CFTR-mediated anion secretion in parathyroid hormone-treated Caco-2 cells is associated with PKA and PI3K phosphorylation but not intracellular pH changes or Na+/K+-ATPase abundance

Rattana Chaimana; Jarinthorn Teerapornpuntakit; Walailak Jantarajit; Kornkamon Lertsuwan; Saowalak Krungchanuchat; Nattapon Panupinthu; Nateetip Krishnamra; Narattaphol Charoenphandhu

doi:10.1016/j.bbrep.2021.101054

CFTR-mediated anion secretion in parathyroid hormone-treated Caco-2 cells is associated with PKA and PI3K phosphorylation but not intracellular pH changes or Na⁺/K⁺-ATPase abundance

Biochem Biophys Rep. 2021 Jun 16:27:101054. doi: 10.1016/j.bbrep.2021.101054. eCollection 2021 Sep.

Authors

Rattana Chaimana^{1

2}, Jarinthorn Teerapornpuntakit^{1

3}, Walailak Jantarajit^{1

2}, Kornkamon Lertsuwan^{1

4}, Saowalak Krungchanuchat¹, Nattapon Panupinthu^{1

2}, Nateetip Krishnamra^{1

2}, Narattaphol Charoenphandhu^{1

2

5

6}

Affiliations

¹ Center of Calcium and Bone Research (COCAB), Faculty of Science, Mahidol University, Bangkok, Thailand.
² Department of Physiology, Faculty of Science, Mahidol University, Bangkok, Thailand.
³ Department of Physiology, Faculty of Medical Science, Naresuan University, Phitsanulok, Thailand.
⁴ Department of Biochemistry, Faculty of Science, Mahidol University, Bangkok, Thailand.
⁵ Institute of Molecular Biosciences, Mahidol University, Nakhon Pathom, Thailand.
⁶ The Academy of Science, The Royal Society of Thailand, Bangkok, Thailand.

Abstract

Parathyroid hormone (PTH) has previously been shown to enhance the transepithelial secretion of Cl^- and HCO₃ ^- across the intestinal epithelia including Caco-2 monolayer, but the underlying cellular mechanisms are not completely understood. Herein, we identified the major signaling pathways that possibly mediated the PTH action to its known target anion channel, i.e., cystic fibrosis transmembrane conductance regulator anion channel (CFTR). Specifically, PTH was able to induce phosphorylation of protein kinase A and phosphoinositide 3-kinase. Since the apical HCO₃ ^- efflux through CFTR often required the intracellular H⁺/HCO₃ ^- production and/or the Na⁺-dependent basolateral HCO₃ ^- uptake, the intracellular pH (pH_i) balance might be disturbed, especially as a consequence of increased endogenous H⁺ and HCO₃ ^- production. However, measurement of pH_i by a pH-sensitive dye suggested that the PTH-exposed Caco-2 cells were able to maintain normal pH despite robust HCO₃ ^- transport. In addition, although the plasma membrane Na⁺/K⁺-ATPase (NKA) is normally essential for basolateral HCO₃ ^- uptake and other transporters (e.g., NHE1), PTH did not induce insertion of new NKA molecules into the basolateral membrane as determined by membrane protein biotinylation technique. Thus, together with our previous data, we concluded that the PTH action on Caco-2 cells is dependent on PKA and PI3K with no detectable change in pH_i or NKA abundance on cell membrane.

Keywords: Anion secretion; Cystic fibrosis transmembrane conductance regulator (CFTR); Parathyroid hormone (PTH); Parathyroid hormone 1 receptor (PTH1R); Phosphoinositide 3-kinase (PI3K); Protein kinase A (PKA).