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Articles by R Whittaker
Total Records ( 2 ) for R Whittaker
  G. A Borillo , M Mason , P Quijada , M Volkers , C Cottage , M McGregor , S Din , K Fischer , N Gude , D Avitabile , S Barlow , R Alvarez , S Truffa , R Whittaker , M. S Glassy , A. B Gustafsson , S Miyamoto , C. C Glembotski , R. A Gottlieb , J. H Brown and M. A. Sussman
 

Rationale: Cardioprotective signaling mediates antiapoptotic actions through multiple mechanisms including maintenance of mitochondrial integrity. Pim-1 kinase is an essential downstream effector of AKT-mediated cardioprotection but the mechanistic basis for maintenance of mitochondrial integrity by Pim-1 remains unexplored. This study details antiapoptotic actions responsible for enhanced cell survival in cardiomyocytes with elevated Pim-1 activity.

Objective: The purpose of this study is to demonstrate that the cardioprotective kinase Pim-1 acts to inhibit cell death by preserving mitochondrial integrity in cardiomyocytes.

Methods and Results: A combination of biochemical, molecular, and microscopic analyses demonstrate beneficial effects of Pim-1 on mitochondrial integrity. Pim-1 protein level increases in the mitochondrial fraction with a corresponding decrease in the cytosolic fraction of myocardial lysates from hearts subjected to 30 minutes of ischemia followed by 30 minutes of reperfusion. Cardiac-specific overexpression of Pim-1 results in higher levels of antiapoptotic Bcl-XL and Bcl-2 compared to samples from normal hearts. In response to oxidative stress challenge, Pim-1 preserves the inner mitochondrial membrane potential. Ultrastructure of the mitochondria is maintained by Pim-1 activity, which prevents swelling induced by calcium overload. Finally, mitochondria isolated from hearts created with cardiac-specific overexpression of Pim-1 show inhibition of cytochrome c release triggered by a truncated form of proapoptotic Bid.

Conclusion: Cardioprotective action of Pim-1 kinase includes preservation of mitochondrial integrity during cardiomyopathic challenge conditions, thereby raising the potential for Pim-1 kinase activation as a therapeutic interventional approach to inhibit cell death by antagonizing proapoptotic Bcl-2 family members that regulate the intrinsic apoptotic pathway.

  S Miyamoto , N. H Purcell , J. M Smith , T Gao , R Whittaker , K Huang , R Castillo , C. C Glembotski , M. A Sussman , A. C Newton and J. H. Brown
  Rationale:

The recently discovered PHLPP-1 (PH domain leucine-rich repeat protein phosphatase-1) selectively dephosphorylates Akt at Ser473 and terminates Akt signaling in cancer cells. The regulatory role of PHLPP-1 in the heart has not been considered.

Objective:

To test the hypothesis that blockade/inhibition of PHLPP-1 could constitute a novel way to enhance Akt signals and provide cardioprotection.

Methods and Results:

PHLPP-1 is expressed in neonatal rat ventricular myocytes (NRVMs) and in adult mouse ventricular myocytes (AMVMs). PHLPP-1 knockdown by small interfering RNA significantly enhances phosphorylation of Akt (p-Akt) at Ser473, but not at Thr308, in NRVMs stimulated with leukemia inhibitory factor (LIF). The increased phosphorylation is accompanied by greater Akt catalytic activity. PHLPP-1 knockdown enhances LIF-mediated cardioprotection against doxorubicin and also protects cardiomyocytes against H2O2. Direct Akt effects at mitochondria have been implicated in cardioprotection and mitochondria/cytosol fractionation revealed a significant enrichment of PHLPP-1 at mitochondria. The ability of PHLPP-1 knockdown to potentiate LIF-mediated increases in p-Akt at mitochondria and an accompanying increase in mitochondrial hexokinase-II was demonstrated. We generated PHLPP-1 knockout (KO) mice and demonstrate that AMVMs isolated from KO mice show potentiated p-Akt at Ser473 in response to agonists. When isolated perfused hearts are subjected to ischemia/reperfusion, p-Akt in whole-heart homogenates and in the mitochondrial fraction is significantly increased. Additionally in PHLPP-1 KO hearts, the increase in p-Akt elicited by ischemia/reperfusion is potentiated and, concomitantly, infarct size is significantly reduced.

Conclusions:

These results implicate PHLPP-1 as an endogenous negative regulator of Akt activity and cell survival in the heart.

 
 
 
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