C-reactive protein mediates CD11b expression in monocytes through the non-receptor tyrosine kinase, Syk, and calcium mobilization but not through cytosolic peroxides.
OBJECTIVE
C-Reactive protein (CRP) can modulate integrin surface expression on monocytes following Fcgamma receptor engagement. We have investigated the signal transduction events causing this phenotypic alteration.


METHODS
CRP-induced signalling events were examined in THP-1 and primary monocytes, measuring Syk phosphorylation by Western blotting, intracellular Ca(2+) ([Ca(2+)](i)) by Indo-1 fluorescence and surface expression of CD11b by flow cytometry. Cytosolic peroxides were determined by DCF fluorescence.


RESULTS
CRP induced phosphorylation of Syk and an increase in [Ca(2+)](i) both of which were inhibitable by the Syk specific antagonist, piceatannol. Piceatannol also inhibited the CRP-induced increase in surface CD11b. In addition, pre-treatment of primary monoytes with the Ca(2+) mobiliser, thapsigargin, increased CD11b expression; this effect was accentuated in the presence of CRP but was abolished in the presence of the [Ca(2+)](i) chelator, BAPTA. CRP also increased cytosolic peroxide levels; this effect was attenuated by antioxidants (ascorbate, alpha-tocopherol), expression of surface CD11b not being inhibited by antioxidants alone.


CONCLUSIONS
CRP induces CD11b expression in monocytes through a peroxide independent pathway involving both Syk phosphorylation and [Ca(2+)](i) release.
Woollard
K J
KJ
Life and Health Sciences, Aston University, Aston Triangle, Birmingham, B4 7ET, UK.
Fisch
C
C
Newby
R
R
Griffiths
H R
HR
D000975:Antioxidants / Q000494:pharmacology; D015153:Blotting, Western; D002097:C-Reactive Protein / Q000494:pharmacology / Q000502:physiology*; D039481:CD11b Antigen / Q000096:biosynthesis* / Q000235:genetics; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D045744:Cell Line, Tumor; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004792:Enzyme Precursors / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005434:Flow Cytometry; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D009000:Monocytes / Q000276:immunology* / Q000378:metabolism; D010545:Peroxides / Q000378:metabolism*; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017452:Receptors, IgG / Q000502:physiology; D015398:Signal Transduction; D013267:Stilbenes / Q000494:pharmacology; D000072377:Syk Kinase; D019284:Thapsigargin / Q000494:pharmacology
D000975:Antioxidants; D039481:CD11b Antigen; D002614:Chelating Agents; D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D010545:Peroxides; D017452:Receptors, IgG; D013267:Stilbenes; D004533:Egtazic Acid; D019284:Thapsigargin; C041525:3,3',4,5'-tetrahydroxystilbene; D002097:C-Reactive Protein; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium