Homer proteins accelerate Ca2+ clearance mediated by the plasma membrane Ca2+ pump in hippocampal neurons

• Published in: Biochemical and biophysical research communications Vol. 424; no. 1; pp. 76 - 81
• Main Authors: Salm, Elizabeth J., Thayer, Stanley A.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 20.07.2012
• Subjects: Animals; Ca2+ signaling; Calcium - metabolism; Carrier Proteins - genetics; Carrier Proteins - metabolism; Cells, Cultured; Gene Knockdown Techniques; Hippocampal neuron; Hippocampus - cytology; Hippocampus - metabolism; Homer; Homer Scaffolding Proteins; Neurons - metabolism; PDZ domain; Plasma Membrane Calcium-Transporting ATPases - metabolism; PMCA; Protein Structure, Tertiary; Rats; RNA, Small Interfering - genetics; Homer; Hippocampal neuron; PDZ domain; Ca2+ signaling; PMCA
• ISSN: 0006-291X; 1090-2104
• DOI: 10.1016/j.bbrc.2012.06.069

► We studied the effects of Homer proteins on plasma membrane Ca2+ pump (PMCA) activity. ► shRNA knockdown of Homer 1 slowed PMCA function in hippocampal neurons. ► Over expression of long or short Homer isoforms failed to affect PMCA function. ► A Homer 2 truncation mutant rescued PMCA function in cells expressing Homer 1 shRNA. ► Short and long Homer proteins tonically stimulate PMCA in hippocampal neurons. The plasma membrane Ca2+ ATPase (PMCA) is responsible for maintaining basal intracellular Ca2+ concentration ([Ca2+]i) and returning small increases in [Ca2+]i back to resting levels. The carboxyl terminus of some PMCA splice variants bind Homer proteins; how binding affects PMCA function is unknown. Here, we examined the effects of altered expression of Homer proteins on PMCA-mediated Ca2+ clearance from rat hippocampal neurons in culture. The kinetics of PMCA-mediated recovery from the [Ca2+]i increase evoked by a brief train of action potentials was determined in the soma of single neurons using indo-1-based photometry. Exogenous expression of Homer 1a, Homer 1c or Homer 2a did not affect PMCA function. However, shRNA mediated knockdown of Homer 1 slowed PMCA mediated Ca2+ clearance by 28% relative to cells expressing non-silencing shRNA. The slowed recovery rate in cells expressing Homer 1 shRNA was reversed by expression of a short Homer 2 truncation mutant. These results indicate that constitutively expressed Homer proteins tonically stimulate PMCA function in hippocampal neurons. We propose a model in which binding of short or long Homer proteins to the carboxyl terminus of the PMCA stimulates Ca2+ clearance rate. PMCA-mediated Ca2+ clearance may be stimulated following incorporation of the pump into Homer organized signaling domains and following induction of the Homer 1a immediate early gene.