The PIN1-YTHDF1 axis promotes breast tumorigenesis via the m6A-dependent stabilization of AURKA mRNA.

The post-transcriptional processing of N6-methyladenosine (m6A)-modified mRNA by YTH domain-containing family protein 1 (YTHDF1) plays a crucial role in the regulation of gene expression. Although YTHDF1 expression is frequently upregulated in breast cancer, the regulatory mechanisms for this remain unclear. In this study, we examined the role of peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (PIN1) in regulating YTHDF1 stability in breast cancer cells. The WW domain of PIN1 interacted with YTHDF1 in a phosphorylation-dependent manner. Additionally, PIN1 overexpression increased YTHDF1 stability by preventing ubiquitin-dependent proteasomal degradation. Furthermore, using the MS2-tagged RNA pull-down assay, we identified Aurora kinase A (AURKA) mRNA as a bona fide substrate of YTHDF1. PIN1-mediated YTHDF1 stabilization increased the stability of AURKA mRNA in an m6A-dependent manner. Furthermore, YTHDF1 knockout reduced AURKA protein expression levels, resulting in anticancer effects in breast cancer cells, including decreased cell proliferation, cell cycle arrest at the G0/G1 phase, apoptotic cell death, and decreased spheroid formation. The anticancer effects induced by YTHDF1 knockout were reversed by AURKA overexpression. Similarly, the knockout of PIN1 produced comparable anticancer effects to those observed in YTHDF1-knockout cells, and these effects were reversed upon overexpression of YTHDF1. In conclusion, the findings of our study suggest that increased YTHDF1 stability induced by PIN1 promotes breast tumorigenesis via the stabilization of AURKA mRNA. Targeting the PIN1/YTHDF1 axis may represent a novel therapeutic strategy for breast cancer.

Sirtuin 5-mediated deacetylation of TAZ at K54 promotes melanoma development.

PURPOSE: Nuclear accumulation of YAP/TAZ promotes tumorigenesis in several cancers, including melanoma. Although the mechanisms underlying the nuclear retention of YAP are known, those underlying the retention of TAZ remain unclear. Our study investigates a novel acetylation/deacetylation switch in TAZ, governing its subcellular localization in melanoma tumorigenesis. METHODS: Immunoprecipitation/Western blot assessed TAZ protein interactions and acetylation. SIRT5 activity was quantified with enzyme-linked immunosorbent assay. Immunofluorescence indicated TAZ nuclear localization. TEAD transcriptional activity was measured through luciferase reporter assays. ChIP detected TAZ binding to the CTGF promoter. Transwell and wound healing assays quantified melanoma cell invasiveness and migration. Metastasis was evaluated using a mouse model via tail vein injections. Clinical relevance was explored via immunohistochemical staining of patient tumors. RESULTS: CBP facilitated TAZ acetylation at K54 in response to epidermal growth factor stimulation, while SIRT5 mediated deacetylation. Acetylation correlated with phosphorylation, regulating TAZ's binding with LATS2 or TEAD. TAZ K54 acetylation enhanced its S89 phosphorylation, promoting cytosolic retention via LATS2 interaction. SIRT5-mediated deacetylation enhanced TAZ-TEAD interaction and nuclear retention. Chromatin IP showed SIRT5-deacetylated TAZ recruited to CTGF promoter, boosting transcriptional activity. In a mouse model, SIRT5 overexpression induced melanoma metastasis to lung tissue following the injection of B16F10 melanocytes via the tail vein, and this effect was prevented by verteporfin treatment. CONCLUSIONS: Our study revealed a novel mechanism of TAZ nuclear retention regulated by SIRT5-mediated K54 deacetylation and demonstrated the significance of TAZ deacetylation in CTGF expression. This study highlights the potential implications of the SIRT5/TAZ axis for treating metastatic melanoma.

METTL3 stabilization by PIN1 promotes breast tumorigenesis via enhanced m6A-dependent translation.

Methyltransferase-like 3 (METTL3) is the catalytic subunit of the N6-adenosine methyltransferase complex responsible for N6-methyladenosine (m6A) modification of mRNA in mammalian cells. Although METTL3 expression is increased in several cancers, the regulatory mechanisms are unclear. We explored the regulatory roles of peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (PIN1) in METTL3 stability and m6A modification of mRNA. PIN1 interacted with METTL3 and prevented its ubiquitin-dependent proteasomal and lysosomal degradation. It stabilized METTL3, which increased the m6A modification of transcriptional coactivator with PDZ-binding motif (TAZ) and epidermal growth factor receptor (EGFR) mRNA, resulting in their efficient translation. PIN1 knockout altered the distribution of TAZ and EGFR mRNA from polysomes into monosomes. Inhibition of MEK1/2 kinases and PIN1 destabilized METTL3, which impeded breast cancer cell proliferation and induced cell cycle arrest at the G0/G1 phases. METTL3 knockout reduced PIN1 overexpression-induced colony formation in MCF7 cells and enhanced tumor growth in 4T1 cells in an orthotopic mouse model. In clinical settings, METTL3 expression significantly increased with tumor progression and was positively correlated with PIN1 expression in breast cancer tissues. Thus, PIN1 plays a regulatory role in mRNA translation, and the PIN1/METTL3 axis may be an alternative therapeutic target in breast cancer.

Regulation of m6A Methylome in Cancer: Mechanisms, Implications, and Therapeutic Strategies.

Reversible N6-adenosine methylation of mRNA, referred to as m6A modification, has emerged as an important regulator of post-transcriptional RNA processing. Numerous studies have highlighted its crucial role in the pathogenesis of diverse diseases, particularly cancer. Post-translational modifications of m6A-related proteins play a fundamental role in regulating the m6A methylome, thereby influencing the fate of m6A-methylated RNA. A comprehensive understanding of the mechanisms that regulate m6A-related proteins and the factors contributing to the specificity of m6A deposition has the potential to unveil novel therapeutic strategies for cancer treatment. This review provides an in-depth overview of our current knowledge of post-translational modifications of m6A-related proteins, associated signaling pathways, and the mechanisms that drive the specificity of m6A modifications. Additionally, we explored the role of m6A-dependent mechanisms in the progression of various human cancers. Together, this review summarizes the mechanisms underlying the regulation of the m6A methylome to provide insight into its potential as a novel therapeutic strategy for the treatment of cancer.

Regulation of Interleukin-36γ/IL-36R Signaling Axis by PIN1 in Epithelial Cell Transformation and Breast Tumorigenesis.

Given the increasing recognition of the relationship between IL-1 cytokines, inflammation, and cancer, the significance of distinct members of the IL-1 cytokine family in the etiology of cancer has been widely researched. In the present study, we investigated the underlying mechanism of the IL-36γ/IL-36R axis during breast cancer progression, which has not yet been elucidated. Initially, we determined the effects of IL-36γ on the proliferation and epithelial cell transformation of JB6 Cl41 mouse epidermal and MCF7 human breast cancer cells using BrdU incorporation and anchorage-independent growth assays. We found that treatment with IL-36γ increased the proliferation and colony formation of JB6 Cl41 and MCF7 cells. Analysis of the mechanism underlying the neoplastic cell transformation revealed that IL-36γ induced IL-36R-mediated phosphorylation of MEK1/2, ERK1/2, JNK1/2, and c-Jun, resulting in increased c-Fos, c-Jun, and AP-1 activities in JB6 Cl41 and MCF7 cells. Furthermore, the IL-36γ-induced tumorigenic capacity of MCF7 cells was considerably enhanced by PIN1, following MEK/ERK and JNK/c-Jun signaling. Interestingly, blocking PIN1 activity using juglone suppressed the IL-36γ-induced increase in the anchorage-independent growth of 4T1 metastatic mouse breast cancer cells. Finally, in a syngeneic mouse model, IL-36γ-induced tumor growth in the breast mammary gland was significantly inhibited following PIN1 knockout.

Potent Imidazothiazole-based Inhibitor of BRAF V600E Overcomes Acquired Resistance via Inhibition of RAF Dimerization in PLX4032-resistant Melanoma.

BACKGROUND/AIM: The B-raf proto-oncogene, serine/threonine kinase (BRAF) V600E mutation is frequent in patients with advanced melanoma. PLX4032, an inhibitor of BRAFV600E kinase, is effective for the treatment of melanoma in BRAF V600E-positive patients; however, resistance eventually develops due to paradoxical activation of the mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinases (ERK) pathway resulting from RAF dimerization. In this study, we investigated the inhibitory effects of a novel imidazothiazole-based compound, KS28, on RAF dimerization and resistance to PLX4032 in melanoma. MATERIALS AND METHODS: The effects of KS28 were examined by immunoblotting, cell viability, terminal deoxynucleotidyl transferase dUTP nick-end labeling, reporter-gene, and soft-agar assays. RESULTS: KS28 treatment inhibited RAF dimerization in PLX4032-resistant A375 (A375R) cells, leading to suppression of the MEK/ERK pathway. In addition, KS28 reduced activator protein 1 transactivation in A375R cells, reduced cell viability, and increased DNA fragmentation. Moreover, treatment with KS28 suppressed anchorage-independent growth of A375R cells. Similarly, in an orthotopic tumor xenograft model, KS28 treatment suppressed the growth of tumors formed by A375R cells in BALB/c mice. CONCLUSION: KS28 plays a vital role in overcoming PLX4032 resistance in melanoma by down-regulating the MEK/ERK pathway.

METTL3 induces PLX4032 resistance in melanoma by promoting m6A-dependent EGFR translation.

Acquired resistance often limits therapeutic efficacy of the BFAF (V600E) kinase inhibitor PLX4032 in patients with advanced melanoma. Epitranscriptomic modification of mRNAs by N6-methyladenosine (m6A) modification contributes to melanoma pathogenesis; however, its role in acquired PLX4032 resistance remains unexplored. Here, we showed that m6A methyltransferase METTL3 expression is upregulated in A375R cells, a PLX4032-resistant subline of A375 melanoma cells, compared with the parental cells. Moreover, METTL3 increased the m6A modification of epidermal growth factor receptor (EGFR) mRNA in A375R cells, which promoted its translation efficiency. In turn, increased EGFR expression facilitated rebound activation of the RAF/MEK/ERK pathway in A375R cells, inducing PLX4032 resistance. In contrast, knockout of METTL3 in A375R cells reduced EGFR expression and restored PLX4032 sensitivity. PLX4032 treatment following METTL3 knockout induced apoptosis and reduced colony formation in A375R cells and reduced A375R cell-derived tumor growth in BALB/c nude mice. These findings indicate that METTL3 promotes rebound activation of the RAF/MEK/ERK pathway through EGFR upregulation and highlight a critical role for METTL3-induced m6A modification in acquired PLX4032 resistance in melanoma, implicating METTL3 as a potential candidate for targeted chemotherapy.

Interleukin-34-CSF1R Signaling Axis Promotes Epithelial Cell Transformation and Breast Tumorigenesis.

IL-34 has been recently identified as a ligand for CSF1R that regulates various cellular processes including cell proliferation, survival, and differentiation. Although the binding of IL-34 to CSF1R modulates several cancer-driving signaling pathways, little is known about the role of IL-34/CSF1R signaling in breast cancer. Herein, we report that IL-34 induces epithelial cell transformation and breast tumorigenesis through activation of MEK/ERK and JNK/c-Jun pathways. IL-34 increased the phosphorylation of MEK1/2, ERK1/2, JNK1/2, and c-Jun through CSF1R in mouse skin epidermal JB6 C141 cells and human breast cancer MCF7 cells. IL-34 enhanced c-Fos and c-Jun promoter activity, resulting in increased AP-1 transactivation activity in JB6 Cl41 and MCF7 cells. Moreover, PIN1 enhanced IL-34-induced phosphorylation of MEK1/2, ERK1/2, JNK1/2, and c-Jun in JB6 Cl41 and MCF7 cells. Inhibition of PIN1 using juglone prevented the IL-34-induced transformation of JB6 C141 cells. Similarly, silencing of PIN1 reduced the IL-34-induced tumorigenicity of MCF7 cells. Consistent with these results, the synergistic model showed that treatment with juglone suppressed the IL-34-induced growth of tumors formed by 4T1 cells in BALB/c mice. Our study demonstrates the role of IL-34-induced MEK/ERK and JNK/c-Jun cascades in breast cancer and highlights the regulatory role of PIN1 in IL-34-induced breast tumorigenesis.

PIN1 facilitates ubiquitin-mediated degradation of serine/threonine kinase 3 and promotes melanoma development via TAZ activation.

The Hippo signaling pathway controls cellular processes including growth, homeostasis, and apoptosis. The kinase STK3 acts upstream in this pathway to activate LATS1/2 kinase, which phosphorylates and inactivates the transcriptional coactivators YAP/TAZ. The dysregulation of Hippo signaling leads to human diseases including cancer; however, the molecular mechanisms underlying its dysregulation in melanoma are unknown. We aimed to determine the role of the PIN1 in Hippo signaling dysregulation and melanoma tumorigenesis. We report that PIN1 interacts with STK3 and induces ubiquitination-dependent proteasomal degradation of STK3. Furthermore, PIN1 plays a critical role in the nuclear translocation of TAZ, which forms a complex with TEAD to increase CTGF expression. PIN1 ablation blocks TAZ/TEAD complex formation and decreases CTGF expression. PIN1-mediated STK3 degradation is associated with enhanced cell growth, induction of cell transformation, and increased tumorigenicity. In clinical context, PIN1 and STK3 levels are inversely correlated in patient melanoma tissues. These findings indicate that PIN1-mediated STK3 destabilization contributes to the dysregulation of Hippo signaling, leading to oncogenic signaling and melanoma tumorigenesis. Our data suggest that inhibition of the PIN1-STK3 axis could be a novel treatment strategy for malignant melanoma.

Novel Imidazo[2,1-b]oxazole Derivatives Inhibit Epithelial Cell Transformation and Triple Negative Breast Cancer Tumorigenesis.

BACKGROUND/AIM: Triple negative breast cancer (TNBC) is an aggressive type of breast cancer with limited targets for chemotherapy. This study evaluated the inhibitory effects of novel imidazo[2,1-b]oxazole-based rapidly accelerated fibrosarcoma (RAF) inhibitors, KIST0215-1 and KIST0215-2, on epithelial cell transformation and TNBC tumorigenesis. MATERIALS AND METHODS: Immunoblotting, BrdU incorporation assay, reporter gene assay, and soft agar assay analyses were performed. In vivo effects were studied using the BALB/c mouse xenograft model. RESULTS: KIST0215-1 and KIST0215-2 inhibited the RAFs-MEK1/2-ERK1/2 signalling pathway induced by EGF in MDA-MB-231 cells, which inhibited c-fos transcriptional activity and activator protein-1 transactivation activity. KIST0215-1 and KIST0215-2 also prevented neoplastic transformation of JB6 C141 mouse epidermal cells induced by EGF and consistently suppressed the growth of tumours formed by 4T1 cells in BALB/c mice. CONCLUSION: Inhibition of RAF kinases using KIST0215-1 and KIST0215-2 is a promising chemotherapeutic strategy to treat TNBC.

All-trans Retinoic Acid Overcomes Acquired Resistance to PLX4032 via Inhibition of PIN1 in Melanoma Cells.

BACKGROUND/AIM: PLX4032 is commonly used in the treatment of advanced melanoma patients with BRAF-V600E mutation. The aim of this study was to elucidate the mechanisms by which up-regulation of PIN1 confers PLX4032 resistance in melanoma. MATERIALS AND METHODS: The expression of PIN1 as well as the cytotoxic effects of combinatorial treatment of PLX4032 and all-trans retinoic acid (ATRA) were investigated by immunoblotting, MTT assay, TUNEL assay, and soft agar assay. RESULTS: PIN1 expression is up-regulated in A375R cells, a PLX4032-resistant subline of melanoma cells generated from an A375 cell line, compared to parental A375 cells. Indeed, PIN1 positively regulated the expression of EGFR in A375R cells and led to activation of the RAF/MEK/ERK pathway. Importantly, PLX4032, when used in combination with ATRA, an inhibitor of PIN1, reduced EGFR expression, and consequently reduced cell viability and anchorage-independent growth of A375R cells compared to PLX4032 alone. Furthermore, co-treatment with ATRA and PLX4032 increased cleaved PARP and DNA fragmentation in A375R cells. CONCLUSION: PIN1 plays an important role in the development of PLX4032 resistance through up-regulation of EGFR expression.

Peptidyl-prolyl cis/trans isomerase NIMA-interacting 1 as a molecular target in breast cancer: a therapeutic perspective of gynecological cancer.

Peptidyl-prolyl cis/trans isomerase NIMA-interacting 1 (PIN1) induces conformational and functional changes to numerous key signaling molecules following proline-directed phosphorylation and its deregulation contributes to disease, particularly cancer. PIN1 is overexpressed in breast cancer, promoting cell proliferation and transformation in collaboration with several oncogenic signaling pathways, and is correlated with a poor clinical outcome. PIN1 level is also increased in certain gynecological cancers such as cervical, ovarian, and endometrial cancers. Although women with breast cancer are at risk of developing a second primary gynecological malignancy, particularly of the endometrium and ovary, the common oncogenic signaling pathway mediated by PIN1 has not been noted to date. This review discusses the roles of PIN1 in breast tumorigenesis and gynecological cancer progression, as well as the clinical effect of targeting this enzyme in breast and gynecological cancers.