Estrogen Regulates Scribble Localization in Endometrial Epithelial Cells Through Acyl Protein Thioesterase (APT)-Mediated S-Palmitoylation in Adenomyosis

Despite its prevalence and the severity of symptoms, little is known about the pathogenesis and etiology of adenomyosis. In our previous study, Scribble localization has been found to be partially translocated to cytoplasm; however, its regulatory mechanism is known. In consideration of the important role of supraphysiologic estrogen production in the endometrium in the development of adenomyosis, we analyzed the effect and mechanism of estrogen on Scribble localization in vivo and in vitro. Firstly, we found Scribble translocation from the basolateral membrane to the cytoplasm was easily to be seen in women and mice with adenomyosis (68% vs 27%, 60% vs 10% separately). After treatment with the S-palmitoylation inhibitor 2-bromopalmitate for 48H, cytoplasmic enrichment of Scribble and the reduced level of palm-Scribble was observed by immunofluorescence, Western blot, and acyl-biotin exchange palmitoylation assay. High estrogen exposure could not only induce partially cytoplasmic translocation of Scribble but also decrease the expression level of palm-Scribble, which can be recovered by estrogen receptor inhibitor ICI182,780. Based on following experiments, we found that estrogen regulated Scribble localization by APT through S-palmitoylation of Scribble protein. At last, IHC was performed to verify the expression of APT1 and APT2 in human clinical tissue specimens and found that they were all increased dramatically. Furthermore, positive correlations were found between APT1 or APT2 and aromatase P450. Therefore, our research may provide a new understanding of the pathogenesis of adenomyosis.

S-Palmitoylation of the serotonin transporter promotes its cell surface expression and serotonin uptake

The neurotransmitter serotonin (5-HT) is transported back into serotonergic neurons by the serotonin transporter (SERT). SERT is a main target of antidepressants, and much effort has therefore focused on finding relationships between SERT and depression. However, it is not fully understood how SERT is regulated at the cellular level. Here, we report post-translational regulation of SERT by S-palmitoylation, in which palmitate is covalently attached to cysteine residues of proteins. Using AD293 cells (a human embryonic kidney 293-derived cell line with improved cell adherence) transiently transfected with FLAG-tagged human SERT, we observed S-palmitoylation of immature SERT containing high-mannose type N-glycans or no N-glycan, which is presumed to be localized in the early secretory pathway, such as the endoplasmic reticulum. Mutational analysis by alanine substitutions shows that S-palmitoylation of immature SERT occurs at least at Cys-147 and Cys-155, juxtamembrane cysteine residues within the first intracellular loop. Furthermore, mutation of Cys-147 reduced cellular uptake of a fluorescent SERT substrate that mimics 5-HT without decreasing SERT on the cell surface. On the other hand, combined mutation of Cys-147 and Cys-155 inhibited SERT surface expression and reduced the uptake of the 5-HT mimic. Thus, S-palmitoylation of Cys-147 and Cys-155 is important for both the cell surface expression and 5-HT uptake capacity of SERT. Given the importance of S-palmitoylation in brain homeostasis, further investigation of SERT S-palmitoylation could provide new insights into the treatment of depression.

ZDHHC12-mediated claudin-3 S-palmitoylation determines ovarian cancer progression

The membrane protein claudin-3 (CLDN3) is critical for the formation and maintenance of tight junction and its high expression has been implicated in dictating malignant progression in various cancers. However, the post-translational modification of CLDN3 and its biological function remains poorly understood. Here, we report that CLDN3 is positively correlated with ovarian cancer progression both in vitro and in vivo. Of interest, CLDN3 undergoes S-palmitoylation on three juxtamembrane cysteine residues, which contribute to the accurate plasma membrane localization and protein stability of CLDN3. Moreover, the deprivation of S-palmitoylation in CLDN3 significantly abolishes its tumorigenic promotion effect in ovarian cancer cells. By utilizing the co-immunoprecipitation assay, we further identify ZDHHC12 as a CLDN3-targating palmitoyltransferase from 23 ZDHHC family proteins. Furthermore, the knockdown of ZDHHC12 also significantly inhibits CLDN3 accurate membrane localization, protein stability and ovarian cancer cells tumorigenesis. Thus, our work reveals S-palmitoylation as a novel regulatory mechanism that modulates CLDN3 function, which implies that targeting ZDHHC12-mediated CLDN3 S-palmitoylation might be a potential strategy for ovarian cancer therapy.

Determination of Protein S-Acylation State by Enhanced Acyl-Switch Methods

S-Acylation is increasingly being recognized as an important dynamic posttranslational modification of cysteine residues in proteins. Various approaches have been described for assaying protein S-acylation with acyl-switch approaches being the most common and accessible. However, these approaches can be time-consuming with low reproducibility as a result of multiple protein precipitation/resuspension cleanup steps. Here we present a faster, cleaner, and more sensitive acyl-switch approach for detecting the S-acylation state of any protein, from any cell or tissue type, that can be detected by western blotting. In the case of acyl-RAC, the procedure is now performed without protein precipitation, greatly increasing speed and improving sample handling in the assay. This also allows for more samples to be processed simultaneously and opens the way for medium-throughput assays. Overall, maleimide scavenging improves the reliability of determination and quantification of protein S-acylation state by acyl-switch methods.

Measuring S-Depalmitoylation Activity In Vitro and In Live Cells with Fluorescent Probes

S-palmitoylation is a reversible lipid posttranslational modification (PTM) that can mediate protein localization, trafficking, interaction with membranes, and a host of other biophysical characteristics. Over the past decade, a suite of chemoproteomic strategies have uncovered the breadth of S-palmitoylation, revealing widespread susceptibility to modification by this PTM throughout the human proteome. A focal point of research toward understanding the role of S-palmitoylation in varied cellular processes has focused on understanding how "writer" and "eraser" proteins function together to control the levels of S-palmitoylation of target proteins. The spatial and temporal regulation of S-palmitoylation by its "erasers"-acyl protein thioesterases (APTs)-is not fully understood. Tools which enable monitoring of the activity levels of the APTs in real-time in live cells illuminate how spatial control of these enzymes redecorate the lipidation state of the local proteome. To this end, we have developed fluorescence-based depalmitoylation probes (DPPs), which report S-depalmitoylase activity in live cells. Using DPPs, we have demonstrated that S-depalmitoylase activity changes in response to growth factor stimulation, unveiling potential regulation of cell growth and metabolism by APTs. Additionally, we recently discovered APTs in mitochondria using targeted DPPs, indicating new roles for S-depalmitoylation in this critical cellular compartment. Here, we present detailed protocols on how to carry out in vitro S-depalmitoylase activity assays and live cell fluorescence imaging employing the growing DPP toolbox.

Decreased protein S-palmitoylation in dorsolateral prefrontal cortex in schizophrenia

Recent reports suggest abnormalities of neurotransmitter receptor trafficking, targeting, dendritic localization, recycling, and degradation in the brain in schizophrenia. We hypothesized that a potential explanation for these findings may be abnormal posttranslational modifications that influence intracellular targeting and trafficking of proteins between subcellular compartments. Dysregulation of protein palmitoylation is a strong candidate for such a process. S-palmitoylation is a reversible thioesterification of palmitoyl-groups to cysteine residues that can regulate trafficking and targeting of intracellular proteins. Using a biotin switch assay to study S-palmitoylation of proteins in human postmortem brain, we identified a pattern of palmitoylated proteins that cluster into 17 bands of discrete molecular masses, including numerous proteins associated with receptor signal transduction. Using mass spectrometry, we identified 219 palmitoylated proteins in human frontal cortex, and individually validated palmitoylation status of a subset of these proteins. Next, we assayed protein palmitoylation in dorsolateral prefrontal cortex from 16 schizophrenia patients and paired comparison subjects. S-palmitoylation was significantly reduced for proteins in most of the 17 schizophrenia bands. In rats chronically treated with haloperidol, the same pattern of palmitoylation was observed but the extent of palmitoylation was unchanged, suggesting that the diminution in protein palmitoylation in schizophrenia is not due to chronic antipsychotic treatment. These results indicate there are changes in the extent of S-palmitoylation of many proteins in the frontal cortex in schizophrenia. Given the roles of this posttranslational modification, these data suggest a potential mechanism reconciling previous observations of abnormal intracellular targeting and trafficking of neurotransmitter receptors in this illness.