Calmodulin Kinase II Constitutively Binds, Phosphorylates, and Inhibits Brush Border Na+/H+ Exchanger 3 (NHE3) by a NHERF2 Protein-dependent Process

Abstract

Background: NHE3 is regulated by a signaling complex on its C terminus, only some of the components of which are known. Results: CaMKII␥ binds to the NHE3 C terminus and phosphorylates and inhibits basal NHE3 activity by altering turnover number. Conclusion: CaMKII␥ is part of an NHE3 signaling complex. Significance: Signaling complexes that form on transport proteins take part in regulation of the transporter

ANG II, ANG-(1-7), ALDO and AVP biphasic effects on Na+/H+ transport: the role of cellular calcium

“…In addition, this regulatory effect requires amino acids in the C-terminal-binding autostimulatory domain that are downstream of NHE3 to interact with CaMKII (aa 690) [45,46]. Hence, CaMKII constitutively binds to, phosphorylates, and inhibits NHE3 via a NHERF2 protein-dependent process [48]. More details of these mechanisms are provided in section 2.…”

“…These events are followed by autophosphorylation at Thr286/287 (depending on the species being studied) or oxidation at Met281 or Met282 [47], which result in a conformational change in CaMKII that allows high affinity interactions with its target proteins and prevents the inactivation of the kinase by re-association between its catalytic domain with the autoinhibitory domain when Ca 2+ returns to basal levels. Similarities in the sequence alignment between the CaMKII binding domain of NHE3 and the CaMKII autoinhibitory domain [48] suggest that the catalytic subunit of the activated CaMKII (freed from its autoinhibitory domain) binds to a domain in its substrate, which resembles the kinase autoinhibitory domain but cannot inactivate the catalytic domain, while preventing access to the kinase autoinhibitory domain [49,50]. Therefore, CaMKII constitutively binds to, phosphorylates, and inhibits NHE3 via a NHERF2 protein-dependent process [48].…”

“…Similarities in the sequence alignment between the CaMKII binding domain of NHE3 and the CaMKII autoinhibitory domain [48] suggest that the catalytic subunit of the activated CaMKII (freed from its autoinhibitory domain) binds to a domain in its substrate, which resembles the kinase autoinhibitory domain but cannot inactivate the catalytic domain, while preventing access to the kinase autoinhibitory domain [49,50]. Therefore, CaMKII constitutively binds to, phosphorylates, and inhibits NHE3 via a NHERF2 protein-dependent process [48]. Because it has multiple functions, NHE3 is regulated by a wide variety of agonists in response to physiological conditions [4,13,51].…”

“…Additionally, under basal conditions, NHE3 is active, and CaMKII binds to the NHE3 C-terminal autoinhibitory domain (aa 586-605). This binding is rapidly reduced by a discrete increase in [Ca2+]i, which causes a conformational change in CaMKII that allows high-affinity interactions with target proteins and prevents the inactivation of the kinase by re-association between the catalytic domain and the autoinhibitory domain after Ca 2+ returns to basal levels [13,47,48]. Other proteins that associate with NHE3 require this NHE3 domain, and these include NHERF1-4, phospholipase Cγ and CK2α [43,44].…”

Insights from Systems Biology in Physiological Studies: Learning from Context

“…CK2, CAMKII, PKA, PKC, etc. )[34-36] and its transcription depends on several transcription factors (e.g. SP1, EGR, etc.…”