Anionic citrate is a major component of venom, but the role of venom citrate in toxicity other than its inhibitory effect on the cation-dependent action of venom toxins is poorly understood. By immobilizing Chinese hamster ovary cells in microcapillary tubes and heparin on sensor chips, we demonstrated that heparan sulfatemediated cell retention of the major cardiotoxin (CTX) from the Taiwan cobra, CTX A3, near membrane surfaces is citrate-dependent. X-ray determination of a CTX A3-heparin hexasaccharide complex structure at 2.4 Å resolution revealed a molecular mechanism for toxin retention in which heparin-induced conformational changes of CTX A3 lead to citrate-mediated dimerization. A citrate ion bound to Lys-23 and Lys-31 near the tip of loop II stabilizes hydrophobic contact of the CTX A3 homodimer at the functionally important loop I and II regions. Additionally, the heparin hexasaccharide interacts with five CTX A3 molecules in the crystal structure, providing another mechanism whereby the toxin establishes a complex network of interactions that result in a strong interaction with cell surfaces presenting heparan sulfate. Our results suggest a novel role for venom citrate in biological activity and reveal a structural model that explains cell retention of cobra CTX A3 through heparan sulfate-CTX interactions.

MicroRNAs are small noncoding RNAs acting as novel biomarkers of various diseases and potential regulators of protein expression and functions. Syndecan-1 is the heparan sulfate proteoglycan associated with malignancy of various cancers, including breast cancer. In this study, we proposed a experimental workflow to investigate potential microRNAs that regulate SDC1 expression and affect breast cancer cell mobility.MicroRNA candidates were selected from available Gene Expression Omnibus datasets on breast malignancy. Further in silico duplex hybridization and multiplex PCR approach were used to screen potential microRNAs. Analysis showed increased syndecan-1 expression but decreased miR-122-5p level upon breast malignancy. Western blot and in vitro luciferase assay confirmed the targeting of 3′-untranslated region of syndecan-1 and suppression of syndecan-1 expression by miR-122-5p. The suppression of syndecan-1 expression by miR-122-5p or shRNAs against syndecan-1 increased breast cancer cell mobility; while overexpression of syndecan-1 inhibited cell mobility. In further, miR-122-5p was enriched in liver cell-derived exosomes that was able to suppress syndecan-1 expression and increase cell mobility in breast cancer cells.In conclusion, our results suggested the downregulation of SDC1 by miR-122-5p or liver-cell-derived exosomes would enhance breast cancer cell mobility. Metastasis or mobility of breast cancer cells might be affected by circulating miR-122-5p and not directly correlated with progression of breast cancer.

Anchorage-independent survival is one of the key features for malignant tumor cells. Whether specific gene alterations contributed by anchorage independency would further affect metastatic phenotypes of melanoma cells was unclear. We adapted suspension culture of melanoma cells to establish anchorage independency. The suspended melanoma cells lost their invasive abilities in vitro. Specific loss of laminin-binding ability in suspended melanoma cells was observed, which was correlated with downregulation of syndecan-1 as revealed by microarray and validated by qPCR and Western blot. Modulation of syndecan-1 expression level affected laminin binding, transwell migration and matrix metalloproteinase-2 secretion in melanoma cells. SDC1 expression and transwell migration were correlated with activity or level of protein kinase Cδ as evidence by specific inhibitors and shRNA transfection. In this study, we compared metastatic phenotypes and gene expressions of adherent and suspended melanoma cells. The anchorage independency led to protein kinase Cδ-mediated syndecan-1 downregulation, which contributed to loss of laminin-binding ability, reduced metalloproteinase-2 secretion and loss of invasiveness.

No abstract