Canonical Wnt signaling regulates Slug activity and links epithelial–mesenchymal transition with epigenetic Breast Cancer 1, Early Onset (BRCA1) repression

Abstract

Slug (Snail2) plays critical roles in regulating the epithelial-mesenchymal transition (EMT) programs operative during development and disease. However, the means by which Slug activity is controlled remain unclear. Herein we identify an unrecognized canonical Wnt/ GSK3β/β-Trcp1 axis that controls Slug activity. In the absence of Wnt signaling, Slug is phosphorylated by GSK3β and subsequently undergoes β-Trcp1-dependent ubiquitination and proteosomal degradation. Alternatively, in the presence of canonical Wnt ligands, GSK3β kinase activity is inhibited, nuclear Slug levels increase, and EMT programs are initiated. Consistent with recent studies describing correlative associations in basal-like breast cancers between Wnt signaling, increased Slug levels, and reduced expression of the tumor suppressor Breast Cancer 1, Early Onset (BRCA1), further studies demonstrate that Slug-as well as Snail-directly represses BRCA1 expression by recruiting the chromatin-demethylase, LSD1, and binding to a series of E-boxes located within the BRCA1 promoter. Consonant with these findings, nuclear Slug and Snail expression are increased in association with BRCA1 repression in a cohort of triple-negative breast cancer patients. Together, these findings establish unique functional links between canonical Wnt signaling, Slug expression, EMT, and BRCA1 regulation.lug (also termed Snail2) is a C 2 H 2 zinc-finger transcriptional repressor belonging to the three-member family of Snail proteins (Snail, Slug, and Smuc) (1, 2). First recognized for its participation in events associated with the epithelial-mesenchymal transition (EMT) programs that characterize early development, more recent studies have identified postnatal roles for Slug in a wide variety of carcinomatous states (1-7). To date, Slug expression has been linked to cancer stem cell formation, cell cycle regulation and apoptosis as well as invasion and metastasis (1-7). However, the Slug protein, like that of Snail, is rapidly turned over by the ubiquitin-proteasome system in vivo, and the key factors responsible for regulating Slug protein stability and activity remain largely undefined (2,8). Interestingly, recent studies have identified a subset of breast cancer patients (the so-called basal-like breast carcinoma phenotype) whose lesions display an EMT-like signature associated with increased Wnt signaling, upregulated Slug expression, and epigenetic silencing of the tumor suppressor BRCA1 (7, 9-13). Despite these associations, however, no molecular pathways have been established that functionally link these potentially disparate phenotypes together.Herein we demonstrate that Slug protein stability and activity are controlled by a heretofore undescribed GSK3β-dependent phosphorylation process that primes phospho-Slug for ubiquitination by the E3 ligase β-Trcp1 and its subsequent proteasomal degradation. In the presence of canonical Wnt agonists, however, GSK3β activity is suppressed and Slug phosphorylation is blocked, thereby allowing Slug protein levels and activity to...

CD151 represses mammary gland development by maintaining the niches of progenitor cells

“…42 As shown in Figure 7A, expression of Ron protein was markedly diminished in mammary tissues in the absence of CD151. In line with this observation was a marked decrease in the phosphorylation at the Y654 residue of b-catenin upon CD151 removal as described in a prior study, 42 while activation of GSK-3b, crucial for Wnt signaling, remained unaffected 43,44 (Fig. 7A).…”

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Vimentin–ERK Signaling Uncouples Slug Gene Regulatory Function

“…In the nucleus, Lats2 interacts with and directly phosphorylates Snail on residue T203, supporting EMT by influencing the stability and nuclear localization of Snail (22). Glycogen synthase kinase 3b (GSK3b) phosphorylates both Slug and Snail and negatively regulates their stability thus maintaining epithelial morphology (23)(24)(25)(26)(27). The activation of oncogenic pathways, including PI3K-Akt and Ras-MAPK signaling, suppresses GSK3b activity and GSK3b-dependent reduction in Snail and Slug phosphorylation resulting in increased transcription factor stability and accumulation and EMT induction.…”