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Lowe syndrome protein OCRL1 interacts with Rac GTPase in the trans-Golgi network

Adèle Faucherre1, Pierrette Desbois, Véronique Satre

  • 1Institut Cochin, Département de Génétiques, Développement et Pathologie Moléculaire, INSERM U567/CNRS UMR8104/Université Paris V, France.

Human Molecular Genetics
|August 14, 2003
PubMed

Insights

The oculocerebrorenal syndrome of Lowe (OCRL) protein binds to Rac GTPase, potentially impacting cellular functions and contributing to mental retardation in Lowe syndrome. This suggests OCRL1 has a dual role beyond its known phosphatase activity.

Area of Science:

  • Biochemistry
  • Cell Biology
  • Genetics

Background:

  • Oculocerebrorenal syndrome of Lowe (OCRL) is a rare X-linked disorder.
  • OCRL1 protein possesses a phosphatidylinositol 4,5-bisphosphate 5-phosphatase activity and a RhoGAP domain.
  • Rho GTPases are crucial for cellular functions and their dysregulation is linked to mental retardation.

Purpose of the Study:

  • Investigate the function of the RhoGAP domain of OCRL1.
  • Determine the interaction of OCRL1 with Rho GTPases.
  • Elucidate the role of OCRL1 in cellular localization and its potential contribution to Lowe syndrome pathogenesis.

Main Methods:

  • In vitro binding assays to study OCRL1 RhoGAP domain interaction with GTPases.
  • Co-immunoprecipitation to detect endogenous OCRL1-Rac interaction.
  • Immunofluorescence microscopy and Golgi perturbation assays to assess cellular localization.
  • Functional assays measuring Rac GTPase activity and cellular ruffling.

Main Results:

  • Activated Rac GTPase stably associates with the OCRL1 RhoGAP domain in vitro and co-immunoprecipitates with endogenous OCRL1.
  • OCRL1 RhoGAP preferentially binds GDP-bound Rac and shows reduced binding to Cdc42, with no binding to RhoA or RhoG.
  • Endogenous Rac co-localizes with OCRL1 and gamma-adaptin in the trans-Golgi network.
  • OCRL1 RhoGAP exhibits low Rac GAP activity in vitro and inhibits RacGTP-dependent ruffles in cells, indicating OCRL1 is an active RacGAP.

Conclusions:

  • OCRL1 is a bifunctional protein with both PIP2 5-phosphatase and Rac GTPase binding activities.
  • The interaction with Rac GTPase may contribute to OCRL1 localization at the trans-Golgi network.
  • Dysregulation of OCRL1 RhoGAP function and associated Rho pathways could contribute to mental retardation in Lowe syndrome.

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