Calcineurin substrate

Recent studies have shown that calcineurin plays a central role in hypertrophy and extracellular matrix (ECM) accumulation in glomeruli at the early stages of diabetic nephropathy. Tropisetron is an effective antiemetic drug which also can potently inhibit calcineurin. The aim of this study was to investigate whether tropisetron can prevent glomerular hypertrophy and ECM expansion in early diabetic nephropathy. Streptozotocin (STZ)-induced diabetic rats were treated with tropisetron and cyclosporine A, a pharmacological calcineurin inhibitor, and the renal function and the expression of calcineurin and fibronectin were then assessed as well as nuclear localization of nuclear factor of activated T-cell c1 (NFATc1). 2 weeks after diabetes induction, all STZ-treated rats showed hyperglycemia, polyuria, body weight loss and renal dysfunction, as evidenced by increased glomerular filtration rate (GFR), along with a marked pathological changes in kidney.

KIF1Bβ is a candidate 1p36 tumor suppressor that regulates apoptosis in the developing sympathetic nervous system. We found that KIF1Bβ activates the Ca(2+)-dependent phosphatase calcineurin (CN) by stabilizing the CN-calmodulin complex, relieving enzymatic autoinhibition and enabling CN substrate recognition. CN is the key mediator of cellular responses to Ca(2+) signals and its deregulation is implicated in cancer, cardiac, neurodegenerative, and immune disease. We show that KIF1Bβ affects mitochondrial dynamics through CN-dependent dephosphorylation of Dynamin-related protein 1 (DRP1), causing mitochondrial fission and apoptosis. Furthermore, KIF1Bβ actuates recognition of all known CN substrates, implying a general mechanism for KIF1Bβ in Ca(2+) signaling and how Ca(2+)-dependent signaling is executed by CN. Pathogenic KIF1Bβ mutations previously identified in neuroblastomas and pheochromocytomas all fail to activate CN or stimulate DRP1 dephosphorylation.

Calcineurin heterodimer, comprised of the catalytic (CnaA) and regulatory (CnaB) subunits, localizes at the hyphal tips and septa to direct growth, septation, and disease in the human pathogen Aspergillus fumigatus. Here we discovered a novel motif (FMDVF) required for this critical CnaA septal localization, including residues Phe368, Asp370 and Phe372 overlapping the cyclosporine A-cyclophilin A-binding domain, CnaB-binding helix and the FK506-FKBP12-binding pocket. Mutations in adjacent residues Asn367, Trp374, and Ser375 confer FK506 resistance without impacting CnaA septal localization. Modeling A. fumigatus CnaA confirmed that the FMDVF motif forms a bridge between the two known substrate-binding motifs, PxIxIT and LxVP, and concurrent mutations (F368A D370A; F368A F372A) in the FMDVF motif disrupt CnaA-substrate interaction at the septum.

Variation in PPP3CC, the gene that encodes the γ isoform of the calcineurin catalytic subunit, has been reported to be associated with schizophrenia. Because of its low expression level in most tissues, there has been little research devoted to the specific function of the calcineurin Aγ (CNAγ) versus the calcineurin Aα (CNAα) and calcineurin Aβ (CNAβ) catalytic isoforms. Consequently, we have a limited understanding of the role of altered CNAγ function in psychiatric disease. In this study, we demonstrate that CNAγ is present in the rodent and human brain and dephosphorylates a presynaptic substrate of calcineurin. Through a combination of immunocytochemistry and immuno-EM, we further show that CNAγ is localized to presynaptic terminals in hippocampal neurons. Critically, we demonstrate that RNAi-mediated knockdown of CNAγ leads to a disruption of synaptic vesicle cycling in cultured rat hippocampal neurons. These data indicate that CNAγ regulates a critical aspect of synaptic vesicle cycling and suggest that variation in PPP3CC may contribute to psychiatric disease by altering presynaptic function.