A G protein–coupled, IP3/protein kinase C pathway controlling the synthesis of phosphaturic hormone FGF23
Qing He, … , Paola Divieti Pajevic, Murat Bastepe
Qing He, … , Paola Divieti Pajevic, Murat Bastepe
Published September 5, 2019
Citation Information: JCI Insight. 2019;4(17):e125007. https://doi.org/10.1172/jci.insight.125007.
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Research Article Endocrinology Nephrology

A G protein–coupled, IP3/protein kinase C pathway controlling the synthesis of phosphaturic hormone FGF23

Abstract

Dysregulated actions of bone-derived phosphaturic hormone fibroblast growth factor 23 (FGF23) result in several inherited diseases, such as X-linked hypophosphatemia (XLH), and contribute substantially to the mortality in kidney failure. Mechanisms governing FGF23 production are poorly defined. We herein found that ablation of the Gq/11α–like, extralarge Gα subunit (XLαs), a product of GNAS, exhibits FGF23 deficiency and hyperphosphatemia in early postnatal mice (XLKO). FGF23 elevation in response to parathyroid hormone, a stimulator of FGF23 production via cAMP, was intact in XLKO mice, while skeletal levels of protein kinase C isoforms α and δ (PKCα and PKCδ) were diminished. XLαs ablation in osteocyte-like Ocy454 cells suppressed the levels of FGF23 mRNA, inositol 1,4,5-trisphosphate (IP3), and PKCα/PKCδ proteins. PKC activation in vivo via injecting phorbol myristate acetate (PMA) or by constitutively active Gqα-Q209L in osteocytes and osteoblasts promoted FGF23 production. Molecular studies showed that the PKC activation–induced FGF23 elevation was dependent on MAPK signaling. The baseline PKC activity was elevated in bones of Hyp mice, a model of XLH. XLαs ablation significantly, but modestly, reduced serum FGF23 and elevated serum phosphate in Hyp mice. These findings reveal a potentially hitherto-unknown mechanism of FGF23 synthesis involving a G protein–coupled IP3/PKC pathway, which may be targeted to fine-tune FGF23 levels.

Authors

Qing He, Lauren T. Shumate, Julia Matthias, Cumhur Aydin, Marc N. Wein, Jordan M. Spatz, Regina Goetz, Moosa Mohammadi, Antonius Plagge, Paola Divieti Pajevic, Murat Bastepe

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Figure 6

PKC activation mediates FGF23 production by promoting MAPK signaling.

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PKC activation mediates FGF23 production by promoting MAPK signaling. (A...
(A) FGF23 mRNA expression in YFP- and XLαs-overexpressing Ocy454 cells. **P < 0.01, and ***P < 0.001, determined by Welch’s t test (2 tailed) followed by Bonferroni’s correction. (B) FGF23 mRNA expression in control or XLαs adenovirus–infected Ocy454 cells treated with PKC inhibitors, bisindolylmaleimide I (Bisindol), Ro-31-8220, or Ro-32-0432. Data are shown as mean ± SEM of 3 independent experiments. *P < 0.05 vs. control group; #P < 0.05 vs. XLαs-overexpressing Ocy454 cells. (C and D) Ocy454 cells were treated with PMA, with PKC inhibitors. qRT-PCR analysis of (C) FGF23 and (D) IL-6 mRNA after 6 hours of treatment. Data are shown as mean ± SEM of 4 independent experiments. *P < 0.05 vs. control group; #P < 0.05 vs. PMA-treated group. (B–D) Significance was calculated by 1-way ANOVA followed by Tukey’s multiple-comparisons test. (E) Representative Western blot of phosphorylated ERK1/2 (p-ERK) and total (phosphorylated and nonphosphorylated) ERK1/2 (total ERK) in femur bone lysate samples from P10 XLKO (KO) and WT mice. Loading control: tubulin. (F) Densitometric analysis of the ratio of p-ERK to total ERK in KO and WT femurs. Data are shown as mean ± SEM of 7 mice from each group. (G) Western blot analysis of p-ERK, ERK, and tubulin levels in control and XLKO Ocy454 cells. (H) Densitometric analysis of p-ERK/total ERK ratio represented in G. Data are shown as mean ± SEM from 3 independent experiments. (F and H) *P < 0.05, **P < 0.01 by 2-tailed Student’s t test. (I) Western blot analysis of p-ERK, ERK, and tubulin in XLKO and control cells treated with PMA or vehicle. (J) Densitometric analysis of p-ERK/ERK ratio represented in I. aP < 0.05 vs. vehicle-treated control cells; bP < 0.05 vs. vehicle-treated KO cells; cP < 0.05 vs. PMA-treated control cells. (K) FGF23 mRNA levels in Ocy454 cells treated with PMA, with or without MEK inhibitor U0126. Data are shown as mean ± SEM of 3 independent experiments. *P < 0.05 vs. control group; #P < 0.05 vs. PMA-treated group. Statistical differences in J and K were assessed with 1-way ANOVA followed by Tukey’s test.