Focal-adhesion kinase regulates the sialylation of N-glycans via the PI4KIIα-PI4P pathway

Glycosylation in neurodevelopment: What oncology teaches?

Neurodevelopment is a highly complex process, sensitive to a multitude of signaling pathways linked to molecular processes involved in neuronal development and function, metabolism, and immune functions. Key pathways include cell-cycle regulation (PI3K/Akt/mTOR, p53/PTEN), JAK-STAT, Notch, SLIT/Robo, epithelial-mesenchymal transition (EMT) and cellular homeostasis processes such as apoptosis, autophagy and hypoxia. Transcription regulation (including histone and epigenetic regulation) and immune regulation (NF-kB, Toll-like receptors (TLRs)) play a crucial role. Glycosylation abnormalities related to these molecular processes have been described in cancer. However, while cancer research and therapies have been revolutionized by the study of glycosylation, mechanistic insights and therapeutic approaches are still struggling to develop in neurodevelopmental pathologies. This study is a blueprint to unravel the key pathological pathways in neurodevelopment by highlighting the benefits of studying the associated regulatory processes of glycosylation, which have led to major advances in cancer research.

Inhibitory effects of β-galactoside α2,6-sialyltransferase 1 on the Hippo pathway in breast cancer cells

The Hippo signaling pathway is crucial in pathological functions such as tumors. Yes-associated protein (YAP), a well-known downstream effector of the Hippo pathway, has been intensively studied; emerging evidence suggests that multiple cell membrane receptors can regulate the Hippo pathway. However, the mechanistic roles of these upstream pathways remain largely unknown. Here, we identified the β-galactoside α2,6-sialyltransferase 1 (ST6GAL1) catalyzed α2,6-sialylation as a pivotal upstream modulator of Hippo pathway by a glycosyltransferases (GTs) overexpression sub-library screening. Depletion of ST6GAL1 results in increased phosphorylation of LATS1 and YAP, which induces YAP's nuclear localization, transcriptional activity, and multiple biological functions in breast cancer cells, including cell adhesion, spreading, growth, migration, and metastasis. These phenotypes were majorly due to the altered signal transduction of cell surface receptors, as deletion of ST6GAL1 exhibited attenuated GPCR, EGFR, and Integrins response and suppression of dephosphorylation of YAP. Mechanistically, these representative membrane receptors are α2,6-sialylated proteins, and their α2,6-sialylation could be inhibited by β-galactoside α2,3-sialyltransferase 4 (ST3GAL4) via substrate competition. In addition, the α2,6-sialylation is essential for Integrin β1-EGFR/LPAR4 complex formation. Altogether, our findings demonstrate ST6GAL1 is an upstream negative regulator of the Hippo pathway in breast cancer cells, providing a new insight into the regulation between N-glycosylation and Hippo signaling.

GOLPH3-mTOR Crosstalk and Glycosylation: A Molecular Driver of Cancer Progression

Originally identified in proteomic-based studies of the Golgi, Golgi phosphoprotein 3 (GOLPH3) is a highly conserved protein from yeast to humans. GOLPH3 localizes to the Golgi through the interaction with phosphatidylinositol-4-phosphate and is required for Golgi architecture and vesicular trafficking. Many studies revealed that the overexpression of GOLPH3 is associated with tumor metastasis and a poor prognosis in several cancer types, including breast cancer, glioblastoma multiforme, and colon cancer. The purpose of this review article is to provide the current progress of our understanding of GOLPH3 molecular and cellular functions, which may potentially reveal therapeutic avenues to inhibit its activity. Specifically, recent papers have demonstrated that GOLPH3 protein functions as a cargo adaptor for COP I-coated intra Golgi vesicles and impinges on Golgi glycosylation pathways. In turn, GOLPH3-dependent defects have been associated with malignant phenotypes in cancer cells. Additionally, the oncogenic activity of GOLPH3 has been linked with enhanced signaling downstream of mechanistic target of rapamycin (mTOR) in several cancer types. Consistent with these data, GOLPH3 controls organ growth in Drosophila by associating with mTOR signaling proteins. Finally, compelling evidence demonstrates that GOLPH3 is essential for cytokinesis, a process required for the maintenance of genomic stability.

O-GlcNAcylation of Focal Adhesion Kinase Regulates Cell Adhesion, Migration, and Proliferation via the FAK/AKT Pathway

Focal Adhesion Kinase (FAK) is a non-receptor tyrosine kinase pivotal in cellular signal transduction, regulating cell adhesion, migration, growth, and survival. However, the regulatory mechanisms of FAK during tumorigenesis and progression still need to be fully understood. Our previous study demonstrated that O-GlcNAcylation regulates integrin-mediated cell adhesion. To further elucidate the underlying molecular mechanism, we focused on FAK in this study and purified it from 293T cells. Using liquid chromatography-mass spectrometry (LC-MS/MS), we identified the O-GlcNAcylation of FAK at Ser708, Thr739, and Ser886. Compared with wild-type FAK expressed in FAK-knockout 293T cells, the FAK mutant, in which Ser708, Thr739, and Ser886 were replaced with Ala, exhibited lower phosphorylation levels of Tyr397 and AKT. Cell proliferation and migration, assessed through MTT and wound healing assays, were significantly suppressed in the FAK mutant cells compared to the wild-type FAK cells. Additionally, the interaction among FAK, paxillin, and talin was enhanced, and cell adhesion was increased in the mutant cells. These data indicate that specific O-GlcNAcylation of FAK plays a critical regulatory role in integrin-mediated cell adhesion and migration. This further supports the idea that O-GlcNAcylation is essential for tumorigenesis and progression and that targeting the O-GlcNAcylation of FAK could offer a promising therapeutic strategy for cancer treatment.

Specific sialylation of N-glycans and its novel regulatory mechanism

Altered glycosylation is a common feature of cancer cells. Some subsets of glycans are found to be frequently enriched on the tumor cell surface and implicated in different tumor phenotypes. Among these, changes in sialylation have long been associated with metastatic cell behaviors such as invasion and enhanced cell survival. Sialylation typically exists in three prominent linkages: α2,3, α2,6, and α2,8, catalyzed by a group of sialyltransferases. The aberrant expression of all three linkages has been related to cancer progression. The increased α2,6 sialylation on N-glycans catalyzed by β-galactoside α2,6 sialyltransferase 1 (ST6Gal1) is frequently observed in many cancers. In contrast, functions of α2,3 sialylation on N-glycans catalyzed by at least three β-galactoside α2,3-sialyltransferases, ST3Gal3, ST3Gal4, and ST3Gal6 remain elusive due to a possibility of compensating for one another. In this minireview, we briefly describe functions of sialylation and recent findings that different α2,3 sialyltransferases specifically modify target proteins, as well as sialylation regulatory mechanisms vis a complex formation among integrin α3β1, Golgi phosphoprotein 3 (GOLPH3), phosphatidylinositol 4-kinase IIα (PI4KIIα), focal adhesion kinase (FAK) and sialyltransferase, which suggests a new concept for the regulation of glycosylation in cell biology.

Novel regulatory mechanisms of N-glycan sialylation: Implication of integrin and focal adhesion kinase in the regulation

BACKGROUND

Sialylation of glycoproteins, including integrins, is crucial in various cancers and diseases such as immune disorders. These modifications significantly impact cellular functions and are associated with cancer progression. Sialylation, catalyzed by specific sialyltransferases (STs), has traditionally been considered to be regulated at the mRNA level.

SCOPE OF REVIEW

Recent research has expanded our understanding of sialylation, revealing ST activity changes beyond mRNA level variations. This includes insights into COPI vesicle formation and Golgi apparatus maintenance and identifying specific target proteins of STs that are not predictable through recombinant enzyme assays.

MAJOR CONCLUSIONS

This review summarizes that Golgi-associated pathways largely influence the regulation of STs. GOLPH3, GORAB, PI4K, and FAK have become critical elements in sialylation regulation. Some STs have been revealed to possess specificity for specific target proteins, suggesting the presence of additional, enzyme-specific regulatory mechanisms.

GENERAL SIGNIFICANCE

This study enhances our understanding of the molecular interplay in sialylation regulation, mainly focusing on the role of integrin and FAK. It proposes a bidirectional system where sialylations might influence integrins and vice versa. The diversity of STs and their specific linkages offer new perspectives in cancer research, potentially broadening our understanding of cellular mechanisms and opening avenues for new therapeutic approaches in targeting sialylation pathways.

An emerging role of N-glycosylation in cancer chemoresistance

Chemoresistance poses a significant obstacle in the effective treatment of cancer, limiting the success of chemotherapy regimens. N-glycosylation, the most important post-translational modification (PTM), plays multifaceted roles in the intricate landscape of cancer progression, particularly drug resistance in cancer cells. This review explores the complex relationship between N-glycosylation and chemoresistance in cancer. Altered glycosylation patterns have been proven to impact drug efflux mechanisms in cancer cells, which can further influence the intracellular concentration of chemotherapy drugs. Moreover, N-glycosylation also plays a regulatory role in cell signaling pathways and apoptosis regulators, continuously affecting the stemness and survival of cancer cells under the selective pressure of chemotherapy. Additionally, the impact of the tumor microenvironment on glycosylation patterns adds complexity to this interplay. This review discusses current research findings, challenges, and future directions based on the roles of N-glycosylation in cancer chemoresistance, emphasizing the potential for targeted therapeutic interventions to enhance the effectiveness of chemotherapy and improve patient outcomes.

Roles and inhibitors of FAK in cancer: current advances and future directions

Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase that exhibits high expression in various tumors and is associated with a poor prognosis. FAK activation promotes tumor growth, invasion, metastasis, and angiogenesis via both kinase-dependent and kinase-independent pathways. Moreover, FAK is crucial for sustaining the tumor microenvironment. The inhibition of FAK impedes tumorigenesis, metastasis, and drug resistance in cancer. Therefore, developing targeted inhibitors against FAK presents a promising therapeutic strategy. To date, numerous FAK inhibitors, including IN10018, defactinib, GSK2256098, conteltinib, and APG-2449, have been developed, which have demonstrated positive anti-tumor effects in preclinical studies and are undergoing clinical trials for several types of tumors. Moreover, many novel FAK inhibitors are currently in preclinical studies to advance targeted therapy for tumors with aberrantly activated FAK. The benefits of FAK degraders, especially in terms of their scaffold function, are increasingly evident, holding promising potential for future clinical exploration and breakthroughs. This review aims to clarify FAK's role in cancer, offering a comprehensive overview of the current status and future prospects of FAK-targeted therapy and combination approaches. The goal is to provide valuable insights for advancing anti-cancer treatment strategies.