Background: AF-6/afadin plays an important role in the formation of adherence junctions. In breast and colon cancer, loss of AF-6/afadin induces cell migration and cell invasion. We aimed to elucidate the role of AF-6/afadin in human endometrial cancer.
Methods: Morphology and AF-6/afadin expression in endometrial cancer cell lines was investigated by 3-dimensional culture. We used Matrigel invasion assay to demonstrate AF-6/afadin knockdown induced invasive capability. Cell proliferation assay was performed to estimate chemoresistance to doxorubicin, paclitaxel and cisplatin induced by AF-6/afadin knockdown. The associations between AF-6/afadin expression and clinicopathological status were determined by immunohistochemical analysis in endometrial cancer tissues. Informed consent was obtained from all patients before the study.
Results: The majority of cell clumps in 3-dimensional cultures of Ishikawa cells that strongly expressed AF-6/afadin showed round gland-like structures. In contrast, the cell clumps in 3-dimensional cultures of HEC1A and AN3CA cells-both weakly expressing AF-6/afadin-showed irregular gland-like structures and disorganized colonies with no gland-like structures, respectively. AF-6/afadin knockdown resulted in reduced number of gland-like structures in 3-dimensional cultures and enhancement of cell invasion and phosphorylation of ERK1/2 and Src in the highly AF-6/afadin-expressing endometrial cancer cell line. Inhibitors of MAPK/ERK kinase (MEK) (U0126) and Src (SU6656) suppressed the AF-6/afadin knockdown-induced invasive capability. AF-6/afadin knockdown induced chemoresistance to doxorubicin, paclitaxel and cisplatin in Ishikawa cells, not in HEC1A. Immunohistochemical analysis showed that AF-6/afadin expression was significantly associated with myometrial invasion and high histological grade.
Conclusions: AF-6/afadin regulates cell morphology and invasiveness. Invasive capability is partly regulated through the ERK and Src pathway. The inhibitors to these pathways might be molecular-targeted drugs which suppress myometrial invasion in endometrial cancer. AF-6/afadin could be a useful selection marker for fertility-sparing therapy for patients with atypical hyperplasia or grade 1 endometrioid adenocarcinoma with no myometrial invasion. AF-6/afadin knockdown induced chemoresistance especially to cisplatin. Therefore, loss of AF-6/afadin might be a predictive marker of chemoresistance to cisplatin.