Signal transduction pathway activity in high-grade serous carcinoma, its precursors and Fallopian tube epithelium

OBJECTIVE: To determine the activity of key signal transduction pathways in serous tubal intraepithelial carcinoma (STIC) and concurrent high-grade serous carcinoma (HGSC) and compare this to pathway activity in normal Fallopian tube epithelium (FTE).

METHODS: We assessed mRNA expression levels of pathway-specific target genes with RT-qPCR in STIC and concurrent HGSC (n = 8) and normal FTE (n = 8). Subsequently, signal transduction pathway assays were used to assess functional activity of the androgen (AR) and estrogen receptor (ER), phosphoinositide-3-kinase (PI3K), Hedgehog (HH), transforming growth factor beta (TGF-β) and canonical wingless-type MMTV integration site (Wnt) pathways.

RESULTS: There were no statistically significant differences in pathway activity between STIC and HGSC, but STIC and HGSC demonstrated significantly lower ER and higher PI3K and HH pathway activity in comparison to normal FTE, suggesting these pathways as putative early drivers. In addition, we determined FOXO3a protein expression by immunohistochemistry and found loss of FOXO3a protein expression in STIC and HGSC compared to normal FTE. This observation confirmed that activation of PI3K signaling by loss of FOXO is an early hallmark of serous carcinogenesis. Furthermore, HGSC demonstrated significant loss of AR and Wnt pathway activity in relation to FTE, suggesting these pathways contribute to disease progression.

CONCLUSION: Our observations, together with the previously described associations between p53 signaling and both PI3K and HH pathway activity, provide evidence that increased PI3K and HH pathway activity and loss of ER pathway activity may be underlying events contributing to neoplastic transformation of FTE into STIC.