P2Y receptor regulation of mitogenesis in vascular smooth muscle cells

This study investigates the effects of nucleotides on the regulation of mitogenesis in explant cultures of human saphenous vein (SV) VSM both in the presence and absence of PDGF at several levels in the mitogenic pathway.;[3H]-thymidine incorporation was used as an index of DNA synthesis and proliferation. PDGF induced increases in proliferation of SV VSMCs. Increases in ERK and JNK activation, but not p38 MAPK, were also observed using phospho-specific antibodies in Western blotting. MEK inhibitors, PD98059 and U0126, attenuated both PDGF-induced ERK activation and DNA synthesis. The activation of JNK was also found to be dependent upon ERK activation when these inhibitors were used. SB203580, LY294002 and Y27632, which were inhibitors of p38 MAPK, P13K and ROCK respectively, attenuated the PDGF-induced increase in DNA synthesis but did not block ERK or JNK activation.;Nucleotides such as ATP, ADP, UTP, UDP, 2MeSATP and ATPgS per se did not induce increases in [3H]-thymidine incorporation in SV cells. However, ATP in the presence of PDGF synergistically enhanced DNA synthesis in SV VSMCs, whereas UTP and UDP inhibited the PDGF-mediated DNA synthesis response. Other nucleotides had no effect. This suggested an antipropliferative role for UTP and UDP and a proliferative role for ATP. Neither ATP or UTP alone or with PDGF stimulated a detectable accumulation of inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) although ATP, UTP and PDGF elevated intracellular calcium levels.;ATP was found to increase the activation of ERK to the same extent as PDGF when incubated on cells for longer than 10 minutes. In the presence of PDGF, ATP synergistically enhanced the PDGF-induced ERK response. UTP and UDP alone did not increase the activation of ERK. Nucleotides did not increase the activation of JNK or p38 MAPK. However, in the presence of PDGF, UTP attenuated the PDGF-induced activation of JNK.