ABSTRACT
Hereditary sensory and autonomic neuropathy type II (HSAN II) leads to severe mutilations because of impaired nociception and autonomic dysfunction. Here we show that loss-of-function mutations in FAM134B, encoding a newly identified cis-Golgi protein, cause HSAN II. Fam134b knockdown results in structural alterations of the cis-Golgi compartment and induces apoptosis in some primary dorsal root ganglion neurons. This implicates FAM134B as critical in long-term survival of nociceptive and autonomic ganglion neurons.
Subject(s)
Golgi Apparatus/metabolism , Hereditary Sensory and Autonomic Neuropathies/genetics , Membrane Proteins/genetics , Mutation , Neoplasm Proteins/genetics , Adult , Animals , Female , Hereditary Sensory and Autonomic Neuropathies/metabolism , Hereditary Sensory and Autonomic Neuropathies/pathology , Humans , Intracellular Signaling Peptides and Proteins , Male , Membrane Proteins/metabolism , Mice , Pedigree , RNA InterferenceABSTRACT
Inhibitor 1 (I-1) is a protein inhibitor of protein phosphatase 1 (PP1), the predominating Ser/Thr phosphatase in the heart. Non-phosphorylated I-1 is inactive, whereas I-1 phosphorylated by protein kinase A (PKA) at Thr35 is a potent PP1 inhibitor. The phosphatases that dephosphorylate I-1Thr35 and thus deactivate I-1 in the heart are not established. Here we overexpressed I-1 in neonatal rat cardiac myocytes with recombinant adenovirus and determined phosphorylation of I-1, and one of the major target proteins of PKA/PP1 in the heart, phospholamban (PLB), by Western blot with phospho-specific antibodies. Incubation with the calcineurin inhibitor cyclosporine A or okadaic acid, used at a concentration preferentially inhibiting phosphatase 2A (PP2A), increased significantly I-1Thr35 (approximately 2- to 6-fold) and PLB Ser16 phosphorylation (approximately 2-fold). The results indicate that calcineurin and PP2A act to maintain a low basal level of phosphorylated (active) I-1 in living cardiac myocytes. Calcineurin may constitute a cross-talk between calcium- and cAMP-dependent pathways.
Subject(s)
Calcineurin/metabolism , Intracellular Signaling Peptides and Proteins/metabolism , Myocytes, Cardiac/metabolism , Phosphoprotein Phosphatases/metabolism , Animals , Animals, Newborn , Cells, Cultured , Cyclosporine/pharmacology , Gene Expression Regulation , Intracellular Signaling Peptides and Proteins/genetics , Myocytes, Cardiac/drug effects , Okadaic Acid/pharmacology , Phosphorylation/drug effects , Protein Phosphatase 1 , Protein Phosphatase 2 , Rats , Serine/metabolism , Threonine/metabolismABSTRACT
OBJECTIVE: The protein phosphatase inhibitor-1 (I-1) is a highly specific and potent inhibitor of type 1 phosphatases (PP1) that is active only in its protein kinase A (PKA)-phosphorylated form. I-1 ablation decreases, I-1 overexpression sensitizes beta-adrenergic signaling in the heart. It is controversial whether I-1 expression is altered in human heart failure (HF), likely because its detection in heart is difficult due to its low abundance. METHODS AND RESULTS: I-1 was >500-fold enriched from left ventricular myocardium (LVM) from patients with terminal HF (n=16) and non-failing controls (NF, n=5) and quantified with an affinity-purified I-1 and a I-1 phosphospecific antiserum. In non-failing I-1 protein levels amounted to 126 fmol/mg protein. In failing hearts, I-1 protein levels were reduced by 58% and I-1 phosphorylation by 77% (P<0.001 vs. NF). I-1 phosphorylation correlated well with serine-16 phosphorylation of phospholamban (PLB) in the same hearts (P<0.001). In contrast, PLB, troponin I (TnI) and PP1 protein and TnI phosphorylation levels did not differ between HF and NF. CONCLUSIONS: The results suggest that the reduction in I-1 protein and phosphorylation in failing human hearts leads to increased phosphatase activity which in turn may result in reduced phosphorylation of cardiac proteins such as PLB.
Subject(s)
Cardiomyopathy, Dilated/metabolism , Carrier Proteins/analysis , Endoribonucleases , Intracellular Signaling Peptides and Proteins , Myocardium/chemistry , RNA-Binding Proteins , Adult , Aged , Animals , Blotting, Western/methods , Calcium-Binding Proteins/analysis , Calcium-Binding Proteins/metabolism , Carrier Proteins/genetics , Case-Control Studies , Female , Humans , Male , Mice , Mice, Knockout , Middle Aged , Phosphoprotein Phosphatases , Phosphorylation , Rabbits , Rats , Troponin I/analysis , Troponin I/metabolismABSTRACT
The protein phosphatase inhibitor-1 (PPI-1) inhibits phosphatase type-1 (PP1) only when phosphorylated by protein kinase A and could play a pivotal role in the phosphorylation/dephosphorylation balance. Rat cardiac PPI-1 was cloned by reverse transcriptase-polymerase chain reaction, expressed in Eschericia coli, evaluated in phosphatase assays, and used to generate an antiserum. An adenovirus was constructed encoding PPI-1 and green fluorescent protein (GFP) under separate cytomegalovirus promotors (AdPPI-1/GFP). A GFP-only virus (AdGFP) served as control. Engineered heart tissue (EHT) from neonatal rat cardiomyocytes and adult rat cardiac myocytes (ARCMs) were used as model systems. PPI-1 expression was determined in human ventricular samples by Northern blots. Compared with AdGFP, AdPPI-1/GFP-infected neonatal rat cardiomyocytes displayed a 73% reduction in PP1 activity. EHTs infected with AdPPI-1/GFP exhibited a fivefold increase in isoprenaline sensitivity. AdPPI-1/GFP-infected ARCMs displayed enhanced cell shortening as well as enhanced phospholamban phosphorylation when stimulated with 1 nM isoprenaline. PPI-1 mRNA levels were reduced by 57+/-12% in failing hearts with dilated and ischemic cardiomyopathy (n=8 each) compared with nonfailing hearts (n=8). In summary, increased PPI-1 expression enhances myocyte sensitivity to isoprenaline, indicating that PPI-1 acts as an amplifier in beta-adrenergic signaling. Decreased PPI-1 in failing human hearts could participate in desensitization of the cAMP pathway.
