JNK-Interacting Leucine Zipper Protein Is a Novel Scaffolding Protein in the Gα₁₃ Signaling Pathway

Abstract

Scaffolding proteins play a critical role in conferring specificity and fidelity to signaling pathways. The JNK-interacting leucine zipper protein (JLP) has been identified as a scaffolding protein involved in linking components of the JNK signaling module. Galpha(12) and Galpha(13), the alpha-subunits of heterotrimeric G proteins G12 and G13, respectively, stimulate the JNK module in diverse cell types. Here, we report that Galpha(13) physically interacts with JLP, and this interaction enhances Galpha(13)-mediated JNK activation. We also demonstrate endogenous interaction between JLP and Galpha(13) in MCF-7 cells. JLP interaction is specific to the G12 family of alpha-subunits via its C-terminal domain (termed GID-JLP), spanning amino acids 1165-1307, and this interaction is more pronounced with the mutationally or functionally activated form of Galpha(13) compared to that of wild-type Galpha(13). The presence of a ternary complex consisting of Galpha(13), JLP, and JNK suggests a role for JLP in tethering Galpha(13) to the signaling components involved in JNK activation. Coexpression of GID-JLP disrupts ternary complex formation in addition to attenuating Galpha(13)-stimulated JNK activity. These findings identify JLP as a novel scaffolding protein in the Galpha(13)-mediated JNK signaling pathway.

Kinesin Adapter JLP Links PIKfyve to Microtubule-based Endosome-to-Trans-Golgi Network Traffic of Furin

“…In addition to the kinesin motor protein (38,41) and PIKfyve (this study), JLP and JIP4 reportedly interact with a number of proteins such as the JNK/p38 MAP kinase signaling modules, the transcription factors c-Myc and Max (37,38), the receptor-like transmembrane protein Cdo (53), and the ␣-subunit of heterotrimeric G 13 (54). Except for the latter, these interactions have been mapped to the N-terminal or middle region of JLP/JIP4 proteins (31).…”

“…It should be emphasized that the relative contribution of JLP/JIP4 in the activation of JNK signaling pathways is presently unclear. Thus, whereas JLP binds to JNK, enhancing its activation (37,41,54,55), JIP4 does not seem to associate with the JNK signaling module, nor does it alter JNK activation (38). Concordant with the latter observations, disruption of Jip4 does not attenuate JNK activation under various stress cues in cells and tissues of JLP Ϫ/Ϫ -deficient mice (39).…”

“…Except for the latter, these interactions have been mapped to the N-terminal or middle region of JLP/JIP4 proteins (31). Reportedly, JLP association with G␣ 13 engages the C-terminal domain, spanning the last 142 residues at the C terminus (residues 1178 -1320 in JLP L ), but shorter fragments have not been exploited (54). Therefore, it is unclear at present whether the JLP binding regions for G␣ 13 and PIKfyve overlap or occupy distinct segments of the JLP C terminus and whether these interactions are related.…”

The Scaffold Protein c-Jun NH2-Terminal Kinase-associated Leucine Zipper Protein Regulates Cell Migration through Interaction with the G Protein G 13

“…Involvement of Rac1 and G 13 in JLP-mediated Cell Migration-To investigate the molecular mechanism underlying the JLP-mediated cell migration, we examined the involvement of Rac1 and G a13 , the latter of which has been shown to interact with the C-terminal domain of JLP (11). Consistent with the previous observation by Kashef et al (11), the deletion mutant mJLPÁC, but not the full-length wild-type mJLP, failed to bind G a13 in a transient coexpression experiment in HEK293T cells (Fig.…”

“…Studies of JLP have mainly focused on identifying its interacting proteins, which include kinesin light chain 1 and G a13 , the a-subunit of the heteromeric G 13 protein (10,11). JLP has also been reported to play an important role in myogenesis by interacting with the cell-surface protein Cdo (12).…”