The Lbc Rho guanine nucleotide exchange factor α-catulin axis functions in serotonin-induced vascular smooth muscle cell mitogenesis and RhoA/ROCK activation.
Serotonin (5-hydroxytryptamine, 5-HT) is mitogenic for several cell types including pulmonary arterial smooth muscle cells (PASMC), and is associated with the abnormal vascular smooth muscle remodeling that occurs in pulmonary arterial hypertension. RhoA/Rho kinase (ROCK) function is required for 5-HT-induced PASMC mitogenesis, and 5-HT activates RhoA; however, the signaling steps are poorly defined. Rho guanine nucleotide exchange factors (Rho GEFs) transduce extracellular signals to Rho, and we found that 5-HT treatment of PASMC led to increased membrane-associated Lbc Rho GEF, suggesting modulation by 5-HT. Lbc knockdown by siRNA attenuated 5-HT-induced thymidine uptake in PASMC, indicating a role in PASMC mitogenesis. 5-HT triggered Rho-dependent serum response factor-mediated reporter activation in PASMC, and this was reduced by Lbc depletion. Lbc knockdown reduced 5-HT-induced RhoA/ROCK activation, but not p42/44 ERK MAP kinase activation, suggesting that Lbc is an intermediary between 5-HT and RhoA/ROCK, but not ERK. 5-HT stimulation of PASMC led to increased association between Lbc, RhoA, and the α-catulin scaffold. Furthermore, α-catulin knockdown attenuated 5-HT-induced PASMC thymidine uptake. 5-HT-induced PASMC mitogenesis was reduced by dominant-negative G(q) protein, suggesting cooperation with Lbc/α-catulin. These results for the first time define a Rho GEF involved in vascular smooth muscle cell growth and serotonin signaling, and suggest that Lbc Rho GEF family members play distinct roles. Thus, the Lbc/α-catulin axis participates in 5-HT-induced PASMC mitogenesis and RhoA/ROCK signaling, and may be an interventional target in diseases involving vascular smooth muscle remodeling.
Bear
Michael D
MD
From the Division of Pulmonary and Critical Care, Tupper Research Institute, Tufts Medical Center, Boston, Massachusetts 02111.
Li
Min
M
From the Division of Pulmonary and Critical Care, Tupper Research Institute, Tufts Medical Center, Boston, Massachusetts 02111.
Liu
Yinglin
Y
From the Division of Pulmonary and Critical Care, Tupper Research Institute, Tufts Medical Center, Boston, Massachusetts 02111.
Giel-Moloney
Maryann A
MA
Department of Physiology, Tufts University School of Medicine, Boston, Massachusetts 02111.
Fanburg
Barry L
BL
From the Division of Pulmonary and Critical Care, Tupper Research Institute, Tufts Medical Center, Boston, Massachusetts 02111.
Toksoz
Deniz
D
From the Division of Pulmonary and Critical Care, Tupper Research Institute, Tufts Medical Center, Boston, Massachusetts 02111. Electronic address: dtoksoz@tuftsmedicalcenter.org.
D054758:A Kinase Anchor Proteins / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects*; D004789:Enzyme Activation / Q000187:drug effects / Q000235:genetics; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000235:genetics / Q000378:metabolism; D055785:Gene Knockdown Techniques; D006801:Humans; D015778:Minor Histocompatibility Antigens; D019950:Mitogen-Activated Protein Kinase 1 / Q000235:genetics / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000235:genetics / Q000378:metabolism; D008934:Mitogens / Q000378:metabolism / Q000494:pharmacology*; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D032389:Myocytes, Smooth Muscle / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D011651:Pulmonary Artery / Q000378:metabolism*; D012701:Serotonin / Q000378:metabolism / Q000494:pharmacology*; D026362:Serum Response Factor / Q000235:genetics / Q000378:metabolism; D014652:Vascular Diseases / Q000235:genetics / Q000378:metabolism; D051178:alpha Catenin / Q000235:genetics / Q000502:physiology*; D054460:rho-Associated Kinases / Q000235:genetics / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*
D054758:A Kinase Anchor Proteins; C085467:AKAP13 protein, human; C495274:CTNNAL1 protein, human; D015778:Minor Histocompatibility Antigens; D008934:Mitogens; D011518:Proto-Oncogene Proteins; C476858:SRF protein, human; D026362:Serum Response Factor; D051178:alpha Catenin; C066737:RHOA protein, human; D012701:Serotonin; D054460:rho-Associated Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D020742:rhoA GTP-Binding Protein