The heparan sulfate proteoglycan syndecan‐1 regulates colon cancer stem cell function via a focal adhesion kinase—Wnt signaling axis

Abstract

In colon cancer, downregulation of the transmembrane heparan sulfate proteoglycan syndecan‐1 (Sdc‐1) is associated with increased invasiveness, metastasis, and dedifferentiation. As Sdc‐1 modulates signaling pathways relevant to stem cell function, we tested the hypothesis that it may regulate a tumor‐initiating cell phenotype. Sdc‐1 small‐interfering RNA knockdown in the human colon cancer cell lines Caco2 and HT‐29 resulted in an increased side population (SP), enhanced aldehyde dehydrogenase 1 activity, and higher expression of CD133, LGR5, EPCAM, NANOG, SRY (sex‐determining region Y)‐box 2, KLF2, and TCF4/TCF7L2. Sdc‐1 knockdown enhanced sphere formation, cell viability, Matrigel invasiveness, and epithelial‐to‐mesenchymal transition‐related gene expression. Sdc‐1‐depleted HT‐29 xenograft growth was increased compared to controls. Decreased Sdc‐1 expression was associated with an increased activation of β1‐integrins, focal adhesion kinase (FAK), and wingless‐type (Wnt) signaling. Pharmacological FAK and Wnt inhibition blocked the enhanced stem cell phenotype and invasive growth. Sequential flow cytometric SP enrichment substantially enhanced the stem cell phenotype of Sdc‐1‐depleted cells, which showed increased resistance to doxorubicin chemotherapy and irradiation. In conclusion, Sdc‐1 depletion cooperatively enhances activation of integrins and FAK, which then generates signals for increased invasiveness and cancer stem cell properties. Our findings may provide a novel concept to target a stemness‐associated signaling axis as a therapeutic strategy to reduce metastatic spread and cancer recurrence.DatabasesThe GEO accession number of the Affymetrix transcriptomic screening is GSE58751.

The Heparan Sulfate Sulfotransferases HS2ST1 and HS3ST2 Are Novel Regulators of Breast Cancer Stem-Cell Properties

“…Finally, while sulfotransferase overexpression promoted functional stem cell properties, it is likely that not only the CSC population, but also the overall tumor cell population was affected by alterations in HS. Possibly a selected analysis of sorted CSCs could lead to an enhancement of the observed changes, as previously demonstrated for the impact of Sdc-1 knockdown on the colon CSC phenotype (Katakam et al, 2020b).…”

“…The underlying mechanisms are apparently complex and require further study. Obvious mechanisms include altered receptor tyrosine kinase signaling conform with the coreceptor concept of HSPGs, as demonstrated for the MAPK pathway in HS2ST1 and HS3ST2 overexpressing cells ( Vijaya Kumar et al, 2014 , 2020 ), and altered signaling via the Wnt pathway, as exemplified by altered expression of the Wnt-dependent transcription factor TCF4 for both sulfotransferases, and by the Sdc-1 and Wnt-dependent modulation of a colon cancer stem cell phenotype ( Katakam et al, 2020b ). Our finding of a upregulated expression of the Wnt receptor FZD7 in HS sulfotransferase overexpressing MDA-MB-231 cells may be mechanistically relevant, as this receptor acts along with Sdc-4 during foregut progenitor development ( Zhang et al, 2016 ).…”

Proteoglycans as Mediators of Cancer Tissue Mechanics

“…In this cancer type, Sdc-1 silencing promoted EMT and a stem-like phenotype and stimulated integrin signaling through FAK kinase phosphorylation. This resulted in accelerated tumor growth and possible resistance to radiation therapy (Katakam et al, 2020). Similarly, in gastric carcinomas, high Sdc-1 expression correlated with a less aggressive tumor phenotype (Charchanti et al, 2019).…”

Focal Adhesion Kinase Fine Tunes Multifaced Signals toward Breast Cancer Progression

“…On the contrary, the disruption of the FAK-scaffolding interaction with endophilin A2 suppressed the mammary CSC population, CSC-related gene expression signature and CSC self-renewal and tumorigenicity [ 119 ]. Similarly, promising results were obtained targeting FAK-mediated CSC expansion in diverse solid malignancies, including breast cancer [ 157 , 158 ]. In this vein, FAK inhibition both in vitro and in vivo reduced the self-renewal capabilities of the mammary ductal carcinoma in situ (DCIS) stem cells abolishing the expression of Wnt family member 3A (Wnt3a) and β-catenin, thus potentiating the effects of the irradiation therapy [ 159 ].…”