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

Abstract

BackgroundThe FHIT tumor suppressor gene is arguably the most commonly altered gene in cancer since it is inactivated in about 60% of human tumors. The Fhit protein is a member of the ubiquitous histidine triad proteins which hydrolyze dinucleoside polyphosphates such as Ap3A. Despite the fact that Fhit functions as a tumor suppressor, the pathway through which Fhit inhibits growth of cancer cells remains largely unknown. Phosphorylation by Src tyrosine kinases provides a linkage between Fhit and growth factor signaling. Since many G proteins can regulate cell proliferation through multiple signaling components including Src, we explored the relationship between Gα subunits and Fhit.ResultsSeveral members of the Gαq subfamily (Gα16, Gα14, and Gαq) were found to co-immunoprecipitate with Fhit in their GTP-bound active state in HEK293 cells. The binding of activated Gαq members to Fhit appeared to be direct and was detectable in native DLD-1 colon carcinoma cells. The use of Gα16/z chimeras further enabled the mapping of the Fhit-interacting domain to the α2-β4 region of Gα16. However, Gαq/Fhit did not affect either Ap3A binding and hydrolysis by Fhit, or the ability of Gαq/16 to regulate downstream effectors including phospholipase Cβ, Ras, ERK, STAT3, and IKK. Functional mutants of Fhit including the H96D, Y114F, L25W and L25W/I10W showed comparable abilities to associate with Gαq. Despite the lack of functional regulation of Gq signaling by Fhit, stimulation of Gq-coupled receptors in HEK293 and H1299 cells stably overexpressing Fhit led to reduced cell proliferation, as opposed to an enhanced cell proliferation typically seen with parental cells.ConclusionsActivated Gαq members interact with Fhit through their α2-β4 region which may result in enhancement of the growth inhibitory effect of Fhit, thus providing a possible avenue for G protein-coupled receptors to modulate tumor suppression.

Assessment of the Prognostic Value of Methylation Status and Expression Levels of FHIT, GSTP1 and p16 in Non-Small Cell Lung Cancer in Egyptian Patients

“…Encouragingly, the development of carcinogen induced tumors in these mice can be prevented by administration of Fhit-expressing viral vectors. Moreover, Fhit overexpression enhances the susceptibility of many types of cancer cells to exogenous inducers of apoptosis (Zuo et al, 2013).…”

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

“…The GST-FHIT (fragile histidine triad protein) expression plasmid was kindly provided by Y.H. Wong, ( 48 ). The pBS5051 expression plasmid contains the Aph1 coding sequence PCR-amplified from plasmid p19 kindly provided by Plateau ( 49 ).…”

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

“…Wild-type Fhit in pCMV-SPORT6 was purchased from Invitrogen (Carlsbad, CA). Gα 16/z chimeras were constructed by overlapping PCR which swapped the corresponding regions of Gα 16 with Gα z as described previously [ 15 ]. Cell culture and Lipofectamine PLUS reagents, and anti-Fhit antibody were purchased from Invitrogen (Carlsbad, CA).…”

“…Fhit-interacting molecules include β-catenin [ 11 ], ferredoxin reductase [ 12 ], Src tyrosine kinase [ 13 ] and ubiquitin conjugating enzyme 9 [ 14 ]. More recently, we have demonstrated that Fhit can distinguish between inactive and active signal transducing Gα subunits of the G q family [ 15 ]. This finding is intriguing as it may link Fhit to Gα q -dependent signals that modulate a variety of cellular events.…”

“…The opposing roles of Fhit and Gα q tend to suggest that they may exert counteracting actions on each other. However, Fhit neither inhibits nor enhances Gα q -induced signals [ 15 ] whereas its own expression becomes translationally up-regulated by activated Gα q [ 23 ]. Given the links between G q signaling and mitogenesis as well as those between Fhit and tumor suppression are well-established, it seems reasonable to expect that the binding of Fhit to activated Gα q would impart functional consequences.…”