Regulator of G protein signaling 19 (RGS19), previously known as Gα-interacting protein (GAIP), belongs to the RZ/A subfamily of regulators of G protein signaling. RGS19 was first isolated from a yeast two-hybrid screening of Gα_i3-interacting proteins. Follow-up functional studies of RGS19 have subsequently revealed that RGS19 serves as a GTPase-activating protein (GAP) for many Gα_i family members, especially Gα_i3, by which it enhances the intrinsic GTPase activity of the Gα subunit. RGS19 has also been demonstrated to associate with other signaling molecules such as GIPN (GAIP-interacting protein N-terminus) and GIPC (GAIP-interacting protein C-terminus). Identification of these interactions diversifies the potential functions of RGS19 in regulating different cellular processe...[ Read more ]

Regulator of G protein signaling 19 (RGS19), previously known as Gα-interacting protein (GAIP), belongs to the RZ/A subfamily of regulators of G protein signaling. RGS19 was first isolated from a yeast two-hybrid screening of Gα_i3-interacting proteins. Follow-up functional studies of RGS19 have subsequently revealed that RGS19 serves as a GTPase-activating protein (GAP) for many Gα_i family members, especially Gα_i3, by which it enhances the intrinsic GTPase activity of the Gα subunit. RGS19 has also been demonstrated to associate with other signaling molecules such as GIPN (GAIP-interacting protein N-terminus) and GIPC (GAIP-interacting protein C-terminus). Identification of these interactions diversifies the potential functions of RGS19 in regulating different cellular processes such as autophagy and growth factor signalings. Recent studies have demonstrated that RGS19 inhibits tumor growth of transformed NIH3T3 cells whereas it promotes cell proliferation in HEK293 cells. Yet, the known RGS19-interacting proteins cannot fully account for its functional roles in these cellular events. Hence, a yeast-two-hybrid screen was embarked in an attempt to isolate additional molecules that directly interact with RGS19. Two rounds of yeast two-hybrid (Y2H) screening were performed by using the full-length RGS19 bait protein against a human liver cDNA library. The first and the second Y2H screens yielded 162 and 411 HIS3⁺ADE2⁺lacZ⁺ clones, respectively. cDNA constructs isolated from these positive clones were categorized and analyzed by a combination of multiple techniques and analysis including restriction digestion (HindIII and HaeIII) and direct DNA sequencing. Thus duplicated clones were eliminated and the remaining clones were segregated into different groups prior to downstream verification steps such as yeast retransformation assay as well as colony lift β-galactosidase assay. By the above categorizations and verifications, 19 unique clones appear to be potential binding partners of RGS19 among the total of 573 clones. The identification of these novel RGS19-binding partners suggests that RGS19 may play a regulatory role in proteosomal degradation, autophagy, growth factor signaling, cellular metabolism and immune response. My present study also validated one of the positive clones, AKAP-Lbc. Co-immunoprecipitation studies between RGS19 and AKAP-Lbc further confirmed their interaction upon overexpressing the two tagged proteins in HEK293 cells. It is envisioned that future validation of the identified proteins as true RGS19-interacting partners will shed light on a better understanding on the non-canonical functions of RGS19 beyond its well-defined GAP activity.