Association of activated Gα(q) 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 G(q) proteins that typically stimulate the phospholipase C pathway. Activated Gα(q) 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 Gα(q)/Fhit interaction. METHODS: To test the relationship of PLCβ with the interaction between Gα(q) and Fhit, co-immunoprecipication assay was performed on HEK293 cells co-transfected with different combinations of Flag-Fhit, Gα(16), Gα(16)QL, pcDNA3 vector, and PLCβ isoforms. Possible associations of Fhit with other effectors of Gα(q) were also demonstrated by co-immunoprecipitation. The regions of Gα(q) for Fhit interaction and PLCβ stimulation were further evaluated by inositol phosphates accumulation assay using a series of Gα(16/z) chimeras with discrete regions of Gα(16) replaced by those of Gα(z). RESULTS: PLCβ1, 2 and 3 interacted with Fhit regardless of the expression of Gα(q). Expression of PLCβ increased the affinities of Fhit for both wild-type and activated Gα(q). Swapping of the Fhit-interacting α2-β4 region of Gα(q) with Gα(i) eliminated the association of Gα(q) with Fhit without affecting the ability of the mutant to stimulate PLCβ. Other effectors of Gα(q) including RGS2 and p63RhoGEF were unable to interact with Fhit. CONCLUSIONS: PLCβ may participate in the regulation of Fhit by G(q) in a unique way. PLCβ interacts with Fhit and increases the interaction between Gα(q) and Fhit. The Gα(q)/PLCβ/Fhit complex formation points to a novel signaling pathway that may negatively regulate tumor cell growth. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12885-015-1802-z) contains supplementary material, which is available to authorized users.