Protein kinase Cε and protein kinase Cθ double-deficient mice have a bleeding diathesis.
BACKGROUND
In comparison to the classical isoforms of protein kinase C (PKC), the novel isoforms are thought to play minor or inhibitory roles in the regulation of platelet activation and thrombosis.


OBJECTIVE
To measure the levels of PKCθ and PKCε and to investigate the phenotype of mice deficient in both novel PKC isoforms.


METHODS
Tail bleeding and platelet activation assays were monitored in mice and platelets from mice deficient in both PKCθ and PKCε.


RESULTS
PKCε plays a minor role in supporting aggregation and secretion following stimulation of the collagen receptor GPVI in mouse platelets but has no apparent role in spreading on fibrinogen. PKCθ, in contrast, plays a minor role in supporting adhesion and filopodial generation on fibrinogen but has no apparent role in aggregation and secretion induced by GPVI despite being expressed at over 10 times the level of PKCε. Platelets deficient in both novel isoforms have a similar pattern of aggregation downstream of GPVI and spreading on fibrinogen as the single null mutants. Strikingly, a marked reduction in aggregation on collagen under arteriolar shear conditions is observed in blood from the double but not single-deficient mice along with a significant increase in tail bleeding.


CONCLUSIONS
These results reveal a greater than additive role for PKCθ and PKCε in supporting platelet activation under shear conditions and demonstrate that, in combination, the two novel PKCs support platelet activation.
Department of Biochemistry, University of Oxford, UK.
A J
AJ
Unsworth
B A
BA
Finney
L
L
Navarro-Nunez
S
S
Severin
S P
SP
Watson
C J
CJ
Pears
D000818:Animals; D001778:Blood Coagulation Disorders / Q000201:enzymology / Q000235:genetics*; D006487:Hemostasis; D007527:Isoenzymes / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D009154:Mutation; D015539:Platelet Activation; D010974:Platelet Aggregation; D011493:Protein Kinase C / Q000235:genetics* / Q000378:metabolism; D051744:Protein Kinase C-epsilon / Q000235:genetics* / Q000378:metabolism; D000074121:Protein Kinase C-theta
D007527:Isoenzymes; C489593:Prkcq protein, mouse; D011493:Protein Kinase C; D051744:Protein Kinase C-epsilon; D000074121:Protein Kinase C-theta