AKT2 Confers Protection Against Aortic Aneurysms and Dissections
Ying H. ShenLin ZhangPingping RenMary NguyenSili ZouDarrell WuXing Li WangJoseph S. CoselliScott A. LeMaire
89
Citation
59
Reference
10
Related Paper
Citation Trend
Abstract:
Rationale: Aortic aneurysm and dissection (AAD) are major diseases of the adult aorta caused by progressive medial degeneration of the aortic wall. Although the overproduction of destructive factors promotes tissue damage and disease progression, the role of protective pathways is unknown. Objective: In this study, we examined the role of AKT2 in protecting the aorta from developing AAD. Methods and Results: AKT2 and phospho-AKT levels were significantly downregulated in human thoracic AAD tissues, especially within the degenerative medial layer. Akt2- deficient mice showed abnormal elastic fibers and reduced medial thickness in the aortic wall. When challenged with angiotensin II, these mice developed aortic aneurysm, dissection, and rupture with features similar to those in humans, in both thoracic and abdominal segments. Aortas from Akt2 -deficient mice displayed profound tissue destruction, apoptotic cell death, and inflammatory cell infiltration that were not observed in aortas from wild-type mice. In addition, angiotensin II–infused Akt2- deficient mice showed significantly elevated expression of matrix metalloproteinase-9 (MMP-9) and reduced expression of tissue inhibitor of metalloproteinase-1 (TIMP-1). In cultured human aortic vascular smooth muscle cells, AKT2 inhibited the expression of MMP-9 and stimulated the expression of TIMP-1 by preventing the binding of transcription factor forkhead box protein O1 to the MMP-9 and TIMP-1 promoters. Conclusions: Impaired AKT2 signaling may contribute to increased susceptibility to the development of AAD. Our findings provide evidence of a mechanism that underlies the protective effects of AKT2 on the aortic wall and that may serve as a therapeutic target in the prevention of AAD.Keywords:
AKT2
PKB (protein kinase B, also known as Akt) is a serine/threonine protein kinase that is important in various signalling cascades and acts as a major signal transducer downstream of activated phosphoinositide 3-kinase. There are three closely related isoforms of PKB in mammalian cells, PKBα (Akt1), PKBβ (Akt2) and PKBγ (Akt3), and this review discusses recent advances in our understanding of the functions of these isoforms in the regulation of adipocyte differentiation, glucose homoeostasis and tumour development.
AKT2
AKT3
Proto-Oncogene Proteins c-akt
Cite
Citations (297)
Recent data have implicated the serine/threonine protein kinase Akt/protein kinase B (PKB) in a diverse array of physiological pathways, raising the question of how biological specificity is maintained. Partial clarification derived from the observation that mice deficient in either of the two isoforms, Akt1/PKBalpha or Akt2/PKBbeta, demonstrate distinct abnormalities, i.e. reduced organismal size or insulin resistance, respectively. However, the question still persists as to whether these divergent phenotypes are due exclusively to tissue-specific differences in isoform expression or distinct capacities for signaling intrinsic to the two proteins. Here we show that Akt2/PKBbeta-/- adipocytes derived from immortalized mouse embryo fibroblasts display significantly reduced insulin-stimulated hexose uptake, clearly establishing that the partial defect in glucose disposal in these mice derives from lack of a cell autonomous function of Akt2/PKBbeta. Moreover, in adipocytes differentiated from primary fibroblasts or immortalized mouse embryo fibroblasts, and brown preadipocytes the absence of Akt2/PKBbeta resulted in reduction of insulin-induced hexose uptake and glucose transporter 4 (GLUT4) translocation, whereas Akt1/PKBalpha was dispensable for this effect. Most importantly, hexose uptake and GLUT4 translocation were completely restored after re-expression of Akt2/PKBbeta in Akt2/PKBbeta-/- adipocytes, but overexpression of Akt1/PKBalpha at comparable levels was ineffective at rescuing insulin action to normal. These results show that the Akt1/PKBalpha and Akt2/PKBbeta isoforms are uniquely adapted to preferentially transmit distinct biological signals, and this property is likely to contribute significantly to the ability of Akt/PKB to play a role in diverse processes.
AKT2
GLUT4
AKT3
Proto-Oncogene Proteins c-akt
Cite
Citations (308)
AKT is a serine/threonine kinase that mediates a number of intracellular processes including proliferation, survival, and metabolism. Three Akt isoforms have been identified in mammals (AKT1, AKT2, and AKT3), and there exist distinct and redundant functions for each. While a great deal of our knowledge regarding the functions of the three AKT isoforms in skeletal muscle has been derived from the use of cell and animal models, there is limited information regarding the expression and actions of AKT isoforms in human skeletal muscle. Given this, we performed a series of experiments to determine the abundances of each AKT isoform in human skeletal muscle, and to identify the principal AKT isoform involved in human myogenesis. We first examined the RNA transcript expression of each AKT isoform from biopsies obtained from human quadriceps. AKT2 was the most highly expressed AKT transcript, exhibiting a15.5‐fold increase over AKT1 and AKT3 transcripts (P<0.001). No significant difference between expression of AKT1 and AKT3 was observed. We next determined the abundance of AKT protein isoforms by using antibody immunoprecipitation followed by Liquid Chromatography‐Parallel Reaction Monitoring/Mass Spectrometry (LC‐PRM/MS). Immunoprecipitation was performed using both mouse and rabbit pan AKT antibodies that were immunoreactive with purified peptides of all three AKT isoforms. Analysis of immunoprecipitates by LC‐PRM/MS revealed that AKT2 was the most highly expressed AKT in quadriceps muscle (4.2‐fold greater than AKT1 using the rabbit antibody (P<0.001) and 1.6‐fold greater than AKT1 using the mouse antibody(P<0.05)). Expression of AKT3 protein was virtually undetectable in quadriceps, suggesting that AKT3 plays little or no role in skeletal muscle physiology. Having found that AKT2 is the most highly expressed AKT isoform in human quadriceps, we next asked whether AKT2 was the principal isoform regulating human myotube formation. To test this, cultured primary human myoblasts were virally‐transduced with cDNAs encoding either wild‐type (WT) or kinase‐dead (KD) AKT1 or AKT2 and allowed to terminally differentiate. Myotubes expressing either WT‐AKT1 or WT‐AKT2 showed enhanced fusion compared to control myotubes(P<0.05 for each), while myotubes expressing KD‐AKT1 showed a 10% reduced fusion index (P<0.05). However, compared to control myotubes, myotubes expressing KD‐AKT2 showed a 63% decrease in fusion index (P<0.001). In conclusion, our findings identify AKT2 as the predominant AKT isoform expressed in human quadriceps muscle and as the principal AKT isoform that regulates differentiation of cultured human skeletal myoblasts. Support or Funding Information The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or reflecting the views of the Army or the Department of Defense.
AKT2
AKT3
Immunoprecipitation
Cite
Citations (3)
Akt is a serine/threonine kinase that mediates signaling downstream of tyrosine kinase receptors like the type I insulin-like growth factor receptor (IGF-IR). In fact, we have previously shown that mammary tumors induced by elevated expression of the IGF-IR are associated with hyperactivation of Akt. However, there are three mammalian isoforms of Akt (Akt1, Akt2 and Akt3) and these isoforms regulate distinct physiologic properties within cells. In this manuscript, the impact of disrupting Akt1 or Akt2 in mammary tumors induced by IGF-IR overexpression were examined to determine whether specific Akt isoforms regulate different aspects of mammary tumorigenesis. Akt1 and Akt2 levels were stably ablated in mammary tumors of MTB-IGFIR transgenic mice by crossing MTB-IGFIR transgenic mice with either Akt1−/− or Akt2−/− mice. Tumor onset, growth rate, and metastasis were determined. Ablation of Akt1 or Akt2 significantly delayed tumor onset and tumor growth rate but did not significantly alter lung metastasis. Despite the absence of Akt1 or Akt2, mammary tumors that developed in the MTB-IGFIR mice maintained detectable levels of phosphorylated Akt. Disruption of Akt1 or Akt2 did not affect cell morphology or the expression of luminal or basal cytokeratins in mammary tumors. Although loss of Akt1 or Akt2 significantly inhibited mammary tumor onset and growth rates the effects were less dramatic than anticipated. Despite the complete loss of Akt1 or Akt2, the level of total phosphorylated Akt remained largely unaffected in the mammary tumors suggesting that loss of one Akt isoform is compensated by enhanced activation of the remaining Akt isoforms. These findings indicate that therapeutic strategies targeting the activation of individual Akt isoforms will prove less effective than simultaneously inhibiting the activity of all three Akt isoforms for the treatment of breast cancer.
AKT2
Mammary tumor
AKT3
Cite
Citations (15)
The serine/threonine protein kinase AKT is frequently over-activated in cancer and is associated with poor prognosis. As a central node in the PI3K/AKT/mTOR pathway, which regulates various processes considered to be hallmarks of cancer, this kinase has become a prime target for cancer therapy. However, AKT has proven to be a highly complex target as it comes in three isoforms (AKT1, AKT2 and AKT3) which are highly homologous, yet non-redundant. The isoform-specific functions of the AKT kinases can be dependent on context (i.e. different types of cancer) and even opposed to one another. To date, there is no isoform-specific inhibitor available and no alternative to genetic approaches to study the function of a single AKT isoform. We have developed and characterized nanobodies that specifically interact with the AKT1 or AKT2 isoforms. These new tools should enable future studies of AKT1 and AKT2 isoform-specific functions. Furthermore, for both isoforms we obtained a nanobody that interferes with the AKT-PIP3-interaction, an essential step in the activation of the kinase. The nanobodies characterized in this study are a new stepping stone towards unravelling AKT isoform-specific signalling.
AKT2
AKT3
Proto-Oncogene Proteins c-akt
Cite
Citations (7)
Abstract Background The serine/threonine protein kinase AKT is frequently over-activated in cancer and is associated with poor prognosis. As a central node in the PI3K/AKT/mTOR pathway, which regulates various processes considered to be hallmarks of cancer, this kinase has become a prime target for cancer therapy. However, AKT has proven to be a highly complex target as it comes in three isoforms (AKT1, AKT2 and AKT3) which are highly homologous, yet non-redundant. The isoform-specific functions of the AKT kinases can be dependent on context (i.e. different types of cancer) and even opposed to one another. To date, there is no isoform-specific inhibitor available and no alternative to genetic approaches to study the function of a single AKT isoform. Results We have developed and characterized nanobodies that specifically interact with the AKT1 or AKT2 isoforms. These new tools should enable future studies of AKT1 and AKT2 isoform-specific functions. Furthermore, for both isoforms we obtained a nanobody that interferes with the AKT-PIP3-interaction, an essential step in the activation of the kinase. Conclusions The nanobodies characterized in this study, which can be expressed in mammalian cells, are a new stepping stone towards unravelling AKT isoform-specific signalling and can lead to the first isoform-specific AKT inhibitor.
AKT2
AKT3
Proto-Oncogene Proteins c-akt
Cite
Citations (3)
AKT2
AKT3
Pleckstrin homology domain
Cite
Citations (0)
Objective To study the molecular mechanism of phosphatidylinositol 3-kinase (PI3K)/Akt active pathway that involve in the regulation of apoptosis. Methods Different tumor cells were seeded into either 96 well or 6 well tissue culture plates and incubated with isoform specific Akt inhibitor for 6 hours. Akt phosphorylation and its activity were evaluated with immunoprecipitation; the activation of phosphorylated Akt were detected by immunoprecipitation and western blotting; Caspase assay has been performed to quantitate apoptosis. Results ①The inhibitors could reduce the phosphorylations of threonine 308 and serine 473 of isoform specific Akt ;②the inhibition of any isoform specific Akt could significantly downregulate the activation and activity of its substrate(GSK3) , but it was not the same case if blocking two isoforms of both Akt1 and Akt2 at the same time;③ PI3K involves in the regulation of apoptosis mainly through its downstream gene(AKT) , specifically the isoforms of Aktl and Akt2. Conclusion PI3K/Akt involves in the regulation of apoptosis, two isoforms of Akt(Akt1 and Akt2) are mainly the regulator of PI3K in terms of the regulation of apoptosis. It is required to inhibit two isoforms of both Akt1 and Akt2 to initiate apoptosis.
AKT2
AKT3
Immunoprecipitation
Proto-Oncogene Proteins c-akt
Cite
Citations (0)
The Akt family of serine-threonine kinases participates in diverse cellular processes, including the promotion of cell survival, glucose metabolism, and cellular protein synthesis. All three known Akt family members, Akt1, Akt2 and Akt3, are expressed in the myocardium, although Akt1 and Akt2 are most abundant. Previous studies demonstrated that Akt1 and Akt3 overexpression results in enhanced myocardial size and function. Yet, little is known about the role of Akt2 in modulating cardiac metabolism, survival, and growth. Here, we utilize murine models with targeted disruption of the akt2 or the akt1 genes to demonstrate that Akt2, but not Akt1, is required for insulin-stimulated 2-[(3)H]deoxyglucose uptake and metabolism. In contrast, akt2(-/-) mice displayed normal cardiac growth responses to provocative stimulation, including ligand stimulation of cultured cardiomyocytes, pressure overload by transverse aortic constriction, and myocardial infarction. However, akt2(-/-) mice were found to be sensitized to cardiomyocyte apoptosis in response to ischemic injury, and apoptosis was significantly increased in the peri-infarct zone of akt2(-/-) hearts 7 days after occlusion of the left coronary artery. These results implicate Akt2 in the regulation of cardiomyocyte metabolism and survival.
AKT2
AKT3
Cite
Citations (159)
SUMMARY Overactivation of the PI3K/AKT signaling pathway is frequently reported in breast cancer, consequently inhibitors targeting this pathway are clinically useful. AKT constitutes a hub in the regulation of several cancer hallmarks, such as proliferation, survival and migration. Three AKT isoforms, named AKT1, AKT2 and AKT3, are identified in humans. AKT alterations, mainly upregulation of phosphorylated AKT in tumors may have prognostic and predictive value. Moreover, the AKT isoforms may possess partly divergent cellular functions and be upregulated in certain breast cancer subtypes, suggesting the importance of isoform-specific analyses. In conclusion, AKT isoform-specific detection and targeting in different tumor subtypes will hopefully result into a further developed personalized medicine.
AKT2
AKT3
Cite
Citations (4)