Rapid Nongenomic Effects of 3,5,3′-Triiodo-l-Thyronine on the Intracellular pH of L-6 Myoblasts Are Mediated by Intracellular Calcium Mobilization and Kinase Pathways

Abstract

L-T3 and L-T4 activated the Na+/H+ exchanger of L-6 myoblasts, with a fast nongenomic mechanism, both in the steady state and when cells undergo acid loading with ammonium chloride. Monitored with the intracellular pH-sensitive fluorescent probe 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein, activation of the exchanger appeared to be initiated at the plasma membrane, because T3-agarose reproduced the effect of L-T3, and triiodothyroacetic acid, a hormone analog previously shown to inhibit membrane actions of thyroid hormone, blocked the action of L-T3 on the exchanger. We show here for the first time that transduction of the hormone signal in this nongenomic response requires tyrosine kinase-dependent phospholipase C activation and two different signaling pathways: 1) mobilization of intracellular calcium, assessed by the fluorescent probe fura-2, through activation of inositol trisphosphate receptors and without contributions from extracellular calcium or ryanodine receptors; and 2) protein phosphorylation involving protein kinase C and MAPK (ERK1/2), as shown by the use of kinase inhibitors and by immunoblotting for activated kinases.

Integrin-Mediated Actions of Thyroid Hormone Analogues on Tumor Cell Chemosensitivity, Integrin-Growth Factor Receptor Crosstalk and Inflammatory Gene Expression

“…Binding of thyroid hormone analogues, including tetrac formulations, at the integrin site changes levels of activation of pools of extracellular regulated kinase 1/2 (ERK1/2) associated with the intracellular domain of the integrin ('feet'). ERK1/2 modulates activity of the Na + /H + antiporter (exchanger) which pumps H + out of cells in exchange for Na + (D'Arezzo et al, 2004), as shown. The authors propose that decreased activity of the exchanger in response to liganding of tetrac by v3 acidifies cells; this action may reduce pump activity of P-glycoprotein (P-gp) (Sharom 2011), leading to cancer cell retention of chemotherapeutic agents usually subject to export by P-gp.…”

“…Because efflux pumps-e.g., P-glycoprotein (P-gp) and other multidrug resistance proteins (MRPs) (Sharom, 2011) are the basis of resistance in tumor cells to certain anti-cancer agents, it was proposed that such pump activity was in fact opposed by tetrac. The molecular basis for this chemosensitizing action of tetrac has not yet been established, but one possibility is that the known inhibitory effect of tetrac on the sodium/proton exchanger (Na + /H + antiporter) (D'Arezzo et al, 2004) acidifies cancer cells, moving intracellular pH away from the optimum of the P-glycoprotein pump. Interference with antiporter function may also remove the contribution to protective acidic extracellular pH that is an attribute of solid tumors, although other factors such as hypoxia may be more important to maintaining this attribute.…”

Thyroid Hormone and Energy Expenditure

“…Most importantly, T3 treatment resulted in pronounced increase in Ca +2 , while Ca +2 chelation by BAPTA resulted in abrogating LC-PTP gating by TH, indicating that THinduced PP2B activity involved mobilization of intracellular Ca +2 (113). Indeed, T3-induced mobilization of intracellular Ca +2 has recently been reported to mediate a variety of nongenomic effects of TH (117,118 (119). IP3R1 is activated by binding of the IP3 ligand and may further be modulated by its phosphorylation by PKA, PKC or CaMKII, its dephosphorylation by PP2B, or by its association with one or more of about 50 proteins, including FKBP12 or Bcl2 (120,121).…”

3,3′,5-Triiodo-l-thyronine inhibits ductal pancreatic adenocarcinoma proliferation improving the cytotoxic effect of chemotherapy

“…The non-genomic effects of thyroid hormone have been described at the plasma membrane level, in the cytoplasm, and in the cellular organelles. These effects are usually associated with secondary messengers signaling pathways and might in some cases persist in genetically modified mice lacking the classical nuclear receptors (Davis & Davis 1996, D'Arezzo et al 2004. Numerous studies have shown that T 3 is able to promote or inhibit cell proliferation in a cell type-dependent manner (Ledda-Columbano et al 2005, Misiti et al 2005, Verga Falzacappa et al 2006.…”