Activation of pyruvate dehydrogenase complex by porcine and biosynthetic human insulin in cultured human fibroblasts

Activation and mitochondrial translocation of protein kinase Cdelta are necessary for insulin stimulation of pyruvate dehydrogenase complex activity in muscle and liver cells

In L6 skeletal muscle cells and immortalized hepatocytes, insulin induced a 2-fold increase in the activity of the pyruvate dehydrogenase (PDH) complex. This effect was almost completely blocked by the protein kinase C (PKC) delta inhibitor Rottlerin and by PKCdelta antisense oligonucleotides. At variance, overexpression of wild-type PKCdelta or of an active PKCdelta mutant induced PDH complex activity in both L6 and liver cells. Insulin stimulation of the activity of the PDH complex was accompanied by a 2.5-fold increase in PDH phosphatases 1 and 2 (PDP1/2) activity with no change in the activity of PDH kinase. PKCdelta antisense blocked insulin activation of PDP1/2, the same as with PDH. In insulin-exposed cells, PDP1/2 activation was paralleled by activation and mitochondrial translocation of PKCdelta, as revealed by cell subfractionation and confocal microscopy studies. The mitochondrial translocation of PKCdelta, like its activation, was prevented by Rottlerin. In extracts from insulin-stimulated cells, PKCdelta co-precipitated with PDP1/2. PKCdelta also bound to PDP1/2 in overlay blots, suggesting that direct PKCdelta-PDP interaction may occur in vivo as well. In intact cells, insulin exposure determined PDP1/2 phosphorylation, which was specifically prevented by PKCdelta antisense. PKCdelta also phosphorylated PDP in vitro, followed by PDP1/2 activation. Thus, in muscle and liver cells, insulin causes activation and mitochondrial translocation of PKCdelta, accompanied by PDP phosphorylation and activation. These events are necessary for insulin activation of the PDH complex in these cells.

Lactic acidosis and mitochondrial dysfunction in two children with peroxisomal disorders

Mitochondrial myopathies and defects in oxidative phosphorylation have been described in some patients with peroxisomal disorders. Although peroxisomes and mitochondria play a role in the beta-oxidation of fatty acids, the metabolic interactions between the two are not well defined. Defects in peroxisomal beta-oxidation are associated with extracellular accumulation of very long-chain fatty acids and may be accompanied by alterations in the intracellular pool of fatty acyl-CoAs, which are known to alter mitochondrial function. This study was initiated to examine alterations in the intracellular pool of acyl-CoAs and mitochondrial function in two children with generalized disorders of peroxisomal function and clinical lactic/pyruvic acidaemia. Fibroblasts were cultured from skin biopsies obtained from one child with neonatal adrenoleukodystrophy (NALD) and another with rhizomelic chondrodysplasia punctata (RCDP). Fibroblast lactate oxidation was significantly inhibited in NALD by 76% and RCDP by 92% compared to control values of 1.9 +/- 0.1 nmol/min per mg protein. Pyruvate dehydrogenase (PDH) (mean +/- SEM; activity nmol/min per mg protein) was: NALD 0.55 +/- 0.02 (p < 0.01), RCDP 0.44 +/- 0.02 (P < 0.01), and controls 0.83 +/- 0.02. The acid-insoluble (long-chain and very long-chain) acyl-CoA levels (mean +/- SEM; pmol/mg protein) were: NALD 129 +/- 69 (p < 0.01), RCDP 65 +/- 15 (p < 0.05), and control 45 +/- 7. These two patients with generalized peroxisomal disorders exhibited an increase in intracellular acyl-CoA species accompanied by decreased PDH activity and clinical lactic/pyruvic acidaemia.

Atrial natriuretic peptide (ANP) is a high-affinity substrate for rat insulin-degrading enzyme

A cytosolic protein specifically binding to and degrading atrial natriuretic peptide (ANP) was purified from rat brain homogenate. Based on partial amino acid sequences and enzymatic properties, this protein with an apparent molecular mass of 112 kDa has been identified as the rat insulin-degrading enzyme (IDE). In addition to the known substrates, insulin and transforming-growth-factor alpha IDE binds also with high affinity (apparent Kd 60 nM) to ANP. Competition studies with structural variants of ANP demonstrate that both the C terminus and the disulfide loop of the molecule are essential for high-affinity binding. The data suggest that IDE might be involved in the cellular processing and/or metabolic clearance of ANP.

Identification of a 42K phosphoprotein of platelets modulated by collagen: the alpha-subunit of pyruvate dehydrogenase

Platelets exposed to collagen sufficient to stimulate the release reaction show an increase in labeling of two intracellular proteins with molecular weights of 20,000 and 42,000. The 20,000 Mr protein has already been identified as the light chain of myosin whereas the identity of the 42,000 Mr protein had not been established. By use of biochemical and immunological techniques, the identify of the 42,000 Mr component of prelabeled platelets found in the 100,000g supernatant of freeze-thawed or sonicated cells appears to be one of the subunits of pyruvate dehydrogenase complex which is translocated from the mitochondria to the 100,000g supernatant during the preparative procedure. Increased phosphorylation of the 42,000 Mr protein occurred after collagen stimulation and was accompanied by diminished pyruvate dehydrogenase activity.

Phytohemagglutinin (PHA) activated human T-lymphocytes: concomitant appearance of insulin binding, degradation and insulin-mediated activation of pyruvate dehydrogenase (PDH)

Binding and degradation of A14125I-Insulin as well as the effect of insulin on pyruvate dehydrogenase (PDH) activation were studied in non-stimulated and phytohemagglutinin (PHA)-stimulated thymic-derived lymphocytes (T-lymphocytes) of man under varying conditions of time, temperature, and cell concentration. The nonstimulated viable T-lymphocytes exhibited neither binding, degradation, nor PDH activation in response to insulin. With PHA stimulation, a time and temperature-dependent binding was noted in T-lymphocytes which paralleled the appearance of cell-associated insulin degrading activity. Concomitant with the emergence of insulin binding and degrading activities in these cells, PDH activation was observed which was responsive to as little as 5.0 microU/ml of insulin. We conclude that in PHA-activated T-lymphocytes of man the process of insulin binding and degradation is closely related to insulin sensitive activation of PDH. These activated cells may serve as a useful model in which to study insulin binding and processing, as well as effects of insulin on postreceptor events.

Activation of pyruvate dehydrogenase complex (PDC) of rat heart mitochondria by glyburide

The effects of the second generation sulfonylurea, glyburide, on the pyruvate dehydrogenase multienzyme complex (PDC) of rat myocardial tissue were examined using rat ventricular slices and isolated mitochondria. Therapeutic concentrations (10(-7) to 10(-6)M) of glyburide produced a 30% increase in the decarboxylation of [1(-14)C] pyruvate by the PDC of ventricular tissue. Addition of glyburide to intact rat heart mitochondria stimulated activity of the PDC in a time- and concentration-dependent manner. Half-maximal stimulation of the enzyme occurred with 6 X 10(-5)M glyburide and maximal activation of the enzyme was achieved with 1 X 10(-4)M glyburide. At the height of stimulation, PDC activities were 6-fold greater than those observed under control conditions with succinate alone. When mitochondria were disrupted by sonication or freeze-thawing, glyburide produced no stimulation of pyruvate decarboxylation. We conclude that glyburide directly stimulates the decarboxylation of pyruvate by the PDC of the myocardium. Furthermore, the presence of intact mitochondria is necessary for the stimulatory action of glyburide on the PDC.