Age-dependent increases in protein kinase C-alpha beta immunoreactivity and activity in the human brain: possible in vivo modulatory effects on guanine nucleotide regulatory G(i) proteins

In the postmortem human brain (20 specimens of frontal cortex, Brodmann area 9) the abundance of immunoreactive protein kinase C (PKC-alpha beta) and the activity of PKC (calcium, phosphatidylserine, and phorbol ester-dependent enzymes) were determined to study the effect of aging (range 1 month to 89 years) on this regulatory enzyme. Also, the abundance of immunoreactive G protein subunits (G alpha i1/2, G alpha i3, G alpha o, G alpha s and G beta) were assessed in parallel to investigate possible relationships with PKC-alpha beta. The abundance of PKC-alpha beta was positively correlated with aging (r = 0.62, n = 20, P < 0.005). Moreover, PKC activity also showed a significant positive correlation with the age of the subject at death (r = 0.55, n = 14, P < 0.05). Because of the known in vitro modulatory role of PKC-alpha beta on G(i) proteins, the existence of an in vivo effect of brain PKC-alpha beta on various G proteins was assessed through correlation analyses. In the brain of the same subjects, there were significant negative correlations between the immunoreactivity of PKC-alpha beta and the immunoreactivities of G alpha i1/2 (r = -0.78, n = 13, P < 0.005) and G alpha i3 (r = -0.58, n = 15, P < 0.005). In the same brains, similar negative, although non-significant, correlations were found between the levels of PKC-alpha beta and those of G alpha o, G alpha s and G beta. The results demonstrate an up-regulation of brain PKC-alpha beta with aging and suggest the existence of a relevant in vivo modulatory role of this regulatory enzyme on inhibitory Gi proteins in the human brain during the process of aging.

Loss of protein kinase C-alpha beta in brain of heroin addicts and morphine-dependent rats

The biochemical status of human brain protein kinase C (PKC)-alpha beta during opiate dependence was studied by means of immunoblotting techniques in postmortem brain of heroin addicts who had died by opiate overdose. In the frontal cortex, a marked decrease (53%, p < 0.05) in the immunoreactivity of PKC-alpha beta was found in heroin addicts compared with matched controls. The loss of PKC-alpha beta in the brain of human addicts paralleled that observed in the frontal cortex of rats after chronic treatment with morphine (10-100 mg/kg i.p. for 5 days) (PKC-alpha beta decreased by 34%, p < 0.05). Chronic treatment with naloxone (1 mg/kg i.p. every 12 h for 5 days) did not alter PKC-alpha beta immunoreactivity in the rat brain. However, in morphine-dependent rats, naloxone-precipitated withdrawal induced a rapid and strong behavioral reaction with a concomitant up-regulation of PKC-alpha beta immunoreactivity to control values. These results indicated that the decrease of brain PKC-alpha beta induced by heroin/morphine is a mu-opioid receptor-mediated effect. The chronic administration of opiates has been associated with a marked sensitization of the adenylyl cyclase/cyclic AMP system, although this phenomenon is not exclusive of the opioid system but the general cellular adaptation to chronic inhibition of adenylyl cyclase. In this context, chronic treatment of rats with other inhibitory agonists (e.g., clonidine, 1 mg/kg i.p. every 12 h for 14 days) acting through receptors (e.g., alpha 2-adrenoceptors) also coupled to adenylyl cyclase did not alter brain PKC-alpha beta immunoreactivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypercalcaemia and increased serum interleukin-6 levels induced by all-trans retinoic acid in patients with multiple myeloma

All-trans retinoic acid (ATRA) inhibits human myeloma cell growth in vitro, presumably through the down-regulation of interleukin 6 receptors (IL-6R). Based on these and other studies, we initiated a phase II clinical trial using ATRA in patients with advanced refractory multiple myeloma (MM). We report that three out of six treated patients developed severe hypercalcaemia following administration of ATRA, which was accompanied by a significant rise in serum IL-6 levels. Normal calcium levels were restored after the discontinuation of the drug and the administration of standard anti-hypercalcaemic care. We suspect that down-regulation of IL-6R resulted in increased serum IL-6 levels, leading to advanced bone resorption and hypercalcaemia. We conclude that the use of ATRA in patients with advanced MM is not warranted.

Differential modulation of protein kinase C isoforms in erythroleukemia during induced differentiation

Induction of erythroid differentiation of murine erythroleukemia cells (MELC) by exposure to hexamethylene bisacetamide (HMBA) involves the modulation of protein kinase C (PKC) activity. Using immuno- and Northern blot techniques, we have demonstrated that MELC express a pattern of PKC isoforms which includes PKC alpha, PKC delta, PKC epsilon, PKC zeta, and PKC eta. We show that MELC resistant to induction by HMBA express significantly less of the nPKC isoform, PKC delta, and slightly less PKC epsilon. Recovery of HMBA sensitivity is associated with reexpression of PKC delta protein. Upon exposure to HMBA, there is a fall in cytosolic PKC delta and PKC epsilon accompanied by a transient increase in membrane-associated forms of these PKC isoforms. HMBA-resistant MELC fail to display this isoform-specific translocation of PKC. Induction of differentiation is accompanied, over the next 24 h of exposure to HMBA, by a progressive fall in cellular PKC activity, associated with a progressive fall in the cellular content of PKC delta, PKC epsilon, and PKC zeta. These studies suggest that PKC delta, and possibly PKC epsilon and PKC zeta as well, play a role in the pathway of HMBA-mediated terminal cell differentiation of MELC.

Antibodies to the human gamma 2 subunit of the gamma-aminobutyric acidA/benzodiazepine receptor

A gamma-aminobutyric acidA (GABAA) receptor (GABAAR) gamma 2 subunit (short form) was cloned from an adult human cerebral cortex cDNA library in bacteriophage lambda gt11. The 261-bp intracellular loop (IL) located between M3 and M4 was amplified using the polymerase chain reaction and inserted into the expression vectors lambda gt11 and pGEX-3X. Both beta-galactosidase (LacZ) and glutathione-S-transferase (GST) fusion proteins containing the gamma 2IL were purified, and a rabbit antibody to the LacZ-gamma 2IL was made. The antibody reacted with the gamma 2IL of both LacZ and GST fusion proteins and immunoprecipitated the GABAAR/benzodiazepine receptor (GABAAR/BZDR) from bovine and rat brain. The antibody reacted in affinity-purified GABAAR/BZDR immunoblots with a wide peptide band of 44,000-49,000 M(r). Immunoprecipitation studies with the anti-gamma 2IL antibody suggest that in the cerebral cortex, 87% of the GABAARs with high affinity for benzodiazepines and 70% of the GABAARs with high affinity for muscimol contain at least a gamma subunit, probably a gamma 2. These results indicate that there are [3H]muscimol binding GABAARs that do not bind [3H]flunitrazepam with high affinity. Immunoprecipitations with this and other anti-GABAAR/BZDR antibodies indicate that the most abundant combination of GABAAR subunits in the cerebral cortex involves alpha 1, gamma 2 (or other gamma), and beta 2 and/or beta 3 subunits. These subunits coexist in > 60% of the GABAAR/BZDRs in the cerebral cortex. The results also show that a considerable proportion (20-25%) of the cerebellar GABAAR/BZDRs is clonazepam insensitive. At least 74% of these cerebellar receptors, which likely contain alpha 6, also contain gamma 2 (or other gamma) subunit(s). The alpha 1 and beta 2 or beta 3 subunits are also frequently associated with gamma 2 (or other gamma) and alpha 6 in these cerebellar receptors.

A rise and fall in 1,2-diacylglycerol content signal hexamethylene bisacetamide-induced erythropoiesis

Previous studies have suggested a role for protein kinase C (PKC) during induction of murine erythroleukemia cell (MELC) differentiation by hexamethylene bisacetamide (HMBA) (Melloni, E., Pontremoli, S., Viotti, P. L., Patrone, M., Marks, P. A., and Rifkind, R. A. (1989) J. Biol. Chem. 264, 18414-18418). The present studies assess the effect of HMBA on the content of 1,2-diacylglycerol (DG), the physiologic activator of PKC, in MELC variants. Exposure of parental Sc9 cells to HMBA induced a rapid rise and fall in DG content. The DG level increased within seconds from 225 pmol.10(6) cells-1 to a maximum of 305 pmol.10(6) cells-1 at 5 min. Thereafter, DG content fell reaching control levels at 30 min and 46% of control at 4 h. Similar DG elevations were detected in HMBA-resistant, phorbol ester-resistant, and vincristine-resistant MELC lines. Early DG elevation was followed by the characteristic rapid fall in both the phorbol ester-resistant and vincristine-resistant lines, both of which differentiate rapidly in response to HMBA. In contrast, in an HMBA-resistant MELC the DG level failed to fall for at least 10 h. Selection of HMBA-resistant cells for vincristine resistance restores both HMBA sensitivity and the rapid fall in DG content. Addition of a synthetic DG, 1-oleyl-2-acetyl glycerol (OAG), along with HMBA and every 2 h for the next 48 h blocked differentiation, as measured by accumulation of benzidine-reactive cells or by the commitment assay in methyl-cellulose. However, if addition of OAG was delayed for just a few minutes, until endogenous DG levels began to fall, differentiation was no longer inhibited. Rapid elevation of DG content is the earliest reported event during HMBA action and a subsequent fall in the DG content appears to be a critical step in the process of commitment to terminal differentiation.

Cloning of a D-type cyclin from murine erythroleukemia cells

We report the complete coding sequence of a cDNA, designated CYL2, derived from a murine erythroleukemia cell library. CYL2 is considered to encode a D-type cyclin because (i) there is cross hybridization with CYL1 (a murine homolog of human cyclin D1) and the encoded protein has 64% amino acid sequence identity with CYL1 and (ii) murine erythroleukemia cell-derived CYL2 contains an amino acid sequence identical to that previously reported for the C-terminal portion of a partially sequenced CYL2. Transcripts of murine erythroleukemia cell CYL2 undergo alternative polyadenylylation like that of human cyclin D1. A major 6.5-kilobase CYL2 transcript changes its expression during the cell cycle with a broad peak through G1 and S phases and a decrease in G2/M phases. The present findings suggest that CYL2 plays a role in the G1 to S phase progression.

Protein kinase C isozymes epsilon and alpha in murine erythroleukemia cells

Protein kinase C (PKC) has a role in signal transduction during hexamethylene bisacetamide (HMBA)-induced differentiation of murine erythroleukemia cells (MELC). Separation of MELC PKC isozymes by hydroxylapatite chromatography yields a major peak (III) and a minor peak (II) of PKC activity, previously reported to contain the PKC alpha and beta isozymes, respectively. In the present study, we confirm that peak III activity is PKC alpha but show that peak II contains PKC epsilon and little or no PKC beta. Immunoblot analysis with isozyme-specific anti-alpha and anti-epsilon PKC antibodies detected PKC alpha in peak III and PKC epsilon in peak II. Peak III activity was markedly enhanced (up to 20-fold) by phosphatidylserine, diolein, and Ca2+, whereas addition of these cofactors to the reaction mixture stimulated peak II activity only 2- to 4-fold. RNase protection analysis of MELC RNA showed that PKC alpha and PKC epsilon RNAs were in a ratio of approximately 2:1, but PKC beta RNA was barely detectable. Taken together, these data indicate that MELC contain PKC alpha and PKC epsilon but little or no PKC beta.

Two types of asymmetric acetylcholinesterase in chick hindlimb muscle: developmental profiles, in vivo and in cell culture, and recovery after inactivation

1. We have analyzed the behavior of two types of asymmetric molecular forms (A forms) of acetylcholinesterase (AChE) during development of chick hindlimb muscle, in vivo and in cell culture, and upon irreversible inactivation of peroneal muscle AChE with diisopropylfluorophosphate (DFP) in vivo. 2. In agreement with previous developmental studies on chick muscle, globular forms of AChE (G forms) are predominant in chick hindlimb at early embryonic ages, being gradually replaced by A forms as hatching (and, therefore, onset of locomotion) approaches. Of the two A-form types, AI appears and accumulates significantly earlier than AII, so that A/G and II/I ratios higher than 1 are attained only at about hatching time. 3. Cultures prepared from 11-day chick embryo hindlimb myoblasts express both types of A forms, with a combined activity of 27% of total AChE after 12 days in culture. AI forms appear again earlier and are much more abundant than type II asymmetric species through the life span of cultures. 4. All AChE activity in the peroneal muscle is irreversibly inactivated by injection of DFP in vivo. The recovery of A forms follows the same sequence described for normal development, with a delayed and slower recovery of AII forms as compared with AI. 5. Several hypotheses involving tail polypeptides or tissue target molecules, or posttranslational interconversion, are proposed to help explain the earlier appearance and accumulation of AI forms in chick muscle.

Isolation and study of a liver alpha-amylase. Comparison with glycogen phosphorylase activity

An oligomaltosaccharide-forming amylase has been observed in mice liver crude homogenate. This enzyme has been isolated by binding to amylose. Some of its functional parameters have been studied and compared with those of glycogen phosphorylase demonstrating that amylase activity is not due to a glycogen phosphorylase isoenzyme. It has been further observed that amylase needs Ca2+ of Mg+2 and Cl- for its activity.