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Panayiotis O. Vacratsis

 

Dr. Panayiotis O. Vacratsis
Biochemistry Ph.D. (Michigan State) vacratsi@uwindsor.ca
Associate Professor
253-3000 Ext: 3541
263 Essex Hall
 

 

 

Signal transduction is a term used to describe the series of events that culminates in a cellular response to an extracellular signal or environmental stimuli. From the engagement of cell surface receptors to the activation of protein kinase cascades, this process involves a variety of molecular participants and regulates numerous cellular processes including cell survival/apoptosis, vesicular trafficking, cell differentiation, mRNA dynamics, and cellular proliferation.

Cellular phosphorylation is regulated by two enzyme superfamilies - kinases and phosphatases and utilization of this post translational modification is at the heart of signal transduction. Activation of kinase and phosphatase cascades leads to strategic changes in intracellular phosphorylation and subsequently the function of target molecules allowing the cell and organism to respond appropriately to its surroundings. Disruption of signaling integrity invariably leads to abnormal phosphorylation, a consequence that often causes or promotes many human diseases.

Our laboratory integrates biological mass spectrometry and other proteomic techniques with traditional biochemical and cell biology methods to decipher the mechanistic details regulating poorly understood kinases and phosphatases predicted to function in processes such as cellular proliferation, cell survival, and neuromuscular signaling.

Current projects include:

I. Molecular mechanisms regulating the Myotubularin lipid phosphatase MTMR2 mutated in the neuromuscular disorder Charcot-Marie Tooth disease - Mutations in the MTMR2 gene has been shown to cause Charcot-Marie Tooth disease 4B1 (CMT4B1). CMT4B1 is a demyelinating neuropathy characterized by abnormally folded myelin sheaths causing inadequate nerve conduction to the muscles eventually leading to muscle weakness and atrophy. We have recently discovered a mechanism of how MTMR2 gains access to its physiological substrate. Our data indicates that phosphorylation of MTMR2 by the kinase ERK1/2, via a sophisticated negative feedback loop, sequesters MTMR2 away from its lipid substrates and is tightly regulated by growth factor signaling pathways that regulate myelination. We are currently investigating the role of MTMR2 phosphorylation during myelination and Schwann cell differentiation. We have also initiated a mass spectrometry based method aimed at identifying target proteins that are affected by MTMR2 enzymatic activity in disease-related cells. We have identified and verified one candidate (RME8) which has a characterized role in vesicular transport and recycling receptors to the cell surface.  We now plan to further define the proteome that interacts with the lipid substrates of MTMR2. 

II. Functional characterization of hYVH1: a unique dual specificity phosphatase overexpressed in late stage cancers - Our laboratory has recently discovered that the evolutionary conserved dual specificity phosphatase hYVH1 (also known as DUSP12) is a potent cell survival enzyme and a novel regulator of RNP dynamics.  In yeast, YVH1 has been shown to be involved in the biogenesis of the 60S ribosome subunit and regulate cell growth.  Furthermore, we have recently determined that its expression regulates cell cycle progression in human cell lines.  Human YVH1 is widely expressed in human tissues and its gene has been found amplified in a wide variety of late stage malignancies.  Our results showing that hYVH1 can function as a regulator of cellular proliferation and as an anti-apoptotic factor (cell survival) coupled with the gene amplification findings, tempts us to speculate that overexpression of the hyvh1 gene will impart on tumour cells the ability to survive unfavourable microenvironments and support metastasis.

Selected Publications:

Geng Q, Xhabija B, Knuckle C, Bonham CA, Vacratsis PO. (2017) The Atypical Dual Specificity Phosphatase hYVH1 Associates with Multiple Ribonucleoprotein Particles. J Biol Chem. 292, 539-550

Gombar R, Pitcher TE, Lewis JA, Auld J, Vacratsis PO. (2017) Proteomic characterization of seminal plasma from alternative reproductive tactics of Chinook salmon (Oncorhynchus tswatchysha). J Proteomics. 157, 1-9.

Xhabija B, Vacratsis PO. (2015) Receptor-mediated Endocytosis 8 Utilizes an N-terminal Phosphoinositide-binding Motif to Regulate Endosomal Clathrin Dynamics. J Biol Chem. 290, 21676-89

Bonham CA, Steevensz AJ, Geng Q, Vacratsis PO. (2014) Investigating redox regulation  of protein tyrosine phosphatases using low pH thiol labeling and enrichment strategies coupled to MALDI-TOF mass spectrometry. Methods. 65, 190-200

Franklin NE, Bonham CA, Xhabija B, Vacratsis PO. (2013) Differential phosphorylation of the phosphoinositide 3-phosphatase MTMR2 regulates its association with early endosomal subtypes. J Cell Sci. 126, 1333-44

Franklin NE, Taylor GS, Vacratsis PO. (2011) Endosomal Targeting of the Phosphoinositide 3-Phosphatase MTMR2 is Regulated by an N-Terminal Phosphorylation site. J Biol Chem, 286, 15841-53

Kozarova A, Hudson JW, Vacratsis PO. (2011) The Dual Specificity Phosphatase hYVH1 (DUSP12) is a Novel Modular of Cellular DNA Content. Cell Cycle. 10, 1669-78 

Xhabija B, Taylor GS, Fujibayashi A, Sekiguchi K, Vacratsis PO. (2011) Receptor mediated endocytosis 8 is a novel PI(3)P Binding Protein Regulated by MTMR2. FEBS Letters. 585, 1722-8.

Faccenda A, Bonham CA, Vacratsis PO, Zhang X, Mutus B. (2010) Gold Nanoparticle Enrichment Method for Identifying S-Nitrosylation and S-Glutathionylation Sites in Proteins. J Am Chem Soc., 132, 11392-4

Bonham CA, Vacratsis PO. (2009) Redox regulation of the dual specificity phosphatase hYVH1 through disulfide bond formation. J Biol Chem., 284, 22853-64

Sharda PR, Bonham CA, Mucaki EJ, Butt Z, Vacratsis PO. (2009) The dual-specificity phosphatase hYVH1 interacts with Hsp70 and prevents heat-shock-induced cell death. Biochem J. 418, 391-401.