SNX14 is a bifunctional negative regulator for neuronal 5-HT6 receptor signaling

Abstract

The 5-hydroxytryptamine (5-HT, also known as serotonin) subtype 6 receptor (5-HT 6 R, also known as HTR6) plays roles in cognition, anxiety and learning and memory disorders, yet new details concerning its regulation remain poorly understood. In this study, we found that 5-HT 6 R directly interacted with SNX14 and that this interaction dramatically increased internalization and degradation of 5-HT 6 R. Knockdown of endogenous SNX14 had the opposite effect. SNX14 is highly expressed in the brain and contains a putative regulator of G-protein signaling (RGS) domain. Although its RGS domain was found to be non-functional as a GTPase activator for Gas, we found that it specifically bound to and sequestered Gas, thus inhibiting downstream cAMP production. We further found that protein kinase A (PKA)-mediated phosphorylation of SNX14 inhibited its binding to Gas and diverted SNX14 from Gas binding to 5-HT 6 R binding, thus facilitating the endocytic degradation of the receptor. Therefore, our results suggest that SNX14 is a dual endogenous negative regulator in 5-HT 6 R-mediated signaling pathway, modulating both signaling and trafficking of 5-HT 6 R.

Structural studies of sorting nexin proteins from two distinct subfamilies

“…Further into the future such peptides may have additional uses such as testing the importance of such pathways in disease states and their therapeutic targeting potential. whereas it is in support to the results of Ha et al (49), which failed to identify a GAP activity for SNX14. This leads me to the speculate that since SNX-RGS proteins bind to Gα s , these proteins may still act as negative regulators of Gα s signaling, whereby they will sequester the G-protein and prevent its interactions with downstream effectors.…”

“…RGS4 and RGS10 demonstrated decreased GAP activity through the palmitoylation of Cys 95 and Cys 66 residues respectively (163). Even though my studies demonstrate the RGS domains of SNX-RGS do not possess GAP activity for Gα s, both SNX13 and SNX14 proteins are previously reported to regulate cAMP signaling (48,49). As mentioned above, This might suggest that GTP hydrolysis by Gα alone is not enough to fully terminate signaling and further sequestration of Gα s -GDP by other proteins such as SNX-RGS may play a key role.…”

“…Until recently it was unknown whether the RGS domain from other SNX-RGS proteins share the same GAP activity as SNX13. Ha et al (2015) studied the activity of the SNX14 RGS domain and found that it does not appear to share this GAP activity. But it did appear to bind specifically to and sequester Gα s and thus inhibit downstream cAMP production, essentially resulting in a similar functional outcome to activating GTP hydrolysis (49).…”

“…Ha et al (2015) studied the activity of the SNX14 RGS domain and found that it does not appear to share this GAP activity. But it did appear to bind specifically to and sequester Gα s and thus inhibit downstream cAMP production, essentially resulting in a similar functional outcome to activating GTP hydrolysis (49). Whether the SNX25 RGS domain possesses GAP or Gα binding activity remains unknown, but has been reported to be involved in transforming growth factor-β (TGF-β) signalling, lysosomal trafficking and degradation of TGF-β receptor 1 (TβRI) by regulating interaction of with TβRI (38,49).…”

“…Zheng et al, has previously identified the RGS domain of SNX13 as GAP protein for Gα s , thus contributing to the regulation of cellular responses mediated by Gα s including adenyl cyclases and cAMP production (48). Recently SNX14 was found to bind and sequester Gα s even though it did not appear to regulate its GTPase activity (49). Neither the binding ability of SNX25 to Gα s nor its GAP activity has been studied so far.…”