Prolactin-stimulated transepithelial calcium transport in duodenum and Caco-2 monolayer are mediated by the phosphoinositide 3-kinase pathway

Abstract

Jantarajit W, Thongon N, Pandaranandaka J, Teerapornpuntakit J, Krishnamra N, Charoenphandhu N. Prolactin-stimulated transepithelial calcium transport in duodenum and Caco-2 monolayer are mediated by the phosphoinositide 3-kinase pathway. Am J Physiol Endocrinol Metab 293: E372-E384, 2007. First published May 8, 2007; doi:10.1152/ajpendo.00142.2007 has been shown to stimulate intestinal calcium absorption but the mechanism was still unknown. This study aimed to investigate the mechanism and signaling pathway by which PRL enhanced calcium transport in the rat duodenum and Caco-2 monolayer. Both epithelia strongly expressed mRNAs and proteins of PRL receptors. Ussing chamber technique showed that the duodenal active calcium fluxes were increased by PRL in a dose-response manner with the maximal effective dose of 800 ng/ml. This response diminished after exposure to LY-294002, a phosphoinositide 3-kinase (PI3K) inhibitor. Caco-2 monolayer gave similar response to PRL with the maximal effective dose of 600 ng/ml. By nullifying the transepithelial potential difference, we showed that the voltage-dependent paracellular calcium transport did not contribute to the PRL-enhanced flux in Caco-2 monolayer. In contrast, the calcium gradient-dependent paracellular transport and calcium permeability were increased by PRL. Effects of PRL on Caco-2 monolayer were abolished by PI3K inhibitors (LY-294002 and wortmannin), but not by inhibitors of MEK (U-0126) or JAK2 (AG-490). To investigate whether the PRL-enhanced paracellular transport was linked to changes in the epithelial charge selectivity, the permeability ratio of sodium and chloride (P Na/PCl) was determined. We found that PRL elevated the P Na/PCl in both epithelia, and the effects were blocked by PI3K inhibitors. In conclusion, PRL directly and rapidly stimulated the active and passive calcium transport in the rat duodenum and Caco-2 monolayer via the nongenomic PI3K-signaling pathway. This PRL-enhanced paracellular calcium transport could have resulted from altered charge selectivity. charge selectivity; dilution potential; paracellular transport; prolactin receptor; tight junction; transcellular transport AS ONE OF THE CALCIUM-REGULATING HORMONES during pregnancy and lactation, prolactin (PRL) has been shown to stimulate intestinal calcium absorption (38), thereby protecting against development of negative calcium balance during these reproductive periods. Further investigations in nonmated female rats also revealed stimulatory actions of PRL on intestinal calcium absorption (11, 54), especially in the duodenum which was the most efficient site for calcium transport (21,32). Although the presence of PRL receptor (PRLR) proteins in duodenal enterocytes of rats was controversial, expression of rat PRLR (rPRLR) transcripts in the duodenal mucosa, demonstrated by in situ hybridization technique (45), implicated a direct action of PRL on the duodenal epithelial cells.Calcium traversed the duodenal epithelium by both active and passive pathways with the former being neglig...

Parathyroid hormone (PTH) rapidly enhances CFTR-mediated HCO3− secretion in intestinal epithelium-like Caco-2 monolayer: a novel ion regulatory action of PTH

“…Finally, the responsible signaling pathways were identified by pretreating Caco-2 monolayers on both apical and basolateral sides with inhibitors of known PTH signaling pathways, i.e., cAMP-dependent PKA (10 mol/l myristoylated PKI 14 -22 amide; Calbiochem, San Diego, CA), intracellular Ca 2ϩ [50 mol/l 1,2-bis(2-aminophenoxy)ethane-N,N,N=,N=-tetraacetic acid tetra(acetoxymethyl ester); BAPTA-AM; Calbiochem], Ca 2ϩ -dependent PKC (1 mol/l GF-109203X; A. G. Scientific, San Diego, CA), and phosphoinositide 3-kinase (PI3K; 200 nmol/l wortmannin and 75 mol/l LY-294002; Tocris Bioscience, Bristol, UK). The signaling pathway inhibitors were of the optimal concentrations as reported previously (10,28,31,65).…”

Comparative genomics reveals tissue-specific regulation of prolactin receptor gene expression

“…In rodents, PRL mediates water uptake and retention during lactation in addition to the uptake of glucose, sodium, chloride and amino acids to support fluid, solute and energy requirements (Ramsey & Bern 1972, Mainoya 1975, Teerapornpuntakit et al 2012. Both active and passive transport mechanisms of calcium uptake are rapidly stimulated by PRL via the phosphoinositide 3-kinase pathway (Jantarajit et al 2007, Ryszka et al 2012. In addition, PRL increases the expression of genes such as CLDN19, which modulates paracellular permeability, FGFR2C, which is required for differentiation and the sodium pump ATP1B2, which is essential for intestinal transport of glucose and calcium (Teerapornpuntakit et al 2014).…”

“…PRL stimulates the uptake of calcium, which is a major ion in milk, in the small intestine (Jantarajit et al 2007, Ryszka et al 2012 and interacts with the renal dopamine system to effect natriuresis in the kidneys (Ibarra et al 2005). The prepartum surge of PRL that is essential for the subsequent lactation also likely increases blood flow to the mammary gland (MG) at the onset of lactation (Hanwell & Linzell 1973, Peaker 1976, Ota & Peaker 1979, given that PRL increases various measures of cardiac output (Nassar et al 1974, Karmazyn et al 1982.…”

High Physiological Prolactin Induced by Pituitary Transplantation Decreases BMD and BMC in the Femoral Metaphysis, but Not in the Diaphysis of Adult Female Rats

“…It could be concluded that high physiological PRL induced a significant osteopenia in the trabecular part, i.e., the metaphysis, of the femora of adult female rats in an estrogen-dependent manner. Since PRL had no detectable effect on the vertebrae, the effects of PRL on bone appeared to be site-specific.Key words: diaphysis, femur, metaphysis, prolactin, vertebrae.Prolactin (PRL), as a calcium-regulating hormone, has been reported to stimulate intestinal calcium absorption, enhance renal calcium reabsorption, and induce high bone turnover in nonmated female rats [1][2][3]. By regulating calcium mobilization in these target organs during pregnancy and lactation, the high physiological PRL of 75-300 ng/ ml increases calcium availability for fetal growth and milk production [4].…”

“…By regulating calcium mobilization in these target organs during pregnancy and lactation, the high physiological PRL of 75-300 ng/ ml increases calcium availability for fetal growth and milk production [4]. Moreover, the basal PRL level of 7-10 ng/ ml was required for the maintenance of normal bone turnover and duodenal calcium absorption in rats [5,6].It has been shown that PRL acted directly on the intestinal absorptive cells to enhance calcium absorption [3]. In bone, osteoblasts but not osteoclasts strongly expressed functional PRL receptors (PRLR), indicating that bone was also a target of PRL [7].…”