Interaction with calmodulin is important for the secretion of thimet oligopeptidase following stimulation

Thimet oligopeptidase (EC 3.4.24.15; EP24.15) was originally described as a neuropeptide-metabolizing enzyme, highly expressed in the brain, kidneys and neuroendocrine tissue. EP24.15 lacks a typical signal peptide sequence for entry into the secretory pathway and is secreted by cells via an unconventional and unknown mechanism. In this study, we identified a novel calcium-dependent interaction between EP24.15 and calmodulin, which is important for the stimulated, but not constitutive, secretion of EP24.15. We demonstrated that, in vitro, EP24.15 and calmodulin physically interact only in the presence of Ca(2+), with an estimated K(d) value of 0.52 mu m. Confocal microscopy confirmed that EP24.15 colocalizes with calmodulin in the cytosol of resting HEK293 cells. This colocalization markedly increases when cells are treated with either the calcium ionophore A23187 or the protein kinase A activator forskolin. Overexpression of calmodulin in HEK293 cells is sufficient to greatly increase the A23187-stimulated secretion of EP24.15, which can be inhibited by the calmodulin inhibitor calmidazolium. The specific inhibition of protein kinase A with KT5720 reduces the A23187-stimulated secretion of EP24.15 and inhibits the synergistic effects of forskolin with A23187. Treatment with calmidazolium and KT5720 nearly abolishes the stimulatory effects of A23187 on EP24.15 secretion. Together, these data suggest that the interaction between EP24.15 and calmodulin is regulated within cells and is important for the stimulated secretion of EP24.15 from HEK293 cells.

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

FAPESP Sao Paulo State Research Foundation[04/04933-2]

National Institutes of Health (NIH)[NS39892]

U.S. National Institutes of Health (NIH)

National Institutes of Health (NIH)[RR09145]

U.S. National Institutes of Health (NIH)

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES)

FAPESP

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Brazilian National Research Council (CNPq)