Baicalein targets STMN1 to inhibit the progression of nasopharyngeal carcinoma via regulating the Wnt/β-catenin pathway

BACKGROUNDS

Nasopharyngeal carcinoma is a common malignancy in the head and neck. Baicalein has been reported to exert the anticancer effects on various cancers. In this study, our aim was to explore the function of baicalein in the development of nasopharyngeal carcinoma and further investigate the potential underlying mechanisms.

METHODS

Cell Counting Kit (CCK)-8 assay, EdU assay, sphere formation assay, flow cytometry, and transwell invasion assay were conducted to determine cell proliferation, stemness, apoptosis, and invasion, respectively. Western blot was performed to examine the protein levels of PCNA, MMP9, STMN1, β-catenin, and Wnt3A. The mRNA level of STMN1 was assessed using real-time quantitative polymerase chain reaction (RT-qPCR). Xenograft tumor model was carried out to evaluate the effects of baicalein on tumor growth in vivo. Immunohistochemistry (IHC) assay was used to detect the levels of PCNA, MMP9, and STMN1 in tumor tissues from mice.

RESULTS

Baicalein significantly induced cell apoptosis and impeded cell proliferation, invasion, and stemness of nasopharyngeal carcinoma cells. STMN1 was highly expressed in nasopharyngeal carcinoma, and baicalein could directly downregulate STMN1 expression. STMN1 knockdown hampered the progression of nasopharyngeal carcinoma cells. Moreover, the effects of baicalein on cell proliferation, stemness, invasion, and apoptosis in nasopharyngeal carcinoma cells were harbored by STMN1 overexpression. Baicalein regulated STMN1 to inhibit the activation of the Wnt/β-catenin pathway. SKL2001, an agonist of the Wnt/β-catenin pathway, could reverse the effects of STMN1 knockdown on the progression of nasopharyngeal carcinoma. In addition, baicalein markedly impeded tumor growth in vivo.

CONCLUSION

Baicalein regulated the STMN1/Wnt/β-catenin pathway to restrain the development of nasopharyngeal carcinoma.

STMN1 promotes cell malignancy and bortezomib resistance of multiple myeloma cell lines via PI3K/AKT signaling

BACKGROUND

This study investigates the biological functions of Stathmin1 (STMN1) involving drug resistance and cell proliferation in multiple myeloma (MM) and its related mechanisms.

METHODS

Bone marrow aspirates were collected from 20 MM patients, and the bone marrow mononuclear cells (BMMCs) were separated by Ficoll-Hypaque density gradient centrifugation. Blood samples of 20 patients with monoclonal gammopathy of undetermined significance (MGUS) and 20 healthy donors were collected. Normal plasma cells sorted from the peripheral blood of MGUS patients and healthy subject as controls. Two bortezomib (BTZ)-resistant MM cell lines were established, namely NCI-H929/BTZ and KM3/BTZ cells, and then transfected with lentiviruses packaging sh-STMN1 to knock down STMN1 level in BTZ-resistant cells. Expression of STMN1 was assessed by RT-qPCR and western blotting. CCK-8 assays were performed to assess 50% growth inhibition (IC50) values. Green fluorescent protein in BTZ-resistant cells infected with lentiviruses was observed by fluorescence microscopy. Cell viability, proliferation, cell cycle, and apoptosis were evaluated through MTT assays, colony formation assays, flow cytometry analyses, and TUNEL staining.

RESULTS

STMN1 was upregulated in MM cells and bone marrow aspirates of MM patients. Additionally, STMN1 depletion attenuated BTZ resistance in MM cells. Moreover, downregulation of STMN1 limited the malignant phenotypes of BTZ-resistant cells. Mechanistically, the PI3K/Akt signaling was inactivated by STMN1 downregulation in BTZ-resistant cells.

CONCLUSION

STMN1 silencing inhibits cell proliferation and BTZ resistance in MM by inactivating the PI3K/Akt signaling.

Stathmin potentiates vinflunine and inhibits Paclitaxel activity

Cell biology and crystallographic studies have suggested a functional link between stathmin and microtubule targeting agents (MTAs). In a previous study we showed that stathmin increases vinblastine (VLB) binding to tubulin, and that conversely VLB increases stathmin binding to tubulin. This constituted the first biochemical evidence of the direct relationship between stathmin and an antimitotic drug, and revealed a new mechanism of action for VLB. The question remained if the observed interaction was specific for this drug or represented a general phenomenon for all MTAs. In the present study we investigated the binding of recombinant stathmin to purified tubulin in the presence of paclitaxel or another Vinca alkaloid, vinflunine, using Isothermal Titration Calorimetry (ITC). These experiments revealed that stathmin binding to tubulin is increased in the presence of vinflunine, whereas no signal is observed in the presence of paclitaxel. Further investigation using turbidity and co-sedimentation showed that stathmin inhibited paclitaxel microtubule-stabilizing activity. Taken together with the previous study using vinblastine, our results suggest that stathmin can be seen as a modulator of MTA activity and binding to tubulin, providing molecular explanation for multiple previous cellular and in vivo studies showing that stathmin expression level affects MTAs efficiency.

Stathmin regulates keratinocyte proliferation and migration during cutaneous regeneration

Cutaneous regeneration utilizes paracrine feedback mechanisms to fine-tune the regulation of epidermal keratinocyte proliferation and migration. However, it is unknown how fibroblast-derived hepatocyte growth factor (HGF) affects these mutually exclusive processes in distinct cell populations. We here show that HGF stimulates the expression and phosphorylation of the microtubule-destabilizing factor stathmin in primary human keratinocytes. Quantitative single cell- and cell population-based analyses revealed that basal stathmin levels are important for the migratory ability of keratinocytes in vitro; however, its expression is moderately induced in the migration tongue of mouse skin or organotypic multi-layered keratinocyte 3D cultures after full-thickness wounding. In contrast, clearly elevated stathmin expression is detectable in hyperproliferative epidermal areas. In vitro, stathmin silencing significantly reduced keratinocyte proliferation. Automated quantitative and time-resolved analyses in organotypic cocultures demonstrated a high correlation between Stathmin/phospho-Stathmin and Ki67 positivity in epidermal regions with proliferative activity. Thus, activation of stathmin may stimulate keratinocyte proliferation, while basal stathmin levels are sufficient for keratinocyte migration during cutaneous regeneration.

Regulation of microtubule dynamic instability in vitro by differentially phosphorylated stathmin

Stathmin is an important regulator of microtubule polymerization and dynamics. When unphosphorylated it destabilizes microtubules in two ways, by reducing the microtubule polymer mass through sequestration of soluble tubulin into an assembly-incompetent T2S complex (two alpha:beta tubulin dimers per molecule of stathmin), and by increasing the switching frequency (catastrophe frequency) from growth to shortening at plus and minus ends by binding directly to the microtubules. Phosphorylation of stathmin on one or more of its four serine residues (Ser(16), Ser(25), Ser(38), and Ser(63)) reduces its microtubule-destabilizing activity. However, the effects of phosphorylation of the individual serine residues of stathmin on microtubule dynamic instability have not been investigated systematically. Here we analyzed the effects of stathmin singly phosphorylated at Ser(16) or Ser(63), and doubly phosphorylated at Ser(25) and Ser(38), on its ability to modulate microtubule dynamic instability at steady-state in vitro. Phosphorylation at either Ser(16) or Ser(63) strongly reduced or abolished the ability of stathmin to bind to and sequester soluble tubulin and its ability to act as a catastrophe factor by directly binding to the microtubules. In contrast, double phosphorylation of Ser(25) and Ser(38) did not affect the binding of stathmin to tubulin or microtubules or its catastrophe-promoting activity. Our results indicate that the effects of stathmin on dynamic instability are strongly but differently attenuated by phosphorylation at Ser(16) and Ser(63) and support the hypothesis that selective targeting by Ser(16)-specific or Ser(63)-specific kinases provides complimentary mechanisms for regulating microtubule function.