Abnormal activation of calpain and protein kinase Cα promotes a constitutive release of matrix metalloproteinase 9 in peripheral blood mononuclear cells from cystic fibrosis patients

Matrix metalloproteinase 9 (MMP9) is physiologically involved in remodeling the extracellular matrix components but its abnormal release has been observed in several human pathologies. We here report that peripheral blood mononuclear cells (PBMCs), isolated from cystic fibrosis (CF) patients homozygous for F508del-cystic fibrosis transmembrane conductance regulator (CFTR), express constitutively and release at high rate MMP9 due to the alteration in their intracellular Ca2+ homeostasis. This spontaneous and sustained MMP9 secretion may contribute to the accumulation of this protease in fluids of CF patients. Conversely, in PBMCs isolated from healthy donors, expression and secretion of MMP9 are undetectable but can be evoked, after 12 h of culture, by paracrine stimulation which also promotes an increase in [Ca2+]i. We also demonstrate that in both CF and control PBMCs the Ca2+-dependent MMP9 secretion is mediated by the concomitant activation of calpain and protein kinase Cα (PKCα), and that MMP9 expression involves extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) phosphorylation. Our results are supported by the fact that either the inhibition of Ca2+ entry or chelation of [Ca2+]i as well as the inhibition of single components of the signaling pathway or the restoration of CFTR activity all promote the reduction of MMP9 secretion.