Atypical P2X receptor pharmacology in two human osteoblast-like cell lines.
OBJECTIVE
The expression and function of P2X(7) receptors in osteoclasts is well established, but less is known about their role in osteoblast-like cells. A study in P2X(7) receptor knockout mice suggested the involvement of these receptors in bone formation. We have investigated the expression and pharmacology of several P2X receptors in two human osteosarcoma cell lines to see if they could be involved in bone turnover in man.


METHODS
Reverse transcriptase-polymerase chain reaction and Western blotting were used to study P2X(2), P2X(4) and P2X(7) receptor expression at mRNA and protein levels, respectively, in human osteoblast-like cells. P2X(7) receptor pharmacology was studied by measuring pore formation in the presence of different agonists and antagonists using the YO-PRO 1 uptake method.


RESULTS
P2X(4) and P2X(7) receptor mRNA and protein were found to be expressed by these cell lines. No evidence was found for P2X(4)/P2X(7) receptor heteropolymerization. 2'-3'-O-(4-benzoylbenzoyl)adenosine 5'-triphosphate (DBzATP) was equipotent to ATP and the antagonists used were either ineffective or weakly blocked pore formation.


CONCLUSIONS
This study demonstrates that P2X(4) and P2X(7) receptors are expressed by human osteoblast-like cells. The affinities of the different agonists suggest that the P2X(7) receptor is mainly responsible for pore formation although P2X(4) receptors may also be involved. The low affinity of DBzATP and the weak action of the antagonists support the previously described atypical pharmacology of the P2X(7) receptor in osteoblasts. Targeting the P2X(7) receptor in osteoblasts could represent a promising new treatment for bone diseases such as osteoporosis and rheumatoid arthritis.
Alqallaf
S M
SM
Welsh School of Pharmacy, Cardiff University, King Edward VII Avenue, Cardiff, UK.
Evans
B A J
BA
Kidd
E J
EJ
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000648:ultrastructure; D006019:Glycolysis; D006801:Humans; D007150:Immunohistochemistry; D047468:Immunoprecipitation; D007559:Ivermectin / Q000494:pharmacology; D010006:Osteoblasts / Q000378:metabolism*; D016062:Porosity; D055503:Protein Multimerization; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D012333:RNA, Messenger / Q000096:biosynthesis; D018048:Receptors, Purinergic P2 / Q000096:biosynthesis; D058848:Receptors, Purinergic P2X4; D058486:Receptors, Purinergic P2X7; D020133:Reverse Transcriptase Polymerase Chain Reaction
C548226:P2RX4 protein, human; C546468:P2RX7 protein, human; C548227:P2rx4 protein, mouse; C546469:P2rx7 protein, mouse; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D012333:RNA, Messenger; D018048:Receptors, Purinergic P2; D058848:Receptors, Purinergic P2X4; D058486:Receptors, Purinergic P2X7; C033901:3'-O-(4-benzoyl)benzoyladenosine 5'-triphosphate; D007559:Ivermectin; D000255:Adenosine Triphosphate