Homocysteine effects classical pathway of GPCR down regulation: Galpha(q/11), Galpha(12/13), G(i/o)

• Published in: Molecular and cellular biochemistry 2009-01, Vol.321 (1-2), p.1
• Main Authors: Vacek, T P, Sen, U, Tyagi, N, Kumar, M, Moshal, K S, Passmore, J C, Tyagi, S C
• Format: Article
• Language: English
• Subjects: Animals; Cells, Cultured; Dose-Response Relationship, Drug; Down-Regulation; Endothelial Cells - cytology; Endothelial Cells - drug effects; Endothelial Cells - physiology; Extracellular Signal-Regulated MAP Kinases - genetics; Extracellular Signal-Regulated MAP Kinases - metabolism; G-Protein-Coupled Receptor Kinase 2 - genetics; G-Protein-Coupled Receptor Kinase 2 - metabolism; GTP-Binding Protein alpha Subunits, G12-G13 - genetics; GTP-Binding Protein alpha Subunits, G12-G13 - metabolism; GTP-Binding Protein alpha Subunits, Gi-Go - genetics; GTP-Binding Protein alpha Subunits, Gi-Go - metabolism; GTP-Binding Protein alpha Subunits, Gq-G11 - genetics; GTP-Binding Protein alpha Subunits, Gq-G11 - metabolism; Homocysteine - metabolism; Homocysteine - pharmacology; Rats; Receptors, G-Protein-Coupled - agonists; Receptors, G-Protein-Coupled - genetics; Receptors, G-Protein-Coupled - metabolism; Signal Transduction - physiology
• ISSN: 1573-4919
• DOI: 10.1007/s11010-008-9904-4

G protein-coupled receptors (GPCRs) are known to modulate intracellular effectors involved in cardiac function. We recently reported homocysteine (Hcy)-induced ERK-phosphorylation was suppressed by pertussis toxin (PTX), which suggested the involvement of GPCRs in initiating signal transduction. An activated GPCR undergoes down regulation via a known mechanism involving ERK, GRK2, beta-arrestin1: ERK activity increases; GRK2 activity increases; beta-arrestin1 is degraded. We hypothesized that Hcy treatment leads to GPCR activation and down regulation. Microvascular endothelial cells were treated with Hcy. Expression of phospho-ERK1 and phospho-GRK2 was determined using Western blot, standardized to ERK1, GRK2, and beta-actin. Hcy was shown to dephosphorylate GRK2, thereby enhancing the activity. The results provided further evidence that Hcy acts as an agonist to activate GPCRs, followed by their down regulation. Hcy was also shown to decrease the content of the following G proteins and other proteins: beta-arrestin1, Galpha(q/11), Galpha(12/13), G(i/o).