Distinct Pathways of ERK1/2 Activation by Hydroxy-Carboxylic Acid Receptor-1

Abstract

Mechanistic investigations have shown that, upon agonist activation, hydroxy-carboxylic acid receptor-1(HCA1) couples to a Gi protein and inhibits adenylate cyclase activity, leading to inhibition of liberation of free fatty acid. However, the underlying molecular mechanisms for HCA1 signaling remain largely unknown. Using CHO-K1 cells stably expressing HCA1, and L6 cells, which endogenously express rat HCA1 receptors, we found that activation of ERK1/2 by HCA1 was rapid, peaking at 5 min, and was significantly blocked by pertussis toxin. Furthermore, time course experiments with different kinase inhibitors demonstrated that HCA1 induced ERK1/2 activation via the extracellular Ca2+, PKC and IGF-I receptor transactivation-dependent pathways. In addition, we observed that pretreated the cells with M119K, an inhibitor of Gβγ subunit-dependent signaling, effectively attenuated the ERK1/2 activation triggered by HCA1, suggesting a critical role for βγ-subunits in HCA1-activated ERK1/2 phosphorylation. Furthermore, the present results also indicated that the arrestin2/3 were not required for ERK1/2 activation. In conclusion, our findings demonstrate that upon binding to agonist, HCA1 receptors initially activate Gi, leading to dissociation of the Gβγ subunit from activated Gi, and subsequently induce ERK1/2 activation via two distinct pathways: one PKC-dependent pathway and the other IGF-IR transactivation-dependent pathway. Our results provide the first in-depth evidence that defines the molecular mechanism of HCA1-mediated ERK1/2 activation.

Lactate increases myotube diameter via activation of MEK/ERK pathway in C2C12 cells

“…The present study demonstrated a significant increase in phosphorylated form of MEK1/2, ERK1/2 and p90RSK following the administration of lactate or 3,5‐DHBA. This result is supported by the previous study showing that 3,5‐DHBA activated MEK/ERK pathway in L6 skeletal muscle cells . On the other hand, no response was observed in the phosphorylated level of Akt‐mTOR‐p70S6K.…”

“…Sodium lactate (lactate) was purchased from Otsuka Pharmaceutical Factory (Naruto, Tokushima, Japan). The concentration of lactate was set between 0 and 20 mmol/L in the conditioned culture medium, considering the previous studies using skeletal muscle cells . Furthermore, these lactate levels were observed in human blood after exercise .…”

“…In addition, IGF‐I‐associated rat skeletal muscle hypertrophy was prevented by the inhibition of ERK1/2 . It is reported that lactate caused GPR81‐mediated activation of MEK/ERK pathway in L6 cultured skeletal muscle cells . Furthermore, recent study demonstrated that lactate stimulates the anabolic signals for muscle hypertrophy in C2C12 skeletal muscle cells .…”

Lactate administration activates the ERK1/2, mTORC1, and AMPK pathways differentially according to skeletal muscle type in mouse

“…In skeletal muscle cell lines as L6 and C2C12, lactate activates the ERK1/2 pathway (Li et al. ) and is also related to both oxidative metabolism (Hashimoto et al. ; Kim et al.…”

“…In vivo lactate administration increases messenger RNA levels of oxidative metabolism-related genes as PGC-1a in skeletal muscle of mouse . In skeletal muscle cell lines as L6 and C2C12, lactate activates the ERK1/2 pathway (Li et al 2014) and is also related to both oxidative metabolism (Hashimoto et al 2007;Kim et al 2017), and hypertrophy signaling (Ohno et al 2018;Oishi et al 2015). However, the molecular signaling activated by lactate in mature skeletal muscle has not been fully unveiled.…”