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Cell Signal. 2014 Dec;26(12):2818-25. doi: 10.1016/j.cellsig.2014.09.002. Epub 2014 Sep 15.

Tissue transglutaminase promotes serotonin-induced AKT signaling and mitogenesis in pulmonary vascular smooth muscle cells.

Author information

1
Pulmonary and Critical Care Division, Tupper Research Institute, Tufts Medical Center, Tufts University School of Medicine, Boston, MA 02111, United States.
2
Dept of Pharmacology and Toxicology, Michigan State University, East Lansing, MI 48824, United States.
3
Pulmonary and Critical Care Division, Tupper Research Institute, Tufts Medical Center, Tufts University School of Medicine, Boston, MA 02111, United States. Electronic address: dtoksoz@tuftsmedicalcenter.org.

Abstract

Tissue transglutaminase 2 (TG2) is a multifunctional enzyme that cross-links proteins with monoamines such as serotonin (5-hydroxytryptamine, 5-HT) via a transglutamidation reaction, and is associated with pathophysiologic vascular responses. 5-HT is a mitogen for pulmonary artery smooth muscle cells (PASMCs) that has been linked to pulmonary vascular remodeling underlying pulmonary hypertension development. We previously reported that 5-HT-induced PASMC proliferation is inhibited by the TG2 inhibitor monodansylcadaverine (MDC); however, the mechanisms are poorly understood. In the present study we hypothesized that TG2 contributes to 5-HT-induced signaling pathways of PASMCs. Pre-treatment of bovine distal PASMCs with varying concentrations of the inhibitor MDC led to differential inhibition of 5-HT-stimulated AKT and ROCK activation, while p-P38 was unaffected. Concentration response studies showed significant inhibition of AKT activation at 50 μM MDC, along with inhibition of the AKT downstream targets mTOR, p-S6 kinase and p-S6. Furthermore, TG2 depletion by siRNA led to reduced 5-HT-induced AKT activation. Immunoprecipitation studies showed that 5-HT treatment led to increased levels of serotonylated AKT and increased TG2-AKT complex formations which were inhibited by MDC. Overexpression of TG2 point mutant cDNAs in PASMCs showed that the TG2 C277V transamidation mutant blunted 5-HT-induced AKT activation and 5-HT-induced PASMC mitogenesis. Finally, 5-HT-induced AKT activation was blunted in SERT genetic knock-out rat cells, but not in their wild-type counterpart. The SERT inhibitor imipramine similarly blocked AKT activation. These results indicate that TG2 contributes to 5-HT-induced distal PASMC proliferation via promotion of AKT signaling, likely via its serotonylation. Taken together, these results provide new insight into how TG2 may participate in vascular smooth muscle remodeling.

KEYWORDS:

AKT; S6; S6K; SERT; Serotonin; Transglutaminase 2

PMID:
25218191
PMCID:
PMC4270091
DOI:
10.1016/j.cellsig.2014.09.002
[Indexed for MEDLINE]
Free PMC Article

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