Flotillin-1 palmitoylation turnover by APT-1 and ZDHHC-19 promotes cervical cancer progression by suppressing IGF-1 receptor desensitization and proteostasis

Metabolic Signaling in Cancer Metastasis

Metastases, which are the leading cause of death in patients with cancer, have metabolic vulnerabilities. Alterations in metabolism fuel the energy and biosynthetic needs of metastases but are also needed to activate cell state switches in cells leading to invasion, migration, colonization, and outgrowth in distant organs. Specifically, metabolites can activate protein kinases as well as receptors and they are crucial substrates for posttranslational modifications on histone and nonhistone proteins. Moreover, metabolic enzymes can have moonlighting functions by acting catalytically, mainly as protein kinases, or noncatalytically through protein-protein interactions. Here, we summarize the current knowledge on metabolic signaling in cancer metastasis.

SIGNIFICANCE

Effective drugs for the prevention and treatment of metastases will have an immediate impact on patient survival. To overcome the current lack of such drugs, a better understanding of the molecular processes that are an Achilles heel in metastasizing cancer cells is needed. One emerging opportunity is the metabolic changes cancer cells need to undergo to successfully metastasize and grow in distant organs. Mechanistically, these metabolic changes not only fulfill energy and biomass demands, which are often in common between cancer and normal but fast proliferating cells, but also metabolic signaling which enables the cell state changes that are particularly important for the metastasizing cancer cells.

Caveolin-2 palmitoylation turnover facilitates insulin receptor substrate-1-directed lipid metabolism by insulin receptor tyrosine kinase

Here, we show that insulin induces palmitoylation turnover of Caveolin-2 (Cav-2) in adipocytes. Acyl protein thioesterases-1 (APT1) catalyzes Cav-2 depalmitoylation, and zinc finger DHHC domain-containing protein palmitoyltransferase 21 (ZDHHC21) repalmitoylation of the depalmitoylated Cav-2 for the turnover, thereby controlling insulin receptor (IR)-Cav-2-insulin receptor substrate-1 (IRS-1)-Akt-driven signaling. Insulin-induced palmitoylation turnover of Cav-2 facilitated glucose uptake and fat storage through induction of lipogenic genes. Cav-2-, APT1-, and ZDHHC21-deficient adipocytes, however, showed increased induction of lipolytic genes and glycerol release. In addition, white adipose tissues from insulin sensitive and resistant obese patients exhibited augmented expression of LYPLA1 (APT1) and ZDHHC20 (ZDHHC20). Our study identifies the specific enzymes regulating Cav-2 palmitoylation turnover, and reveals a new mechanism by which insulin-mediated lipid metabolism is controlled in adipocytes.

Depalmitoylation and cell physiology: APT1 as a mediator of metabolic signals

More than half of the global population is obese or overweight, especially in Western countries, and this excess adiposity disrupts normal physiology to cause chronic diseases. Diabetes, an adiposity-associated epidemic disease, affects >500 million people, and cases are projected to exceed 1 billion before 2050. Lipid excess can impact physiology through the posttranslational modification of proteins, including the reversible process of S-palmitoylation. Dynamic palmitoylation cycling requires the S-acylation of proteins by acyltransferases and the depalmitoylation of these proteins mediated in part by acyl-protein thioesterases (APTs) such as APT1. Emerging evidence points to tissue-specific roles for the depalmitoylase APT1 in maintaining homeostasis in the vasculature, pancreatic islets, and liver. These recent findings raise the possibility that APT1 substrates can be therapeutically targeted to treat the complications of metabolic diseases.

Flotillin-1 palmitoylation is essential for its stability and subsequent tumor promoting capabilities

Flotillin-1 contributes to invasion and metastasis in triple negative breast cancer (TNBC) and is modified post-translationally through palmitoylation. Palmitoylation, the process of conjugating palmitoyl-CoA to proteins, plays an essential role in protein stability and trafficking. Thus far, there has not been any investigation into the role of flotillin-1 palmitoylation in the context of metastasis in vivo. To address the role of flotillin-1 palmitoylation in metastasis, MDA-MB-231 cells expressing palmitoylation defective flotillin-1 constructs were used as models. Compared to flotillin-1 WT expressing tumors, flotillin-1 palmitoylation defective displayed abrogated tumor progression and lung metastasis in vivo in both spontaneous and experimental models. Further mechanistic investigation led to the identification of zDHHC5 as the main palmitoyl acyltransferase responsible for palmitoylating endogenous flotillin-1. Modulation of flotillin-1 palmitoylation status through mutagenesis, zDHHC5 silencing, and 2-bromopalmitate inhibition all resulted in the proteasomal degradation of flotillin-1 protein. To assess if flotillin-1 palmitoylation can be inhibited for potential clinical relevance, we designed a competitive peptide fused to a cell penetrating peptide sequence, which displayed efficacy in blocking flotillin-1 palmitoylation in vitro without altering palmitoylation of other zDHHC5 substrates, highlighting its specificity. Additionally, TNBC xenograft tumor models expressing a doxycycline inducible flotillin-1 palmitoylation inhibiting peptide displayed attenuated tumor growth and lung metastasis. Collectively, these results reveal a novel palmitoylation dependent mechanism which is essential for the stability of flotillin-1 protein. More specifically, disruption of flotillin-1 palmitoylation through mutagenesis or competitive peptide promoted flotillin-1 protein degradation, subsequently impeding its tumor promoting and metastasis-inducing effects in TNBC tumor models.

ZDHHC5-mediated S-palmitoylation of FAK promotes its membrane localization and epithelial-mesenchymal transition in glioma

BACKGROUND

Abnormal activation of FAK is associated with tumor development and metastasis. Through interactions with other intracellular signalling molecules, FAK influences cytoskeletal remodelling, modulation of adhesion signalling, and activation of transcription factors, promoting migration and invasion of tumor cells. However, the exact mechanism that regulates these processes remains unresolved. Herein, our findings indicate that the S-palmitoylation of FAK is crucial for both its membrane localization and activation.

METHODS

The palmitoylation of FAK in U251 and T98G cells was assessed by an acyl-PEG exchange (APE) assay and a metabolic incorporation assay. Cellular palmitoylation was inhibited using 2-bromopalmitate, and the palmitoylation status and cellular localization of FAK were determined. A metabolic incorporation assay was used to identify the potential palmitoyl acyltransferase and the palmitoylation site of FAK. Cell Counting Kit-8 (CCK8) assays, colony formation assays, and Transwell assays were conducted to assess the impact of ZDHHC5 in GBM. Additionally, intracranial GBM xenografts were utilized to investigate the effects of genetically silencing ZDHHC5 on tumor growth.

RESULTS

Inhibiting FAK palmitoylation leads to its redistribution from the membrane to the cytoplasm and a decrease in its phosphorylation. Moreover, ZDHHC5, a protein-acyl-transferase (PAT), catalyzes this key modification of FAK at C456. Knockdown of ZDHHC5 abrogates the S-palmitoylation and membrane distribution of FAK and impairs cell proliferation, invasion, and epithelial-mesenchymal transition (EMT). Taken together, our research reveals the crucial role of ZDHHC5 as a PAT responsible for FAK S-palmitoylation, membrane localization, and activation.

CONCLUSIONS

These results imply that targeting the ZDHHC5/FAK axis has the potential to be a promising strategy for therapeutic interventions for glioblastoma (GBM). Video Abstract.

Diverse Roles of Protein Palmitoylation in Cancer Progression, Immunity, Stemness, and Beyond

Protein S-palmitoylation, a type of post-translational modification, refers to the reversible process of attachment of a fatty acyl chain-a 16-carbon palmitate acid-to the specific cysteine residues on target proteins. By adding the lipid chain to proteins, it increases the hydrophobicity of proteins and modulates protein stability, interaction with effector proteins, subcellular localization, and membrane trafficking. Palmitoylation is catalyzed by a group of zinc finger DHHC-containing proteins (ZDHHCs), whereas depalmitoylation is catalyzed by a family of acyl-protein thioesterases. Increasing numbers of oncoproteins and tumor suppressors have been identified to be palmitoylated, and palmitoylation is essential for their functions. Understanding how palmitoylation influences the function of individual proteins, the physiological roles of palmitoylation, and how dysregulated palmitoylation leads to pathological consequences are important drivers of current research in this research field. Further, due to the critical roles in modifying functions of oncoproteins and tumor suppressors, targeting palmitoylation has been used as a candidate therapeutic strategy for cancer treatment. Here, based on recent literatures, we discuss the progress of investigating roles of palmitoylation in regulating cancer progression, immune responses against cancer, and cancer stem cell properties.

Identifying prognostic markers in spatially heterogeneous breast cancer microenvironment

To gain deeper insights into the microenvironment of breast cancer, we utilized GeoMx Digital Spatial Profiling (DSP) technology to analyze transcripts from 107 regions of interest in 65 untreated breast cancer tissue samples. Our study revealed spatial heterogeneity in the expression of marker genes in tumor cell enriched, immune cell enriched, and normal epithelial areas. We evaluated a total of 55 prognostic markers in tumor cell enriched regions and 15 in immune cell enriched regions, identifying that tumor cell enriched regions had higher levels of follicular helper T cells, resting dendritic cells, and plasma cells than immune cell enriched regions, while the levels of resting CD4 memory in T cells and regulatory (Treg) T cells were lower. Additionally, we analyzed the heterogeneity of HLA gene families, immunological checkpoints, and metabolic genes in these areas. Through univariate Cox analysis, we identified 5 prognosis-related metabolic genes. Furthermore, we conducted immunostaining experiments, including EMILIN2, SURF4, and LYPLA1, to verify our findings. Our investigation into the spatial heterogeneity of the breast cancer tumor environment has led to the discovery of specific diagnostic and prognostic markers in breast cancer.