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Type I phosphotidylinosotol 4-phosphate 5-kinase ? regulates osteoclasts in a bifunctional manner.

ABSTRACT: Type 1 phosphotidylinosotol-4 phosphate 5 kinase ? (PIP5KI?) is central to generation of phosphotidylinosotol (4,5)P(2) (PI(4,5)P(2)). PIP5KI? also participates in cytoskeletal organization by delivering talin to integrins, thereby enhancing their ligand binding capacity. As the cytoskeleton is pivotal to osteoclast function, we hypothesized that absence of PIP5KI? would compromise their resorptive capacity. Absence of the kinase diminishes PI(4,5) abundance and desensitizes precursors to RANK ligand-stimulated differentiation. Thus, PIP5KI?(-/-) osteoclasts are reduced in number in vitro and confirm physiological relevance in vivo. Despite reduced numbers, PIP5KI?(-/-) osteoclasts surprisingly have normal cytoskeletons and effectively resorb bone. PIP5KI? overexpression, which increases PI(4,5)P(2), also delays osteoclast differentiation and reduces cell number but in contrast to cells lacking the kinase, its excess disrupts the cytoskeleton. The cytoskeleton-disruptive effects of excess PIP5KI? reflect its kinase activity and are independent of talin recognition. The combined arrested differentiation and disorganized cytoskeleton of PIP5KI?-transduced osteoclasts compromises bone resorption. Thus, optimal PIP5KI? and PI(4,5)P(2) expression, by osteoclasts, are essential for skeletal homeostasis.

SUBMITTER: Zhu T

PROVIDER: S-EPMC3581369 | biostudies-literature | 2013 Feb

REPOSITORIES: biostudies-literature

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Type I phosphotidylinosotol 4-phosphate 5-kinase γ regulates osteoclasts in a bifunctional manner.

Zhu Tingting T Chappel Jean C JC Hsu Fong-Fu FF Turk John J Aurora Rajeev R Hyrc Krzysztof K De Camilli Pietro P Broekelmann Thomas J TJ Mecham Robert P RP Teitelbaum Steven L SL Zou Wei W

The Journal of biological chemistry 20130107 8

Type 1 phosphotidylinosotol-4 phosphate 5 kinase γ (PIP5KIγ) is central to generation of phosphotidylinosotol (4,5)P(2) (PI(4,5)P(2)). PIP5KIγ also participates in cytoskeletal organization by delivering talin to integrins, thereby enhancing their ligand binding capacity. As the cytoskeleton is pivotal to osteoclast function, we hypothesized that absence of PIP5KIγ would compromise their resorptive capacity. Absence of the kinase diminishes PI(4,5) abundance and desensitizes precursors to RANK l ...[more]

PMID: 23300084

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Project description:Inorganic phosphate (Pi) has been recognized as an important signaling molecule that modulates chondrocyte maturation and cartilage mineralization. However, conclusive experimental evidence for its involvement in early chondrogenesis is still lacking. Here, using high-density monolayer (2D) and pellet (3D) culture models of chondrogenic ATDC5 cells, we demonstrate that the cell response to Pi does not correlate with the Pi concentration in the culture medium but is better predicted by the availability of Pi on a per cell basis (Pi abundance). Both culture models were treated with ITS+, 10mM ?-glycerophosphate (?GP), or ITS+/10mM ?GP, which resulted in three levels of Pi abundance in cultures: basal (Pi/DNA <10ng/µg), moderate (Pi/DNA=25.3 - 32.3ng/µg), and high abundance (Pi/DNA >60ng/µg). In chondrogenic medium alone, the abundance levels were at the basal level in 2D culture and moderate in 3D cultures. The addition of 10mM ?GP resulted in moderate abundance in 2D and high abundance in 3D cultures. Moderate Pi abundance enhanced early chondrogenesis and production of aggrecan and type II collagen whereas high Pi abundance inhibited chondrogenic differentiation and induced rapid mineralization. Inhibition of sodium phosphate transporters reduced phosphate-induced expression of chondrogenic markers. When 3D ITS+/?GP cultures were treated with levamisole to reduce ALP activity, Pi abundance was decreased to moderate levels, which resulted in significant upregulation of chondrogenic markers, similar to the response in 2D cultures. Delay of phosphate delivery until after early chondrogenesis occurs (7 days) no longer enhanced chondrogenesis, but instead accelerated hypertrophy and mineralization. Together, our data highlights the dependence of chondroprogenitor cell response to Pi on its availability to individual cells and the chondrogenic maturation stage of these cells and suggest that appropriate temporal delivery of phosphate to ATDC5 cells in 3D cultures represents a rapid model for mechanistic studies into the effects of exogenous cues on chondrogenic differentiation, chondrocyte maturation, and matrix mineralization.

Dataset Information

Type I phosphotidylinosotol 4-phosphate 5-kinase ? regulates osteoclasts in a bifunctional manner.

Publications

Type I phosphotidylinosotol 4-phosphate 5-kinase γ regulates osteoclasts in a bifunctional manner.

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