. In the 3'-5' pathway, the exosome generates free cap dinucleotides (m7GpppN) or capped oligoribonucleotides that are hydrolyzed by the Scavenger Decapping Enzyme (DcpS) forming m7GMP. In the 5'-3' pathway, the decapping enzyme Dcp2 generates m7GDP. We investigated the fate of m7GDP and m7GpppN produced by RNA decay in extracts and cells. This defined a pathway involving DcpS, NTPs and the nucleoside diphosphate kinase for m7GDP elimination. Interestingly, we identified and characterized in vitro and in vivo a new scavenger decapping enzyme involved in m7GpppN degradation. We show that activities mediating cap elimination identified in yeast are essentially conserved in human. Their alteration may contribute to pathologies, possibly through the interference of cap (di)nucleotide with cellular function.

Activation of Gαq subunits up-regulates the expression of the tumor suppressor Fhit

The tumor suppressor Fhit protein is defective or absent in many tumor cells due to methylation, mutation or deletion of the FHIT gene. Despite numerous attempts to unravel the functions of Fhit, the mechanisms by which the function and expression of Fhit are regulated remain poorly understood. We have recently shown that activated Gαq subunits interact directly with Fhit and enhance its inhibitory effect on cell growth. Here we investigated the regulation of Fhit expression by Gq. Our results showed that Fhit was up-regulated specifically by activating Gα subunits of the Gq subfamily but not by those of the other G protein subfamilies. This up-regulation effect was mediated by a PKC/MEK pathway independent of Src-mediated Fhit Tyr(114) phosphorylation. We further demonstrated that elevated Fhit expression was due to the specific regulation of Fhit protein synthesis in the ribosome by activated Gαq, where the regulations of cap-dependent protein synthesis were apparently not required. Moreover, we showed that activated Gαq could increase cell-cell adhesion through Fhit. These findings provide a possible handle to modulate the level of the Fhit tumor suppressor by manipulating the activity of Gq-coupled receptors.