ARF6 Activated by the LHCG Receptor through the Cytohesin Family of Guanine Nucleotide Exchange Factors Mediates the Receptor Internalization and Signaling

Abstract

Background:The mechanisms by which ARF6 regulate LHCGR internalization and signaling are unknown. Results: Heterotrimeric G-protein, PI 3-kinase, cytohesin ARF GEFs and ARF GAPs function upstream whereas dynamin and clathrin act downstream of ARF6 in the regulation of HLHCGR internalization and signaling. Conclusion: Dissected the molecular mechanisms underlying ARF6 involvement in LHCGR internalization and signaling. Significance: This study provides insight into the mechanisms responsible for HLHCGR regulation by ARF6.

Luteinizing hormone/chorionic gonadotrophin receptor overexpressed in granulosa cells from polycystic ovary syndrome ovaries is functionally active

“…It has been shown previously that ARF6 small GTPase activated by LHCGR through cytohesin family ARF GEFs mediates the receptor internalisation and signalling (Kanamarlapudi et al, 2012b). Since LHCGR is overexpressed in PCOS group, we also analysed, in this study, whether LHCGR overexpression has any effect on ARF6 small GTPase expression and activity in PCOS GCs.…”

“…ARF6 function depends on its activation by GEFs such as cytohesins (Davies et al, 2014a, Davies et al, 2014b). We and others have shown the involvement of cytohesin2, through ARF6 activation, in agonist-induced internalisation of LHCGR (Hunzicker-Dunn et al, 2002, Kanamarlapudi et al, 2012b. We investigated here whether the chemical inhibitor of cytohesin family of ARF GEFs, secinH3 (Hafner et al, 2006), inhibits LHCGR internalisation and thereby increases cAMP production in GCs (Figure 4B).…”

“…GCs cultured in 24-well plates were used for cAMP estimation as described (Kanamarlapudi et al, 2012b). Briefly, GCs were serum starved for 2h and incubated with 0.25mM of phosphodiesterase inhibitor Ro201724 at 37°C for 15min.…”

“…. ARF6 small GTPase plays a crucial role in agonist-induced LHCGR internalisation whereas ARF1 is important for protein trafficking at the Golgi (Hunzicker-Dunn et al, 2002, Kanamarlapudi et al, 2012b, Donaldson and Jackson, 2011. To determine whether the expression of ARF1 and/or ARF6 is altered in PCOS, the expression of ARF1 and ARF6 proteins in GCs from normal and PCOS women was analysed by immunoblotting.…”

“…After agonist stimulation, LHCGR internalises through ARF6 small GTPase mediated β-arrestin-clathrin-dynamin pathway (Kanamarlapudi et al, 2012b, Hunzicker-Dunn et al, 2002. LHCGR internalisation and recycling regulate the density of cell surface receptors and thereby the sensitivity of the cells to LH (Bhaskaran and Ascoli, 2005).…”