Abstract
Simple SummaryA feature of pancreatic cancer (PC) is the frequent overexpression of tyrosine kinase membrane receptor HER2 along with its membrane partner the MUC4 oncomucin in the early stages of the pancreatic carcinogenesis. However, therapeutic approaches targeting HER2 in PC are not efficient. MUC4 could indeed represent an alternative therapeutic strategy to target HER2 signaling pathway, but this approach needs to characterize MUC4/HER2 interaction at the molecular level. In this study, we successfully showed the impact of the EGF domains of MUC4 on HER2 binding affinity and demonstrated their “growth factor-like” biological activities in PC cells. Moreover, homology models of the MUC4EGF/HER2 complexes allowed identification of binding hotspots mediating binding affinity with HER2 and PC cell proliferation. These results allow a better understanding of the mechanisms involved in the MUC4/HER2 complex formation and may lead to the design of potential MUC4/HER2 inhibitors.The HER2 receptor and its MUC4 mucin partner form an oncogenic complex via an extracellular region of MUC4 encompassing three EGF domains that promotes tumor progression of pancreatic cancer (PC) cells. However, the molecular mechanism of interaction remains poorly understood. Herein, we decipher at the molecular level the role and impact of the MUC4EGF domains in the mediation of the binding affinities with HER2 and the PC cell tumorigenicity. We used an integrative approach combining in vitro bioinformatic, biophysical, biochemical, and biological approaches, as well as an in vivo study on a xenograft model of PC. In this study, we specified the binding mode of MUC4EGF domains with HER2 and demonstrate their “growth factor-like” biological activities in PC cells leading to stimulation of several signaling proteins (mTOR pathway, Akt, and β-catenin) contributing to PC progression. Molecular dynamics simulations of the MUC4EGF/HER2 complexes led to 3D homology models and identification of binding hotspots mediating binding affinity with HER2 and PC cell proliferation. These results will pave the way to the design of potential MUC4/HER2 inhibitors targeting the EGF domains of MUC4. This strategy will represent a new efficient alternative to treat cancers associated with MUC4/HER2 overexpression and HER2-targeted therapy failure as a new adapted treatment to patients.
Highlights
The MUC4 membrane-bound mucin is one of the largest multimodular glycoproteins at the cell surface characterized by two noncovalent subunits
Among the TM mucins/HER complexes, the interaction of MUC4 with HER2 has drawn a lot attention since they are both overexpressed at the pancreatic cancer (PC) cell surface, forming an oncogenic complex participating in cancer cell tumorigenic properties and in activation of different oncogenic signaling pathways leading to tumor progression [1,3,9,10]
In addition to showing that endogenous MUC4 directly interacts with HER2 in PC cell lines (Supplementary Materials Figure S1A,B), we quantified the binding affinity between MUC4β and HER2 using microscale thermophoresis and showed that the interaction is mediated by the three epidermal growth factor (EGF) domains [25]
Summary
The MUC4 membrane-bound mucin is one of the largest multimodular glycoproteins at the cell surface characterized by two noncovalent subunits. HER2 targeting in cancers is currently following two approaches: (i) targeted therapies using monoclonal antibodies preventing HER2 interaction, or (ii) tyrosine kinase inhibitors blocking phosphorylation of HER2, thereby inhibiting its downstream signaling activity [11,12]. These approaches, even though they show patient response at the beginning of the treatment, rapidly develop resistance, which inevitably leads to disease progression and death [13,14]. The present study involves the structure–function relationship between MUC4EGF domains and HER2 at the molecular level and their biological activity on human pancreatic cancer cells, confirming the potency for developing small inhibitory molecules targeting MUC4EGF domains with therapeutic value
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