2004 — 2006 |
Robinson, Fred L |
F32Activity Code Description: To provide postdoctoral research training to individuals to broaden their scientific background and extend their potential for research in specified health-related areas. |
Regulation of Mtmr2 by the Inactive Phosphatase Mtmr13 @ University of California San Diego
DESCRIPTION (provided by applicant): Myotubularin related protein 2 (MTMR2) is a phospho-lipid phosphatase specific for the 3 positions of PI(3)P and Pl(3,5)P2. Loss of function mutations in MTMR2 cause the demyelinating peripheral neuropathy Charcot-Maire-Tooth disease type 4B (CMT-4B), a severely debilitating, hereditary condition characterized by focally folded myelin sheaths. Recessive mutations in a second myotubularin family member, MTMR13 (also called SET domain binding factor 2 [SBF2]) also cause CMT-4B. MTMR13 is a catalytically inactive member of the myotubularin inositol lipid phosphatase family. Recent data from our laboratory indicate that MTMR2 also binds to and is regulated by the closely related protein MTMR5 (also called SBF1). MTMR5 is 59% identical to MTMR13, has an identical domain composition, and is also an inactive phosphatase. However, MTMR5 is unlikely to be involved in CMT-4B. We propose to investigate how the lipid phosphatase activity of MTMR2 is regulated. Specifically, the effect of MTMR13 on MTMR2 function will be examined. Initial experiments will involve investigating whether the MTMR2 and MTMR13 proteins physically interact. The effect of MTMR13 association on the catalytic activity of MTMR2 will be analyzed both in vitro and in cell biological experiments. The effect of MTMR2-MTMR13 interactions on the cellular localization of both proteins will also be investigated. Finally, experiments are proposed to identify additional proteins that associate with MTMR13 and MTMR2.
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2007 — 2011 |
Robinson, Fred L |
K99Activity Code Description: To support the initial phase of a Career/Research Transition award program that provides 1-2 years of mentored support for highly motivated, advanced postdoctoral research scientists. R00Activity Code Description: To support the second phase of a Career/Research Transition award program that provides 1 -3 years of independent research support (R00) contingent on securing an independent research position. Award recipients will be expected to compete successfully for independent R01 support from the NIH during the R00 research transition award period. |
Roles of Myotubularin Pi 3-Phosphatases in Demyelinating Peripheral Neuropathy @ University of California San Diego
[unreadable] DESCRIPTION (provided by applicant): [unreadable] [unreadable] The Candidate, Dr. Fred Robinson, has been training for the last four years as a fellow in the laboratory of Dr. Jack Dixon. Dr. Dixon's Laboratory is in the Department of Pharmacology at the University of California San Diego (UCSD) School of Medicine. UCSD is a renowned research institution, particularly strong in the fields of neuroscience, signal transduction and cancer biology. Dr. Dixon is a world leader in the study of protein and lipid phosphatases. The Candidate has established a fledgling research program focused on understanding how mutations in myotubularin family phosphoinositide (PI) 3-phosphatases lead to Charcot-Marie-Tooth (CMT) peripheral neuropathy. CMT is the most common inherited neurological disorder, affecting about 1 in 2000 in the United States. CMT causes progressive degeneration of the muscles of the extremities and loss of sensory function. Type 4B CMT (CMT4B) is a severe form of the disease in which the myelin sheaths of peripheral nerves are abnormal. Mutations in the genes for either myotubularin related protein 2 (MTMR2) or MTMR13 cause CMT4B. The Candidate recently demonstrated that the MTMR2 and MTMR13 PI 3-phosphatases form a membrane-associated complex capable of regulating 3-phosphoinositides. As loss of either MTMR2 or MTMR13 is sufficient to cause CMT4B, MTMR13 is likely an essential regulator of MTMR2. To further probe the relationship between MTMR2 and MTMR13, the Candidate has generated Mtmrl 3-deficient mice. The specific aims of the proposal are (1) Validate Mtmrl 3-deficient mice as a model of CMT4B disease, (2) Examine the impact of loss of Mtmrl 3 on Mtmr2 function, and (3) Determine how 3-phosphoinositide homeostasis and endosomal-lysosomal trafficking are perturbed in Mtmrl 3-deficient Schwann cells. Understanding how the Schwann cell endosomal-lysosomal pathway is altered by the dysregulation of 3- phosphoinositides may allow us to consider pharmacological modulation of the pathway as a therapeutic strategy. [unreadable] The initial phase of the work (1-2 years) will be carried under Dr. Dixon's supervision. The Candidate will also be mentored by Dr. Katerina Akassoglou, an expert in peripheral nerve biology and demyelination. This phase will focus on characterization of Mtmrl 3-deficient mice and on other aspects of the project for which key training is available at UCSD. Later, as an independent investigator, the Candidate will continue studying Mtmrl 3-deficient mice, focusing more specifically on Schwann cell biology. [unreadable] [unreadable] [unreadable]
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2014 — 2018 |
Robinson, Fred L |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Myotubularin Pi 3-Phosphatases as Regulators of Peripheral Nerve Myelination @ Oregon Health & Science University
DESCRIPTION (provided by applicant): The overall goal of the proposed research is to determine the mechanisms by which disturbances in phosphoinositide (PI) regulation lead to abnormal membrane trafficking and cellular signaling in myelinating Schwann cells. We are studying this question in the context of a specific form of demyelinating Charcot-Marie-Tooth peripheral neuropathy (type 4B~ CMT4B), which is characterized by abnormal myelination and severe axonal degeneration. CMT is one of the most common inherited neurological disorders, affecting about 1 in 2500 worldwide. This condition leads to progressive degeneration of the muscles of the extremities and loss of sensory function. CMT4B is caused by loss of function mutations in either myotubularin-related protein 2 (MTMR2) or MTMR13, which belong to a large family of phosphatases that act as key regulators of PI signaling. MTMR2 is a PI 3-phosphatase that specifically dephosphorylates phosphatidylinositol 3-phosphate (PI3P) and phosphatidylinositol 3,5-bisphosphate (PI[3,5]P2). PI3P and PI(3,5)P2 regulate membrane traffic within the endosomal/lysosomal pathway. Therefore, it is theorized that CMT4B arises from defects in membrane transport in Schwann cells. MTMR13 is a catalytically inactive pseudophosphatase that associates directly with MTMR2. MTMR13 appears to function as a scaffold protein that regulates MTMR2. The first aim of this proposal is to define the phosphoinositide kinase-phosphatase network that controls PI3P and PI(3,5)P2 regulation in Schwann cells. The impact of the loss of PI kinases and phosphatases on phosphoinositide levels will be evaluated using HPLC-based phosphoinositide profiling. In parallel, the impact of the loss of PI kinases and phosphatases on myelination will be assessed using in vitro myelinating cultures and morphological examination of peripheral nerves of knockout mice. The second aim of the study is to define the function of the Mtmr13 pseudophosphatase in Schwann cell membrane traffic by determining how Mtmr13's activation of Rab GTPases regulates myelination, and by assessing the role of the Mtmr2-Mtmr13 complex in the regulation of endocytosis. These goals will be accomplished using biochemical studies to identify interacting Rab GTPases, as well as in vitro myelinating co-cultures to assess the relevance of specific interactions to myelination. The final aim of this proposal is to determine which domains of Mtmr13 control its specific functions. Collectively, these studies will allow us to define the specific, critical roles of phosphoinositides in myelinating Schwann cells. These studies also may well form the basis of a rational approach to the treatment of CMT4B by pharmacological targeting of the PI3P-PI(3,5)P2 pathway.
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