Editors' ChoiceBiochemistry

Regulating Ras Trafficking with FKPB12

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Science Signaling  25 Jan 2011:
Vol. 4, Issue 157, pp. ec23
DOI: 10.1126/scisignal.4157ec23

The Ras family of guanosine triphosphatases plays key roles in signaling downstream of growth factors, and mutations in the encoding genes are associated with various types of cancer. All of the proteins are prenylated, and H-Ras, N-Ras, and K-Ras4A (but not K-Ras4B) are also palmitoylated at the Golgi and depalmitoylated at the plasma membrane. Indeed, the palmitoylation status of the proteins controls their cellular localization, with palmitoylation promoting transport to the plasma membrane and depalmitoylation returning Ras to the Golgi to reinitiate the cycle. Ahearn et al. show that the prolyl isomerase FKBP12 (named for its ability to bind the immunosuppressive agent FK506 that binds and inhibits this protein; see Liu et al.) bound to palmitoylated Ras isoforms and promoted their depalmitoylation and thus their trafficking to the Golgi. The authors noticed that a green fluorescent protein (GFP) fusion construct with only 10 amino acids of the H-Ras C-terminal tail (GFP-H-Ras10aaTail) showed reduced localization at the Golgi compared with full-length tagged H-Ras, whereas a construct with 19 amino acids of the H-Ras C-terminal tail (GFP-H-Ras19aaTail) had a distribution more like that of the full-length protein. GFP-H-Ras10aaTail had more palmitoylation than did GFP-H-Ras19aaTail. Because the GFP-H-Ras19aaTail contained several proline residues not present in the GFP-H-Ras10aaTail, the authors examined the effects of inhibition or knockdown of prolyl isomerases and found that reducing the activity of FKPB12 specifically enhanced full-length H-Ras and GFP-H-Ras19aaTail palmitoylation and that this depended on the presence of Pro179. Coimmunoprecipitation experiments with both tagged proteins and endogenous proteins revealed that FKBP12 only bound to those Ras isoforms that could be palmitoylated and that mutation of the palmitoylated residues blocked the interaction, although Pro179 was not required for the interaction. Inhibition of FKBP12 reduced the abundance of GFP-H-Ras19aaTail or full-length H-Ras at the Golgi and enhanced the activation of H-Ras but not K-Ras. Furthermore, application of FK506 to a neuronal-like cell line (PC12 cells) increased the proportion of neurites formed in response to transfection of constitutively active H-Ras and N-Ras but not K-Ras. This work reveals a previously unknown function for the prolyl isomerase activity of FKBP12 in promoting Ras depalmitoylation and shows that proline-directed conformational changes influence its posttranslational processing.

I. M. Ahearn, F. D. Tsai, H. Court, M. Zhou, B. C. Jennings, M. Ahmed, N. Fehrenbacher, M. E. Linder, M. R. Philips, FKPB12 binds to acylated H-Ras and promotes depalmitoylation. Mol. Cell 41, 173–185 (2011). [PubMed]

J. O. Liu, D. V. Titov, Y. Dang, Q. He, Regulator of Ras depalmitoylation and retrograde trafficking: A new hat for FKBP. Mol. Cell 41, 131–133 (2011). [PubMed]

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