Autophagy regulator BECN1 suppresses mammary tumorigenesis driven by WNT1 activation and following parity

Earlier studies reported allelic deletion of the essential autophagy regulator BECN1 in breast cancers implicating BECN1 loss, and likely defective autophagy, in tumorigenesis. Recent studies have questioned the tumor suppressive role of autophagy, as autophagy-related gene (Atg) defects generally suppress tumorigenesis in well-characterized mouse tumor models. We now report that, while it delays or does not alter mammary tumorigenesis driven by Palb2 loss or ERBB2 and PyMT overexpression, monoallelic Becn1 loss promotes mammary tumor development in 2 specific contexts, namely following parity and in association with wingless-type MMTV integration site family, member 1 (WNT1) activation. Our studies demonstrate that Becn1 heterozygosity, which results in immature mammary epithelial cell expansion and aberrant TNFRSF11A/TNR11/RANK (tumor necrosis factor receptor superfamily, member 11a, NFKB activator) signaling, promotes mammary tumorigenesis in multiparous FVB/N mice and in cooperation with the progenitor cell-transforming WNT1 oncogene. Similar to our Becn1(+/-);MMTV-Wnt1 mouse model, low BECN1 expression and an activated WNT pathway gene signature correlate with the triple-negative subtype, TNFRSF11A axis activation and poor prognosis in human breast cancers. Our results suggest that BECN1 may have nonautophagy-related roles in mammary development, provide insight in the seemingly paradoxical roles of BECN1 in tumorigenesis, and constitute the basis for further studies on the pathophysiology and treatment of clinically aggressive triple negative breast cancers (TNBCs).

The phosphoinositide-binding protein TRAF4 modulates tight junction stability and migration of cancer cells

Tumor necrosis factor (TNF) receptor-associated factor 4 (TRAF4), a protein localized in TJs in normal epithelial cells, is frequently overexpressed in carcinomas. We recently found that TRAF4 impedes TJ formation/stability and favors cell migration, 2 hallmarks of cancer progression. In addition TRAF4 contributes to the TGF-β-induced epithelial-mesenchymal transition (EMT), metastasis, and p53 destabilization. TRAF4 recruitment to TJs is a prerequisite for its biological function on TJ formation/stability and on cell migration. Interestingly, TRAF4 is targeted to TJs through lipid-binding. The trimeric TRAF domain of TRAF4 binds 3 phosphoinositide (PIP) molecules. These findings shed new light on the role of TRAF4 in cancer progression; they provide a novel link between lipid metabolism and cancer progression and support the notion that TRAF4 could be a relevant target for cancer therapies. TRAF4 belongs to a family of 7 human proteins involved in different biological processes, such as inflammation, immunity and embryonic development. While the lipid-binding ability of the TRAF domain is conserved among the whole TRAF protein family, its functional role remains to be established for the remaining TRAF proteins.