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Acetylation of glucokinase regulatory protein decreases glucose metabolism by suppressing glucokinase activity.

Park JM, Kim TH, Jo SH, Kim MY, Ahn YH - Sci Rep (2015)

Bottom Line: Post-translationally, GK is regulated by binding the glucokinase regulatory protein (GKRP), resulting in GK retention in the nucleus and its inability to participate in cytosolic glycolysis.Acetylated GKRP is resistant to degradation by the ubiquitin-dependent proteasome pathway, suggesting that acetylation increases GKRP stability and binding to GK, further inhibiting GK nuclear export.Deacetylation of GKRP is effected by the NAD(+)-dependent, class III histone deacetylase SIRT2, which is inhibited by nicotinamide.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, Yonsei University College of Medicine, 50-1 Yonsei-ro, Seodaemun-gu, Seoul 120-752, Republic of Korea.

ABSTRACT
Glucokinase (GK), mainly expressed in the liver and pancreatic β-cells, is critical for maintaining glucose homeostasis. GK expression and kinase activity, respectively, are both modulated at the transcriptional and post-translational levels. Post-translationally, GK is regulated by binding the glucokinase regulatory protein (GKRP), resulting in GK retention in the nucleus and its inability to participate in cytosolic glycolysis. Although hepatic GKRP is known to be regulated by allosteric mechanisms, the precise details of modulation of GKRP activity, by post-translational modification, are not well known. Here, we demonstrate that GKRP is acetylated at Lys5 by the acetyltransferase p300. Acetylated GKRP is resistant to degradation by the ubiquitin-dependent proteasome pathway, suggesting that acetylation increases GKRP stability and binding to GK, further inhibiting GK nuclear export. Deacetylation of GKRP is effected by the NAD(+)-dependent, class III histone deacetylase SIRT2, which is inhibited by nicotinamide. Moreover, the livers of db/db obese, diabetic mice also show elevated GKRP acetylation, suggesting a broader, critical role in regulating blood glucose. Given that acetylated GKRP may affiliate with type-2 diabetes mellitus (T2DM), understanding the mechanism of GKRP acetylation in the liver could reveal novel targets within the GK-GKRP pathway, for treating T2DM and other metabolic pathologies.

No MeSH data available.


Related in: MedlinePlus

Increased acetylation of GKRP in db/db mice.(A) Western blot of acetylated GKRP in db/db mouse livers. Cell lysates were immunoprecipitated by an anti-GKRP antibody and immunoblot performed to detect endogenous acetylated GKRP using an anti-Ac-Lys antibody. (B) Band intensities of acetylated GKRP, as quantified by Image J software. The values from db/m + mice were set to 1.0 (n = 8). (C) Interactions between GK and GKRP in control and db/db mice. Endogenous GKRP was immunoprecipitated from liver homogenates of db/m + and db/db mice, using GKRP antibody, and then immunoblotted by an anti-GK antibody. (D) Band intensities of the GK-GKRP complexes were quantified using Image J software. The values from db/m + mice were set to 1.0 (n = 4). Values are expressed as means ± SEM, *p ≤ 0.05.
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f5: Increased acetylation of GKRP in db/db mice.(A) Western blot of acetylated GKRP in db/db mouse livers. Cell lysates were immunoprecipitated by an anti-GKRP antibody and immunoblot performed to detect endogenous acetylated GKRP using an anti-Ac-Lys antibody. (B) Band intensities of acetylated GKRP, as quantified by Image J software. The values from db/m + mice were set to 1.0 (n = 8). (C) Interactions between GK and GKRP in control and db/db mice. Endogenous GKRP was immunoprecipitated from liver homogenates of db/m + and db/db mice, using GKRP antibody, and then immunoblotted by an anti-GK antibody. (D) Band intensities of the GK-GKRP complexes were quantified using Image J software. The values from db/m + mice were set to 1.0 (n = 4). Values are expressed as means ± SEM, *p ≤ 0.05.

Mentions: To assess the functional relevance of GKRP acetylation to T2DM, we performed acetylation studies in the db/db mouse model of diabetes, dyslipidemia, and obesity24. As shown in Fig. 5A,B, GKRP acetylation levels were elevated in db/db mice, in addition to its increased interaction with GK (Fig. 5C,D, p ≤ 0.05). These findings suggest that increasing GKRP stability and interaction with GK suppresses GK activity, thus impairing glucose homeostasis, in db/db mice.


Acetylation of glucokinase regulatory protein decreases glucose metabolism by suppressing glucokinase activity.

Park JM, Kim TH, Jo SH, Kim MY, Ahn YH - Sci Rep (2015)

Increased acetylation of GKRP in db/db mice.(A) Western blot of acetylated GKRP in db/db mouse livers. Cell lysates were immunoprecipitated by an anti-GKRP antibody and immunoblot performed to detect endogenous acetylated GKRP using an anti-Ac-Lys antibody. (B) Band intensities of acetylated GKRP, as quantified by Image J software. The values from db/m + mice were set to 1.0 (n = 8). (C) Interactions between GK and GKRP in control and db/db mice. Endogenous GKRP was immunoprecipitated from liver homogenates of db/m + and db/db mice, using GKRP antibody, and then immunoblotted by an anti-GK antibody. (D) Band intensities of the GK-GKRP complexes were quantified using Image J software. The values from db/m + mice were set to 1.0 (n = 4). Values are expressed as means ± SEM, *p ≤ 0.05.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4664969&req=5

f5: Increased acetylation of GKRP in db/db mice.(A) Western blot of acetylated GKRP in db/db mouse livers. Cell lysates were immunoprecipitated by an anti-GKRP antibody and immunoblot performed to detect endogenous acetylated GKRP using an anti-Ac-Lys antibody. (B) Band intensities of acetylated GKRP, as quantified by Image J software. The values from db/m + mice were set to 1.0 (n = 8). (C) Interactions between GK and GKRP in control and db/db mice. Endogenous GKRP was immunoprecipitated from liver homogenates of db/m + and db/db mice, using GKRP antibody, and then immunoblotted by an anti-GK antibody. (D) Band intensities of the GK-GKRP complexes were quantified using Image J software. The values from db/m + mice were set to 1.0 (n = 4). Values are expressed as means ± SEM, *p ≤ 0.05.
Mentions: To assess the functional relevance of GKRP acetylation to T2DM, we performed acetylation studies in the db/db mouse model of diabetes, dyslipidemia, and obesity24. As shown in Fig. 5A,B, GKRP acetylation levels were elevated in db/db mice, in addition to its increased interaction with GK (Fig. 5C,D, p ≤ 0.05). These findings suggest that increasing GKRP stability and interaction with GK suppresses GK activity, thus impairing glucose homeostasis, in db/db mice.

Bottom Line: Post-translationally, GK is regulated by binding the glucokinase regulatory protein (GKRP), resulting in GK retention in the nucleus and its inability to participate in cytosolic glycolysis.Acetylated GKRP is resistant to degradation by the ubiquitin-dependent proteasome pathway, suggesting that acetylation increases GKRP stability and binding to GK, further inhibiting GK nuclear export.Deacetylation of GKRP is effected by the NAD(+)-dependent, class III histone deacetylase SIRT2, which is inhibited by nicotinamide.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, Yonsei University College of Medicine, 50-1 Yonsei-ro, Seodaemun-gu, Seoul 120-752, Republic of Korea.

ABSTRACT
Glucokinase (GK), mainly expressed in the liver and pancreatic β-cells, is critical for maintaining glucose homeostasis. GK expression and kinase activity, respectively, are both modulated at the transcriptional and post-translational levels. Post-translationally, GK is regulated by binding the glucokinase regulatory protein (GKRP), resulting in GK retention in the nucleus and its inability to participate in cytosolic glycolysis. Although hepatic GKRP is known to be regulated by allosteric mechanisms, the precise details of modulation of GKRP activity, by post-translational modification, are not well known. Here, we demonstrate that GKRP is acetylated at Lys5 by the acetyltransferase p300. Acetylated GKRP is resistant to degradation by the ubiquitin-dependent proteasome pathway, suggesting that acetylation increases GKRP stability and binding to GK, further inhibiting GK nuclear export. Deacetylation of GKRP is effected by the NAD(+)-dependent, class III histone deacetylase SIRT2, which is inhibited by nicotinamide. Moreover, the livers of db/db obese, diabetic mice also show elevated GKRP acetylation, suggesting a broader, critical role in regulating blood glucose. Given that acetylated GKRP may affiliate with type-2 diabetes mellitus (T2DM), understanding the mechanism of GKRP acetylation in the liver could reveal novel targets within the GK-GKRP pathway, for treating T2DM and other metabolic pathologies.

No MeSH data available.


Related in: MedlinePlus