Conserved residues in the N-terminus of lipin-1 are required for binding to protein phosphatase-1c, nuclear translocation and phosphatidate phosphatase activity [Enzymology]

February 20th, 2014 by Kok, B. P. C., Skene-Arnold, T. D., Ling, J., Benesch, M. G. K., Dewald, J., Harris, T. E., Holmes, C. F. B., Brindley, D. N.

Lipin-1 is a phosphatidate phosphatase in glycerolipid biosynthesis and signal transduction. It also serves as a transcriptional co-regulator to control lipid metabolism and adipogenesis. These functions are controlled partly by its subcellular distribution. Hyper-phosphorylated lipin-1 remains sequestered in the cytosol, whereas hypo-phosphorylated lipin-1 translocates to the endoplasmic reticulum and nucleus. The serine/threonine protein phosphatase-1 catalytic subunit (PP-1c) is a major protein dephosphorylation enzyme. Its activity is controlled by interactions with different regulatory proteins, many of which contain conserved RVXF binding motifs. We found that lipin-1 binds to PP-1cγ through a similar HVRF binding motif. This interaction depends on Mg2+ or Mn2+ and is competitively inhibited by R/H-VXF-containing peptides. Mutating the HVRF motif in the highly conserved N-terminus of lipin-1 greatly decreases PP-1cγ interaction. Moreover, mutations of other residues in the N-terminus of lipin-1 also modulate PP-1cγ binding. PP-1cγ binds poorly to a phosphomimetic mutant of lipin-1 and binds well to the non-phosphorylatable lipin-1 mutant. This indicates that lipin-1 is dephosphorylated before PP-1cγ binds to its HVRF motif. Importantly, mutating the HVRF motif also abrogates the nuclear translocation and phosphatidate phosphatase activity of lipin-1. In conclusion, we provide novel evidence of the importance of the lipin-1 N-terminal domain for its catalytic activity, nuclear localization and binding to PP-1cγ.
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