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MUC13 Interaction with Receptor Tyrosine Kinase HER2 Drives Pancreatic Ductal Adenocarcinoma Progression
Sheema Khan2, Stephen W. Behrman*1, Nadeem Zafar3, Meena Jaggi4, Subhash C. Chauhan5
1Surgery, Univ. of Tennessee, Memphis, TN; 2Pharmaceutical Sciences, University of Tennessee Health Science Center, Memphis, TN; 3Pathology, University of Tennessee Health Science Center, Memphis, TN; 4Pharmaceutical Sciences, University of Tennessee Health Science Center, Memphis, TN; 5Pharmaceutical Sciences, University of Tennessee Health Science Center, Memphis, TN

Background: Pancreatic Ductal Adenocarcinoma (PDAC) is the fourth leading cause of cancer related death in the United States and has a very poor survival rate due to late diagnosis. MUC13 is a recently identified high molecular weight glycoprotein that is upregulated in PDAC and its progression is allowed via alterations of multiple signaling pathways. MUC13 is aberrantly expressed in PDAC and generally correlates with increased expression of HER2, however, the underlying mechanism remains poorly understood. MUC13 consists of three EGF-like domains that may serve as a ligand for EGF receptors, such as HER2, and modulate EGFR signaling pathways. We sought to better characterize the interaction of MUC13 with HER2 in PDAC.
Methods: MUC13 and HER2 interaction was studied using reciprocal co-immunoprecipitation, immunofluorescence, proximity ligation, Western blotting, co-capping assays in human PDAC cell lines and immunohistofluorescence techniques in human tissues. Tissue microarrays prepared from formalin-fixed, paraffin-embedded specimens of PDAC were assessed for expression of MUC13 and HER2 using our own laboratory generated anti-MUC13 mouse monoclonal antibody (MAb) through confocal immunofluorescence. The association of MUC13 and HER2 co-localization with nuclear chromatin organization was analyzed to study the stage or degree of aggressiveness of the pancreatic cancer using Dapi stained confocal images of tissues.
Results: MUC13 co-localizes and interacts with HER2 in PDAC cell lines. The results from this study demonstrate that MUC13 functionally interacts and activates HER2 at Tyrp1248 in PDAC cells, leading to stimulation of HER2 signaling cascade including, ERK1/2, FAK, AKT and PAK1 as well as regulation of the growth, cytoskeleton remodeling, motility and invasion of PDAC cells - all collectively contributing to PDAC progression. The interaction between MUC13-HER2 binding resulting in their tumorigenic characteristics likely occurs at the 1st and 2nd but not the 3rd domains of MUC13 as the EGF 1 and 2 deletion mutant constructs of MUC13 failed to promote proliferation and invasion of cells. These phenotypic effects of MUC13-HER2 co-localization could be effectively compromised by depleting MUC13. MUC13-HER2 co-localization also held true in PDAC human tissues with a strong functional correlation that contributed to an increased degree of disorder and cancer aggressiveness.
Conclusions: 1) MUC13 can be detected in formalin-fixed paraffin-embedded tissues using our anti-MUC13 MAb. 2) MUC13 co-localizes and activates HER2 and its downstream signaling cascade promoting PDAC progression in both cell lines and human tissue. 3) This process is reversed by depletion of MUC13. 4) This MUC13-HER2 interaction may potentially be manipulated for targeted therapeutics in patients harboring PDAC.

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