Characterization of protein kinase C and its isoforms in human T lymphocytes

Protein kinase C (PKC) regulates numerous T cell functions and is present in abundance in normal human T cells and certain T cell lines. Although crude Triton X-100 soluble material obtained from T cell pellets contains minimal PKC activity, DEAE chromatography revealed that 12 to 37% of cellular PKC was membrane associated, probably due to removal of an inhibitor through column chromatography. As in other tissues, PKC from lymphoid tissue was phospholipid and Ca2+ dependent and diolein reduced the Ca2+ requirements for enzyme activity. Hydroxylapatite chromatography revealed that T cells possess two major peaks of PKC activity. Although, the enzyme in these peaks had similar m.w. and identical iso-electric mobility, the proteins differed with respect to their autophosphorylation sites and immunoreactivity toward an isoform specific antibody. Furthermore, differences in their activities in the presence of phospholipid, diolein, and limiting amounts of Ca2+ imply that these isoforms may be differentially activated. We discuss optimal conditions for activation of PKC and its isoforms for study of T lymphocyte cellular function.     

Polymyxin B causes coordinate inhibition of phorbol ester-induced C-kinase activity and proliferation of B lymphocytes

Lymphocytes were found to be rich in phospholipid/Ca2+-dependent (C-kinase) activity. Addition of polymyxin B (PMB) to in vitro assays of endogenous and exogenous phosphorylation resulted in profound inhibition of C-kinase activity. The phorbol ester 12-o-tetradecanoyl phorbol-13-acetate (TPA) directly activated C-kinase, leading to increased phosphorylation of the same substrates. TPA also stimulated proliferation of B cells as assessed by 3H-thymidine uptake, and PMB strongly inhibited this effect. This coordinate inhibition of TPA-induced phosphorylation and mitogenesis indicates that PMB is a potentially useful inhibitor of C-kinase activity, and that this enzyme may play an important role in mediating B cell responses.     

Role of ultrasonography in diagnosing early rheumatoid arthritis and remission of rheumatoid arthritis - a systematic review of the literature

Introduction

Ultrasonography (US) might have an added value to clinical examination in diagnosing early rheumatoid arthritis (RA) and assessing remission of RA. We aimed to clarify the added value of US in RA in these situations performing a systematic review.

Methods

A systematic literature search was performed for RA, US, diagnosis and remission. Methodological quality was assessed; the wide variability in the design of studies prohibited pooling of results.

Results

Six papers on the added value of US diagnosing early RA were found, in which at least bilateral metacarpophalangeal (MCP), wrists and metatarsophalangeal (MTP) joints were scanned. Compared to clinical examination, US was superior with regard to detecting synovitis and predicting progression to persistent arthritis or RA. Eleven papers on assessing remission were identified, in which at least the wrist and the MCP joints of the dominant hand were scanned. Often US detected inflammation in patients clinically in remission, irrespective of the remission criteria used. Power Doppler signs of synovitis predicted X-ray progression and future flare in patients clinically in remission.

Conclusions

US appears to have added value to clinical examination for diagnosing of RA when scanning at least MCP, wrist and MTP joints, and, when evaluating remission of RA, scanning at least wrist and MCP joints of the dominant hand. For both purposes primarily power Doppler US might be used since its results are less equivocal than those of greyscale US.     

Notch Pathway Activation Contributes to Inhibition of C2C12 Myoblast Differentiation by Ethanol

The loss of muscle mass in alcoholic myopathy may reflect alcohol inhibition of myogenic cell differentiation into myotubes. Here, using a high content imaging system we show that ethanol inhibits C2C12 myoblast differentiation by reducing myogenic fusion, creating smaller and less complex myotubes compared with controls. Ethanol administration during C2C12 differentiation reduced MyoD and myogenin expression, and microarray analysis identified ethanol activation of the Notch signaling pathway target genes Hes1 and Hey1. A reporter plasmid regulated by the Hes1 proximal promoter was activated by alcohol treatment in C2C12 cells. Treatment of differentiating C2C12 cells with a gamma secretase inhibitor (GSI) abrogated induction of Hes1. On a morphological level GSI treatment completely rescued myogenic fusion defects and partially restored other myotube parameters in response to alcohol. We conclude that alcohol inhibits C2C12 myoblast differentiation and the inhibition of myogenic fusion is mediated by Notch pathway activation.     

Nerve Growth Factor Stimulates Multisite Tyrosine Phosphorylation and Activation of the Atypical Protein Kinase C's via a src Kinase Pathway

Atypical protein kinase C (PKC) isoforms are required for nerve growth factor (NGF)-initiated differentiation of PC12 cells. In the present study, we report that PKC-iota becomes tyrosine phosphorylated in the membrane coincident with activation posttreatment with nerve growth factor. Tyrosine phosphorylation and activation of PKC-iota were inhibited in a dose-dependent manner by both PP2 and K252a, src and TrkA kinase inhibitors. Purified src was observed to phosphorylate and activate PKC-iota in vitro. In PC12 cells deficient in src kinase activity, both NGF-induced tyrosine phosphorylation and activation of PKC-iota were also diminished. Furthermore, we demonstrate activation of src by NGF along with formation of a signal complex including the TrkA receptor, src, and PKC-iota. Recruitment of PKC-iota into the complex was dependent on the tyrosine phosphorylation state of PKC-iota. The association of src and PKC-iota was constitutive but was enhanced by NGF treatment, with the src homology 3 domain interacting with a PXXP sequence within the regulatory domain of PKC-iota (amino acids 98 to 114). Altogether, these findings support a role for src in regulation of PKC-iota. Tyrosine 256, 271, and 325 were identified as major sites phosphorylated by src in the catalytic domain. Y256F and Y271F mutations did not alter src-induced activation of PKC-iota, whereas the Y325F mutation significantly reduced src-induced activation of PKC-iota. The functional relevance of these mutations was tested by determining the ability of each mutant to support TRAF6 activation of NF-kappaB, with significant impairment by the Y325F PKC-iota mutant. Moreover, when the Y352F mutant was expressed in PC12 cells, NGF's ability to promote survival in serum-free media was reduced. In summary, we have identified a novel mechanism for NGF-induced activation of atypical PKC involving tyrosine phosphorylation by c-Src.     

Onchocerca volvulus: limited heterogeneity in the nuclear and mitochondrial genomes

West African populations of Onchocerca volvulus endemic to the rain forest and savanna bioclimes of West Africa differ in their ability to induce ocular disease in infected individuals. In recent years, both clinical- and animal-model-based studies have implicated particular parasite antigens in the development of ocular onchocerciasis. To test the hypothesis that the difference in pathogenic potential of blinding and nonblinding parasites might be reflected in qualitative differences in antigens that have been implicated in the development of ocular onchocerciasis, we compared the sequences of two parasite antigens implicated in the development of ocular disease in blinding- and nonblinding-strain parasites. The results demonstrated a high level of homogeneity between the parasite strains in these genes. The study was extended to include additional nuclear genes encoding antigens that are commonly recognized by individuals infected with O. volvulus and to the mitochondrial genome of the parasite. The results demonstrate a high degree of homogeneity in both the nuclear and the mitochondrial genomes among O. volvulus isolates collected from several different sites in Africa and in the Americas. This high degree of genetic homogeneity may reflect the passage of the parasite through a recent genetic bottleneck.     

aPKC Phosphorylation of HDAC6 Results in Increased Deacetylation Activity

The Class II histone deacetylase, HDAC6, has been shown to be involved in cell motility, aggresome formation and mitochondria transport. HDAC6 deacetylase activity regulates α-tubulin acetylation levels and thus plays a critical role in these processes. In turn, HDAC6 activity can be regulated by interaction with various proteins including multiple kinases. Kinase mediated phosphorylation of HDAC6 can lead to either increased or reduced activity. Our previous research has shown that sequestosome1/p62 (SQSTM1/p62) interacts with HDAC6 and regulates its activity. As SQSTM1/p62 is a scaffolding protein known to interact directly with the zeta isoform of Protein Kinase C (PKCζ), we sought to examine if HDAC6 could be a substrate for PKCζ phosphorylation and if so, how its activity might be regulated. Our data demonstrate that HDAC6 is not only present in a protein complex with PKCζ but can also be phosphorylated by PKCζ. We also show that specific phosphorylation of HDAC6 by PKCζ increases HDAC6 deacetylase activity resulting in reduced acetylated tubulin levels. Our findings provide novel insight into the molecular mechanism by which HDAC6, PKCζ and SQSTM1/p62 function together in protein aggregate clearance. These results also highlight a new research direction which may prove fruitful for understanding the underlying cause of several neurodegenerative diseases.     

Modulation of ζ-Protein Kinase C by Cyclic AMP in PC12 Cells Occurs Through Phosphorylation by Protein Kinase A

Abstract: Although cyclic AMP (cAMP) has been reported to cross talk with the protein kinase C (PKC) system, effects of elevated intracellular cAMP on the activities of specific PKC isoforms have not been studied. We report findings from a permeabilized cell assay that was used to examine changes in the activity of the atypical PKC isoforms brought about by exposure of PC12 cells to agents that elevate intracellular cAMP. We found that increases in intracellular cAMP led to rapid stimulation of atypical PKC activity, 40–70% above control, for a sustained period of time, a response that occurred independent of the phorbol 12-myristate 13-acetate (PMA)-sensitive PKC isoforms. Changes in intracellular cAMP levels resulted in a dose-dependent redistribution of ζ-PKC to the cytoplasm with a concomitant increase in the phosphorylation state of the enzyme. Incubation of purified ζ-PKC with increasing concentrations of PKA likewise caused a twofold increase in the phosphorylation state of ζ-PKC. In contrast to the positive effect that PKA-mediated phosphorylation had on the activity of ζ-PKC, the enzyme displayed reduced binding to ras when phosphorylated. Taken together, these findings are consistent with the hypothesis that protein phosphorylation of PKC acts as a positive effector of its enzyme activity and may serve as a negative modulator for interaction with other proteins.     

Control and optimization of apheresis procedures in a COBE 2997 cell separator

To obtain more efficient operation of a COBE Model 2997 clinical cell separator using either a Single Stage II (SS II) or a Dual Stage separation chamber, modifications were made to allow complete computer control. Product cell density was detected using an optical sensor and controlled by automatic feedback through a microcomputer interface. Control was accomplished by automatically adjusting the red blood cell (RBC) and plasma product flow rates using a proportional-integral (PI) algorithm. Results show that, using either chamber, the product cell density can be maintained at a preselected value for extended periods of time without operator intervention. This system allowed investigation of optimal operating regions for plateletpheresis and leukapheresis procedures. The effects of centrifuge rpm and controller set point on centrifuge operation were investigated using a second order factorial experimental design. Theoretical significance of model parameters was assessed with the aid of a hindered settling model and simple reasoning about the interface position relative to the collection port. The results suggest that, in either chamber, the optimum operating region for plateletpheresis procedures occurs at moderate controller set points and high centrifuge rpm. The resultant operating efficiency and product purity values are approximately 63 percent and 0.65 respectively in the SS II chamber and approximately 70 percent and 0.70 respectively in the Dual Chamber. In the SS II, the optimum operating region for leukapheresis procedures occurred at high controller set point values for any centrifuge rpm above 1200 with an operating efficiency near 100 percent. However, in the Dual Chamber, the optimum operating region for leukapheresis procedures occurred at high controller set points and high centrifuge rpm's, again providing an operating efficiency near 100 percent.