Specificity of G alpha q and G alpha 11 gene expression in platelets and erythrocytes. Expressions of cellular differentiation and species differences.
G alpha q and G alpha 11, members of the Gq family of G-proteins, transduce signals from receptors to the beta isoenzymes of phosphatidyl-inositol-specific phospholipase C (PI-PLC). The receptor specificity of these alpha subunits is unknown. G alpha q and G alpha 11 are ubiquitously expressed in tissues; however, there have been conflicting reports of the presence or absence of G alpha 11 protein in haematopoietic cells. Platelet thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptors activate PI-PLC via G alpha q, but the role of G alpha 11 is uncertain. To define their roles in platelet activation we studied G alpha q and G alpha 11 gene expression by immunotransfer blotting and by reverse transcription of mRNA followed by PCR (RT-PCR) and direct sequencing. An antiserum specific for mouse G alpha 11 failed to identify G alpha 11 in dog or human platelets or in dog liver, a tissue known to contain G alpha 11. RT-PCR performed with gene-specific primers demonstrated G alpha q mRNA, but not G alpha 11 mRNA, in normal human and mouse platelets and in thromboxane-sensitive and thromboxane-insensitive dog platelets. Studies of mouse and dog liver and human retina confirmed that the cDNA, primers and probes used could amplify and recognize G alpha 11 in other tissues. However, species-specific oligonucleotide primers and probes were essential to demonstrate G alpha 11, but not G alpha q, mRNA. Compared with mouse cDNA, dog and human G alpha 11 cDNA had twice as many nucleotide substitutions (approx. 12% compared with approx. 6%) as G alpha q, G alpha q mRNA was also found in mature erythrocytes but G alpha 11 mRNA was not identified, whereas both G alpha q and G alpha 11 mRNAs were found in bone marrow stem cells. Therefore G alpha 11 gene expression in haematopoietic cells is linked with cellular differentiation. The lack of G alpha 11 indicates that signal transduction from platelet TXA2/PGH2 receptors to PI-PLC occurs via G alpha q, and that G alpha 11 deficiency is not responsible for defective activation of PI-PLC in thromboxane-insensitive dog platelets. Despite the high degree of similarity that exists between G alpha q and G alpha 11, significantly greater species-specific variation in nucleotide sequence is present in G alpha 11 than in G alpha q. Cellular specificity and species specificity are important characteristics of these Gq family G-proteins.
Johnson
G J
GJ
Department of Medicine, VA Medical Center, Minneapolis, MN, USA.
Leis
L A
LA
Dunlop
P C
PC
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001792:Blood Platelets / Q000378:metabolism*; D002454:Cell Differentiation; D018076:DNA, Complementary / Q000235:genetics; D004285:Dogs; D004912:Erythrocytes / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000097:blood* / Q000235:genetics*; D015870:Gene Expression; D006801:Humans; D066298:In Vitro Techniques; D051379:Mice; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D014018:Tissue Distribution
D018076:DNA, Complementary; D012333:RNA, Messenger; D019204:GTP-Binding Proteins