All together now: Polo joins the kinase network controlling the spindle assembly checkpoint in Drosophila

Extraction of Protein and Bioactive Compounds from Mediterranean Red Algae (Sphaerococcus coronopifolius and Gelidium spinosum) Using Various Innovative Pretreatment Strategies

In this study, the release of proteins and other biomolecules into an aqueous media from two red macroalgae (Sphaerococcus coronopifolius and Gelidium spinosum) was studied using eight different cell disruption techniques. The contents of carbohydrates, pigments, and phenolic compounds coextracted with proteins were quantified. In addition, morphological changes at the cellular level in response to the different pretreatment methods were observed by an optical microscope. Finally, the antioxidant capacity of obtained protein extracts was evaluated using three in vitro tests. For both S. coronopifolius and G. spinosum, ultrasonication for 60 min proved to be the most effective technique for protein extraction, yielding values of 3.46 ± 0.06 mg/g DW and 9.73 ± 0.41 mg/g DW, respectively. Furthermore, the highest total contents of phenolic compounds, flavonoids, and carbohydrates were also recorded with the same method. However, the highest pigment contents were found with ultrasonication for 15 min. Interestingly, relatively high antioxidant activities like radical scavenging activity (31.57-65.16%), reducing power (0.51-1.70, OD at 700 nm), and ferrous iron-chelating activity (28.76-61.37%) were exerted by the different protein extracts whatever the pretreatment method applied. This antioxidant potency could be attributed to the presence of polyphenolic compounds, pigments, and/or other bioactive substances in these extracts. Among all the used techniques, ultrasonication pretreatment for 60 min appears to be the most efficient method in terms of destroying the macroalgae cell wall and extracting the molecules of interest, especially proteins. The protein fractions derived from the two red macroalgae under these conditions were precipitated with ammonium sulfate, lyophilized, and their molecular weight distribution was determined using SDS-PAGE. Our results showed that the major protein bands were observed between 25 kDa and 60 kDa for S. coronopifolius and ranged from 20 kDa to 150 kDa for G. spinosum. These findings indicated that ultrasonication for 60 min could be sufficient to disrupt the algae cells for obtaining protein-rich extracts with promising biological properties, especially antioxidant activity.

Monopolar spindle 1 contributes to tamoxifen resistance in breast cancer through phosphorylation of estrogen receptor α

PURPOSE

The overexpression of mitotic kinase monopolar spindle 1 (Mps1) has been identified in many tumor types, and targeting Mps1 for tumor therapy has shown great promise in multiple preclinical cancer models. However, the role played by Mps1 in tamoxifen (TAM) resistance in breast cancer has never been reported.

METHODS

The sensitivity of breast cancer cells to tamoxifen was analysed in colony formation assays and wound healing assays. Enhanced transactivational activity of estrogen receptor α (ERα) led by Mps1 overexpression was determined by luciferase assays. The interaction between Mps1 and ERα was verified by co-immunoprecipitation and proximity ligation assay. Phosphorylation of ERα by Mps1 was detected by in vitro kinase assay and such phosphorylation process in vivo was proven by co-immunoprecipitation. The potential phosphorylation site(s) of ERα were analyzed by mass spectrometry.

RESULTS

Mps1 determines the sensitivity of breast cancer cells to tamoxifen treatment. Mps1 overexpression rendered breast cancer cells more resistant to tamoxifen, while an Mps1 inhibitor or siMps1 oligos enabled cancer cells to overcome tamoxifen resistance. Mechanistically, Mps1 interacted with estrogen receptor α and stimulated its transactivational activity in a kinase activity-dependent manner. Mps1 was critical for ERα phosphorylation at Thr224 amino acid site. Importantly, Mps1 failed to enhance the transactivational activity of the ERα-T224A mutant.

CONCLUSION

Mps1 contributes to tamoxifen resistance in breast cancer and is a potential therapeutic that can overcome tamoxifen resistance in breast cancer.

Regulation of intestinal stem cell activity by a mitotic cell cycle regulator Polo in Drosophila

Maintaining a definite and stable pool of dividing stem cells plays an important role in organ development. This process requires an appropriate progression of mitosis for proper spindle orientation and polarity to ensure the ability of stem cells to proliferate and differentiate correctly. Polo-like kinases (Plks)/Polo are the highly conserved serine/threonine kinases involved in the initiation of mitosis as well as in the progression of the cell cycle. Although numerous studies have investigated the mitotic defects upon loss of Plks/Polo in cells, little is known about the in vivo consequences of stem cells with abnormal Polo activity in the context of tissue and organism development. The current study aimed to investigate this question using the Drosophila intestine, an organ dynamically maintained by the intestinal stem cells (ISCs). The results indicated that the polo depletion caused a reduction in the gut size due to a gradual decrease in the number of functional ISCs. Interestingly, the polo-deficient ISCs showed an extended G2/M phase and aneuploidy and were subsequently eliminated by premature differentiation into enterocytes (ECs). In contrast, the constitutively active Polo (poloT182D) suppressed ISC proliferation, induced abnormal accumulation of β-tubulin in cells, and drove ISC loss via apoptosis. Therefore, Polo activity should be properly maintained for optimal stem cell function. Further analysis suggested that polo was a direct target gene of Sox21a, a Sox transcription factor that critically regulates stem cell activity. Together, this study provided a novel perspective on the correlation between the progression of mitosis and the ISC function in Drosophila.

Prognostic importance of Aurora Kinases and mitotic spindle genes transcript levels in Myelodysplastic syndrome

Myelodysplastic syndrome (MDS) are a heterogeneous group of clonal disease characterized by insufficiency of bone marrow, increase of apoptosis and increased risk of acute leukemia progression. Proteins related to the mitotic spindle (AURKA, AURKB, TPX2), to the mitotic checkpoint (MAD2, CDC20) and the regulation of the cell cycle (p21) are directly related to chromosomal stability and tumor development. This study aimed to evaluate the mRNA expression levels of these genes in 101 MDS patients using a real-time PCR methodology. We identified that CDC20 expression are increased in patients with dysmegakaryopoiesis (p=0.024), thrombocytopenia (p=0.000) and high-risk patients (p=0.014, 0.018) MAD2 expression are decreased in patients with 2 or 3 cytopenias (p=0.000) and neutrophil below 800/mm³. TPX2 is also overexpressed in patients presenting dysmegakaryopoiesis (p=0.009). A decrease in AURKA and AURKB expression were observed in patients with altered karyotype (p=0.000), who presented dysplasia in 3 lineages (p=0.000; 0.017) and hemoglobin inferior to 8g/dL (p=0.024). The expression of AURKA, AURKB and MAD2 (p=0.000; 0.001; 0.025) were decreased in patients with hypoplastic MDS, associated with high frequency of chromosomal alterations and high mortality rate. This study reaffirms the importance of aurora kinases and mitotic spindle genes to the pathogenesis and clinical evolution of MDS.

Loss of Polo ameliorates APP-induced Alzheimer's disease-like symptoms in Drosophila

The amyloid precursor protein (APP) has been implicated in the pathogenesis of Alzheimer’s disease (AD). Despite extensive studies, little is known about the regulation of APP’s functions in vivo. Here we report that expression of human APP in Drosophila, in the same temporal-spatial pattern as its homolog APPL, induced morphological defects in wings and larval NMJ, larva and adult locomotion dysfunctions, male choice disorder and lifespan shortening. To identify additional genes that modulate APP functions, we performed a genetic screen and found that loss of Polo, a key regulator of cell cycle, partially suppressed APP-induced morphological and behavioral defects in larval and adult stages. Finally, we showed that eye-specific expression of APP induced retina degeneration and cell cycle re-entry, both phenotypes were mildly ameliorated by loss of Polo. These results suggest Polo is an important in vivo regulator of the pathological functions of APP, and provide insight into the role of cell cycle re-entry in AD pathogenesis.