Abstract
Porcupine O-acyltransferase (PORCN) is considered essential for Wnt secretion and signaling. However, we observed that PORCN inhibition does not phenocopy the effects of WNT4 knockdown in WNT4-dependent breast cancer cells. This suggests a unique relationship between PORCN and WNT4 signaling. To examine the role of PORCN in WNT4 signaling, here we overexpressed WNT4 or WNT3A in breast cancer, ovarian cancer, and fibrosarcoma cell lines. Conditioned media from these lines and co-culture systems were used to assess the dependence of Wnt secretion and activity on the critical Wnt secretion proteins PORCN and Wnt ligand secretion (WLS) mediator. We observed that WLS is universally required for Wnt secretion and paracrine signaling. In contrast, the dependence of WNT3A secretion and activity on PORCN varied across the cell lines, and WNT4 secretion was PORCN-independent in all models. Surprisingly, WNT4 did not exhibit paracrine activity in any tested context. Absent the expected paracrine activity of secreted WNT4, we identified cell-autonomous Wnt signaling activation by WNT4 and WNT3A, independent of PORCN or Wnt secretion. The PORCN-independent, cell-autonomous Wnt signaling demonstrated here may be critical in WNT4-driven cellular contexts or in those that are considered to have dysfunctional Wnt signaling.
Highlights
Porcupine O-acyltransferase (PORCN) is considered essential for Wnt secretion and signaling
Proliferation and cell death were monitored by live-cell imaging of MDA MB 134VI (MM134) (ILC) cells either transfected with siRNA targeting PORCN or treated with PORCN inhibitor (PORCNi) LGK974
PORCN-mediated palmitoylation of Wnt proteins is commonly described as required for Wnt binding to Wnt ligand secretion (WLS) and transport to the cell surface for secretion, so we examined the requisite of PORCN or WLS for Wnt secretion
Summary
WNT4 is critical in mammary gland development, as Wnt knockout in mouse mammary gland prevents progesterone-driven ductal elongation and branching during pregnancy [34, 35] In this context, activated progesterone receptor drives expression of Wnt in mammary gland luminal cells resulting in paracrine signaling that supports maintenance of the mammary stem cell niche [6, 36,37,38]. WNT4-driven signaling in ILC has yet to be fully elucidated, ILC cells lack the capacity to engage canonical Wnt signaling, as the characteristic genetic loss of E-cadherin in ILC leads to loss of -catenin protein [41, 42]. Treatment of ILC cells with PORCN inhibitors did not suppress growth or survival These unexpected results initiated further studies into the mechanisms underlying WNT4 secretion and signaling. Our observations challenge the paradigm that PORCN-mediated secretion is required for Wnt signaling and suggest a novel process by which Wnt proteins, including WNT4, can initiate -catenin–independent Wnt signaling
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
