Microtubule-Actin Crosslinking Factor 1 and Plakins as Therapeutic Drug Targets

Microtubule actin crosslinking factor 1, a brain tumor oncoprotein (Review)

Microtubule actin crosslinking factor 1 (MACF1), is a cytoskeletal protein that functions as a crosslinker between microtubules and actin filaments, with early studies expanding the role of this spectraplakin protein to the central nervous system and Wnt signaling. In the early 2000's, genetic alterations of MACF1 were identified in several cancers suggesting that this cytoskeletal crosslinker was involved in tumor development and progression, while preclinical studies provided evidence that MACF1 is a potential diagnostic and prognostic biomarker and therapeutic target in glioblastomas, a central nervous system cancer derived from astrocytes and neural progenitor stem cells. Furthermore, investigations in glioblastomas demonstrated that genetic inhibitory targeting of this spectraplakin protein alone and in combination with DNA damaging agents had synergistic antitumorigenic effects. The established role of MACF1 in Wnt signaling, a known mechanistic driver of central nervous system development and pro-tumorigenic cell behavior in glioblastomas, provide a premise for addressing the potential of this spectraplakin protein as a novel oncoprotein in cancers with origins in the nervous system. The present review provides a summary of the role and function of MACF1 in the central nervous system, Wnt signaling and cancer development, specifically as an oncoprotein that underlie the transformation and oncogenic properties of glioblastomas.

The role of MACF1 on acute myeloid leukemia cell proliferation is involved in Runx2-targeted PI3K/Akt signaling

Acute myeloid leukemia (AML) is a type of hematologic diseases, which is related to abnormal genes. The aberrant microtubule actin cross-linking factor 1 (MACF1) is associated with progression of multiple tumors by initiating cell proliferation. Nevertheless, the function and action mechanism of MACF1 in AML cell proliferation remain mostly unknown. Our study aimed to explore the influence of MACF1 on AML cell proliferation by CCK-8 and EdU staining assays. Moreover, we aimed to explore the effect of MACF1 on downstream Runx2 and the PI3K/Akt signaling. MACF1 expression in AML patients was predicted by bioinformatics analysis. Cells were transfected with si-con, si-MACF1 or Runx2 using Lipofectamine 2000. Upregulated MACF1 was found in AML patients and predicted worse overall survival. MACF1 expression was upregulated in AML cells compared with that in hematopoietic stem and progenitor cells. MACF1 silencing reduced AML cell proliferation. Runx2 level was increased in AML cells, and decreased by silencing MACF1. Runx2 upregulation rescued MACF1 silencing-mediated inhibition of proliferation. MACF1 downregulation inhibited activation of the PI3K/Akt pathway by decreasing Runx2. Activation of the PI3K/Akt pathway abrogated the suppressive role of MACF1 downregulation in AML cell proliferation. In conclusion, MACF1 knockdown decreased AML cell proliferation by reducing Runx2 and inactivating the PI3K/Akt signaling.

The Tongue Squamous Carcinoma Cell Line Cal27 Primarily Employs Integrin α6β4-Containing Type II Hemidesmosomes for Adhesion Which Contribute to Anticancer Drug Sensitivity

Integrins are heterodimeric cell surface glycoproteins used by cells to bind to the extracellular matrix (ECM) and regulate tumor cell proliferation, migration and survival. A causative relationship between integrin expression and resistance to anticancer drugs has been demonstrated in different tumors, including head and neck squamous cell carcinoma. Using a Cal27 tongue squamous cell carcinoma model, we have previously demonstrated that de novo expression of integrin αVβ3 confers resistance to several anticancer drugs (cisplatin, mitomycin C and doxorubicin) through a mechanism involving downregulation of active Src, increased cell migration and invasion. In the integrin αVβ3 expressing Cal27-derived cell clone 2B1, αVβ5 expression was also increased, but unrelated to drug resistance. To identify the integrin adhesion complex (IAC) components that contribute to the changes in Cal27 and 2B1 cell adhesion and anticancer drug resistance, we isolated IACs from both cell lines. Mass spectrometry (MS)-based proteomics analysis indicated that both cell lines preferentially, but not exclusively, use integrin α6β4, which is classically found in hemidesmosomes. The anticancer drug resistant cell clone 2B1 demonstrated an increased level of α6β4 accompanied with increased deposition of a laminin-332-containing ECM. Immunofluorescence and electron microscopy demonstrated the formation of type II hemidesmosomes by both cell types. Furthermore, suppression of α6β4 expression in both lines conferred resistance to anticancer drugs through a mechanism independent of αVβ3, which implies that the cell clone 2B1 would have been even more resistant had the upregulation of α6β4 not occurred. Taken together, our results identify a key role for α6β4-containing type II hemidesmosomes in regulating anticancer drug sensitivity.

Quantitative proteomic analysis of human peripheral nerves from subjects with type 2 diabetes

AIMS

Diabetic peripheral neuropathy (DPN) is a common and severe complication to type 2 diabetes. The pathogenesis of DPN is not fully known, but several pathways and gene polymorphisms contributing to DPN are described. DPN can be studied using nerve biopsies, but studies on the proteome of the nerve itself, and its surrounding tissue as a whole, are lacking. Studies on the posterior interosseous nerve (PIN) have proposed PIN a useful indicator of DPN.

METHODS

A quantitative mass spectrometry-based proteomics analysis was made of peripheral nerves from age- and gender-matched living human male tissue donors; nine type 2 diabetes subjects, with decreased sural nerve action potentials indicating DPN, and six controls without type 2 diabetes, with normal electrophysiology results.

RESULTS

A total of 2617 proteins were identified. Linear regression was used to discover which proteins were differentially expressed between type 2 diabetes and controls. Only soft signals were found. Therefore, clustering of the 500 most variable proteins was made to find clusters of similar proteins in type 2 diabetes subjects and healthy controls.

CONCLUSIONS

This feasibility study shows, for the first time, that the use of quantitative mass spectrometry enables quantification of proteins from nerve biopsies from subjects with and without type 2 diabetes, which may aid in finding biomarkers of importance to DPN development.

Expression and Clinical Significance of Microtubule-Actin Cross-Linking Factor 1 in Serous Ovarian Cancer

BACKGROUND

Ovarian Cancer (OC) remains the first leading cause of gynecologic malignancy. The survival rate from Serous Ovarian Cancer (SOC) is very low, and the present prognostic predictors of SOC are not very sensitive or specific.

OBJECTIVE

The present study aimed to investigate Microtubule-Actin Cross-Linking Factor 1 (MACF1) expression in SOC tissues (including paraffin-embedded and fresh tissues) and to assess its expression and significant value in patients with SOC.

METHODS

A total of 18 fresh SOC tissues and their paired paratumor tissues were performed with reverse-transcription quantitative PCR analysis to detect MACF1 mRNA expression. Moreover, 175 paraffin-embedded SOC tissues and 41 paratumor tissues were assessed for MACF1 expression using immunohistochemistry.

RESULTS

The mRNA and protein expression of MACF1, both were higher in cancer tissues than that in paratumor tissues, and the high expression of MACF1 was associated with shorter Recurrence Free Survival (RFS) and Overall Survival (OS) in patients with SOC. Furthermore, multivariate regression analysis showed that high MACF1 expression was an independent poor survival predictor of patients with SOC.

CONCLUSION

MACF1 is upregulated in SOC, and it may be used as a useful prognostic biomarker in SOC.

The spectraplakin Dystonin antagonizes YAP activity and suppresses tumourigenesis

Aberrant expression of the Spectraplakin Dystonin (DST) has been observed in various cancers, including those of the breast. However, little is known about its role in carcinogenesis. In this report, we demonstrate that Dystonin is a candidate tumour suppressor in breast cancer and provide an underlying molecular mechanism. We show that in MCF10A cells, Dystonin is necessary to restrain cell growth, anchorage-independent growth, self-renewal properties and resistance to doxorubicin. Strikingly, while Dystonin maintains focal adhesion integrity, promotes cell spreading and cell-substratum adhesion, it prevents Zyxin accumulation, stabilizes LATS and restricts YAP activation. Moreover, treating DST-depleted MCF10A cells with the YAP inhibitor Verteporfin prevents their growth. In vivo, the Drosophila Dystonin Short stop also restricts tissue growth by limiting Yorkie activity. As the two Dystonin isoforms BPAG1eA and BPAG1e are necessary to inhibit the acquisition of transformed features and are both downregulated in breast tumour samples and in MCF10A cells with conditional induction of the Src proto-oncogene, they could function as the predominant Dystonin tumour suppressor variants in breast epithelial cells. Thus, their loss could deem as promising prognostic biomarkers for breast cancer.

Cellular Interactome Dynamics during Paclitaxel Treatment

Cell-cycle inhibitors, including paclitaxel, are among the most widely used and effective cancer therapies. However, several challenges limit the success of paclitaxel, including drug resistance and toxic side effects. Paclitaxel is thought to act primarily by stabilizing microtubules, locking cells in a mitotic state. However, the resulting cytotoxicity and tumor shrinkage rates observed cannot be fully explained by this mechanism alone. Here we apply quantitative chemical cross-linking with mass spectrometry analysis to paclitaxel-treated cells. Our results provide large-scale measurements of relative protein levels and, perhaps more importantly, changes to protein conformations and interactions that occur upon paclitaxel treatment. Drug concentration-dependent changes are revealed in known drug targets including tubulins, as well as many other proteins and protein complexes involved in apoptotic signaling and cellular homeostasis. As such, this study provides insight into systems-level changes to protein structures and interactions that occur with paclitaxel treatment.

Biomedical potential of mammalian spectraplakin proteins: Progress and prospect

The cytoskeleton is an essential element of a eukaryotic cell which informs both form and function and ultimately has physiological consequences for the organism. Equally as important as the major cytoskeletal networks are crosslinkers which coordinate and regulate their activities. One such category of crosslinker is the spectraplakins, a family of giant, evolutionarily conserved crosslinking proteins with the rare ability to interact with each of the three major cytoskeletal networks. In particular, a mammalian spectraplakin isotype called MACF1 (microtubule actin crosslinking factor 1), also known as ACF7 (actin crosslinking factor 7), has been of particular interest in the years since its discovery; MACF1 has come under such scrutiny due to the mounting list of biological phenomena in which it has been implicated. This review is an overview of the current knowledge on the structure and function of the known spectraplakin isotypes with an emphasis on MACF1, recent studies on MACF1, and finally, an analysis of the potential of MACF1 to advance medicine.

Impact statement

Spectraplakins are a highly conserved group of proteins which have the rare ability to bind to each of the three major cytoskeletal networks. The mammalian spectraplakin MACF1/ACF7 has proven to be instrumental in many cellular processes (e.g. signaling and cell migration) since its identification and, as such, has been the focus of various research studies. This review is a synthesis of scientific reports on the structure, confirmed functions, and implicated roles of MACF1/ACF7 as of 2019. Based on what has been revealed thus far in terms of MACF1/ACF7’s role in complex pathologies such as metastatic cancers and inflammatory bowel disease, it appears that MACF1/ACF7 and the continued study thereof hold great potential to both enhance the design of future therapies for various diseases and vastly expand scientific understanding of organismal physiology as a whole.

Comorbidities and Treatment Strategies in Bullous Pemphigoid: An Appraisal of the Existing Litterature

Bullous Pemphigoid is an autoimmune skin blistering disease. It is caused by deposition of auto antibodies along the dermal-epidermal border leading to inflammation. The antibodies are directed against anchoring filaments in the epidermis, but these antigens are also present in the neurological tissues and this has led to speculation of an association between multiple sclerosis and bullous pemphigoid. Additionally recent epidemiological studies have pointed at an increased risk of cardio-vascualr diseases and an increased moratality among the patients with bullous pemphigoid. In this mini review we present the recent findings in this area and as well as the treatment strategies when comorbidities are taken into consideration.

Mammalian Plakins, Giant Cytolinkers: Versatile Biological Functions and Roles in Cancer

Cancer is a highly lethal disease that is characterized by aberrant cell proliferation, migration, and adhesion, which are closely related to the dynamic changes of cytoskeletons and cytoskeletal-adhesion. These will further result in cell invasion and metastasis. Plakins are a family of giant cytolinkers that connect cytoskeletal elements with each other and to junctional complexes. With various isoforms composed of different domain structures, mammalian plakins are broadly expressed in numerous tissues. They play critical roles in many cellular processes, including cell proliferation, migration, adhesion, and signaling transduction. As these cellular processes are key steps in cancer development, mammalian plakins have in recent years attracted more and more attention for their potential roles in cancer. Current evidence shows the importance of mammalian plakins in various human cancers and demonstrates mammalian plakins as potential biomarkers for cancer. Here, we introduce the basic characteristics of mammalian plakins, review the recent advances in understanding their biological functions, and highlight their roles in human cancers, based on studies performed by us and others. This will provide researchers with a comprehensive understanding of mammalian plakins, new insights into the development of cancer, and novel targets for cancer diagnosis and therapy.