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Molecular and Cellular Biology, June 1999, p. 4379-4389, Vol. 19, No. 6
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Ajuba, a Novel LIM Protein, Interacts with Grb2, Augments Mitogen-Activated Protein Kinase Activity in Fibroblasts, and Promotes Meiotic Maturation of Xenopus Oocytes in a Grb2- and Ras-Dependent Manner

Rakesh K. Goyal,1,dagger Phoebe Lin,2 Josna Kanungo,2 Aimee S. Payne,3 Anthony J. Muslin,2,3 and Gregory D. Longmore2,3,*

Departments of Pediatrics,1 Medicine,2 and Cell Biology,3 Washington University School of Medicine, St. Louis, Missouri 63110

Received 25 August 1998/Returned for modification 22 October 1998/Accepted 8 February 1999

LIM domain-containing proteins contribute to cell fate determination, the regulation of cell proliferation and differentiation, and remodeling of the cell cytoskeleton. These proteins can be found in the cell nucleus, cytoplasm, or both. Whether and how cytoplasmic LIM proteins contribute to the cellular response to extracellular stimuli is an area of active investigation. We have identified and characterized a new LIM protein, Ajuba. Although predominantly a cytosolic protein, in contrast to other like proteins, it did not localize to sites of cellular adhesion to extracellular matrix or interact with the actin cytoskeleton. Removal of the pre-LIM domain of Ajuba, including a putative nuclear export signal, led to an accumulation of the LIM domains in the cell nucleus. The pre-LIM domain contains two putative proline-rich SH3 recognition motifs. Ajuba specifically associated with Grb2 in vitro and in vivo. The interaction between these proteins was mediated by either SH3 domain of Grb2 and the N-terminal proline-rich pre-LIM domain of Ajuba. In fibroblasts expressing Ajuba mitogen-activated protein kinase activity persisted despite serum starvation and upon serum stimulation generated levels fivefold higher than that seen in control cells. Finally, when Ajuba was expressed in fully developed Xenopus oocytes, it promoted meiotic maturation in a Grb2- and Ras-dependent manner.

* Corresponding author. Mailing address: Division of Hematology, Washington University School of Medicine, Campus Box 8125, 660 South Euclid Ave., St. Louis, MO 63110. Phone: (314) 362-8834. Fax: (314) 362-8826. E-mail: longmorg{at}medicine.wustl.edu.

dagger Present address: Department of Pediatrics, University of Pittsburgh, Pittsburgh, PA 15213-2583.

Molecular and Cellular Biology, June 1999, p. 4379-4389, Vol. 19, No. 6
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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