SPAG6 silencing inhibits the growth of the malignant myeloid cell lines SKM-1 and K562 via activating p53 and caspase activation-dependent apoptosis

SPAG6 regulates cell proliferation and apoptosis via TGF-β/Smad signal pathway in adult B-cell acute lymphoblastic leukemia

Adult B-cell acute lymphoblastic leukemia (B-ALL) prognosis remains unsatisfactory, and searching for new therapeutic targets is crucial for improving patient prognosis. Sperm-associated antigen 6 (SPAG6), a member of the cancer-testis antigen family, plays an important role in tumors, especially hematologic tumors; however, it is unknown whether SPAG6 plays a role in adult B-ALL. In this study, we demonstrated for the first time that SPAG6 expression was up-regulated in the bone marrow of adult B-ALL patients compared to healthy donors, and expression was significantly reduced in patients who achieved complete remission (CR) after treatment. In addition, patients with high SPAG6 expression were older (≥ 35 years; P = 0.015), had elevated white blood cell counts (WBC > 30 × 109/L; P = 0.021), and a low rate of CR (P = 0.036). We explored the SPAG6 effect on cell function by lentiviral transfection of adult B-ALL cell lines BALL-1 and NALM-6, and discovered that knocking down SPAG6 significantly inhibited cell proliferation and promoted apoptosis. We identified that SPAG6 knockdown might regulate cell proliferation and apoptosis via the transforming growth factor-β (TGF-β)/Smad signaling pathway.

Comprehensive analysis of SPAG1 expression as a prognostic and predictive biomarker in acute myeloid leukemia by integrative bioinformatics and clinical validation

Background

Recently, an increasing number of studies have reported that sperm-associated antigen (SPAG) proteins play crucial roles in solid tumorigenesis, and may serve as potentially helpful biomarkers for cancer diagnosis and prognosis. However, very few studies systematically investigated the expression of SPAG family members and their clinical significance in acute myeloid leukemia (AML).

Methods

The expression of SPAGs and their prognostic significance in AML were determined by a systematic analysis on data gathered from public databases, and the results were validated in clinical samples.

Results

Using public data, we identified only increased SPAG1 expression negatively associated with survival in AML by Cox regression (P < 0.001) and Kaplan–Meier analysis (P < 0.001). The prognostic value of SPAG1 expression was further confirmed in other independent cohorts. Clinically, higher SPAG1 expression was significantly correlated with white blood cell counts (P = 0.014) and French–American–British (FAB) subtypes (P = 0.024). Moreover, higher SPAG1 expression was more common in + 8 patients (P = 0.034), rarely found with t(8;21) (P = 0.014), and correlated with FLT3 (P < 0.001) and DNMT3A mutations (P = 0.001). Despite these associations, multivariate analysis confirmed the independent prognostic value of SPAG1 expression in AML (P < 0.001). Notably, AML patients with higher SPAG1 expression may benefit from hematopoietic stem cell transplantation (HSCT), whereas patients with lower SPAG1 expression appeared less likely to benefit. Finally, we further validated that SPAG1 expression was significantly increased in newly diagnosed AML patients compared with normal controls (P < 0.001) and with AML patients who achieved complete remission (P < 0.001). Additionally, SPAG1 expression could act as a potentially helpful biomarker for the diagnosis and prognosis of AML (P < 0.001 and = 0.034, respectively).

Conclusions

Our findings demonstrated that SPAG1 overexpression may serve as an independent prognostic biomarker and may guide the choice between HSCT and chemotherapy in patients with AML.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-022-01193-0.

[Effects of SPAG6 silencing and decitabine treatment on apoptosis and phosphatase and tensin homolog methylation in SKM-1 cells]

Objective: To investigate the effects of SPAG6 silencing and decitabine on apoptosis and phosphatase and tensin homolog (PTEN) methylation in SKM-1 cells in vitro and in vivo. Methods: SKM-1 cells were transfected with a lentiviral vector to silence the expression of SPAG6. Cell survival rate was detected by CCK8 after treatment with decitabine, and cell apoptosis was detected by flow cytometry. Protein expression and methylation of PTEN were detected using Western blot and merozoite surface protein (MSP) . An non-obese diabetic/severe combined inmunodeficiency disease (NOD/SCID) mice xenograft tumor model was established, and the apoptosis and PTEN expression of tumor tissue were observed through terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) and immunohistochemistry (IHC) , respectively. Results: After lentivirus transfection, SPAG6 in the interference group was silenced successfully. CCK8 results indicated that the cell survival rate of SKM-1 cells treated with decitabine decreased. Flow cytometry showed that the apoptosis rate of cells treated with decitabine [ (17.35±3.37) %] was higher than that of the untreated group (5.09%±2.06%) and the apoptosis rate of the SPAG6 silencing combined with the decitabine treatment group was the highest [ (36.34±4.00) %]. After treatment with decitabine, the expression of DNMT1 decreased, while the expression of PTEN increased, and the promoter methylation degree of PTEN also decreased. Moreover, the increased protein level caused by PTEN demethylation was the most obvious in the SPAG6 in the interference shRNA group treated with decitabine. In NOD/SCID mice, the tumor volume of the decitabine group was significantly smaller than that of the placebo group, and the tumor volume of the SPAG6 silencing combined with the decitabine treatment group was the smallest. Additionally, the apoptosis rate was the highest (the positive ratio was 3.57±0.48) . Conclusion: SPAG6 silencing may enhance the apoptosis level and the effect of PTEN demethylation in SKM-1 cells and enhance the antitumor effect of decitabine in the NOD/SCID xenograft mouse model.

Role and Clinical Utility of Cancer/Testis Antigens in Head and Neck Squamous Cell Carcinoma

Cancer/testis (CT) antigens exhibit selective expression predominantly in immunoprivileged tissues in non-pathological contexts but are aberrantly expressed in diverse cancers. Due to their expression pattern, they have historically been attractive targets for immunotherapies. A growing number of studies implicate CT antigens in almost all hallmarks of cancer, suggesting that they may act as cancer drivers. CT antigens are expressed in head and neck squamous cell carcinomas. However, their role in the pathogenesis of these cancers remains poorly studied. Given that CT antigens hold intriguing potential as therapeutic targets and as biomarkers for prognosis and that they can provide novel insights into oncogenic mechanisms, their further study in the context of head and squamous cell carcinoma is warranted.

Ccdc103 promotes myeloid cell proliferation and migration independent of motile cilia

The pathology of primary ciliary dyskinesia (PCD) is predominantly attributed to impairment of motile cilia. However, PCD patients also have perplexing functional defects in myeloid cells, which lack motile cilia. Here, we show that coiled-coil domain-containing protein 103 (CCDC103), one of the genes that, when mutated, is known to cause PCD, is required for the proliferation and directed migration of myeloid cells. CCDC103 is expressed in human myeloid cells, where it colocalizes with cytoplasmic microtubules. Zebrafish ccdc103/schmalhans (smh) mutants have macrophages and neutrophils with reduced proliferation, abnormally rounded cell morphology and an inability to migrate efficiently to the site of sterile wounds, all of which are consistent with a loss of cytoplasmic microtubule stability. Furthermore, we demonstrate that direct interactions between CCDC103 and sperm associated antigen 6 (SPAG6), which also promotes microtubule stability, are abrogated by CCDC103 mutations from PCD patients, and that spag6 zebrafish mutants recapitulate the myeloid defects observed in smh mutants. In summary, we have illuminated a mechanism, independent of motile cilia, to explain functional defects in myeloid cells from PCD patients. This article has an associated First Person interview with the first author of the paper.

SPAG6 promotes cell proliferation and inhibits apoptosis through the PTEN/PI3K/AKT pathway in Burkitt lymphoma

The main purpose of the present study was to elucidate the role of sperm‑associated antigen 6 (SPAG6) in the occurrence and development of Burkitt lymphoma (BL) and explore the underlying molecular mechanisms. A correlation was observed between the expression of SPAG6 and the prognosis of patients with lymphoma using The Cancer Genome Atlas (TCGA) database analysis. It was demonstrated that the levels of SPAG6 in BL cells were higher compared with that in IM‑9 cells by reverse transcription‑PCR and western blot assays. Moreover, silencing of SPAG6 significantly decreased proliferation and increased apoptosis of Daudi and Raji cells, whereas SPAG6 overexpression exerted the opposite effects on CA46 and NAMALWA cells. When investigating the possible mechanism, it was first observed that the level of phosphatase and tensin homolog (PTEN) protein was significantly increased, while that of phosphorylated (p‑)AKT protein was markedly reduced in the SPAG6‑knockdown group compared with the blank control group in Daudi and Raji cells by western blot analysis. It was further ascertained whether the phosphoinositide 3‑kinase (PI3K)/PTEN/protein kinase B (AKT) pathway mediates the effects of SPAG6 on cell proliferation and apoptosis, and the results demonstrated that silencing of SPAG6 suppressed the viability of Daudi and Raji cells, whereas PTEN knockdown using siRNA or SF1670 (a specific PTEN inhibitor) reversed the inhibitory effect on cell proliferation and the promoting effect on cell apoptosis induced by SPAG6 depletion in vitro as well as in vivo. These data revealed that SPAG6 may promote the proliferation and inhibit the apoptosis of BL cells via the PTEN/PI3K/AKT pathway. The results of the present study suggest that SPAG6 may play a key role in the progression of BL and may be of value as a predictive prognostic biomarker in patients with BL.

SPAG6 silencing induces autophagic cell death in SKM-1 cells via the AMPK/mTOR/ULK1 signaling pathway

As a member of the cancer-testis antigen family, sperm-associated antigen 6 (SPAG6) has been reported to be associated with the pathogenesis of myelodysplastic syndromes (MDS). Previous studies have demonstrated that SPAG6 is upregulated in bone marrow from patients with MDS and MDS-transformed acute myeloid leukemia and that knockdown of SPAG6 expression levels suppressed proliferation and promote apoptosis and differentiation in SKM-1 cells. However, the association between SPAG6 and autophagy in SKM-1 cells remains unclear. Hence, the aim of the present study was to investigate this association and its underlying mechanism. The present study used a short hairpin RNA (shRNA) lentivirus to silence SPAG6 expression levels in SKM-1 cells and demonstrated that SPAG6 knockdown increased autophagy and apoptosis. Furthermore, pharmacologically inhibiting autophagy with chloroquine and 3-methyladenine decreased SPAG6 knockdown-mediated apoptosis, indicating that SPAG6 knockdown-mediated autophagy promoted apoptosis in SKM-1 cells. Additionally, compared with the expression levels in negative control-shRNA lentivirus-transfected SKM-1 cells, the protein expression levels of phosphorylated AMP-activated protein kinase (p-AMPK) and phosphorylated unc-51-like autophagy activating kinase 1 (p-ULK1) were upregulated, while phosphorylated mammalian target of rapamycin (p-mTOR) protein expression was downregulated in SPAG6-shRNA lentivirus-transfected cells. Moreover, inhibiting AMPK expression levels with Compound C, a specific inhibitor of AMPK, attenuated SPAG6 knockdown-induced autophagy and apoptosis, suggesting that AMPK-mediated autophagy enhanced the pro-apoptotic effect of SPAG6 knockdown in SKM-1 cells. Taken together, the results of the present study demonstrated that SPAG6 silencing triggered autophagy via regulation of the AMPK/mTOR/ULK1 signaling pathway, which further contributed to the apoptosis of SKM-1 cells induced by SPAG6 knockdown. Thus, the current results indicate that SPAG6 may be a potential therapeutic target against MDS, and that autophagy may represent a potential mechanism for the treatment of MDS.

The Emerging Role of Sperm-Associated Antigen 6 Gene in the Microtubule Function of Cells and Cancer

Accumulated evidence shows that sperm-associated antigen 6 (SPAG6) gene has multiple biological functions. It maintains the normal function of a variety of cells including ciliary/flagellar biogenesis and polarization, neurogenesis, and neuronal migration. Moreover, SPAG6 is found to be critically involved in auditory transduction and the fibroblast life cycle. Furthermore, SPAG6 plays an essential role in immuno-regulation. Notably, SPAG6 has been demonstrated to participate in the occurrence and progression of a variety of human cancers. New evidence shows that SPAG6 gene regulates tumor cell proliferation, apoptosis, invasion, and metastasis. Therefore, in this review, we describe the physiological function and mechanism of SPAG6 in human normal cells and cancer cells. We also highlight that SPAG6 gene may be an effective biomarker for the diagnosis of human cancer. Taken together, targeting SPAG6 could be a novel strategy for the treatment of human diseases including cancer.

The sperm-associated antigen 6 interactome and its role in spermatogenesis

Mammalian SPAG6, the orthologue of Chlamydomonas reinhardtii PF16, is a component of the central apparatus of the '9 + 2' axoneme that controls ciliary/flagellar motility, including sperm motility. Recent studies revealed that SPAG6 has functions beyond its role in the central apparatus. Hence, we reexamined the role of SPAG6 in male fertility. In wild-type mice, SPAG6 was present in cytoplasmic vesicles in spermatocytes, the acrosome of round and elongating spermatids and the manchette of elongating spermatids. Spag6-deficient testes showed abnormal spermatogenesis, with abnormalities in male germ cell morphology consistent with the multi-compartment pattern of SPAG6 localization. The armadillo repeat domain of mouse SPAG6 was used as a bait in a yeast two-hybrid screen, and several proteins with diverse functions appeared multiple times, including Snapin, SPINK2 and COPS5. Snapin has a similar localization to SPAG6 in male germ cells, and SPINK2, a key protein in acrosome biogenesis, was dramatically reduced in Spag6-deficient mice which have defective acrosomes. SPAG16L, another SPAG6-binding partner, lost its localization to the manchette in Spag6-deficient mice. Our findings demonstrate that SPAG6 is a multi-functional protein that not only regulates sperm motility, but also plays roles in spermatogenesis in multiple cellular compartments involving multiple protein partners.

Distribution of sperm antigen 6 (SPAG6) and 16 (SPAG16) in mouse ciliated and non-ciliated tissues

The cilia and flagella of eukaryotic cells serve many functions, exhibiting remarkable conservation of both structure and molecular composition in widely divergent eukaryotic organisms. SPAG6 and SPAG16 are the homologous in the mice to Chlamydomonas reinhardtii PF16 and PF20. Both proteins are associated with the axonemal central apparatus and are essential for ciliary and flagellar motility in mammals. Recent data derived from high-throughput studies revealed expression of these genes in tissues that do not contain motile cilia. However, the distribution of SPAG6 and SPAG16 in ciliated and non-ciliated tissues is not completely understood. In this work, we performed a quantitative analysis of the expression of Spag6 and Spag16 genes in parallel with the immune-localization of the proteins in several tissues of adult mice. Expression of mRNA was higher in the testis and tissues bearing motile cilia than in the other analyzed tissues. Both proteins were present in ciliated and non-ciliated tissues. In the testis, SPAG6 was detected in spermatogonia, spermatocytes, and in the sperm flagella whereas SPAG16 was found in spermatocytes and in the sperm flagella. In addition, both proteins were detected in the cytoplasm of cells from the brain, spinal cord, and ovary. A small isoform of SPAG16 was localized in the nucleus of germ cells and some neurons. In a parallel set of experiments, we overexpressed EGFP-SPAG6 in cultured cells and observed that the protein co-localized with a subset of acetylated cytoplasmic microtubules. A role of these proteins stabilizing the cytoplasmic microtubules of eukaryotic cells is discussed.

Upregulation of SPAG6 in Myelodysplastic Syndrome: Knockdown Inhibits Cell Proliferation via AKT/FOXO Signaling Pathway

Recently, sperm-associated antigen 6 (SPAG6), a member of the cancer-testis antigen family, has been shown to be involved in tumorigenesis. An increasing number of studies have shown that SPAG6 expression is associated with the pathogenesis of myelodysplastic syndrome (MDS). However, the mechanism has not been clearly elucidated. Our previous results indicated that SPAG6 affected cell apoptosis in MDS. In this study, we used reverse transcription-quantitative polymerase chain reaction (RT-qPCR) to demonstrate that the mRNA expression of SPAG6 in bone marrow cells of patients with MDS or MDS-derived acute myeloid leukemia (MDS-AML) was higher than that of cancer-free patients. Kaplan-Meier survival curve analysis of published AML found that patients with high expression of SPAG6 had poor survival. The results of the cell counting kit-8, FACS, RT-qPCR, and Western blotting assays indicated that SPAG6 knockdown in the SKM-1 cell line inhibited cell proliferation, and affected cell cycle and differentiation. Furthermore, we found that SPAG6 knockdown affected the proliferation of SKM-1 cells by mediating the G1-to-S transition of the cell cycle. Moreover, we demonstrated that the antiproliferative effect of SPAG6 knockdown was associated with the upregulation of the cyclin-dependent kinase inhibitor p27Kip1, and regulation of the AKT/FOXO pathway. These findings indicated that SPAG6 might be a potential therapeutic target.

Imidazo[1,2-b]pyrazole-7-carboxamides Induce Apoptosis in Human Leukemia Cells at Nanomolar Concentrations

Leukemia, the malignancy of the hematopoietic system accounts for 10% of cancer cases with poor overall survival rate in adults; therefore, there is a high unmet medical need for the development of novel therapeutics. Eight imidazo[1,2-b]pyrazole-7-carboxamides have been tested for cytotoxic activity against five leukemia cell lines: Acute promyelocytic leukemia (HL-60), acute monocytic leukemia (THP-1), acute T-lymphoblastic leukemia (MOLT-4), biphenotypic B myelomonocytic leukemia (MV-4-11), and erythroleukemia (K-562) cells in vitro. Imidazo[1,2-b]pyrazole-7-carboxamides hampered the viability of all five leukemia cell lines with different potential. Optimization through structure activity relationship resulted in the following IC50 values for the most effective lead compound DU385: 16.54 nM, 27.24 nM, and 32.25 nM on HL-60, MOLT-4, MV-4-11 cells, respectively. Human primary fibroblasts were much less sensitive in the applied concentration range. Both monolayer or spheroid cultures of murine 4T1 and human MCF7 breast cancer cells were less sensitive to treatment with 1.5⁻10.8 μM IC50 values. Flow cytometry confirmed the absence of necrosis and revealed 60% late apoptotic population for MV-4-11, and 50% early apoptotic population for HL-60. MOLT-4 cells showed only about 30% of total apoptotic population. Toxicogenomic study of DU385 on the most sensitive MV-4-11 cells revealed altered expression of sixteen genes as early (6 h), midterm (12 h), and late response (24 h) genes upon treatment. Changes in ALOX5AP, TXN, and SOD1 expression suggested that DU385 causes oxidative stress, which was confirmed by depletion of cellular glutathione and mitochondrial membrane depolarization induction. Imidazo[1,2-b]pyrazole-7-carboxamides reported herein induced apoptosis in human leukemia cells at nanomolar concentrations.

Exploring the Role of Fallopian Ciliated Cells in the Pathogenesis of High-Grade Serous Ovarian Cancer

High-grade serous epithelial ovarian cancer (HGSOC) is the fifth leading cause of cancer death in women and the first among gynecological malignancies. Despite an initial response to standard chemotherapy, most HGSOC patients relapse. To improve treatment options, we must continue investigating tumor biology. Tumor characteristics (e.g., risk factors and epidemiology) are valuable clues to accomplish this task. The two most frequent risk factors for HGSOC are the lifetime number of ovulations, which is associated with increased oxidative stress in the pelvic area caused by ovulation fluid, and a positive family history due to genetic factors. In the attempt to identify novel genetic factors (i.e., genes) associated with HGSOC, we observed that several genes in linkage with HGSOC are expressed in the ciliated cells of the fallopian tube. This finding made us hypothesize that ciliated cells, despite not being the cell of origin for HGSOC, may take part in HGSOC tumor initiation. Specifically, malfunction of the ciliary beat impairs the laminar fluid flow above the fallopian tube epithelia, thus likely reducing the clearance of oxidative stress caused by follicular fluid. Herein, we review the up-to-date findings dealing with HGSOC predisposition with the hypothesis that fallopian ciliated cells take part in HGSOC onset. Finally, we review the up-to-date literature concerning genes that are located in genomic loci associated with epithelial ovarian cancer (EOC) predisposition that are expressed by the fallopian ciliated cells.

SPAG6 silencing induces apoptosis in the myelodysplastic syndrome cell line SKM‑1 via the PTEN/PI3K/AKT signaling pathway in vitro and in vivo

Apoptosis is a multi-step mechanism of cell self‑destruction for maintaining cellular homeostatic balance. Accumulating evidence indicates that abnormal apoptosis promotes the evolution and progression of myelodysplastic syndromes (MDS). As a novel cancer-testis antigen, sperm‑associated antigen 6 (SPAG6) has been reported to regulate apoptosis through the tumor necrosis factor-related apoptosis-inducing ligand signaling pathway in the MDS cell line SKM‑1. However, the mechanism of the intrinsic cell death pathway for apoptosis induction by SPAG6 silencing is unclear. In the present study, the in vitro effects of SPAG6 silencing were investigated in SKM‑1 cells through extensive biochemical and molecular approaches. Western blotting and reverse transcription-quantitative polymerase chain reaction were used to detect the expression of SPAG6 and activation of PTEN/PI3K/AKT signal pathway. Additionally, SKM‑1 cells transduced with SPAG6 short hairpin RNA (shRNA) lentivirus were treated with the phosphatidylionositol 3-kinase (PI3K) inhibitor LY294002 or pan caspase inhibitor z‑VAD‑fmk and the apoptosis rates were measured by flow cytometry, and the expressions of associated proteins were examined by western blot analysis. A mouse xenograft model was also used to further evaluate the effects of SPAG6 knockdown on inducing tumor apoptosis in vivo. Lentivirus-mediated knockdown of SPAG6 in SKM‑1 cells increased phosphatase and tensin homolog (PTEN) expression and reduced protein kinase B (AKT) phosphorylation, which in turn resulted in cell apoptosis as evidenced by induced myeloid leukaemia cell differentiation protein Mcl‑1 downregulation, cytochrome c release and increased caspase‑9 expression. Consistently, the PI3K inhibitor LY294002 synergistically enhanced apoptosis of SKM‑1 cells when co-administered with SPAG6 shRNA lentivirus. Furthermore, treatment with the pan caspase inhibitor z‑VAD‑fmk failed to prevent PTEN activation upon SPAG6 knockdown, suggesting that SPAG6-regulated PTEN expression was caspase activation-independent. In addition, SPAG6 knockdown was associated with DNMT1 downregulation, implying that SPAG6 may indirectly control PTEN expression via DNA methylation. Furthermore, tumor tissues from nonobese diabetic/severe combined immunodeficient mice inoculated with SPAG6-shRNA lentivirus pre-infected SKM‑1 cells exhibited significantly elevated apoptosis in the extrinsic and intrinsic pathways. These results demonstrate that SPAG6 silencing induces PTEN expression to regulate apoptosis though the PI3K/AKT pathway, indicating that SPAG6 may be a potential therapeutic target for MDS.

Spag6 Mutant Mice Have Defects in Development and Function of Spiral Ganglion Neurons, Apoptosis, and Higher Sensitivity to Paclitaxel

Mammalian Sperm Associated Antigen 6 (SPAG6) is the orthologue of Chlamydomonas PF16, a protein localized in the axoneme central apparatus. Recent studies showed that Spag6 has a role in brain neuronal proliferation and differentiation. The mammalian spiral ganglion neurons (SGNs) are specialzed bipolar neurons in the inner ear. However, the role of SPAG6 in SGN has not been elucidated. Therefore, We hypothesized that a Spag6 knockout would affect the development and function of SGNs. We utilized Spag6-deficient mice and SGN explants to define the role of SPAG6. On postnatal day 30 (P30) mutant mice had lower SGN density compared to their wild-type littermates, and more apoptosis was evident in the mutants. Increased Bax expression, a disturbed distribution of cytochrome c, and cleaved caspase-3 positive staining indicated that increased apoptosis involved a mitochondrial pathway. Transmission electron microscopy revealed abnormalities in the ultrastructure of mutant SGNs as early as P7. In vitro, lack of SPAG6 affected the growth of neurites and growth cones. Additionally, SPAG6 deficiency decreased synapse density in SGN explants. Finally, Spag6 mutant SGNs were more sensitive to the microtubule stabilizing agent, paclitaxel. These findings suggest that Spag6 plays a crucial role in SGN development and function.

SPAG6 and L1TD1 are transcriptionally regulated by DNA methylation in non-small cell lung cancers

BACKGROUND

DNA methylation regulates together with other epigenetic mechanisms the transcriptional activity of genes and is involved in the pathogenesis of malignant diseases including lung cancer. In non-small cell lung cancer (NSCLC) various tumor suppressor genes are already known to be tumor-specifically methylated. However, from the vast majority of a large number of genes which were identified to be tumor-specifically methylated, tumor-specific methylation was unknown so far. Thus, the major aim of this study was to investigate in detail the mechanism(s) responsible for transcriptional regulation of the genes SPAG6 and L1TD1 in NSCLCs.

METHODS

We analysed publically available RNA-sequencing data and performed gene expression analyses by RT-PCR. DNA methylation analyses were done by methylation-sensitive high-resolution melt analyses and bisulfite genomic sequencing. We additionally investigated protein expression using immunohistochemistry. Cell culture experiments included tumor cell growth, proliferation, viability as well as colony formation assays. Moreover, we performed xenograft experiments using immunodeficient mice.

RESULTS

We observed frequent downregulation of SPAG6 and L1TD1 mRNA expression in primary tumor (TU) samples compared to corresponding non-malignant lung tissue (NL) samples of NSCLC patients. We furthermore observed re-expression of both genes after treatment with epigenetically active drugs in most NSCLC cell lines with downregulated SPAG6 and L1TD1 mRNA expression. Frequent tumor-specific DNA methylation of SPAG6 and L1TD1 was detected when we analysed TU and corresponding NL samples of NSCLC patients. ROC curve analyses demonstrated that methylation of both genes is able to distinguish between TU and NL samples of these patients. Immunohistochemistry revealed a close association between SPAG6/L1TD1 methylation and downregulated protein expression of these genes. Moreover, by performing functional assays we observed reduced cell growth, proliferation and viability of pCMV6-L1TD1 transfected NSCLC cells. In addition, reduced volumes of tumors derived from pCMV6-L1TD1 compared to pCMV6-ENTRY transfected NCI-H1975 cells were seen in a xenograft tumor model.

CONCLUSIONS

Overall, our results demonstrate that SPAG6 and L1TD1 are tumor-specifically methylated in NSCLCs and that DNA methylation is involved in the transcriptional regulation of these genes. Moreover, in vitro as well as in vivo experiments revealed tumor-cell growth suppressing properties of L1TD1 in NSCLC cells.

Sperm Associated Antigen 6 (SPAG6) Regulates Fibroblast Cell Growth, Morphology, Migration and Ciliogenesis

Mammalian Spag6 is the orthologue of Chlamydomonas PF16, which encodes a protein localized in the axoneme central apparatus, and regulates flagella/cilia motility. Most Spag6-deficient mice are smaller in size than their littermates. Because SPAG6 decorates microtubules, we hypothesized that SPAG6 has other roles related to microtubule function besides regulating flagellar/cilia motility. Mouse embryonic fibroblasts (MEFs) were isolated from Spag6-deficient and wild-type embryos for these studies. Both primary and immortalized Spag6-deficient MEFs proliferated at a much slower rate than the wild-type MEFs, and they had a larger surface area. Re-expression of SPAG6 in the Spag6-deficient MEFs rescued the abnormal cell morphology. Spag6-deficient MEFs were less motile than wild-type MEFs, as shown by both chemotactic analysis and wound-healing assays. Spag6-deficient MEFs also showed reduced adhesion associated with a non-polarized F-actin distribution. Multiple centrosomes were observed in the Spag6-deficient MEF cultures. The percentage of cells with primary cilia was significantly reduced compared to the wild-type MEFs, and some Spag6-deficient MEFs developed multiple cilia. Furthermore, SPAG6 selectively increased expression of acetylated tubulin, a microtubule stability marker. The Spag6-deficient MEFs were more sensitive to paclitaxel, a microtubule stabilizer. Our studies reveal new roles for SPAG6 in modulation of cell morphology, proliferation, migration, and ciliogenesis.