PKC‐ε‐dependent cytosol‐to‐membrane translocation of pendrin in rat thyroid PC Cl3 cells

Abstract

We studied the expression and the hormonal regulation of the PDS gene product, pendrin, which is, in thyrocytes, responsible for the iodide transport out of the cell. We show that PC Cl3 cells, a fully differentiated thyroid cell line, grown without TSH and insulin, express very low level of PDS mRNA; such expression is greatly increased after stimulation with insulin or TSH. (125)I pre-loaded cells showed an (125)I efflux accelerated in chloride-containing buffer with respect to chloride-free buffer, suggesting that this efflux is chloride dependent. By immunoblotting, pendrin was found in agonists-stimulated cells, whereas it was barely detectable in un-stimulated cells. An increase in both PDS mRNA and protein was also obtained using phorbol ester PMA, or using 8-Br-cAMP and forskolin. Stimulation with insulin (1 microg/ml; 0-40 min) provoked the cytosol-to-membrane translocation of pendrin and a decrease of intracellular I(-) content in (125)I pre-loaded cells. Insulin- or PMA-treated cells also showed a cytosol-to-membrane translocation of PKC-delta and -epsilon. Inhibition of both PKC-delta and -epsilon activities by GF109203X blocked pendrin translocation, whilst the inhibition of PKA did not. The selective inhibition of PKC-delta by rottlerin did not affect the insulin-provoked translocation of pendrin whilst it was inhibited by a PKC-epsilon translocation inhibitor peptide and also by PKC-epsilon downregulation using the small interfering RNA, thus indicating that such translocation was due to PKC-epsilon activity. In conclusion, our study demonstrates that, in PC Cl3 cells, pendrin expression and localisation are regulated by insulin and influenced by a PKC-epsilon-dependent intracellular pathway.

Controversies Concerning the Role of Pendrin as an Apical Iodide Transporter in Thyroid Follicular Cells

“…In FRTL-5 rat thyroid cells, low doses of TSH do not induce SLC26A4 mRNA determined by Northern blot analyses [37]. This contrasts with findings in the same cell line documenting induction of SLC26A4 mRNA by RT-PCR after exposure to TSH and forskolin [42], as well as findings in the PCCL3 rat thyroid cell line reporting increased expression of pendrin mRNA, determined by RT-PCR, and protein after exposure to high doses of TSH, forskolin and 8-Bromo-cAMP [43]. It is well established, that iodide efflux at the apical membrane is rapidly accelerated by TSH [44][45][46].…”

Transcriptional Regulation of the Pendrin Gene

“…Northern blot analysis [60] has demonstrated induction of PDS expression by low concentration of Tg, but not by TSH, insulin NaI or interferon γ (IFN-γ) in the rat thyroid cell line FRTL-5. In contrast, in the more differentiated rat thyroid PC Cl3 cell line, TSH increased PDS mRNA expression, and pendrin expression and localization were regulated by insulin and influenced by PKC-ε-dependent intracellular pathway [61]. In addition, the transcription factor TTF-1, a regulator of thyroid differentiation in vivo, was found also to regulate the expression of pendrin in rat FRTL-5 cells [62].…”

Rise and Fall of Kir2.2 Current by TLR4 Signaling in Human Monocytes: PKC-Dependent Trafficking and PI3K-Mediated PIP2 Decrease

“…Based on the pharmacological selectivity of the agents described above, it is likely that a PKCε-dependent signaling mechanism is at least partly responsible for the Kir2.2 trafficking. The involvement of PKCε in the membrane trafficking of an ion channel (NMDA receptor) and a transporter (pendrin) has also been suggested elsewhere (39,40). Because the pharmacological selectivity of the PKC inhibitors are generally not highly reliable, careful interpretation is required.…”