In vivo evidence for an interplay of FGF23/Klotho/PTH axis on the phosphate handling in renal proximal tubules

Phosphate homeostasis is primarily maintained in the renal proximal tubules, where the expression of sodium/phosphate cotransporters (Npt2a and Npt2c) is modified by the endocrine actions of both fibroblast growth factor 23 (FGF23) and parathyroid hormone (PTH). However, the specific contribution of each regulatory pathway in the proximal tubules has not been fully elucidated in vivo. We have previously demonstrated that proximal tubule-specific deletion of the FGF23 coreceptor Klotho results in mild hyperphosphatemia with little to no change in serum levels of FGF23, 1,25(OH)₂D₃, and PTH. In the present study, we characterized mice in which the PTH receptor PTH1R was specifically deleted from the proximal tubules, either alone or in combination with Klotho ( PT-PTH1R^-/- and PT-PTH1R/KL^-/-, respectively). PT-PTH1R^-/- mice showed significant increases in serum FGF23 and PTH levels, whereas serum phosphate levels were maintained in the normal range, and Npt2a and Npt2c expression in brush border membrane (BBM) did not change compared with control mice. In contrast, PT-PTH1R/KL^-/- mice displayed hyperphosphatemia and an increased abundance of Npt2a and Npt2c in the renal BBM, along with increased circulating FGF23 levels. While serum calcium was normal, 1,25(OH)₂D₃ levels were significantly decreased, leading to extremely high levels of PTH. Collectively, mice with a deletion of PTH1R alone in proximal tubules results in only minor changes in phosphate regulation, whereas deletion of both PTH1R and Klotho leads to a severe disturbance, including hyperphosphatemia with increased sodium/phosphate cotransporter expression in BBM. These results suggest an important interplay between the PTH/PTH1R and FGF23/Klotho pathways to affect renal phosphate handling in the proximal tubules.

Citrate Suppresses Tumor Growth in Multiple Models through Inhibition of Glycolysis, the Tricarboxylic Acid Cycle and the IGF-1R Pathway

In this study we have tested the efficacy of citrate therapy in various cancer models. We found that citrate administration inhibited A549 lung cancer growth and additional benefit accrued in combination with cisplatin. Interestingly, citrate regressed Ras-driven lung tumors. Further studies indicated that citrate induced tumor cell differentiation. Additionally, citrate treated tumor samples showed significantly higher infiltrating T-cells and increased blood levels of numerous cytokines. Moreover, we found that citrate inhibited IGF-1R phosphorylation. In vitro studies suggested that citrate treatment inhibited AKT phosphorylation, activated PTEN and increased expression of p-eIF2a. We also found that p-eIF2a was decreased when PTEN was depleted. These data suggest that citrate acts on the IGF-1R-AKT-PTEN-eIF2a pathway. Additionally, metabolic profiling suggested that both glycolysis and the tricarboxylic acid cycle were suppressed in a similar manner in vitro in tumor cells and in vivo but only in tumor tissue. We reproduced many of these observations in an inducible Her2/Neu-driven breast cancer model and in syngeneic pancreatic tumor (Pan02) xenografts. Our data suggests that citrate can inhibit tumor growth in diverse tumor types and via multiple mechanisms. Dietary supplementation with citrate may be beneficial as a cancer therapy.

Parathyroid Hormone Directs Bone Marrow Mesenchymal Cell Fate

Intermittent PTH administration builds bone mass and prevents fractures, but its mechanism of action is unclear. We genetically deleted the PTH/PTHrP receptor (PTH1R) in mesenchymal stem cells using Prx1Cre and found low bone formation, increased bone resorption, and high bone marrow adipose tissue (BMAT). Bone marrow adipocytes traced to Prx1 and expressed classic adipogenic markers and high receptor activator of nuclear factor kappa B ligand (Rankl) expression. RANKL levels were also elevated in bone marrow supernatant and serum, but undetectable in other adipose depots. By cell sorting, Pref1⁺RANKL⁺ marrow progenitors were twice as great in mutant versus control marrow. Intermittent PTH administration to control mice reduced BMAT significantly. A similar finding was noted in male osteoporotic patients. Thus, marrow adipocytes exhibit osteogenic and adipogenic characteristics, are uniquely responsive to PTH, and secrete RANKL. These studies reveal an important mechanism for PTH's therapeutic action through its ability to direct mesenchymal cell fate.

Design and synthesis of emodin derivatives as novel inhibitors of ATP-citrate lyase

Aberrant cellular metabolism drives cancer proliferation and metastasis. ATP citrate lyase (ACL) plays a critical role in generating cytosolic acetyl CoA, a key building block for de novo fatty acid and cholesterol biosynthesis. ACL is overexpressed in cancer cells, and siRNA knockdown of ACL limits cancer cell proliferation and reduces cancer stemness. We characterized a new class of ACL inhibitors bearing the key structural feature of the natural product emodin. Structure-activity relationship (SAR) study led to the identification of 1d as a potent lead that demonstrated dose-dependent inhibition of proliferation and cancer stemness of the A549 lung cancer cell line. Computational modeling indicates this class of inhibitors occupies an allosteric binding site and blocks the entrance of the substrate citrate to its binding site.

Low-Dose Farnesyltransferase Inhibitor Suppresses HIF-1α and Snail Expression in Triple-Negative Breast Cancer MDA-MB-231 Cells In Vitro

The aggressiveness of triple-negative breast cancer (TNBC), which lacks estrogen receptor, progesterone receptor and epidermal growth factor receptor 2 (HER2), represents a major challenge in breast cancer. Migratory and self-renewal capabilities are integral components of invasion, metastasis and recurrence of TNBC. Elevated hypoxia-inducible factor-1α (HIF-1α) expression is associated with aggressiveness of cancer. Nonetheless, how HIF-1α expression is regulated and how HIF-1α induces aggressive phenotype are not completely understood in TNBC. The cytotoxic effects of farnesyltransferase (FTase) inhibitors (FTIs) have been studied in cancer and leukemia cells. In contrast, the effect of FTIs on HIF-1α expression has not yet been studied. Here, we show that clinically relevant low-dose FTI, tipifarnib (300 nM), decreased HIF-1α expression, migration and tumorsphere formation in human MDA-MB-231 TNBC cells under a normoxic condition. In contrast, the low-dose FTIs did not inhibit cell growth and activity of the Ras pathway in MDA-MB 231 cells. Tipifarnib-induced decrease in HIF-1α expression was associated with amelioration of the Warburg effect, hypermetabolic state, increases in Snail expression and ATP release, and suppressed E-cadherin expression, major contributors to invasion, metastasis and recurrence of TBNC. These data suggest that FTIs may be capable of ameliorating the aggressive phenotype of TNBC by suppressing the HIF-1α-Snail pathway. J. Cell. Physiol. 232: 192-201, 2017. © 2016 Wiley Periodicals, Inc.

A prospective epigenetic paradigm between cellular senescence and epithelial-mesenchymal transition in organismal development and aging

Epigenetic states can govern the plasticity of a genome to be adaptive to environments where many stress stimuli and insults compromise the homeostatic system with age. Although certain elastic power may autonomously reset, reprogram, rejuvenate, or reverse the organismal aging process, enforced genetic manipulations could at least reset and reprogram epigenetic states beyond phenotypic plasticity and elasticity in cells, which can be further manipulated into organisms. The question, however, remains how we can rejuvenate intrinsic resources and infrastructures in a noninvasive manner, particularly in a whole complex aging organism. Given inevitable increase of cancer with age, presumably any failure of resetting, reprogramming, or even rejuvenation could be a prominent causative factor of malignancy. Accompanied by progressive deteriorations of physiological functions in organisms with advancing age, aging-associated cancer risk may essentially arise from unforeseen complications in cellular senescence. At the cellular level, epithelial-mesenchymal plasticity (dynamic and reversible transitions between epithelial and mesenchymal phenotypic states) is enabled by underlying shifts in epigenetic regulation. Thus, the epithelial-mesenchymal transition (EMT) and its reversal (mesenchymal-epithelial transition [MET]) function as a key of cellular transdifferentiation programs. On the one hand, the EMT-MET process was initially appreciated in developmental biology, but is now attracting increasing attention in oncogenesis and senescence, because the process is involved in the malignant progression vs regression of cancer. On the other hand, senescence is often considered the antithesis of early development, but yet between these 2 phenomena, there may be common factors and governing mechanisms such as the EMT-MET program, to steer toward rejuvenation of the biological aging system, thereby precisely controlling or avoiding cancer through epigenetic interventions.

Targeting lactate dehydrogenase--a inhibits tumorigenesis and tumor progression in mouse models of lung cancer and impacts tumor-initiating cells

The lactate dehydrogenase-A (LDH-A) enzyme catalyzes the interconversion of pyruvate and lactate, is upregulated in human cancers, and is associated with aggressive tumor outcomes. Here we use an inducible murine model and demonstrate that inactivation of LDH-A in mouse models of NSCLC driven by oncogenic K-RAS or EGFR leads to decreased tumorigenesis and disease regression in established tumors. We also show that abrogation of LDH-A results in reprogramming of pyruvate metabolism, with decreased lactic fermentation in vitro, in vivo, and ex vivo. This was accompanied by reactivation of mitochondrial function in vitro, but not in vivo or ex vivo. Finally, using a specific small molecule LDH-A inhibitor, we demonstrated that LDH-A is essential for cancer-initiating cell survival and proliferation. Thus, LDH-A can be a viable therapeutic target for NSCLC, including cancer stem cell-dependent drug-resistant tumors.

Statin-induced muscle damage and atrogin-1 induction is the result of a geranylgeranylation defect

Statins are widely used to treat hypercholesterolemia but can lead to a number of side effects in muscle, including rhabdomyolysis. Our recent findings implicated the induction of atrogin-1, a gene required for the development of muscle atrophy, in statin-induced muscle damage. Since statins inhibit many biochemical reactions besides cholesterol synthesis, we sought to define the statin-inhibited pathways responsible for atrogin-1 expression and muscle damage. We report here that lovastatin-induced atrogin-1 expression and muscle damage in cultured mouse myotubes and zebrafish can be prevented in the presence of geranylgeranol but not farnesol. Further, inhibitors of the transfer of geranylgeranyl isoprene units to protein targets cause statin muscle damage and atrogin-1 induction in cultured cells and in fish. These findings support the concept that dysfunction of small GTP-binding proteins lead to statin-induced muscle damage since these molecules require modification by geranylgeranyl moieties for their cellular localization and activity. Collectively, our animal and in vitro findings shed light on the molecular mechanism of statin-induced myopathy and suggest that atrogin-1 may be regulated by novel signaling pathways.

Lipocalin 2 antagonizes the proangiogenic action of ras in transformed cells

Lipocalin 2 is an iron-binding secreted protein that converts embryonic kidney mesenchyme to epithelia. Previously, we reported that lipocalin 2 could revert 4T1-ras-transformed mesenchymal tumor cells to a more epithelial phenotype, increase E-cadherin expression, and suppress cell invasiveness in vitro and in vivo, indicating that lipocalin 2 is a metastasis suppressor. Here, we show that lipocalin 2 can suppress the ras-induced expression of vascular endothelial growth factor in 4T1 cells via down-regulation of ras mitogen-activated protein kinase and ras phosphatidylinositol-3-kinase signaling. In addition, the expression of thrombospondin-1 (an antiangiogenic molecule) was increased in tumors formed by 4T1-ras cells into which lipocalin 2 was stably introduced. Tumor angiogenesis, assessed via an intradermal tumor angiogenesis assay, was also suppressed by lipocalin 2. We also show that caveolin-1 is a critical mediator of this activity. These data provide new insights into the action of lipocalin 2 and raise the possibility that the administration of lipocalin 2 may be useful for inhibiting tumor angiogenesis, in addition to suppressing tumor metastasis, in cancers which show ras activation.

A novel endothelial-specific heat shock protein HspA12B is required in both zebrafish development and endothelial functions in vitro

A zebrafish transcript dubbed GA2692 was initially identified via a whole-mount in situ hybridization screen for vessel specific transcripts. Its mRNA expression during embryonic development was detected in ventral hematopoietic and vasculogenic mesoderm and later throughout the vasculature up to 48 hours post fertilization. Morpholino-mediated knockdown of GA2692 in embryos resulted in multiple defects in vasculature, particularly, at sites undergoing active capillary sprouting: the intersegmental vessels, sub-intestinal vessels and the capillary sprouts of the pectoral fin vessel. During the course of these studies, a homology search indicated that GA2692 is the zebrafish orthologue of mammalian HspA12B, a distant member of the heat shock protein 70 (Hsp70) family. By a combination of northern blot and real-time PCR analysis, we showed that HspA12B is highly expressed in human endothelial cells in vitro. Knockdown of HspA12B by small interfering RNAs (siRNAs) in human umbilical vein endothelial cells blocked wound healing, migration and tube formation, whereas overexpression of HspA12B enhanced migration and accelerated wound healing - data that are consistent with the in vivo fish phenotype obtained in the morpholino-knockdown studies. Phosphorylation of Akt was consistently reduced by siRNAs against HspA12B. Overexpression of a constitutively active form of Akt rescued the inhibitory effects of knockdown of HspA12B on migration of human umbilical vein endothelial cells. Collectively, our data suggests that HspA12B is a highly endothelial-cell-specific distant member of the Hsp70 family and plays a significant role in endothelial cells during development and angiogenesis in vitro, partially attributable to modulation of Akt phosphorylation.

Cell surface glypicans are low-affinity endostatin receptors

Endostatin, a collagen XVIII fragment, is a potent anti-angiogenic protein. We sought to identify its endothelial cell surface receptor(s). Alkaline phosphatase- tagged endostatin bound endothelial cells revealing two binding affinities. Expression cloning identified glypican, a cell surface proteoglycan as the lower-affinity receptor. Biochemical and genetic studies indicated that glypicans' heparan sulfate glycosaminoglycans were critical for endostatin binding. Furthermore, endostatin selected a specific octasulfated hexasaccharide from a sequence in heparin. We have also demonstrated a role for endostatin in renal tubular cell branching morphogenesis and show that glypicans serve as low-affinity receptors for endostatin in these cells, as in endothelial cells. Finally, antisense experiments suggest the critical importance of glypicans in mediating endostatin activities.

Hgs (Hrs), a FYVE domain protein, is involved in Smad signaling through cooperation with SARA

Smad proteins are effector molecules that transmit signals from the receptors for the transforming growth factor beta (TGF-beta) superfamily to the nucleus; of the Smad proteins, Smad2 and Smad4 are essential components for mouse early embryogenesis. We demonstrated that Hgs, a FYVE domain protein, binds to Smad2 in its C-terminal half and cooperates with another FYVE domain protein, the Smad anchor for receptor activation (SARA), to stimulate activin receptor-mediated signaling through efficient recruitment of Smad2 to the receptor. Furthermore, a LacZ knock-in allele of the C-terminal half-deletion mutant of mouse Hgs was created by gene targeting. The introduced mutation causes an embryonic lethality between embryonic days 8.5 and 10.5. Mutant cells showed significantly decreased responses to stimulation with activin and TGF-beta. These findings suggest that the two FYVE domain proteins, Hgs and SARA, are prerequisites for receptor-mediated activation of Smad2.

Expression of transfected human Na+/H+ exchanger (NHE-1) in the the basolateral membrane of opossum kidney cells

Some epithelial cells have Na+/H+ exchanger (NHE) activity in both apical and basolateral membranes. Amiloride-sensitive NHE-1 is generally identified in the basolateral membrane. The renal cell line, OK7a, targets amiloride-resistant NHE predominantly to the apical membrane. It is controversial whether the transfected NHE-1 is targeted preferentially to the basolateral membrane in OK7a cells, when human NHE-1 is chronically expressed under control of constitutively active promoters. We tried to identify the membranes in which the transfected human NHE-1 could be detected following acute expression in OK7a cells. We have always observed small Na(+)-dependent pH recovery in the basolateral membrane in OK7a cells. It is, however, controversial whether or not OK7a cells express NHE activity in the basolateral membrane. We also characterized Na(+)-dependent pH recovery in the basolateral membrane. It was not inhibited by [4,4'diisothiocyanatostilbene-2,2'-disulfonic acid] (DIDS), [4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid] (SITS), or contralateral amiloride. Li+ but not K+, chol+, or NMG+ could replace Na+. These results are consistent with the presence of the NHE in the basolateral membrane. NHE activities were predominant in the apical membrane and those in both membranes were resistant to amiloride analogs. After stable transfection with human NHE-1 in a vector utilizing the metallothionein promoter, overnight induction with Zn(2+)increased the NHE activity and its sensitivity to amiloride only in the basolateral membrane in OK7a cells. We conclude that the transfected human NHE-1 is exclusively targeted to the basolateral membrane of OK7a cells during acute induction.

Role of p300, a transcriptional coactivator, in signalling of TGF-beta

BACKGROUND

Smad proteins are novel transcriptional regulators mediating the signalling of the transforming growth factor-beta (TGF-beta) superfamily. Coactivators such as p300/CBP promote transactivation by various transcription factors through a direct interaction with them. Adenoviral oncoprotein E1A, which binds p300, was shown to inhibit the signalling of TGF-beta. These findings raise the possibility that p300 may be involved in TGF-beta signalling.

RESULTS

We investigated whether p300 is involved in transactivation by Smads. p300 enhanced the Smad-induced transactivation of p3TP-Lux, a TGF-beta responsive reporter. E1A inhibited this enhancement, and the inhibition required its ability to bind p300/CBP. p300 and Smad3, as well as Smad2, interacted in vivo in a ligand-dependent manner. The binding region in Smad3 was its C-terminal half that was previously shown to possess an intrinsic transactivation activity. The binding region in p300 was mapped to its C-terminal 678 amino acids. The minimal Smad2/3-interacting region, as well as the rest of the p300, inhibited the transactivation of p3TP-Lux in a dominant-negative fashion.

CONCLUSION

p300 interacted with Smad2 and Smad3 in a ligand-dependent manner, and enhanced the transactivation by Smads. Our results present the molecular basis of the transactivation by Smad proteins.

Na+/H+ exchanger (NHE) in the basolateral membrane is encoded by NHE-1 mRNA in LLC-PK1 clone 4 cells

Several isoforms of Na+/H+ exchanger (NHE-1-5) have been identified. LLC-PK1 clone 4 (CL4) expresses the amiloride-sensitive type of NHE predominantly in the basolateral membrane, which is believed to be NHE-1. It is not clear whether CL4 expresses NHE in the apical membrane and which side of NHE is encoded by the NHE-1 mRNA. Using acidified CL4 cells on the filter membrane, we examined Na(+)-dependent pH recovery of the apical and basolateral membranes separately. Na+ applied to the apical membrane recovered cell pH. Na(+)-dependent pH recovery in the apical membrane was not inhibited by SITS, DIDS, or contralateral amiloride. Li+ but not K+, chol+, or NMG+ could replace Na+. These data are consistent with the presence of NHE in the apical membrane. Transfection with an antisense oligonucleotide corresponding to the 5' terminal site of NHE-1 cDNA of CL4 decreased NHE activity in the basolateral membrane but not in the apical membrane. We conclude that CL4 expresses NHE activities in both apical and basolateral membranes and that NHE-1 mRNA encodes NHE only in the basolateral membrane.