(The) role of interferon, gamma-inducible protein 16 in the estrogen signaling during breast cancer progression

Abstract

Interferon, gamma-inducible protein 16 (IFI16) is a member of the HIN-200 family that has been implicated in apoptosis and inflammation in breast cancer. Recently, it was reported that IFI16 forms complex with metastasis-associated protein 1 (MTA1) and class II histone deacetylases (HDACs) and the complex represses the transcription of estrogen receptor alpha (ERα). However, the role of IFI16 in breast cancer cell growth or tumor progression remains largely unknown. Therefore, we aimed to identify the effects of IFI16 on hormone-dependent proliferation and estrogen signaling in breast cancer cells. First, we established stable subline that expresses shRNA of IFI16 or MTA1 using ERα-negative breast cancer cell line, MDA-MB-231, in order to investigate the cellular growth properties according to silencing of each gene. As reported, we confirmed the increase of mRNA and protein levels of ERα by knockdown of MTA1 or IFI16 in these stable sublines. Moreover, in cell proliferation assay, clonogenic survival assay and xenograft tumor growth experiment, we verified that treatment of tamoxifen, which is an anti-hormone drug targeting ERα, significantly reduced cell growth compared with shGFP-expressing control cell. Next, we profiled the estrogen receptor (ER) signaling-related gene expression pattern using the PCR array in MDA-MB-231 after knockdown or overexpression of IFI16. Nine genes were up- or down-regulated more than 1.5-fold. Among them, induction of Cytochrome P450, Family 19, Subfamily A, Polypeptide 1 (CYP19A1 or aromatase) by IFI16 was confirmed by qPCR in ERα-positive breast cancer cell line, MCF7. We also observed that concentration of estradiol in cell culture media was increased by 1.7-fold after transfection of IFI16 when measured by enzyme immunoassay (EIA). In addition, we demonstrated that IFI16 repressed the expression of AR, which is known to competitively suppress ERα-mediated transcription. When IFI16 was overexpressed, DNA binding of AR was reduced and that of ERα was induced at the promoter region of ERα-downstream gene, pS2 or progesterone receptor (PR), followed by increase of pS2 and PR mRNA levels. Furthermore, in MCF7 cell that stably overexpresses IFI16, cell growth was stimulated consistent with the activation of estrogen signaling. Taken together, our results indicate that IFI16 induces tamoxifen resistance in ERα-negative breast cancer and activates estrogen signaling and cell proliferation via regulating expression of CYP19 and AR. This study extends understanding of the roles of IFI16 in breast cancer progression and suggests a new target for prevention and treatment of breast cancer.