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Dr. Amrik  Singh  Dds image

Dr. Amrik Singh Dds

132 N Addison Ave
Elmhurst IL 60126
630 344-4140
Medical School: Other - Unknown
Accepts Medicare: No
Participates In eRX: No
Participates In PQRS: No
Participates In EHR: No
License #:
NPI: 1396883609
Taxonomy Codes:
1223G0001X

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Publications

Cell-cycle-regulated activation of Akt kinase by phosphorylation at its carboxyl terminus. - Nature
Akt, also known as protein kinase B, plays key roles in cell proliferation, survival and metabolism. Akt hyperactivation contributes to many pathophysiological conditions, including human cancers, and is closely associated with poor prognosis and chemo- or radiotherapeutic resistance. Phosphorylation of Akt at S473 (ref. 5) and T308 (ref. 6) activates Akt. However, it remains unclear whether further mechanisms account for full Akt activation, and whether Akt hyperactivation is linked to misregulated cell cycle progression, another cancer hallmark. Here we report that Akt activity fluctuates across the cell cycle, mirroring cyclin A expression. Mechanistically, phosphorylation of S477 and T479 at the Akt extreme carboxy terminus by cyclin-dependent kinase 2 (Cdk2)/cyclin A or mTORC2, under distinct physiological conditions, promotes Akt activation through facilitating, or functionally compensating for, S473 phosphorylation. Furthermore, deletion of the cyclin A2 allele in the mouse olfactory bulb leads to reduced S477/T479 phosphorylation and elevated cellular apoptosis. Notably, cyclin A2-deletion-induced cellular apoptosis in mouse embryonic stem cells is partly rescued by S477D/T479E-Akt1, supporting a physiological role for cyclin A2 in governing Akt activation. Together, the results of our study show Akt S477/T479 phosphorylation to be an essential layer of the Akt activation mechanism to regulate its physiological functions, thereby providing a new mechanistic link between aberrant cell cycle progression and Akt hyperactivation in cancer.
Perioperative hypotension and myocardial ischemia: diagnostic and therapeutic approaches. - Annals of cardiac anaesthesia
Although perioperative hypotension is a common problem, its true incidence is largely unknown. There is evidence that postoperative outcome, including the incidence of myocardial adverse events, may be linked to the prolonged episodes of perioperative hypotension. Despite this, there are very few comprehensive resources available in the literature regarding diagnosis and management of these not so uncommon clinical occurrences, especially during non-cardiac surgery. Most anesthesia providers consider intraoperative hypotension to be caused by systemic vasodilatation and relative hypovolemia and so treat it empirically. The introduction of new monitoring devices including transesophageal echocardiography and arterial pressure waveform based stroke volume measurement have provided additional tools to narrow the differential diagnoses and initiate optimal treatment measures. Understanding the basic pathophysiology of hypotension and myocardial ischemia can further assist in providing goal directed management. This article serves as a comprehensive guide for anesthesiologists to diagnose and treat hypotension and myocardial ischemia. A summary of available techniques to monitor perioperative myocardial ischemia and their limitations are also discussed.
Harnessing the tumor suppressor function of FOXO as an alternative therapeutic approach in cancer. - Current drug targets
The promotion of cellular survival, dedifferentiation, and uncontrolled proliferation via the suppression of apoptotic effectors is a fundamental characteristic of tumor cells. As substrates that are negatively regulated by oncogenic signaling cascades driven by AKT, SGK (serum- and glucocorticoid-inducible kinase), IkB kinase (IKK), ERK, and cyclin-dependent kinases (CDK), forkhead box-class O (FOXO) transcription factors have emerged as bona fide tumor suppressors. These transcription factors indeed regulate a variety of cellular responses and themselves are regulated by reversible phosphorylation, acetylation, ubiquitination and miRNAs. This review will discuss our current understanding of mechanisms for FOXO regulation and the potential implications for therapeutically restoring FOXO transcriptional activity.© 2011 Bentham Science Publishers Ltd.
PEST motif serine and tyrosine phosphorylation controls vascular endothelial growth factor receptor 2 stability and downregulation. - Molecular and cellular biology
The internalization and degradation of vascular endothelial growth factor receptor 2 (VEGFR-2), a potent angiogenic receptor tyrosine kinase, is a central mechanism for the regulation of the coordinated action of VEGF in angiogenesis. Here, we show that VEGFR-2 is ubiquitinated in response to VEGF, and Lys 48-linked polyubiquitination controls its degradation via the 26S proteosome. The degradation and ubiquitination of VEGFR-2 is controlled by its PEST domain, and the phosphorylation of Ser1188/Ser1191 is required for the ubiquitination of VEGFR-2. F-box-containing β-Trcp1 ubiquitin E3 ligase is recruited to S1188/S1191 VEGFR-2 and mediates the ubiquitination and degradation of VEGFR-2. The PEST domain also controls the activation of p38 mitogen-activated protein kinase (MAPK) through phospho-Y1173. The activation of p38 stabilizes VEGFR-2, and its inactivation accelerates VEGFR-2 downregulation. The VEGFR-2-mediated activation of p38 is established through the protein kinase A (PKA)/MKK6 pathway. PKA is recruited to VEGFR-2 through AKAP1/AKAP149, and its phosphorylation requires Y1173 of VEGFR-2. The study has identified a unique mechanism in which VEGFR-2 stability and degradation is modulated. The PEST domain acts as a dual modulator of VEGFR-2; the phosphorylation of S1188/S1191 controls ubiquitination and degradation via β-Trcp1, where the phosphorylation of Y1173 through PKA/p38 MAPK controls the stability of VEGFR-2.
Perioperative pharmacology in elderly patients. - Current opinion in anaesthesiology
Populations across the world are getting older and requiring more surgery. Elderly patients present unique challenges to the anesthesiologist and anesthesia-care team. This review addresses some concerns when caring for an elderly patient. Specifically, we discuss postoperative cognitive decline (POCD) and postoperative delirium, perioperative beta-blockade and use of newer drugs, as well as older drugs.POCD has emerged as a new concern for anesthesiologists and their older patients. Several recent studies indicate that POCD is common after noncardiac surgery, with an incidence approaching 30-40% at discharge, although this incidence declines at 3 months. Some data suggest that POCD imparts risk for death. However, there is conflicting evidence. With regard to beta-blocker therapy, there has been growing concern about widespread use of beta-blocker therapy in the perioperative period, especially because such therapy might increase the risk for stroke.Elderly patients require focused diligent care. They are particularly sensitive to the many drugs that are administered in the perioperative period. Recent data suggest that POCD is a real concern, but it is unclear what, if anything, can be done to prevent this complication. Beta-blocker therapy is beneficial in select patients but its widespread use cannot be supported.
Protein phosphatase 2A reactivates FOXO3a through a dynamic interplay with 14-3-3 and AKT. - Molecular biology of the cell
Forkhead box transcription factor FOXO3a, a key regulator of cell survival, is regulated by reversible phosphorylation and subcellular localization. Although the kinases regulating FOXO3a activity have been characterized, the role of protein phosphatases (PP) in the control of FOXO3a subcellular localization and function is unknown. In this study, we detected a robust interaction between FOXO3a and PP2A. We further demonstrate that 14-3-3, while not impeding the interaction between PP2A and FOXO3a, restrains its activity toward AKT phosphorylation sites T32/S253. Disruption of PP2A function revealed that after AKT inhibition, PP2A-mediated dephosphorylation of T32/S253 is required for dissociation of 14-3-3, nuclear translocation, and transcriptional activation of FOXO3a. Our findings reveal that distinct phosphatases dephosphorylate conserved AKT motifs within the FOXO family and that PP2A is entwined in a dynamic interplay with AKT and 14-3-3 to directly regulate FOXO3a subcellular localization and transcriptional activation.
Surgery in the patient with liver disease. - Anesthesiology clinics
Liver dysfunction is a prominent entity in Western medicine that has historically affected patients suffering from chronic viral or alcoholic hepatitis. The incidence of these conditions has not changed dramatically in recent years but the overall number of patients with liver dysfunction has increased considerably with the emergence of the obesity epidemic. Nonalcoholic fatty liver disease (NAFLD) has become increasingly recognized as the most common cause of chronic liver disease in the United States. Although the rate of progression of NAFLD to overt cirrhosis is low, the high prevalence of this condition, combined with the moderate degree of liver dysfunction it engenders, has resulted in a significant increase in the number of patients with liver disease that can be encountered by a surgical practice. Any degree of clinically evident liver disease in a prospective surgical patient should raise concern for the entire surgical team. This particularly applies to intraabdominal surgery whereby the presence of hepatomegaly, portal hypertension, variceal bleeding, and ascites can turn even the most routine operation into a morbid and life-threatening procedure. Nonabdominal surgery avoids some of the technical challenges presented by liver disease but the anesthetic management of a cirrhotic patient still makes any operation potentially more dangerous. In this article, approaches to minimize the risk when surgery becomes necessary in the presence of liver disease are discussed.
Surgery in the patient with liver disease. - The Medical clinics of North America
Liver dysfunction is a prominent entity in Western medicine that has historically affected patients suffering from chronic viral or alcoholic hepatitis. The incidence of these conditions has not changed dramatically in recent years but the overall number of patients with liver dysfunction has increased considerably with the emergence of the obesity epidemic. Nonalcoholic fatty liver disease (NAFLD) has become increasingly recognized as the most common cause of chronic liver disease in the United States. Although the rate of progression of NAFLD to overt cirrhosis is low, the high prevalence of this condition, combined with the moderate degree of liver dysfunction it engenders, has resulted in a significant increase in the number of patients with liver disease that can be encountered by a surgical practice. Any degree of clinically evident liver disease in a prospective surgical patient should raise concern for the entire surgical team. This particularly applies to intraabdominal surgery whereby the presence of hepatomegaly, portal hypertension, variceal bleeding, and ascites can turn even the most routine operation into a morbid and life-threatening procedure. Nonabdominal surgery avoids some of the technical challenges presented by liver disease but the anesthetic management of a cirrhotic patient still makes any operation potentially more dangerous. In this article, approaches to minimize the risk when surgery becomes necessary in the presence of liver disease are discussed.
Experimental approaches to investigate the proteasomal degradation pathways involved in regulation of apoptosis. - Methods in enzymology
Ubiquitin-mediated proteolysis plays a major role in a variety of cellular functions, including cell metabolism, cell cycle progression, cellular response to DNA damage, and programmed cell death. In most cases, the crucial regulators involved in the control of these diverse cellular functions are modified by specific E3 ubiquitin ligases through the attachment of multiple ubiquitin molecules, a signal that triggers the subsequent destruction by the 26S proteasome complex. Recent studies revealed that the proteasomal degradation pathway regulates the cellular apoptosis process on multiple levels. Thus, a better understanding of the molecular mechanisms that underlie the ubiquitination and destruction of these specific regulators of apoptosis will provide us with insight on how apoptosis is properly controlled in normal cells and how tumor cells evade the apoptosis pathways. This chapter provides an overview of the common methods used to examine whether a target protein is ubiquitinated, as well as the protocols to examine how a putative E3 ligase controls the destruction of the target protein.
FoxO tumor suppressors and BCR-ABL-induced leukemia: a matter of evasion of apoptosis. - Biochimica et biophysica acta
Numerous studies have revealed that the BCR-ABL oncoprotein abnormally engages a multitude of signaling pathways, some of which may be important for its leukemogenic properties. Central to this has been the determination that the tyrosine kinase function of BCR-ABL is mainly responsible for its transforming potential, and can be targeted with small molecule inhibitors, such as imatinib mesylate (Gleevec, STI-571). Despite this apparent success, the development of clinical resistance to imatinib therapy, and the inability of imatinib to eradicate BCR-ABL-positive malignant hematopoietic progenitors demand detailed investigations of additional effector pathways that can be targeted for CML treatment. The promotion of cellular survival via the suppression of apoptotic pathways is a fundamental characteristic of tumor cells that enables resistance to anti-cancer therapies. As substrates of survival kinases such as Akt, the FoxO family of transcription factors, particularly FoxO3a, has emerged as playing an important role in the cell cycle arrest and apoptosis of hematopoietic cells. This review will discuss our current understanding of BCR-ABL signaling with a focus on apoptotic suppressive mechanisms and alternative approaches to CML therapy, as well as the potential for FoxO transcription factors as novel therapeutic targets.

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