The Mucin Muc4 Potentiates Neuregulin Signaling by Increasing the Cell-surface Populations of ErbB2 and ErbB3

Melanie Funes,Jamie K Miller,Cary Lai,Kermit L Carraway,Colleen Sweeney

doi:10.1074/jbc.m603225200

Abstract

Mucins provide a protective barrier for epithelial surfaces, and their overexpression in tumors has been implicated in malignancy. We have previously demonstrated that Muc4, a transmembrane mucin that promotes tumor growth and metastasis, physically interacts with the ErbB2 receptor tyrosine kinase and augments receptor tyrosine phosphorylation in response to the neuregulin-1beta (NRG1beta) growth factor. In the present study we demonstrate that Muc4 expression in A375 human melanoma cells, as well as MCF7 and T47D human breast cancer cells, enhances NRG1beta signaling through the phosphatidylinositol 3-kinase pathway. In examining the mechanism underlying Muc4-potentiated ErbB2 signaling, we found that Muc4 expression markedly augments NRG1beta binding to A375 cells without altering the total quantity of receptors expressed by the cells. Cell-surface protein biotinylation experiments and immunofluorescence studies suggest that Muc4 induces the relocalization of the ErbB2 and ErbB3 receptors from intracellular compartments to the plasma membrane. Moreover, Muc4 interferes with the accumulation of surface receptors within internal compartments following NRG1beta treatment by suppressing the efficiency of receptor internalization. These observations suggest that transmembrane mucins can modulate receptor tyrosine kinase signaling by influencing receptor localization and trafficking and contribute to our understanding of the mechanisms by which mucins contribute to tumor growth and progression.

Highlights

Dimer formation is followed by autophosphorylation of receptor intracellular domains, recruitment of intracellular signaling proteins, and the initiation of a number of signaling cascades that regulate cellular growth, motility, and survival
Our previous expression studies demonstrate that the interaction of Muc4 and ErbB2 is mediated by their extracellular regions, and the N-terminal epidermal growth factor (EGF)-like domain of ASGP-2 is required for their association [10]
Muc4 Potentiates NRG1␤-stimulated ErbB2 Tyrosine Phosphorylation and PI3K Signaling—We have previously shown that Muc4 expression potentiates NRG1␤-stimulated tyrosine phosphorylation of ErbB2 and ErbB3 and that these effects cannot be accounted for by an increase in overall receptor expression levels in cells [10]

Summary

Introduction

Dimer formation is followed by autophosphorylation of receptor intracellular domains, recruitment of intracellular signaling proteins, and the initiation of a number of signaling cascades that regulate cellular growth, motility, and survival. Expression of Muc4 in A375 human melanoma cells results in the augmented tyrosine phosphorylation of ErbB2 and ErbB3 in response to growth factor [10].

Results

Conclusion