Cyclin-dependent kinase 5 activates guanine nucleotide exchange factor GIV/Girdin to orchestrate migration–proliferation dichotomy

Abstract

Signals propagated by receptor tyrosine kinases (RTKs) can drive cell migration and proliferation, two cellular processes that do not occur simultaneously—a phenomenon called “migration–proliferation dichotomy.” We previously showed that epidermal growth factor (EGF) signaling is skewed to favor migration over proliferation via noncanonical transactivation of Gαi proteins by the guanine exchange factor (GEF) GIV. However, what turns on GIV-GEF downstream of growth factor RTKs remained unknown. Here we reveal the molecular mechanism by which phosphorylation of GIV by cyclin-dependent kinase 5 (CDK5) triggers GIV's ability to bind and activate Gαi in response to growth factors and modulate downstream signals to establish a dichotomy between migration and proliferation. We show that CDK5 binds and phosphorylates GIV at Ser1674 near its GEF motif. When Ser1674 is phosphorylated, GIV activates Gαi and enhances promigratory Akt signals. Phosphorylated GIV also binds Gαs and enhances endosomal maturation, which shortens the transit time of EGFR through early endosomes, thereby limiting mitogenic MAPK signals. Consequently, this phosphoevent triggers cells to preferentially migrate during wound healing and transmigration of cancer cells. When Ser1674 cannot be phosphorylated, GIV cannot bind either Gαi or Gαs, Akt signaling is suppressed, mitogenic signals are enhanced due to delayed transit time of EGFR through early endosomes, and cells preferentially proliferate. These results illuminate how GIV-GEF is turned on upon receptor activation, adds GIV to the repertoire of CDK5 substrates, and defines a mechanism by which this unusual CDK orchestrates migration–proliferation dichotomy during cancer invasion, wound healing, and development.

GIV/Girdin activates Gαi and inhibits Gαs via the same motif

“…Although the published work led us to conclude that a main function of GIV is to orchestrate the migration-proliferation dichotomy by enhancing cell migration and inhibiting mitosis (9,11,12) and that GIV must dually couple to both Gαi and Gαs to orchestrate such dichotomy, several questions remained unanswered. For example, what determines GIV's preference for one or the other G protein, and how does dual coupling to Gαi and Gαs impact signals downstream of both G proteins and receptor tyrosine kinases and cellular responses to growth factors?…”

“…Thus GIV is ubiquitously expressed (10), can be recruited to different subcellular compartments (reviewed in ref. 4), binds to both Gαi and Gαs (9)(10)(11), and affects a number of important physiologic and pathologic processes.…”

“…5). However, selective ablation of GIV's GBA motif not only disables cells' ability to migrate in response to a stimulus but also results in an unexpected gain in phenotype, i.e., cells begin to proliferate (11)(12)(13). How GIV's GBA motif actively suppresses cell proliferation remained unclear.…”

The GAPs, GEFs, GDIs and…now, GEMs: New kids on the heterotrimeric G protein signaling block

“…They showed that in the case of the prototypical GEM GIV, sequential phosphorylation of 2 Ser residues that flank the bifunctional GEF/GDI motif on GIV by 2 kinases, CDK5 35 and PKCu, 36 ensures that GIV exerts its GEF and GDI activities on Gai and Gas, respectively, in a temporally and spatially segregated manner (Fig. 2).…”

“…Schematic showing the spatially separated GEF and GDI actions of GIV-GEM on Gai and Gas, respectively. Upon EGF stimulation, activated CDK5 kinase phosphorylates GIV on S1674 35 , thereby turning 'on' its GEF function toward Gai. Subsequently, GIV is phosphorylated also at S1689 by PKCu 36 ; this phosphoevent turns 'off' GIV's GEF function, but turns 'on' its GDI function toward Gas.…”