Naslov
IQGAP-related protein IqgC finely tunes cellular feeding

Autori
Filić, Vedrana

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
15th National and 1st International Congress of Histology and Embryology : Abstract book / Tanriover, Gamze - , 2022, 168-168

Skup
15th National and 1st International Congress of Histology and Embryology (NICHE2022)

Mjesto i datum
Online, 26.05.2022. - 28.05.2022

Vrsta sudjelovanja
Pozvano predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
IQGAP ; IqgC ; RasGAP ; macropinocytosis

Sažetak
Cellular feeding describes different ways of nutrient uptake. Metazoan cells surrounded by extracellular fluids internalize nutrients via membrane transporters or by receptor-mediated endocytosis. Mammalian cells are also capable of a bulk, nonspecific uptake of extracellular fluid, named macropinocytosis, but to what extent is this process used for feeding is still not clear. On the other hand, macropinocytosis and phagocytosis (particle uptake), collectively termed large-scale endocytosis (LSE), is the only way of nutrient uptake for a unicellular, soil-living amoeba that predominantly feeds on bacteria. LSE requires extensive remodelling of the actin cytoskeleton to produce macropinocytic or phagocytic cups. GTPases of the Ras, Rho and Rab families regulate the organization of these protrusions. Ras proteins promote macropinocytosis in both mammalian cells and amoeba Dictyostelium. Moreover, tumour cells with overly activated Ras use this ancient process for feeding on proteins in the microenvironment scarce in amino acids. This finding underlines the importance of both timely activation and inactivation of Ras GTPases for normal cell functioning. Inactivation of Ras GTPases is catalysed by RasGAPs (GTPase activating proteins) that promote intrinsic GTP-hydrolytic activity of a GTPase. We investigated the biological function of an IQGAP-related protein IqgC in Dictyostelium discoideum. Unlike other IQGAPs that have lost GAP activity, IqgC turned out to be a genuine RasGAP that exerts GAP activity toward human H-Ras and its endogenous partner, RasG. Using confocal microscopy and functional assays with both IqgC knock-out and overexpressing cells, we demonstrated that IqgC localizes to macropinocytic and phagocytic cups, and negatively regulates both types of LSE. More specifically, we showed that IqgC restricts the size of macropinocytic cups. Further, IqgC colocalizes with the active Ras on macropinosome, and using rasG null cells or mutated IqgC, we proved RasG indispensable for IqgC recruitment to the forming macropinosome. However, IqgC stayed on the internalized macropinosome even after Ras has dissociated from the vesicle. This suggested novel, RasG-independent functions of IqgC, probably in early endosome maturation. Indeed, using GST-Rab5A-pull-down assay with purified IqgC, we found an early endosome marker, Rab5A, to be a direct interactor of IqgC. Moreover, IqgC and Rab5A colocalize on the primary macropinocytic vesicle. RasG is essential for IqgC loading to macropinocytic cups where IqgC suppresses RasG activity to finely tune nutrient uptake. However, after Ras has dissociated, IqgC interacts with another small GTPase, Rab5A, but the functional consequences of this interaction are currently unknown.

Izvorni jezik
Engleski

Znanstvena područja
Biologija

POVEZANOST RADA