Baicalein targets STMN1 to inhibit the progression of nasopharyngeal carcinoma via regulating the Wnt/ß-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, ß-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/ß-catenin pathway. SKL2001, an agonist of the Wnt/ß-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/ß-catenin pathway to restrain the development of nasopharyngeal carcinoma.

STMN1 Promotes Tumor Metastasis in Non-small Cell Lung Cancer Through Microtubule-dependent And Nonmicrotubule-dependent Pathways.

The relationship between STMN1 and cancer metastasis is controversial. The purpose of this study was to explore the role and mechanism of STMN1 in NSCLC metastasis. In this study, we reported that STMN1 was highly expressed in NSCLC tissues and associated with poor prognosis. Both in vivo and in vitro functional assays confirmed that STMN1 promoted NSCLC metastasis. Further studies confirmed that STMN1 promoted cell migration by regulating microtubule stability. The results of Co-IP and LC‒MS/MS illustrated that STMN1 interacts with HMGA1. HMGA1 decreases microtubule stability by regulating the phosphorylation level of STMN1 at Ser16 and Ser38 after interacting with STMN1. This result suggested that STMN1 could be activated by HMGA1 to further promote NSCLC metastasis. Meanwhile, it has been found that STMN1 could promote cell migration by activating the p38MAPK/STAT1 signaling pathway, which is not dependent on microtubule stability. However, activating p38MAPK can decrease microtubule stability by promoting the dephosphorylation of STMN1 at ser16. A positive feedback loop was formed between STMN1 and p38MAPK to synergistically promote cell migration. In summary, our study demonstrated that STMN1 could promote NSCLC metastasis through microtubule-dependent and nonmicrotubule-dependent mechanisms. STMN1 has the potential to be a therapeutic target to inhibit metastasis.

AKT/FOXM1/STMN1 signaling pathway activation by SMC1A promotes tumor growth in breast cancer.

BACKGROUND: Upregulation of SMC1A (Structural maintenance of chromosomes 1A) is linked with many types of cancer and its oncogenic function, which has been associated with crucial cellular mechanisms (cell division, cell cycle checkpoints regulation and DNA repair). Recent studies have shown that SMC1A was involved in breast cancer, although the exact mechanisms of SMC1A remain to be determined. METHODS: Using The Cancer Genome Atlas (TCGA) database, we examined SMC1A expression and its relation to other genes, including FOXM1 and STMN1. Short hairpin RNA was used to subsequently examine the biological roles of SMC1A in MDA-MB-231 and MDA-MB-468 cell lines. Bioinformatics were performed to identify the SMC1A-related gene FOXM1. RESULTS: Here, we used the TCGA database to show that SMC1A is overexpressed in breast cancer. Later investigations showed SMC1A's role in breast cancer cell survival, apoptosis and invasion. Using bioinformatics and western blot assays, we confirmed that FOXM1 acted as the downstream of SMC1A, and SMC1A knockdown significantly downregulated the FOXM1 expression via the AKT signal pathway. Interestingly, the inhibition effects induced by SMC1A downregulation could be reversed by FOXM1 overexpression. In the clinic, SMC1A expression is favorably linked with FOXM1 expression in breast cancer tumor tissues. CONCLUSIONS: Collectively, our results not only enhance our knowledge of SMC1A's molecular pathways in breast cancer, but also suggest a potential new therapeutic target.

Deficiency of copper responsive gene stmn4 induces retinal developmental defects.

As part of the central nervous system (CNS), the retina senses light and also conducts and processes visual impulses. The damaged development of the retina not only causes visual damage, but also leads to epilepsy, dementia and other brain diseases. Recently, we have reported that copper (Cu) overload induces retinal developmental defects and down-regulates microtubule (MT) genes during zebrafish embryogenesis, but whether the down-regulation of microtubule genes mediates Cu stress induced retinal developmental defects is still unknown. In this study, we found that microtubule gene stmn4 exhibited obviously reduced expression in the retina of Cu overload embryos. Furthermore, stmn4 deficiency (stmn4-/-) resulted in retinal defects similar to those seen in Cu overload embryos, while overexpression of stmn4 effectively rescued retinal defects and cell apoptosis occurred in the Cu overload embryos and larvae. Meanwhile, stmn4 deficient embryos and larvae exhibited reduced mature retinal cells, the down-regulated expression of microtubules and cell cycle-related genes, and the mitotic cell cycle arrests of the retinal cells, which subsequently tended to apoptosis independent on p53. The results of this study demonstrate that Cu stress might lead to retinal developmental defects via down-regulating expression of microtubule gene stmn4, and stmn4 deficiency leads to impaired cell cycle and the accumulation of retinal progenitor cells (RPCs) and their subsequent apoptosis. The study provides a certain referee for copper overload in regulating the retinal development in fish.

The knockdown of stathmin with si-RNA inhibits invasion of mesothelioma.

BACKGROUND: To investigate the mechanism of action of stathmin1 (STMN1) in mesothelioma (MSM) and whether it has any role in its treatment. METHODS: STMN1 expression was examined using immunohistochemistry in biopsy tissues taken from MSM patients. The relationships between the levels of STMN1 expression in the pathology preparations of MSM patients, and the clinicopathological characteristics of these patients, and their survival times were investigated. Transfection of STMN1-specific siRNA into SPC212 cells was compared to negative control siRNAs. The mRNA levels of genes that may play a role in invasion, apoptosis, and autophagy were evaluated by RT-PCR. RESULTS: The expression of STMN1 was shown to be high in MSM tissues (p < 0.05). It was found that the only independent predictor factor affecting the survival time of MSM patients was the disease stage (p < 0.05). STMN1 was significantly reduced after siRNA intervention (81.5%). STMN1 with specific siRNA has been shown to suppress invasion by reducing the mRNA levels of cadherin-6 (CDH6), fibroblast growth factor-8 (FGF8), hypoxia-inducible factor 1 (HIF1A), matrix metallopeptidase 1-2 (gelatinase A) (MMP1-2), and TIMP metallopeptidase inhibitor 2 (TIMP2), which are important markers for invasion. Although the expression of apoptosis and autophagy-related genes, caspase-2 (Casp2) and LC-3, was reduced by silencing STMN1 with specific siRNA in western blot analysis, this effect was not observed in PCR results. CONCLUSIONS: Immunohistochemical analysis of STMN1 may contribute to the differential diagnosis of MSM, and STMN1 may also be considered as a potential therapeutic target in the early invasive stage of MSM therapy.

Cryptic splicing of stathmin-2 and UNC13A mRNAs is a pathological hallmark of TDP-43-associated Alzheimer's disease.

Nuclear clearance and cytoplasmic accumulations of the RNA-binding protein TDP-43 are pathological hallmarks in almost all patients with amyotrophic lateral sclerosis (ALS) and up to 50% of patients with frontotemporal dementia (FTD) and Alzheimer's disease. In Alzheimer's disease, TDP-43 pathology is predominantly observed in the limbic system and correlates with cognitive decline and reduced hippocampal volume. Disruption of nuclear TDP-43 function leads to abnormal RNA splicing and incorporation of erroneous cryptic exons in numerous transcripts including Stathmin-2 (STMN2, also known as SCG10) and UNC13A, recently reported in tissues from patients with ALS and FTD. Here, we identify both STMN2 and UNC13A cryptic exons in Alzheimer's disease patients, that correlate with TDP-43 pathology burden, but not with amyloid-ß or tau deposits. We also demonstrate that processing of the STMN2 pre-mRNA is more sensitive to TDP-43 loss of function than UNC13A. In addition, full-length RNAs encoding STMN2 and UNC13A are suppressed in large RNA-seq datasets generated from Alzheimer's disease post-mortem brain tissue. Collectively, these results open exciting new avenues to use STMN2 and UNC13A as potential therapeutic targets in a broad range of neurodegenerative conditions with TDP-43 proteinopathy including Alzheimer's disease.

Stathmin-2 loss leads to neurofilament-dependent axonal collapse driving motor and sensory denervation.

The mRNA transcript of the human STMN2 gene, encoding for stathmin-2 protein (also called SCG10), is profoundly impacted by TAR DNA-binding protein 43 (TDP-43) loss of function. The latter is a hallmark of several neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). Using a combination of approaches, including transient antisense oligonucleotide-mediated suppression, sustained shRNA-induced depletion in aging mice, and germline deletion, we show that stathmin-2 has an important role in the establishment and maintenance of neurofilament-dependent axoplasmic organization that is critical for preserving the caliber and conduction velocity of myelinated large-diameter axons. Persistent stathmin-2 loss in adult mice results in pathologies found in ALS, including reduced interneurofilament spacing, axonal caliber collapse that drives tearing within outer myelin layers, diminished conduction velocity, progressive motor and sensory deficits, and muscle denervation. These findings reinforce restoration of stathmin-2 as an attractive therapeutic approach for ALS and other TDP-43-dependent neurodegenerative diseases.

Association Between High Expression of Phosphorylated-STMN1 and Mesenchymal Marker Expression and Cancer Stemness in Breast Cancer.

BACKGROUND/AIM: In patients with breast cancer, the expression of stathmin1 (STMN1) has been significantly related to a poor prognosis, cancer aggressiveness, and expression of cancer stem cell markers. The STMN1 protein is closely regulated by phosphorylation in four sites. However, few studies have investigated the relationship between the expression of phosphorylated STMN1 (pSTMN1) and clinicopathological findings, including tumor-aggressive biomarkers, in patients with breast cancer. MATERIALS AND METHODS: The expression levels of four pSTMN1 (Ser16, Ser25, Ser38, and Ser63) were immunohistochemically analyzed in 213 breast cancer cases. The clinicopathological factors evaluated included epithelial-mesenchymal transition (EMT) markers and cancer stem cell markers. RESULTS: The cytoplasmic expression of pSTMN1 (Ser16, Ser25, Ser38, and Ser63) in normal breast tissues was low. The positive expression ratios of Ser25 (54.5%) and Ser38 (39.0%) were high compared to those of Ser16 (25.8%) and Ser63 (23.9%). The overexpression of pSTMN1 (Ser38) was associated with tumor-aggressive characteristics, such as triple-negative breast cancer (TNBC) phenotypes, high mesenchymal marker, and expression of cancer stem cell markers. CONCLUSION: STMN1 phosphorylation might be associated with clinicopathological factors, breast cancer subtypes, and expression of mesenchymal markers and breast cancer stem cell markers through the regulation of STMN1 function. Ser38 phosphorylation of STMN1 may be a novel biomarker for high-grade TNBC associated with mesenchymal marker expression and cancer stemness.

Hsa_circ_0119412 is a tumor promoter in hepatocellular carcinoma by inhibiting miR-526b-5p to upregulate STMN1.

Hepatocellular carcinoma (HCC) is always deemed a deadly malignancy worldwide. Non-coding RNAs, including circRNAs, are becoming more widely recognized as essential regulators of the malignant development of HCC. Thus, we elaborated the regulating role of hsa_circ_0119412 in HCC advancement. The qRT-PCR was done to estimate the expressions of hsa_circ_0119412, miR-526b-5p, and Stathmin 1 (STMN1) in HCC (clinical samples and cell lines), and immunoblotting was used to detect STMN1 protein level in HCC cell lines. The stability of the circRNA was checked by processing with ribonuclease R. The proliferative potential of HCC cells was examined via the CCK-8 assay and the migratory potential by the wound healing assay. Immunoblotting was done to examine Bax and Bcl-2 (apoptosis-related proteins). Luciferase and RIP assays were employed to establish the direct interactions among miR-526b-5p and hsa_circ 0119412/STMN1. In vivo tumor growth was measured by doing a xenograft tumor experiment. In the tissues of HCC patients and cell lines derived from HCC cells, hsa_circ_0119412 was distinctly over-expressed. Knocking down hsa_circ_0119412 impeded proliferation and migration while inducing apoptosis in HCC cells. Moreover, silencing hsa_circ_0119412 diminished tumor weight and volume in vivo. Interestingly, miR-526b-5p inhibition partially restored the anti-tumor effects of silencing hsa_circ_0119412. STMN1 expression was also abundant in HCC, suggesting that it play a tumor-promoting role. Mechanistically, hsa_circ_0119412 sponged miR-526b-5p, resulting in STMN1 upregulation and thus facilitating the progression of HCC. In conclusion, this study reveals that hsa_circ_0119412 knockdown attenuates the progression of HCC by targeting miR-526b-5p/STMN1 axis.

SCG10 is required for peripheral axon maintenance and regeneration in mice.

Proper microtubule dynamics are critical for neuronal morphogenesis and functions, and their dysregulation results in neurological disorders and regeneration failure. Superior cervical ganglion-10 (SCG10, also known as stathmin-2 or STMN2) is a well-known regulator of microtubule dynamics in neurons, but its functions in the peripheral nervous system remain largely unknown. Here, we show that Scg10 knockout mice exhibit severely progressive motor and sensory dysfunctions with significant sciatic nerve myelination deficits and neuromuscular degeneration. Additionally, increased microtubule stability, shown by a significant increase in tubulin acetylation and decrease in tubulin tyrosination, and decreased axonal transport were observed in Scg10 knockout dorsal root ganglion (DRG) neurons. Furthermore, SCG10 depletion impaired axon regeneration in both injured mouse sciatic nerve and cultured DRG neurons following replating, and the impaired axon regeneration was found to be induced by a lack of SCG10-mediated microtubule dynamics in the neurons. Thus, our results highlight the importance of SCG10 in peripheral axon maintenance and regeneration.

STNM1 in human cancers: role, function and potential therapy sensitizer.

STMN1 belongs to the stathmin gene family, it encodes a cytoplasmic phosphorylated protein, stathmin1, which is commonly observed in vertebrate cells. STMN1 is a structural microtubule-associated protein (MAP) that binds to microtubule protein dimers rather than microtubules, with each STMN1 binding two microtubule protein dimers and preventing their aggregation, leading to microtubule instability. STMN1 expression is elevated in a number of malignancies, and inhibition of its expression can interfere with tumor cell division. Its expression can change the division of tumor cells, thereby arresting cell growth in the G2/M phase. Moreover, STMN1 expression affects tumor cell sensitivity to anti-microtubule drug analogs, including vincristine and paclitaxel. The research on MAPs is limited, and new insights on the mechanism of STMN1 in different cancers are emerging. The effective application of STMN1 in cancer prognosis and treatment requires further understanding of this protein. Here, we summarize the general characteristics of STMN1 and outline how STMN1 plays a role in cancer development, targeting multiple signaling networks and acting as a downstream target for multiple microRNAs, circRNAs, and lincRNAs. We also summarize recent findings on the function role of STMN1 in tumor resistance and as a therapeutic target for cancer.

The effect of propofol on chemosensitivity of paclitaxel in cervical cancer cells.

BACKGROUND: Propofol is a drug with potential anticancer effect. This study aimed to explore the effect of propofol on chemosensitivity of cervical cancer cells to paclitaxel. METHODS: HeLa and CaSki cells were selected for drug experiments. Cell viability was evaluated via CCK-8 assay, and the combination index (CI) was calculated by CompuSyn software. A clinically relevant concentration and IC30 of propofol were selected in combination with 5 nM paclitaxel. BrdU incorporation, transwell, and flow cytometry assays were utilized to evaluate cell proliferation, migration, invasion, and apoptosis. The expression of ß-tubulin, stathmin 1, and GAPDH proteins was evaluated by Western blot. The stathmin 1 cDNA plasmid was used to establish stathmin 1-overexpressing CaSki cells. RESULTS: At clinically relevant concentrations (0-80 µM), propofol did not affect cancer cell viability, but high concentrations (100-800 µM) reduced cell viability. The CI values of propofol with IC30 (200 µM in HeLa; 400 µM in CaSki) combined with 5 nM paclitaxel were <1. The effect of propofol with IC30 combined with paclitaxel on cell proliferation, migration, invasion, and apoptosis were stronger than individual effect, while 30 µM propofol had no effect. The Western blot results showed 30 µM propofol did not affect ß-tubulin and stathmin 1 expression in cells, although paclitaxel upregulated ß-tubulin expression while downregulating stathmin 1 expression. Compared with paclitaxel alone, cotreatment with propofol at its IC30 and paclitaxel decreased stathmin 1 expression but had no effect on ß-tubulin expression. High stathmin 1 expression weakened the effect of paclitaxel on cell viability and apoptosis, while propofol partially reversed these effect. CONCLUSION: Propofol at clinically relevant concentrations had no effect on the malignant biological behaviors of cervical cancer cells, while propofol at high concentrations decreased.Propofol with IC30 and paclitaxel had synergetic effect on cancer cells through a reduction in stathmin 1 expression.

The Stathmin-2 membrane-targeting domain is required for axon protection and regulated degradation by DLK signaling.

Axon integrity is essential for functional connectivity in the nervous system. The degeneration of stressed or damaged axons is a common and sometimes initiating event in neurodegenerative disorders. Stathmin-2 (Stmn2) is an axon maintenance factor that is depleted in amyotrophic lateral sclerosis, and replenishment of Stmn2 can restore neurite outgrowth in diseased neurons. However, mechanisms responsible for Stmn2-mediated axon maintenance in injured neurons are not known. We used primary sensory neurons to interrogate the role of Stmn2 in the degeneration of severed axons. We discover that membrane association of Stmn2 is critical for its axon-protective activity. Structure-function studies revealed that axonal enrichment of Stmn2 is driven by palmitoylation as well as tubulin interaction. Using live imaging, we discover that another Stmn, Stmn3, comigrates with Stmn2-containing vesicles. We also demonstrate that Stmn3 undergoes regulated degradation through dual leucine zipper kinase (DLK)-c-Jun N-terminal kinase signaling. The Stmn2 membrane-targeting domain is both necessary and sufficient for localization to a specific vesicle population and confers sensitivity to DLK-dependent degradation. Our findings reveal a broader role for DLK in tuning the local abundance of palmitoylated Stmns in axon segments. Moreover, palmitoylation is a critical component of Stmn-mediated axon protection, and defining the Stmn2-containing vesicle population will provide important clues toward mechanisms of axon maintenance.

GTSE1 promotes the growth of NSCLC by regulating microtubule-associated proteins through the ERK/MAPK pathway.

The role of G2 and S phase-expressed-1 (GTSE1), a microtubule-localized protein, in non-small-cell lung cancer (NSCLC) remains unknown. We explored its role in NSCLC growth. GTSE1 was detected in NSCLC tissues and cell lines using quantitative real-time polymerase chain reaction. The clinical significance of GTSE1 levels was evaluated. Biological and apoptotic effects of GTSE1 were evaluated using transwell, cell-scratch, and MTT assays, and flow cytometry and western blotting, respectively. Its association with cellular microtubules was shown by western blotting and immunofluorescence. GTSE1 expression was upregulated in NSCLC tissues and cell lines. GTSE1 levels correlated with lymph node metastasis. Higher GTSE1 mRNA expression correlated with shorter progression-free survival. GTSE1-knockdown decreased proliferation, colony formation, invasion, and migration of NSCLC cells, and inhibited tau and stathmin-1 microtubule-associated protein expression, via the extracellular-regulated protein kinase/mitogen-activated protein kinase (ERK/MAPK) signaling pathway, and microtubule disruption. GTSE1 may promote NSCLC growth by regulating tau and stathmin-1 through the ERK/MAPK signaling pathway.

Mechanism of STMN2 cryptic splice-polyadenylation and its correction for TDP-43 proteinopathies.

Loss of nuclear TDP-43 is a hallmark of neurodegeneration in TDP-43 proteinopathies, including amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). TDP-43 mislocalization results in cryptic splicing and polyadenylation of pre-messenger RNAs (pre-mRNAs) encoding stathmin-2 (also known as SCG10), a protein that is required for axonal regeneration. We found that TDP-43 binding to a GU-rich region sterically blocked recognition of the cryptic 3' splice site in STMN2 pre-mRNA. Targeting dCasRx or antisense oligonucleotides (ASOs) suppressed cryptic splicing, which restored axonal regeneration and stathmin-2-dependent lysosome trafficking in TDP-43-deficient human motor neurons. In mice that were gene-edited to contain human STMN2 cryptic splice-polyadenylation sequences, ASO injection into cerebral spinal fluid successfully corrected Stmn2 pre-mRNA misprocessing and restored stathmin-2 expression levels independently of TDP-43 binding.

Analysis of STMN2 CA repeats in italian ALS patients shows no association.

Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disease caused by a complex interaction of genetic and environmental factors. Recently, a polymorphic intronic CA repeat in STMN2 gene has been proposed as risk factor for ALS. The presence of long/long CA genotype, especially if one allele had 24 CA, was reported to be significantly associated with the disease in a cohort of sporadic ALS patients. We tested an Italian cohort of 366 ALS patients and 353 healthy controls and we found no association between CA length and ALS risk.

STMN2 overexpression promotes cell proliferation and EMT in pancreatic cancer mediated by WNT/ß-catenin signaling.

STMN2, as a key regulator in microtubule disassembly and dynamics, has recently been shown to participate in cancer development. However, the corresponding role in pancreatic ductal adenocarcinoma (PC), to our knowledge, has not been reported yet. In the current study, we systematically investigate the potential role of STMN2 in the progression of PC in vitro and vivo. Overexpression of STMN2 was prevalently observed in 81 human cases of PC tissues compared with that in the paired adjacent pancreas (54.3% vs 18.5%, P < 0.01), which was positively associated with multiple advanced clinical stages of PC patients (tumor size, T stage, lymph-node metastasis and the poor prognosis). Meanwhile, a close correlation between high STMN2 and cytoplasmic/nuclear ß-catenin expression (P = 0.007) was observed in PC tissues and cell lines. STMN2 overexpression induced EMT and cell proliferation in vitro via stimulating EMT-like cellular morphology, cell motility and proliferation, and the change of EMT (Snail1, E-cadherin and Vimentin) and Cyclin D1 signaling. However, XAV939 inhibited STMN2 overexpression-enhanced EMT and proliferation. Conversely, KY19382 reversed STMN2 silencing- inhibited EMT and cell proliferation in vitro. Furthermore, activated STMN2 and ß-catenin were co-localized in cytoplasm/nuclear in vitro. ß-catenin/TCF-mediated the transcription of STMN2 by the potential binding sites (TTCAAAG). Finally, STMN2 promoted subcutaneous tumor growth following the activation of EMT and Cyclin D1 signaling. STMN2 overexpression promotes the aggressive clinical stage of PC patients and promotes EMT and cell proliferation in vitro and vivo. ß-catenin/TCF-mediated the transcription of STMN2.

Protein Phosphatase 1 Subunit PPP1R14B Stabilizes STMN1 to Promote Progression and Paclitaxel Resistance in Triple-Negative Breast Cancer.

Triple-negative breast cancer (TNBC) represents the most lethal subtype of breast cancer due to its aggressive clinical features and the lack of effective therapeutic targets. To identify novel approaches for targeting TNBC, we examined the role of protein phosphatases in TNBC progression and chemoresistance. Protein phosphatase 1 regulatory subunit 14B (PPP1R14B), a poorly defined member of the protein phosphatase 1 regulatory subunits, was aberrantly upregulated in TNBC tissues and predicted poor prognosis. PPP1R14B was degraded mainly through the ubiquitin-proteasome pathway. RPS27A recruited deubiquitinase USP9X to deubiquitinate and stabilize PPP1R14B, resulting in overexpression of PPP1R14B in TNBC tissues. Gain- and loss-of-function assays demonstrated that PPP1R14B promoted TNBC cell proliferation, colony formation, migration, invasion, and resistance to paclitaxel in vitro. PPP1R14B also induced xenograft tumor growth, lung metastasis, and paclitaxel resistance in vivo. Mechanistic investigations revealed that PPP1R14B maintained phosphorylation and stability of oncoprotein stathmin 1 (STMN1), a microtubule-destabilizing phosphoprotein critically involved in cancer progression and paclitaxel resistance, which was dependent on PP1 catalytic subunits α and γ. Importantly, the tumor-suppressive effects of PPP1R14B deficiency could be partially rescued by ectopic expression of wild-type but not phosphorylation-deficient STMN1. Moreover, PPP1R14B decreased STMN1-mediated α-tubulin acetylation, microtubule stability, and promoted cell-cycle progression, leading to resistance of TNBC cells to paclitaxel. Collectively, these findings uncover a functional and mechanistic role of PPP1R14B in TNBC progression and paclitaxel resistance, indicating PPP1R14B is a potential therapeutic target for TNBC. SIGNIFICANCE: PPP1R14B upregulation induced by RPS27A/USP9X in TNBC increases STMN1 activity, leading to cancer progression and paclitaxel resistance.

Stathmin expression alters the antiproliferative effect of eribulin in leiomyosarcoma cells.

Uterine leiomyosarcoma is an aggressive soft tissue tumor. Stathmin, a phosphoprotein that modulates microtubule dynamics, is highly expressed in many malignancies including leiomyosarcoma. The microtubule-depolymerizing agent eribulin has been recently approved for treating malignant soft tissue tumors. Although eribulin inhibits microtubule polymerization, little is known about the relationship between eribulin treatment and stathmin dynamics. In this study, we explored the role of stathmin expression in the action of eribulin in leiomyosarcoma cells. Eribulin induced phosphorylation of stathmin and reduced expression of subunits A and C of protein phosphatase 2A (PP2A) in a leiomyosarcoma cell line. The PP2A activator FTY720 reduced levels of phosphorylated stathmin. Eribulin decreased stathmin protein levels without affecting stathmin mRNA expression. Furthermore, stathmin knockdown attenuated the inhibitory effects of eribulin on cell viability, whereas stathmin overexpression enhanced the anti-proliferative effect of eribulin. Eribulin-resistant leiomyosarcoma cell lines had enhanced expression of the class Ⅰ ß-tubulin TUBB1, multi-drug resistance 1 protein MDR1 and breast cancer-resistance protein BCRP, and decreased expression of stathmin. Taken together, these results suggest that stathmin expression modulates the pharmacological efficacy of eribulin in uterine leiomyosarcoma cells.