PP2A inhibitor SET promotes mTORC1 and Bmi1 signaling through Akt activation and maintains the colony-formation ability of cancer cells.

Protein phosphatase 2A (PP2A) is an essential tumor suppressor, with its activity often hindered in cancer cells by endogenous PP2A inhibitory proteins like SE translocation (SET). SET/PP2A axis plays a pivotal role in the colony-formation ability of cancer cells and the stabilization of c-Myc and E2F1 proteins implicated in this process. However, in osteosarcoma cell line HOS, SET knock-down (KD) suppresses the colony-formation ability without affecting c-Myc and E2F1. This study aimed to unravel the molecular mechanism through which SET enhances the colony-formation ability of HOS cells and determine if it is generalized to other cancer cells. Transcriptome analysis unveiled that SET KD suppressed mTORC1 signaling. SET KD inhibited Akt phosphorylation, an upstream kinase for mTORC1. PP2A inhibitor blocked SET KD-mediated decrease in phosphorylation of Akt and a mTORC1 substrate p70S6K. A constitutively active Akt restored decreased colony-formation ability by SET KD, indicating the SET/PP2A/Akt/mTORC1 axis. Additionally, enrichment analysis highlighted that Bmi-1, a polycomb group protein, is affected by SET KD. SET KD decreased Bmi-1 protein by Akt inhibition but not by mTORC1 inhibition, and exogenous Bmi-1 expression rescued the reduced colony formation by SET KD. Four out of eight cancer cell lines exhibited decreased Bmi-1 by SET KD. Further analysis of these cell lines revealed that Myc activity plays a role in SET KD-mediated Bmi-1 degradation. These findings provide new insights into the molecular mechanism of SET-regulated colony-formation ability, which involved Akt-mediated activation of mTORC1/p70S6K and Bmi-1 signaling.

The luciferase-based in vivo protein-protein interaction assay revealed that CHK1 promotes PP2A and PME-1 interaction.

Protein phosphatase 2A (PP2A) is an essential serine/threonine protein phosphatase, and its dysfunction is involved in the onset of cancer and neurodegenerative disorders. PP2A functions as a trimeric holoenzyme whose composition is regulated by the methyl-esterification (methylation) of the PP2A catalytic subunit (PP2Ac). Protein phosphatase methylesterase-1 (PME-1) is the sole PP2Ac methylesterase, and the higher PME-1 expression is observed in various cancer and neurodegenerative diseases. Apart from serving as a methylesterase, PME-1 acts as a PP2A inhibitory protein, binding directly to PP2Ac and suppressing its activity. The intricate function of PME-1 hinders drug development by targeting the PME-1/PP2Ac axis. This study applied the NanoBiT system, a bioluminescence-based protein interaction assay, to elucidate the molecular mechanism that modulates unknown PME-1/PP2Ac protein-protein interaction (PPI). Compound screening identified that the CHK1 inhibitors inhibited PME-1/PP2Ac association without affecting PP2Ac methylation levels. CHK1 directly phosphorylates PP2Ac to promote PME-1 association. Phospho-mass spectrometry identified multiple phospho-sites on PP2Ac, including the Thr219, that affect PME-1 interaction. An anti-phospho-Thr219 PP2Ac antibody was generated and showed that CHK1 regulates the phosphorylation levels of this site in cells. On the contrary, in vitro phosphatase assay showed that CHK1 is the substrate of PP2A, and PME-1 hindered PP2A-mediated dephosphorylation of CHK1. Our data provides novel insights into the molecular mechanisms governing the PME-1/PP2Ac PPI and the triad relationship between PP2A, PME-1, and CHK1.

Protein phosphatase 6 promotes stemness of colorectal cancer cells.

Colorectal cancer (CRC) remains a significant global health concern, demanding a more profound comprehension of its molecular foundations for the development of improved therapeutic strategies. This study aimed to elucidate the role of protein phosphatase 6 (PP6), a member of the type 2A protein phosphatase family, in CRC. Protein phosphatase 6 functions as a heterotrimer with a catalytic subunit (PP6c), regulatory subunits (PP6Rs; PP6R1, PP6R2, and PP6R3), and scaffold subunits (ANKRD28, ANKRD44, and ANKRD52). Elevated PP6c expression has been identified in CRC tissues compared to normal mucosa, aligning with its potential involvement in CRC pathogenesis. PP6c knockdown resulted in decreased colony-forming ability and in vivo proliferation of various CRC cell lines. Transcriptome analysis revealed that PP6c knockdown resulted in altered expression of genes associated with cancer stemness. Notably, the PP6c-PP6R3 complex is a key player in regulating cancer stem cell (CSC) markers. Additionally, increased PP6c expression was observed in CSC-like cells induced by sphere formation, implicating the role of PP6c in CSC maintenance. This study highlights the role of PP6c in CRC and suggests that it is a potential therapeutic target disrupting a pathway critical for CRC progression and stem cell maintenance.

Low pH modulates lipopolysaccharide-induced tumor necrosis factor-alpha expression and macropinocytotic activity in RAW264.7 cells.

Inflammation triggers various types of diseases that need to be addressed. Macrophages play important roles in the inflammatory responses. As atherosclerosis progresses, macrophages transform into foam cells. Extracellular acidification is observed at and around bacterial infection and atherosclerotic sites. However, the effects of acidification on the inflammatory response of macrophages and the progression of atherosclerosis have not been fully understood. This study investigates the impact of extracellular acidification on lipopolysaccharide-induced tumor necrosis factor-alpha (TNF-α) expression and macropinocytotic activity in RAW264.7 cells. TNF-α expression is measured by real-time polymerase chain reaction (relative value to glyceraldehyde-3-phosphate dehydrogenase expression). Macropinocytotic activity is measured by neutral red uptake (absorbance at 540 nm). Results show that TNF-α expression increased with decreasing extracellular pH in both un-foamed and foamed cells. Macropinocytotic activity was upregulated at pH 6.8 in un-foamed cells, but downregulated in foamed cells stimulated at low pH. Proton-sensing G protein-coupled receptors (GPCRs) were involved in the expression of TNF-α and in the macropinocytotic activity of foamed cells. In conclusion, this study reveals that extracellular acidification differently affect various inflammatory responses such as LPS-induced TNF-α expression and macropinocytotic activity of RAW264.7 cells and different proton-sensing GPCRs are involved in the different inflammatory responses.

Pulmonary Infection Caused by Mycobacterium malmoense and the Difficulties in Distinguishing It From the Pulmonary Mycobacterium tuberculosis Infection.

Mycobacterium malmoense is a rare species of non-tuberculosis mycobacteria detected in Japan that causes pulmonary infection and cervical lymphadenitis. Here, we report a case of pulmonary infection caused by M. malmoense, which was difficult to distinguish from Mycobacterium tuberculosis (Mtb) infection. A 64-year-old Japanese woman with a history of pulmonary tuberculosis had bloody phlegm, a cough, and discomfort in her chest. Chest computed tomography revealed a cavity, infiltration, and a nodule. A smear test for acid-fast bacilli was positive, a Mycobacterium avium complex transcription reverse-transcription concerted (TRC) test was negative, and an Mtb TRC test was withheld because the internal control was negative. After diluting the specimens, the internal control tested positive, and the sample tested negative. We diagnosed pulmonary M. malmoense infection based on a culture test. In conclusion, attention should be paid to the concentration of bacteria in Mtb TRC test samples, ensuring that the internal control provides expected results.

Corrigendum to "Oncostatin M mediates cardioprotection via angiogenesis in ischemic heart disease" [Am. Heart J. Plus Cardiol. Res. Pract. vol. 35, 2023, 100331].

[This corrects the article DOI: 10.1016/j.ahjo.2023.100331.].

Takotsubo syndrome associated with coronary microvascular dysfunction: A case study.

The patient, a 68-year-old man, presented to our emergency room with chest pain, prompting an emergency cardiac catheterization due to elevated cardiac troponin-I levels. While no obvious coronary artery stenosis was found, there was evidence of apical ballooning wall motion in the left ventricle, leading to a diagnosis of takotsubo syndrome. Three months later, he occasionally experienced chest pain at rest, prompting us to conduct another cardiac catheterization. Left ventriculography showed normal contraction. Suddenly, he experienced chest pain accompanied by ST elevation, which occurred spontaneously. Subsequently, slow-flow phenomenon was observed in the intermediate part of left anterior descending artery (LAD). We promptly administered nitroglycerin to alleviate the symptoms. Following the diagnosis of coronary microvascular dysfunction (CMD), he started calcium-channel blocker therapy and remained asymptomatic. One year later, we re-performed cardiac catheterization to further explore his condition. Acetylcholine provocation test was performed, which showed no epicardial coronary spasm. However, lactic acid elevation was observed in the coronary sinus blood sample. Additionally, a coronary physiological measurement in the LAD revealed a high index of microcirculatory resistance and low coronary flow reserve. Based on this series of clinical events, we inferred a significant contribution of CMD to the patient's condition. Learning objective: Coronary microvascular dysfunction (CMD) is increasingly recognized as an important cardiovascular disease, leading to myocardial ischemia, which is occasionally associated with takotsubo syndrome (TTS). In this report, we present a case of spontaneous CMD associated with TTS. This case emphasizes the significance of accurate diagnosis and appropriate treatment, highlighting the importance of recognizing CMD in patients with TTS.

Cholesterol Crystal Embolism: Autopsy-proven Gastrointestinal Lesions, Pancreatitis, and End-stage Kidney Disease Which Developed after Undergoing Selective Abdominal Angiography.

A 78-year-old man with atherosclerosis was diagnosed with hepatocellular carcinoma by transfemoral angiography of the celiac and superior mesenteric arteries (SMA). After surgery, a serum examination revealed progressive renal failure with eosinophilia, leading to end-stage kidney disease, in addition to active gastric ulcers and pancreatitis. Cyanosis in the bilateral toes showed a cholesterol crystal embolism (CCE) in a skin biopsy. Autopsy revealed that CCE involved the arterioles of multiple organs, and its distribution was anatomically consistent with the vascular territories of the celiac artery and SMA. CCE should therefore be considered in patients presenting with multiple types of tissue damage in the vascular territories after angiography.

Oncostatin M mediates cardioprotection via angiogenesis in ischemic heart disease.

Objective: Oncostatin M (OSM) is an inflammatory cytokine belonging to the interleukin-6 family member, which plays an important role in various cardiovascular diseases. We recently reported increased serum OSM levels in patients with coronary artery disease. However, the specific role in HF with ischemic heart disease (IHD) remains unclear. Methods and results: A total of 120 patients with HF and 48 control subjects were enrolled in this study. Serum OSM levels were measured using a sandwich technique immunoassay during the compensated state. The results revealed significantly higher serum OSM levels in HF patients compared to controls. Importantly, HF patients with IHD had higher OSM levels, and those with collateral flow showed the even higher levels, indicating a potential involvement in angiogenesis. Furthermore, a positive correlation was found between serum OSM levels and levels of vascular endothelial growth factor (VEGF). In vitro experiments demonstrated that recombinant OSM upregulated VEGF production in cultured human coronary artery endothelial cells. We additionally observed that endogenous OSM levels were enhanced through exercise. Lastly, we identified the potential of SGLT2 inhibitors to enhance OSM production. Conclusions: Serum OSM levels were elevated in HF patients, particularly in those with IHD Our data indicated that endogenous OSM induces VEGF production in the heart, suggesting the activation of angiogenesis, which can be further enhanced by exercise or SGLT2 inhibitors.