Ever since the tumor suppressor protein PTEN was shown to have similarity to dual specificity protein tyrosine phosphatases (PTPs) and to be able to dephosphorylate the lipid second messenger phosphatidylinositol 3,4,5-trisphosphate, there has been interest in identifying other PTPs that recognize inositol lipids as substrates. Taylor et al. now report that a member of the myotubularin family of enzymes dephosphorylates the second messenger phosphatidylinositol 3-phosphate (PI3P), a lipid that controls membrane trafficking and interacts with proteins containing a PI3P-binding FYVE domain. Overexpression of myotubularin in cultured cells decreased intracellular PI3P by 20% compared with control cells. Mutant proteins corresponding to mutations in the myotubularin gene that cause human myotubular myopathy showed decreased phosphatase activity toward PI3P. The authors propose that by regulating the availability of PI3P, mytotubularin could affect signaling pathways involving FYVE-domain-containing proteins.
Taylor, G.S., Maehama, T., and Dixon, J.E. (2000) Myotubularin, a protein tyrosine phosphatase mutated in myotubular myopathy, dephosphorylates the lipid second messenger phosphatidylinositol 3-phosphate. Proc. Natl. Acad. Sci. U.S.A. 97: 8910-8915. [Abstract] [Full Text]