Inflammatory Breast Cancer (IBC) is a highly aggressive form of breast cancer, primarily diagnosed by its clinical characteristics of inflammation. Aberrant activation downstream of the
inflammatory cytokine IL-6 of the JAK/STAT signaling pathway occurs in more than 50% of primary breast cancers and breast cancer cell lines. However, the contribution of this pathway to IBC development is poorly understood.
1. Compare the expression of IL-6/JAK/STAT pathway components in vitro using breast cancer cell lines of various molecular subtypes.
2. Assess whether activation of the IL-6/JAK/STAT pathway in IBC cell lines promotes cell proliferation.
3. Determine the effects of inhibiting IL-6 signalling in IBC cell lines.
4. Establish whether IL-6 can function via an autocrine/paracrine loop in vitro within IBC cell lines of different molecular subtypes to promote pathway activation and proliferation.
Quantitative RT-PCR (QRT-PCR) was used to assess the expression of JAK/STAT pathway components at the transcript level, and Western blot analysis to monitor the extent of active, tyrosine phosphorylated-STAT3 (pSTAT3). Forced activation of the JAK/STAT pathway was conducted through stimulation with IL-6. Cell proliferation was determined following stimulation with IL-6 +/- an IL-6 Receptor specific antibody, Tocilizumab. IBC cell lines were treated with conditioned, concentrated media, with pathway activation and cell viability determined by previously described techniques.
QRT-PCR results indicate wide expression levels of JAK/STAT signaling components, independent of breast cancer subtype. Western blot analysis confirmed that IBC cell lines show elevated STAT3 activation. Stimulation with IL-6 promoted STAT3 activation and cell proliferation of IBC cell lines, which could be attenuated with Tocilizumab. Conditioned media from one IBC cell line could stimulate STAT3 activation and increase proliferation similar to levels seen following IL-6 exposure.This effect was confirmed to be IL-6 specific as Tocilizumab treatment was capable of decreasing this activation and proliferation.
This study suggests that IBC cell lines show elevated activation and expression of various JAK/STAT pathway components. It remains to be established in larger cohorts whether this pathway may be constitutively activated in IBC lesions and thus potentially serve as a novel therapeutic target.