PACE4 Undergoes an Oncogenic Alternative Splicing Switch in Cancer

Inhibition of PACE4, a proprotein convertase that is overexpressed in prostate cancer, has been shown to block cancer progression in an androgen-independent manner. However, the basis for its overexpression and how its growth inhibitory effects are mitigated and uncertain. Here we report that PACE4 pre-mRNA undergoes DNA methylation-sensitive alternative splicing of its terminal exon 3' untranslated region, generating an oncogenic, C-terminally modified isoform (PACE4-altCT). We found this isoform to be strongly expressed in prostate cancer cells, where it displayed an enhanced auto-activating process and a distinct intracellular routing that prevented its extracellular secretion. Together these events led to a dramatic increase in processing of the pro-growth differentiation factor pro-GDF15 as the first PACE4 substrate to be identified in prostate cancer. We detected robust expression of PACE4-altCT in other cancer types, suggesting that an oncogenic switch for this pro-enzyme may offer a therapeutic target not only in advanced prostate cancer but perhaps also more broadly in human cancer. 

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