Lineage-specific defect in gene expression in human platelet phospholipase C-β2 deficiency

Abstract

Phospholipase C (PLC)-β2 plays a major role in platelet activation. Previous studies have described a unique patient with impaired receptor-mediated platelet aggregation, secretion, calcium mobilization, and phospholipase C (PLC) activation associated with a selective decrease in platelet PLC-β2 isozyme. To identify the mechanisms leading to the defect, platelet RNA from the patient and healthy subjects was subjected to reverse transcription-polymerase chain reaction (RT-PCR) and the products sequenced. The PLC-β2 cDNA sequence in the patient showed no abnormalities. Platelet PLC-β2 and β-actin (internal control) mRNA levels were assessed by RT-PCR; the ratio of PLC-β2 to β-actin mRNA levels was 0.80 to 0.95 in 4 healthy subjects and 0.28 in the patient. PLC-β2 mRNA levels were similarly reduced compared with GPIIb and Gαq mRNA levels. PLC-γ2 and platelet factor 4 mRNA levels were normal. Calcium mobilization was studied in neutrophils upon activation with formyl-MetLeu-Phe (fMLP), adenosine diphosphate (ADP), platelet-activating factor (PAF), interleukin-8 (IL-8), C5a, and leukotriene B4 (LTB4), and it was normal. Neutrophil elastase secretion upon activation with fMLP, ADP, PAF, IL-8, C5a, and LTB4 was normal, as were neutrophil PLC-β2 mRNA and PLC-β2 on immunoblotting. Thus, responses to activation, PLC-β2 protein, and PLC-β2 mRNA are decreased in patient platelets but not in neutrophils, providing evidence for a hitherto undescribed lineage (platelet)-specific defect in PLC-β2 gene expression. These studies provide a physiologically relevant model to delineate regulation of PLC-β2 gene and its tissue-specific expression. © 2002 by The American Society of Hematology.