Bestatin inhibits cell growth, cell division, and spore cell differentiation in Dictyostelium discoideum. Eukaryot Cell. 2012;11:545-557. [PMID: 22345351 DOI: 10.1128/EC.05311-11]

Bestatin attenuates breast cancer stemness by targeting puromycin-sensitive aminopeptidase

Breast cancer is a prevalent malignant tumor among women with an increasing incidence rate annually. Breast cancer stem cells (BCSCs) are integral in impeding tumor advancement and addressing drug resistance. Bestatin serves as an adjuvant chemotherapy, triggering apoptosis in cancer cells. In this study, the effects of bestatin on sorted BCSCs from breast cancer cell lines have been studied. Our results indicated that bestatin inhibits the migration and proliferation of breast cancer cells by reducing the stemness of BCSCs both in vitro and in vivo. Puromycin-sensitive aminopeptidase is implicated in the process through the regulation of cell cycle, resulting in heightened cell apoptosis and diminished cell proliferation of BCSCs. Our study suggest that targeting cancer stem cell may offer a promising approach in breast cancer treatment, presenting noval therapeutic strategies for patients with breast cancer.

Zinc Transporters Serve as Prognostic Predictors and their Expression Correlates with Immune Cell Infiltration in Specific Cancer: A Pan-cancer Analysis

The disruption of zinc (Zn) homeostasis has been implicated in cancer development and progression through various signaling pathways. Maintaining intracellular zinc balance is crucial in the context of cancer. Human cells rely on two families of transmembrane transporters, SLC30A/ZNT and SLC39A/ZIP, to coordinate zinc homeostasis. While some ZNTs and ZIPs have been linked to cancer progression, limited information is available regarding the expression patterns of zinc homeostasis-related genes and their potential roles in predicting prognosis and developing therapeutic strategies for specific cancers. In this study, a systematic analysis was conducted to examine the expression of all genes from the SLC30A and SLC39A families at both mRNA and protein levels across different cancers. As a result, three SLC39A genes (SLC39A1, SLC39A4, and SLC39A8) were found to be significantly dysregulated in specific cancers, including cervical squamous cell carcinoma and endocervical adenocarcinoma (CESC), liver hepatocellular carcinoma (LIHC), pancreatic adenocarcinoma (PAAD), and kidney renal papillary cell carcinoma (KIRP). Moreover, the dysregulation of these genes was tightly associated with the prognosis of patients with those cancers. Furthermore, we found that the gene SLC39A8 exhibited the lowest mutation frequency in KIRP, whereas mutations in SLC39A4 were found to significantly impact overall survival (OS), disease-free (DF), and progress-free survival (PFS) in cancer patients, particularly in those with PAAD. Additionally, immune infiltration analysis revealed that SLC39A1, SLC39A4, and SLC39A8 may function as immune regulators in cancers. This provides new insights into understanding the complex relationship between zinc homeostasis and cancer progression.

Recent advance of clinically approved small-molecule drugs for the treatment of myeloid leukemia

Myeloid leukemia denotes a hematologic malignancy characterized by aberrant proliferation and impaired differentiation of blood progenitor cells within the bone marrow. Despite the availability of several treatment options, the clinical outlook for individuals afflicted with myeloid leukemia continues to be unfavorable, making it a challenging disease to manage. Over the past, substantial endeavors have been dedicated to the identification of novel targets and the advancement of enhanced therapeutic modalities to ameliorate the management of this disease, resulting in the discovery of many clinically approved small-molecule drugs for myeloid leukemia, including histone deacetylase inhibitors, hypomethylating agents, and tyrosine kinase inhibitors. This comprehensive review succinctly presents an up-to-date assessment of the application and synthetic routes of clinically sanctioned small-molecule drugs employed in the treatment of myeloid leukemia. Additionally, it provides a concise exploration of the pertinent challenges and prospects encompassing drug resistance and toxicity. Overall, this review effectively underscores the considerable promise exhibited by clinically endorsed small-molecule drugs in the therapeutic realm of myeloid leukemia, while concurrently shedding light on the prospective avenues that may shape the future landscape of drug development within this domain.

Parasite Metalo-aminopeptidases as Targets in Human Infectious Diseases

BACKGROUND

Parasitic human infectious diseases are a worldwide health problem due to the increased resistance to conventional drugs. For this reason, the identification of novel molecular targets and the discovery of new chemotherapeutic agents are urgently required. Metalo- aminopeptidases are promising targets in parasitic infections. They participate in crucial processes for parasite growth and pathogenesis.

OBJECTIVE

In this review, we describe the structural, functional and kinetic properties, and inhibitors, of several parasite metalo-aminopeptidases, for their use as targets in parasitic diseases.

CONCLUSION

Plasmodium falciparum M1 and M17 aminopeptidases are essential enzymes for parasite development, and M18 aminopeptidase could be involved in hemoglobin digestion and erythrocyte invasion and egression. Trypanosoma cruzi, T. brucei and Leishmania major acidic M17 aminopeptidases can play a nutritional role. T. brucei basic M17 aminopeptidase down-regulation delays the cytokinesis. The inhibition of Leishmania basic M17 aminopeptidase could affect parasite viability. L. donovani methionyl aminopeptidase inhibition prevents apoptosis but not the parasite death. Decrease in Acanthamoeba castellanii M17 aminopeptidase activity produces cell wall structural modifications and encystation inhibition. Inhibition of Babesia bovis growth is probably related to the inhibition of the parasite M17 aminopeptidase, probably involved in host hemoglobin degradation. Schistosoma mansoni M17 aminopeptidases inhibition may affect parasite development, since they could participate in hemoglobin degradation, surface membrane remodeling and eggs hatching. Toxoplasma gondii M17 aminopeptidase inhibition could attenuate parasite virulence, since it is apparently involved in the hydrolysis of cathepsin Cs- or proteasome-produced dipeptides and/or cell attachment/invasion processes. These data are relevant to validate these enzymes as targets.

Interactions between the WEE-1.3 kinase and the PAM-1 aminopeptidase in oocyte maturation and the early C. elegans embryo

Puromycin-sensitive aminopeptidases are found across phyla and are known to regulate the cell-cycle and play a protective role in neurodegenerative disease. PAM-1 is a puromycin-sensitive aminopeptidase important for meiotic exit and polarity establishment in the one-cell Caenorhabditis elegans embryo. Despite conservation of this aminopeptidase, little is known about its targets during development. In order to identify novel interactors, we conducted a suppressor screen and isolated four suppressing mutations in three genes that partially rescued the maternal-effect lethality of pam-1 mutants. Suppressed strains show improved embryonic viability and polarization of the anterior–posterior axis. We identified a missense mutation in wee-1.3 in one of these suppressed strains. WEE-1.3 is an inhibitory kinase that regulates maturation promoting factor. Although the missense mutation suppressed polarity phenotypes in pam-1, it does so without restoring centrosome–cortical contact or altering the cortical actomyosin cytoskeleton. To see if PAM-1 and WEE-1.3 interact in other processes, we examined oocyte maturation. Although depletion of wee-1.3 causes sterility due to precocious oocyte maturation, this effect was lessened in pam-1 worms, suggesting that PAM-1 and WEE-1.3 interact in this process. Levels of WEE-1.3 were comparable between wild-type and pam-1 strains, suggesting that WEE-1.3 is not a direct target of the aminopeptidase. Thus, we have established an interaction between PAM-1 and WEE-1.3 in multiple developmental processes and have identified suppressors that are likely to further our understanding of the role of puromycin-sensitive aminopeptidases during development.

Calmodulin-mediated events during the life cycle of the amoebozoan Dictyostelium discoideum

This review focusses on the functions of intracellular and extracellular calmodulin, its target proteins and their binding proteins during the asexual life cycle of Dictyostelium discoideum. Calmodulin is a primary regulatory protein of calcium signal transduction that functions throughout all stages. During growth, it mediates autophagy, the cell cycle, folic acid chemotaxis, phagocytosis, and other functions. During mitosis, specific calmodulin-binding proteins translocate to alternative locations. Translocation of at least one cell adhesion protein is calmodulin dependent. When starved, cells undergo calmodulin-dependent chemotaxis to cyclic AMP generating a multicellular pseudoplasmodium. Calmodulin-dependent signalling within the slug sets up a defined pattern and polarity that sets the stage for the final events of morphogenesis and cell differentiation. Transected slugs undergo calmodulin-dependent transdifferentiation to re-establish the disrupted pattern and polarity. Calmodulin function is critical for stalk cell differentiation but also functions in spore formation, events that begin in the pseudoplasmodium. The asexual life cycle restarts with the calmodulin-dependent germination of spores. Specific calmodulin-binding proteins as well as some of their binding partners have been linked to each of these events. The functions of extracellular calmodulin during growth and development are also discussed. This overview brings to the forefront the central role of calmodulin, working through its numerous binding proteins, as a primary downstream regulator of the critical calcium signalling pathways that have been well established in this model eukaryote. This is the first time the function of calmodulin and its target proteins have been documented through the complete life cycle of any eukaryote.

Proteins of the Nucleolus of Dictyostelium discoideum: Nucleolar Compartmentalization, Targeting Sequences, Protein Translocations and Binding Partners

The nucleoli of Dictyostelium discoideum have a comparatively unique, non-canonical, localization adjacent to the inner nuclear membrane. The verified nucleolar proteins of this eukaryotic microbe are detailed while other potential proteins are introduced. Heat shock protein 32 (Hsp32), eukaryotic translation initiation factor 6 (eIF6), and tumour necrosis factor receptor-associated protein 1 (TRAP1) are essential for cell survival. NumA1, a breast cancer type 1 susceptibility protein-C Terminus domain-containing protein linked to cell cycle, functions in the regulation of nuclear number. The cell cycle checkpoint kinase 2 homologue forkhead-associated kinase A (FhkA) and BRG1-associated factor 60a homologue Snf12 are also discussed. While nucleoli appear homogeneous ultrastructurally, evidence for nucleolar subcompartments exists. Nucleolar localization sequences (NoLS) have been defined that target proteins to either the general nucleolar area or to a specific intranucleolar domain. Protein translocations during mitosis are protein-specific and support the multiple functions of the Dictyostelium nucleolus. To enrich the picture, binding partners of NumA1, the most well-characterized nucleolar protein, are examined: nucleolar Ca²⁺-binding protein 4a (CBP4a), nuclear puromycin-sensitive aminopeptidase A (PsaA) and Snf12. The role of Dictyostelium as a model for understanding the contribution of nucleolar proteins to various diseases and cellular stress is discussed throughout the review.

Progress in research of surface markers of liver cancer stem cells

In recent years, cancer stem cell theory, in which a tumor is considered to consist of a handful of tumor stem cells and most common tumor cells, has been put forward by many scientists, which helps researchers to understand cancer from a new perspective. Isolating tumor stem cells is based mainly on their markers and in this way, many kinds of cancer stem cell markers have been confirmed, including live cancer stem cells. Isolating and identifying live cancer stem cells will provide a new hope for curing cancer. This paper mainly discusses seven liver cancer stem cell surface markers and their clinical significance.

Extracellular matrix dynamics and functions in the social amoeba Dictyostelium: A critical review

BACKGROUND

The extracellular matrix (ECM) is a dynamic complex of glycoproteins, proteoglycans, carbohydrates, and collagen that serves as an interface between mammalian cells and their extracellular environment. Essential for normal cellular homeostasis, physiology, and events that occur during development, it is also a key functionary in a number of human diseases including cancer. The social amoeba Dictyostelium discoideum secretes an ECM during multicellular development that regulates multicellularity, cell motility, cell differentiation, and morphogenesis, and provides structural support and protective layers to the resulting differentiated cell types. Proteolytic processing within the Dictyostelium ECM leads to specific bioactive factors that regulate cell motility and differentiation.

SCOPE OF REVIEW

Here we review the structure and functions of the Dictyostelium ECM and its role in regulating multicellular development. The questions and challenges that remain and how they can be answered are also discussed.

MAJOR CONCLUSIONS

The Dictyostelium ECM shares many of the features of mammalian and plant ECM, and thus presents an excellent system for studying the structure and function of the ECM.

GENERAL SIGNIFICANCE

As a genetically tractable model organism, Dictyostelium offers the potential to further elucidate ECM functions, and to possibly reveal previously unknown roles for the ECM.

Aminopeptidase N inhibitor 4cc synergizes antitumor effects of 5-fluorouracil on human liver cancer cells through ROS-dependent CD13 inhibition

Aminopeptidase N (APN, also known as CD13) is involved in cellular processes of various types of tumors and a potential anti-cancer therapeutic target. Here, we report the effect of an APN inhibitor 4cc in enhancing sensitivity of hepatocellular carcinoma (HCC) cell lines and xenograft model in response to 5-fluorouracil (5-FU) in vivo and in vitro. The treatment of the combination of 4cc with 5-FU, compared to the combination of bestain with 5-FU, markedly suppressed cell growth and induced apoptosis of HCC cells, accompanying the increase in the level of reactive oxygen species (ROS) and followed by a decrease in the mitochondrial membrane potential (ΔΨM). Furthermore, the combination of 4cc and 5-FU showed a significant inhibitory effect on the growth of HCC xenograft tumors. In addition, following the treatment of 4cc, APN activity and clonogenic formation and the number of CD13-positive cells in PLC/PRF/5 cells were significantly decreased, suggesting that 4cc may also inhibit liver cancer stem cells by CD13 inhibition. These results showed that the APN inhibitor 4cc synergizes antitumor effects of 5-FU on human liver cancer cells via ROS-mediated drug resistance inhibition and concurrent activation of the mitochondrial pathways of apoptosis.

Essential Role for an M17 Leucine Aminopeptidase in Encystation of Acanthamoeba castellanii

Encystation of Acanthamoeba leads to the formation of resilient cysts from vegetative trophozoites. This process is essential for parasite survival under unfavorable conditions such as starvation, low temperatures, and exposure to biocides. During encystation, a massive turnover of intracellular components occurs, and a large number of organelles and proteins are degraded by proteases. Previous studies with specific protease inhibitors have shown that cysteine and serine proteases are involved in encystation of Acanthamoeba, but little is known about the role of metalloproteases in this process. Here, we have biochemically characterized an M17 leucine aminopeptidase of Acanthamoeba castellanii (AcLAP) and analyzed its functional involvement in encystation of the parasite. Recombinant AcLAP shared biochemical properties such as optimal pH, requirement of divalent metal ions for activity, substrate specificity for Leu, and inhibition profile by aminopeptidase inhibitors and metal chelators with other characterized M17 family LAPs. AcLAP was highly expressed at a late stage of encystation and mainly localized in the cytoplasm of A. castellanii. Knockdown of AcLAP using small interfering RNA induced a decrease of LAP activity during encystation, a reduction of mature cyst formation, and the formation of abnormal cyst walls. In summary, these results indicate that AcLAP is a typical M17 family enzyme that plays an essential role during encystation of Acanthamoeba.

Nucleocytoplasmic protein translocation during mitosis in the social amoebozoan Dictyostelium discoideum

Mitosis is a fundamental and essential life process. It underlies the duplication and survival of all cells and, as a result, all eukaryotic organisms. Since uncontrolled mitosis is a dreaded component of many cancers, a full understanding of the process is critical. Evolution has led to the existence of three types of mitosis: closed, open, and semi-open. The significance of these different mitotic species, how they can lead to a full understanding of the critical events that underlie the asexual duplication of all cells, and how they may generate new insights into controlling unregulated cell division remains to be determined. The eukaryotic microbe Dictyostelium discoideum has proved to be a valuable biomedical model organism. While it appears to utilize closed mitosis, a review of the literature suggests that it possesses a form of mitosis that lies in the middle between truly open and fully closed mitosis-it utilizes a form of semi-open mitosis. Here, the nucleocytoplasmic translocation patterns of the proteins that have been studied during mitosis in the social amoebozoan D. discoideum are detailed followed by a discussion of how some of them provide support for the hypothesis of semi-open mitosis.

The cyclin-dependent kinase family in the social amoebozoan Dictyostelium discoideum

Cyclin-dependent kinases (Cdk) are a family of serine/threonine protein kinases that regulate eukaryotic cell cycle progression. Their ability to modulate the cell cycle has made them an attractive target for anti-cancer therapies. Cdk protein function has been studied in a variety of Eukaryotes ranging from yeast to humans. In the social amoebozoan Dictyostelium discoideum, several homologues of mammalian Cdks have been identified and characterized. The life cycle of this model organism is comprised of a feeding stage where single cells grow and divide mitotically as they feed on their bacterial food source and a multicellular developmental stage that is induced by starvation. Thus it is a valuable system for studying a variety of cellular and developmental processes. In this review I summarize the current knowledge of the Cdk protein family in Dictyostelium by highlighting the research efforts focused on the characterization of Cdk1, Cdk5, and Cdk8 in this model Eukaryote. Accumulated evidence indicates that each protein performs distinct functions during the Dictyostelium life cycle with Cdk1 being required for growth and Cdk5 and Cdk8 being required for processes that occur during development. Recent studies have shown that Dictyostelium Cdk5 shares attributes with mammalian Cdk5 and that the mammalian Cdk inhibitor roscovitine can be used to inhibit Cdk5 activity in Dictyostelium. Together, these results show that Dictyostelium can be used as a model system for studying Cdk protein function.

Rad53 homologue forkhead-associated kinase A (FhkA) and Ca2+-binding protein 4a (CBP4a) are nucleolar proteins that differentially redistribute during mitosis in Dictyostelium

BACKGROUND

During mitosis most nucleolar proteins redistribute to other locales providing an opportunity to study the relationship between nucleolar protein localization and function. Dictyostelium is a model organism for the study of several fundamental biological processes and human diseases but only two nucleolar proteins have been studied during mitosis: NumA1 and Snf12. Both of them are linked to the cell cycle. To acquire a better understanding of nucleolar protein localization and dynamics in Dictyostelium we studied the nucleolar localization of two additional proteins during mitosis: Snf12-linked forkhead-associated kinase A (FhkA), which is involved in the cell cycle, and Ca2+-binding protein 4a (CBP4a), which is a binding partner of NumA1.

METHODS

Polyclonal antibodies were produced in-house. Cells were fixed and probed with either anti-FhkA or anti-CBP4a in order to determine cellular localization during interphase and throughout the stages of mitosis. Colocalization with DAPI nuclear stain allowed us to determine the location of the nucleus and nucleolus while colocalization with anti-α-tubulin allowed us to determine the cell cycle stage.

RESULTS

Here we verify two novel nucleolar proteins, Rad53 homologue FhkA which localized around the edge of the nucleolus and CBP4a which was detected throughout the entire nucleolus. Treatment with the Ca2+ chelator BAPTA (5 mM) showed that the nucleolar localization of CBP4a is Ca2+-dependent. In response to actinomycin D (0.05 mg/mL) CBP4a disappeared from the nucleolus while FhkA protruded from the nucleus, eventually pinching off as cytoplasmic circles. FhkA and CBP4a redistributed differently during mitosis. FhkA redistributed throughout the entire cell and at the nuclear envelope region from prometaphase through telophase. In contrast, during prometaphase CBP4a relocated to many large, discrete "CBP4a islands" throughout the nucleoplasm. Two larger "CBP4a islands" were also detected specifically at the metaphase plate region.

CONCLUSIONS

FhkA and CBP4a represent the sixth and seventh nucleolar proteins that have been verified to date in Dictyostelium and the third and fourth studied during mitosis. The protein-specific distributions of all of these nucleolar proteins during interphase and mitosis provide unique insight into nucleolar protein dynamics in this model organism setting the stage for future work.

Cyclin-dependent kinase 5 is a calmodulin-binding protein that associates with puromycin-sensitive aminopeptidase in the nucleus of Dictyostelium

Cyclin-dependent kinase 5 (Cdk5) is a serine/threonine kinase that has been implicated in a number of cellular processes. In Dictyostelium, Cdk5 localizes to the nucleus and cytoplasm, interacts with puromycin-sensitive aminopeptidase A (PsaA), and regulates endocytosis, secretion, growth, and multicellular development. Here we show that Cdk5 is a calmodulin (CaM)-binding protein (CaMBP) in Dictyostelium. Cdk5, PsaA, and CaM were all present in isolated nuclei and Cdk5 and PsaA co-immunoprecipitated with nuclear CaM. Although nuclear CaMBPs have previously been identified in Dictyostelium, the detection of CaM in purified nuclear fractions had not previously been shown. Putative CaM-binding domains (CaMBDs) were identified in Cdk5 and PsaA. Deletion of one of the two putative CaMBDs in Cdk5 ((132)LLINRKGELKLADFGLARAFGIP(154)) prevented CaM-binding indicating that this region encompasses a functional CaMBD. This deletion also increased the nuclear distribution of Cdk5 suggesting that CaM regulates the nucleocytoplasmic transport of Cdk5. A direct binding between CaM and PsaA could not be determined since deletion of the one putative CaMBD in PsaA prevented the nuclear localization of the deletion protein. Together, this study provides the first direct evidence for nuclear CaM in Dictyostelium and the first evidence in any system for Cdk5 being a CaMBP.

Nucleoplasmic/nucleolar translocation and identification of a nuclear localization signal (NLS) in Dictyostelium BAF60a/SMARCD1 homologue Snf12

Dictyostelium is a model eukaryote for the study of several cellular processes; however, comparatively little is known about its nucleolus. Identification of nucleolar proteins is key to understanding this nuclear subcompartment, but only four have been identified in Dictyostelium. As discussed in this article, a potential relationship between nucleolar NumA1 and BAF60a/SMARCD1 suggested BAF60a may also reside in the nucleolus. Here, we identify BAF60a homologue Snf12 as the fifth nucleolar protein in Dictyostelium. Immunolocalization experiments demonstrate that Snf12 is nucleoplasmic, but translocates to nucleoli upon actinomycin-D-induced transcription inhibition (0.05 mg/mL, 4 h). Translocation was accompanied by a microtubule-independent protrusion of nucleolar Snf12 regions from the nucleus followed by detection of Snf12 in cytoplasmic circles for at least 48 h. Residues (372)KRKR(375) are both necessary and sufficient for nucleoplasmic localization of Snf12 and represent a functional nuclear localization signal (NLS), similar to recently identified NLSs in other Dictyostelium proteins. Since nucleolar and nucleoplasmic proteins redistribute during mitosis, we investigated Snf12 dynamics during this time. Dictyostelium undergoes closed mitosis, meaning its nuclear envelope remains intact. Despite this, during metaphase and anaphase Snf12 redistributed throughout the cytoplasm before reaccumulating in the nucleus during telophase, unlike the previously reported nucleoplasmic redistribution of nucleolar NumA1. The nuclear exit of Snf12 was independent of its putative nuclear export signal and not inhibited by exportin inhibition, suggesting that the redistribution of nuclear proteins during mitosis in Dictyostelium is mediated by other mechanisms. Snf12 is the second Dictyostelium nucleolar protein for which its dynamics during mitosis have been investigated.