Mechanisms of P2 receptor-evoked DNA synthesis in thyroid FRTL-5 cells

The expression of the P2 receptors and their functional responses were studied in rat thyroid FRTL‐5 cells. RT‐PCR analysis revealed transcripts for the G protein‐coupled P2Y2, P2Y4 and P2Y6 receptors, and for the transmitter‐gated ion channel P2X3, P2X4 and P2X5 subunits. In Fura‐2‐loaded cells, UTP, ATP, ATPγS or UDP increased [Ca2+]i, and behaved as potent full agonists, while 2‐Methylthio‐ATP (2‐MeSATP), α,β‐methylene‐ATP (α,β‐meATP) and pure ADP were weak agonists. The agonist‐mediated [Ca2+ ]i increases were diminished in Ca2+ ‐free buffer, and by pertussis toxin (PTX) or suramin treatments. ATP, UTP, UDP and ATPγS increased 3H‐thymidine incorporation into DNA and expression of the protooncogenes c‐Fos and c‐Jun, while 2‐MeSATP was ineffective, and α,β‐meATP gave a response only at 100‐μM dose. The ATP‐stimulated expression of c‐Fos and c‐Jun was dependent on Ca2+, and protein kinase C, but not on calmodulin or Ca2+/calmodulin‐dependent protein kinase II. Extracellular signal‐regulated kinases (ERK1 and ERK2) are also involved as the MEK inhibitor, PD98059, reduced both ATP‐evoked 3H‐thymidine incorporation and c‐Fos and c‐Jun expression. These results indicate that multiple P2Y receptor subtypes and at least the P2X5 subtype are functionally expressed in FRTL‐5 cells, and that nucleotides acting via P2 receptors are involved in the regulation of DNA‐synthesis. © 2001 Wiley‐Liss, Inc.