Abstract

Background: Peripheral myelin protein (PMP22), a member of the GAS3 family of tetraspan proteins, is associated with a variety of neurological diseases, but its physiologic roles in normal cellular functions are poorly understood. In this study, we examined the function of PMP22 in epithelial cell biology, specifically its possible interactions with certain integrin isoforms in the endometrium. Previous studies have suggested a link between PMP22 and α6 integrin, and therefore we asked whether PMP22 could associate or potentially modulate the expression of α6 integrin. Methods: To test the hypothesis that PMP22 expression may modulate integrin expression and cell adhesion, HEC-1A human endometrial adenocarcinoma cell lines were generated to express varying levels of PMP22, and subsequently examined for the expression of integrins and binding onto extracellular matrix proteins. Human endometrial samples at proliferative and secretory phases were also obtained and analyzed for PMP22 and α6 integrin expression by immunohistochemistry. The membrane expression of α6 integrin in HEC-1A cells with varying PMP22 expression levels was assessed by flow cytometry. Through confocal microscopy and co-immunoprecipitation analysis of HEC-1A cell lines, we further investigated the possible association of PMP22 and α6-integrin. Finally, adhesion assays were performed using the extracellular matrix substrates laminin, fibronectin, and poly-d-lysine to translate the functional effect of changes in PMP22 expression levels on α6 integrin ligand specificity. Results: Expression of both PMP22 and α6 integrin were detected in the endometrium, and both proteins share a similar pattern of expression, with greater expression in the proliferative phase compared to the secretory phase of the menstrual cycle. By confocal microscopy and co-immunoprecipitation analysis we demonstrate that PMP22 and α6-integrin associate together. Dramatically, overexpression of PMP22 was sufficient to increase α6-integrin surface expression, while a reduction in PMP22 suppressed α6 integrin surface expression. Finally, overexpression of PMP22 altered the binding onto various extracellular matrix proteins, namely laminin. Conclusion: These findings suggest a physiologic role for PMP22 on the expression of α6 integrin. This role may be relevant to the disease biology associated with altered levels of α6 integrin expression in the endometrium, such as endometriosis.