PROTEIN SYNTHESIS POST-TRANSLATION MODIFICATION AND DEGRADATION
p38 JAB1 Binds to the Intracellular Precursor of the Lutropin/Choriogonadotropin Receptor and Promotes Its Degradation*

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Using the C-terminal tail of the rat lutropin/choriogonadotropin receptor (rLHR) as “bait” in a yeast two-hybrid screen resulted in the identification of p38 JAB1 (a protein initially identified as a co-activator of c-Jun) as a putative rLHR binding partner. More recently p38 JAB1 has been shown to promote the degradation of a cyclin-dependent kinase inhibitor and to be a component of the COP9 signalosome. Microscopic localization of an epitope-tagged p38 JAB1 expressed in 293 cells revealed a punctuated perinuclear and cytosolic localization, while cell fractionation studies showed that most of the p38 JAB1 was in a high speed supernatant. Co-transfection of 293 cells revealed that p38 JAB1 binds to the immature 68-kDa precursor of the rLHR that resides in the endoplasmic reticulum and promotes its degradation. It does not appear to interact with the cell surface rLHR, however, and it does not affect its expression. When transfected into HeLa cells, p38 JAB1 potentiates the transcriptional activity of c-Jun, but co-transfection with rLHR prevents this effect. We conclude that p38 JAB1 interacts with the rLHR precursor and promotes its degradation. These results reveal a novel protein binding partner of the rLHR and are consistent with current views of the functions of p38 JAB1.

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This work was supported by National Institutes of Health Grant CA-40629 (to M. A.). The services and facilities provided by the Diabetes and Endocrinology Research Center of the University of Iowa were supported by National Institutes of Health Grant DK-25295.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.