Role of Melanoma Inhibitor of Apoptosis (ML-IAP) Protein, a Member of the Baculoviral IAP Repeat (BIR) Domain Family, in the Regulation of C-RAF Kinase and Cell Migration

Tripat Kaur Oberoi-Khanuja,Christiaan Karreman,Sarit Larisch,Ulf R Rapp,Krishnaraj Rajalingam

doi:10.1074/jbc.m112.341297

Abstract

Inhibitor of apoptosis (IAPs) proteins are characterized by the presence of evolutionarily conserved baculoviral inhibitor of apoptosis repeat (BIR) domains, predominantly known for their role in inhibiting caspases and, thereby, apoptosis. We have shown previously that multi-BIR domain-containing IAPs, cellular IAPs, and X-linked IAP can control tumor cell migration by directly regulating the protein stability of C-RAF kinase. Here, we extend our observations to a single BIR domain containing IAP family member melanoma-IAP (ML-IAP). We show that ML-IAP can directly bind to C-RAF and that ML-IAP depletion leads to an increase in C-RAF protein levels, MAPK activation, and cell migration in melanoma cells. Thus, our results unveil a thus far unknown role for ML-IAP in controlling C-RAF stability and cell migration.

Highlights

The possible role of ML-Inhibitor of apoptosis (IAPs) in regulating MAPK signaling and cell migration is examined
ML-IAP Directly Interacts with C-RAF via Its baculoviral inhibitor of apoptosis repeat (BIR) Domain— We have shown previously that C-RAF kinase can directly bind to multi-BIR domain-containing IAPs, cIAP1, cIAP2, and XIAP in a BIR domain-dependent manner [34]
We extended these studies to ML-IAP, a single BIR domain containing IAP

Summary

Background

The possible role of ML-IAP in regulating MAPK signaling and cell migration is examined. We have shown previously that multi-BIR domain-containing IAPs, cellular IAPs, and X-linked IAP can control tumor cell migration by directly regulating the protein stability of C-RAF kinase. RING domains act as E3 ubiquitin ligases and catalyze the conjugation of ubiquitin moieties to the substrates contributing to cellular signaling or substrate protein degradation via the proteasomes or lysosomes [4] These domains are shown to be responsible for heteromerization between the IAPs and for their cross-regulation [5]. C-RAF phosphorylates and activates MEK1/2, leading to further activation of ERK1/2, forming the prototype of a three-tier MAPK cascade to transmit signals from outside the cells to the nucleus [31, 32] This cascade regulates various cellular processes, including proliferation, migration, differentiation, and survival, and deregulation of the components of this pathway is often associated with cancers [33]. We characterize the mode of interaction between ML-IAP and C-RAF and further present evidence that IAPs interact with each other, emphasizing a role for IAP-IAP heteromeric complexes in regulating C-RAF stability

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION