Aggregation of spectrin and PKCtheta is an early hallmark of fludarabine/mitoxantrone/dexamethasone-induced apoptosis in Jurkat T and HL60 cells

SPTAN1 Expression Predicts Treatment and Survival Outcomes in Colorectal Cancer

Simple Summary

Colorectal cancer (CRC) is a common and deadly form of cancer. Non-erythroid spectrin αII (SPTAN1), a protein of the cytoskeleton, is thought to be involved in CRC development and progression. In this study, we explore whether measuring SPTAN1 levels in resected CRC specimens might help to predict patient survival outcomes and response to chemotherapy. Indeed, we find that higher SPTAN1 protein and mRNA levels in CRC specimens associate with longer patient survival times. Using cell culture experiments, we then show that cells with lower SPTAN1 levels are less susceptible to FOLFOX chemotherapy, a standard treatment regimen for patients with CRC. Overall, our study underscores the importance of cytoskeletal proteins in shaping tumour biology and treatment responses and nominates SPTAN1 as a biomarker to improve patient stratification and refine therapeutic decisions in CRC.

Abstract

Colorectal cancer (CRC) is a leading cause of cancer-related morbidity and mortality. In a cohort of 189 patients with CRC, we recently showed that expression of the cytoskeletal scaffolding protein non-erythroid spectrin αII (SPTAN1) was lower in advanced metastatic tumours. The aim of the present study was to clarify the association of intratumoural SPTAN1 expression levels with treatment and survival outcomes in patients with CRC. The analysis was based on histologic assessment of SPTAN1 protein levels in our own CRC cohort, and transcriptome data of 573 CRC cases from The Cancer Genome Atlas (TCGA). We first establish that high intratumoural levels of SPTAN1 protein and mRNA associate with favourable survival outcomes in patients with CRC. Next, a response prediction signature applied to the TCGA data reveals a possible link between high SPTAN1 transcript levels and improved patient responses to FOLFOX chemotherapy. Complementary in vitro experiments confirm that SPTAN1 knockdown strains of the colon cancer cell lines HT-29, HCT116 mlh1-2 and Caco-2 are less responsive to FOLFOX chemotherapy compared with SPTAN1-proficient control strains. Taken together, we identify SPTAN1 as a novel prognostic biomarker in CRC and show that SPTAN1 expression levels may predict patient responses to chemotherapy. These investigations illustrate how an affordable, histology-based diagnostic test could directly impact therapeutic decision-making at the bedside.

α-Fodrin is required for the organization of functional microtubules during mitosis

The cytoskeleton protein α-fodrin plays a major role in maintaining structural stability of membranes. It was also identified as part of the brain γ-tubulin ring complex, the major microtubule nucleator. Here, we investigated the requirement of α-fodrin for microtubule spindle assembly during mitotic progression. We found that α-fodrin depletion results in abnormal mitosis with uncongressed chromosomes, leading to prolonged activation of the spindle assembly checkpoint and a severe mitotic delay. Further, α-fodrin repression led to the formation of shortened spindles with unstable kinetochore-microtubule attachments. We also found that the mitotic kinesin CENP-E had reduced levels at kinetochores to likely account for the chromosome misalignment defects in α-fodrin-depleted cells. Importantly, we showed these cells to exhibit reduced levels of detyrosinated α-tubulin, which primarily drives CENP-E localization. Since proper microtubule dynamics and chromosome alignment are required for completion of normal mitosis, this study reveals an unforeseen role of α-fodrin in regulating mitotic progression. Future studies on these lines of observations should reveal important mechanistic insight for fodrin's involvement in cancer.

The Role of Nonerythroid Spectrin αII in Cancer

Nonerythroid spectrin αII (SPTAN1) is an important cytoskeletal protein that ensures vital cellular properties including polarity and cell stabilization. In addition, it is involved in cell adhesion, cell-cell contact, and apoptosis. The detection of altered expression of SPTAN1 in tumors indicates that SPTAN1 might be involved in the development and progression of cancer. SPTAN1 has been described in cancer and therapy response and proposed as a potential marker protein for neoplasia, tumor aggressiveness, and therapeutic efficiency. On one hand, the existing data suggest that overexpression of SPTAN1 in tumor cells reflects neoplastic and tumor promoting activity. On the other hand, nuclear SPTAN1 can have tumor suppressing effects by enabling DNA repair through interaction with DNA repair proteins. Moreover, SPTAN1 cleavage products occur during apoptosis and could serve as markers for the efficacy of cancer therapy. Due to SPTAN1's multifaceted functions and its role in adhesion and migration, SPTAN1 can influence tumor growth and progression in both positive and negative directions depending on its specific regulation. This review summarizes the current knowledge on SPTAN1 in cancer and depicts several mechanisms by which SPTAN1 could impact tumor development and aggressiveness.

Downregulation of SPTAN1 is related to MLH1 deficiency and metastasis in colorectal cancer

Introduction

Colorectal cancers (CRCs) deficient in the DNA mismatch repair protein MutL homolog 1 (MLH1) display distinct clinicopathological features and require a different therapeutic approach compared to CRCs with MLH1 proficiency. However, the molecular basis of this fundamental difference remains elusive. Here, we report that MLH1-deficient CRCs exhibit reduced levels of the cytoskeletal scaffolding protein non-erythroid spectrin αII (SPTAN1), and that tumor progression and metastasis of CRCs correlate with SPTAN1 levels.

Methods and results

To investigate the link between MLH1 and SPTAN1 in cancer progression, a cohort of 189 patients with CRC was analyzed by immunohistochemistry. Compared with the surrounding normal mucosa, SPTAN1 expression was reduced in MLH1-deficient CRCs, whereas MLH1-proficient CRCs showed a significant upregulation of SPTAN1. Overall, we identified a strong correlation between MLH1 status and SPTAN1 expression. When comparing TNM classification and SPTAN1 levels, we found higher SPTAN1 levels in stage I CRCs, while stages II to IV showed a gradual reduction of SPTAN1 expression. In addition, SPTAN1 expression was lower in metastatic compared with non-metastatic CRCs. Knockdown of SPTAN1 in CRC cell lines demonstrated decreased cell viability, impaired cellular mobility and reduced cell-cell contact formation, indicating that SPTAN1 plays an important role in cell growth and cell attachment. The observed weakened cell-cell contact of SPTAN1 knockdown cells might indicate that tumor cells expressing low levels of SPTAN1 detach from their primary tumor and metastasize more easily.

Conclusion

Taken together, we demonstrate that MLH1 deficiency, low SPTAN1 expression, and tumor progression and metastasis are in close relation. We conclude that SPTAN1 is a candidate molecule explaining the tumor progression and metastasis of MLH1-deficient CRCs. The detailed analysis of SPTAN1 is now mandatory to substantiate its relevance and its potential value as a candidate protein for targeted therapy, and as a predictive marker of cancer aggressiveness.

Delineating SPTAN1 associated phenotypes: from isolated epilepsy to encephalopathy with progressive brain atrophy

De novo in-frame deletions and duplications in the SPTAN1 gene, encoding the non-erythrocyte αII spectrin, have been associated with severe West syndrome with hypomyelination and pontocerebellar atrophy. We aimed at comprehensively delineating the phenotypic spectrum associated with SPTAN1 mutations. Using different molecular genetic techniques, we identified 20 patients with a pathogenic or likely pathogenic SPTAN1 variant and reviewed their clinical, genetic and imaging data. SPTAN1 de novo alterations included seven unique missense variants and nine in-frame deletions/duplications of which 12 were novel. The recurrent three-amino acid duplication p.(Asp2303_Leu2305dup) occurred in five patients. Our patient cohort exhibited a broad spectrum of neurodevelopmental phenotypes, comprising six patients with mild to moderate intellectual disability, with or without epilepsy and behavioural disorders, and 14 patients with infantile epileptic encephalopathy, of which 13 had severe neurodevelopmental impairment and four died in early childhood. Imaging studies suggested that the severity of neurological impairment and epilepsy correlates with that of structural abnormalities as well as the mutation type and location. Out of seven patients harbouring mutations outside the α/β spectrin heterodimerization domain, four had normal brain imaging and three exhibited moderately progressive brain and/or cerebellar atrophy. Twelve of 13 patients with mutations located within the spectrin heterodimer contact site exhibited severe and progressive brain, brainstem and cerebellar atrophy, with hypomyelination in most. We used fibroblasts from five patients to study spectrin aggregate formation by Triton-X extraction and immunocytochemistry followed by fluorescence microscopy. αII/βII aggregates and αII spectrin in the insoluble protein fraction were observed in fibroblasts derived from patients with the mutations p.(Glu2207del), p.(Asp2303_Leu2305dup) and p.(Arg2308_Met2309dup), all falling in the nucleation site of the α/β spectrin heterodimer region. Molecular modelling of the seven SPTAN1 amino acid changes provided preliminary evidence for structural alterations of the A-, B- and/or C-helices within each of the mutated spectrin repeats. We conclude that SPTAN1-related disorders comprise a wide spectrum of neurodevelopmental phenotypes ranging from mild to severe and progressive. Spectrin aggregate formation in fibroblasts with mutations in the α/β heterodimerization domain seems to be associated with a severe neurodegenerative course and suggests that the amino acid stretch from Asp2303 to Met2309 in the α20 repeat is important for α/β spectrin heterodimer formation and/or αII spectrin function.

Antiosteoporotic Effects of Huangqi Sanxian Decoction in Cultured Rat Osteoblasts by Proteomic Characterization of the Target and Mechanism

Huangqi Sanxian decoction (HQSXD) is routinely used for the treatment of osteoporosis in the Chinese traditional healthcare system. However, the targets and mechanism underlying the effect of HQSXD on osteoporosis have not been documented. In the present study, seropharmacology and proteomic approaches (two-dimensional gel electrophoresis combined with mass spectrometry) were used to investigate the effects and possible target proteins of HQSXD on osteoblast. We found that HQSXD-treated rat serum significantly enhanced osteoblast proliferation, differentiation, and mineralization. In HQSXD-S-treated osteoblasts, there were increases in the expression of N-formyl peptide receptor 2 and heparan sulfate (glucosamine) 3-O-sulfotransferase 3A1 and reduction in the expression of alpha-spectrin, prohibitin, and transcription elongation factor B (SIII), polypeptide 1. The identified proteins are associated with cell proliferation, differentiation, signal transcription, and cell growth. These findings might provide valuable insights into the mechanism of antiosteoporotic effect affected by HQSXD treatment in osteoblasts.

The Novel PKCθ from Benchtop to Clinic

The protein kinases C (PKCs) are a family of serine/threonine kinases involved in regulating multiple essential cellular processes such as survival, proliferation, and differentiation. Of particular interest is the novel, calcium-independent PKCθ which plays a central role in immune responses. PKCθ shares structural similarities with other PKC family members, mainly consisting of an N-terminal regulatory domain and a C-terminal catalytic domain tethered by a hinge region. This isozyme, however, is unique in that it translocates to the immunological synapse between a T cell and an antigen-presenting cell (APC) upon T cell receptor-peptide MHC recognition. Thereafter, PKCθ interacts physically and functionally with downstream effectors to mediate T cell activation and differentiation, subsequently leading to inflammation. PKCθ-specific perturbations have been identified in several diseases, most notably autoimmune disorders, and hence the modulation of its activity presents an attractive therapeutic intervention. To that end, many inhibitors of PKCs and PKCθ have been developed and tested in preclinical and clinical studies. And although selectivity remains a challenge, results are promising for the future development of effective PKCθ inhibitors that would greatly advance the treatment of several T-cell mediated diseases.

Spectrins: a structural platform for stabilization and activation of membrane channels, receptors and transporters

This review focuses on structure and functions of spectrin as a major component of the membrane skeleton. Recent advances on spectrin function as an interface for signal transduction mediation and a number of data concerning interaction of spectrin with membrane channels, adhesion molecules, receptors and transporters draw a picture of multifaceted protein. Here, we attempted to show the current depiction of multitask role of spectrin in cell physiology. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters. Guest Editor: Jean Claude Hervé.

Release of an ~55kDa fragment containing the actin-binding domain of β-spectrin by caspase-8 during FND-induced apoptosis depends on the presence of protein 4.1

Analyses of the status of the membrane spectrin-based skeleton during fludarabine/mitoxantrone/dexamethasone-induced (FND-induced) apoptosis revealed proteolytic degradation of β-spectrin, with the prevalent appearance of a specific fragment with a molecular weight of ~55kDa, containing the actin-binding domain (ABD). Appearance of this fragment was dependent on induction of apoptosis. In silico proteolysis of spectrin identified caspase-8 as a candidate protease responsible for the generation of this ~55kDa ABD-containing fragment. Analyses of spectrin and procaspase-8 localization during early apoptosis indicated temporary (<30-120min) submembranous colocalization of both proteins. Proteolytic release of the N-terminal ~55kDa fragment of purified spectrin by recombinant caspase-8 does not occur in normal cells, but does occur in isolated membrane, such as red blood cell ghosts, or in vitro in the presence of apoptotic cell extracts. Surprisingly, proteolysis of purified spectrin by recombinant caspase-8 resulted in the generation of the ~55kDa fragment only in the presence of purified protein 4.1. This suggests that only the appropriate spatial arrangement of the spectrin-based membrane skeleton or the appropriate conformational state of spectrin, which are both known to be induced by 4.1, can sensitize β-spectrin to cleavage by caspase-8 at the N-terminal ABD-containing region.

The emerging role of protein kinase Cθ in cytoskeletal signaling

Cytoskeletal rearrangements often occur as the result of transduction of signals from the extracellular environment. Efficient awakening of this powerful machinery requires multiple activation and deactivation steps, which usually involve phosphorylation or dephosphorylation of different signaling units by kinases and phosphatases, respectively. In this review, we discuss the signaling characteristics of one of the nPKC isoforms, PKCθ, focusing on PKCθ-mediated signal transduction to cytoskeletal elements, which results in cellular rearrangements critical for cell type-specific responses to stimuli. PKCθ is the major PKC isoform present in hematopoietic and skeletal muscle cells. PKCθ plays roles in T cell signaling through the IS, survival responses in adult T cells, and T cell FasL-mediated apoptosis, all of which involve cytoskeletal rearrangements and relocation of this enzyme. PKCθ has been linked to the regulation of cell migration, lymphoid cell motility, and insulin signaling and resistance in skeletal muscle cells. Additional roles were suggested for PKCθ in mitosis and cell-cycle regulation. Comprehensive understanding of cytoskeletal regulation and the cellular "modus operandi" of PKCθ holds promise for improving current therapeutic applications aimed at autoimmune diseases.

Spectrin-based skeleton as an actor in cell signaling

This review focuses on the recent advances in functions of spectrins in non-erythroid cells. We discuss new data concerning the commonly known role of the spectrin-based skeleton in control of membrane organization, stability and shape, and tethering protein mosaics to the cellular motors and to all major filament systems. Particular effort has been undertaken to highlight recent advances linking spectrin to cell signaling phenomena and its participation in signal transduction pathways in many cell types.