Emerging Role of Cellular Prion Protein in the Maintenance and Expansion of Glioma Stem Cells

A Potential biomarker for the early diagnosis of OSCC: saliva and serum PrPC

Background: Oral squamous cell carcinoma (OSCC) is frequently diagnosed at an advanced stage, and the high mortality of patients is mainly due to the delay of diagnosis. Cellular prion protein (PrPC) contributes to the occurrence and development of many malignant tumors. However, little has been known about the clinical and diagnostic value of PrPC in OSCC. This study investigated the levels of PrPC in the saliva and serum of patients with OSCC, OPMD and control group and their diagnostic value. Methods: The Cancer Genome Atlas (TCGA), Gene Expression Omnibus (GEO) and Clinical Proteome Tumor Analysis Consortium (CPTAC) databases were analyzed to evaluate the expression of human prion protein gene (PRNP) mRNA and PrPC in OSCC. Enzyme-linked Immunosorbent Assay (ELISA) was utilized to detect the expression of PrPC in saliva and serum samples of OSCC, OPMD and control groups. Furthermore, diagnostic value and clinical significance of PrPC in OSCC was identified. Protein-protein interaction (PPI) network was constructed by STRING. GO and KEGG analysis were performed by ClusterProfiler. Results: The levels of PRNP mRNA and PrPC in OSCC were significantly higher than those in the control group from databases (P<0.05). Besides, salivary and serum PrPC of OSCC patients showed increased levels compared with OPMD and control groups (P<0.05). The expression of salivary and serum PrPC of OSCC was correlated with the degree of differentiation (P<0.05), and the expression of PrPC from CPTAC was related to tumor stage of OSCC (P<0.05). The areas under the diagnostic curves (AUCs) of salivary and serum PrPC were 0.807 and 0.671, respectively. GO and KEGG analysis revealed that PrPC might be related to cell adhesion, cell differentiation, signal transduction and apoptosis, and participate in the pathways of focal adhesion, PI3K-Akt signaling pathway and ECM- receptor interaction in OSCC. Conclusion: PrPC in saliva and serum may be a potential biomarker for early diagnosis of OSCC.

The Multifaceted Functions of Prion Protein (PrPC) in Cancer

The cellular prion protein (PrPC) is a glycoprotein anchored to the cell surface by glycosylphosphatidylinositol (GPI). PrPC is expressed both in the brain and in peripheral tissues. Investigations on PrPC's functions revealed its direct involvement in neurodegenerative and prion diseases, as well as in various physiological processes such as anti-oxidative functions, copper homeostasis, trans-membrane signaling, and cell adhesion. Recent findings have revealed the ectopic expression of PrPC in various cancers including gastric, melanoma, breast, colorectal, pancreatic, as well as rare cancers, where PrPC promotes cellular migration and invasion, tumor growth, and metastasis. Through its downstream signaling, PrPC has also been reported to be involved in resistance to chemotherapy and tumor cell apoptosis. This review summarizes the variance of expression of PrPC in different types of cancers and discusses its roles in their development and progression, as well as its use as a potential target to treat such cancers.

Plasma PRPC Levels Correlate With Severity and Prognosis of Intracerebral Hemorrhage

Background

Cellular prion protein (PRPC) exerts brain-protective effects. We determined the relationship between plasma PRPC levels and disease severity plus clinical outcome after acute intracerebral hemorrhage (ICH).

Methods

A total of 138 ICH patients and 138 healthy controls were included in this prospective, observational study. Hematoma volume and Glasgow coma scale (GCS) score were used to assess disease severity. Glasgow outcome scale (GOS) scores of 1–3 and 4–5 at 90 days after stroke were defined as a poor outcome and good outcome, respectively. Using multivariate analysis, we discerned the relation of plasma PRPC levels to disease severity and poor outcome. The receiver operating characteristic (ROC) curve was built to evaluate the prognostic predictive capability.

Results

Plasma PRPC levels in ICH patients were significantly higher than those in healthy controls (median, 4.20 vs. 2.02 ng/ml; P &lt; 0.001), and were independently correlated with GCS score (r = −0.645, P &lt; 0.001) and hematoma volume (r = 0.627, P &lt; 0.001). Plasma PRPC levels were highly correlated with GOS score (r = −0.762, P &lt; 0.001), and were substantially higher in patients with poor outcomes than in those with the good outcomes. Using maximum Youden index, plasma PRPC levels &gt;3.893 ng/ml distinguished the risk of poor outcome at 90 days, with a sensitivity of 86.4% and a specificity of 65.8% (area under the curve, 0.809; 95% confidence interval (CI), 0.737–0.881, P &lt; 0.001). Plasma PRPC levels &gt;3.893 ng/ml were independently associated with a poor 90-day outcome with an odds ratio of 12.278 (95% CI, 5.101–29.554).

Conclusion

Elevated plasma PRPC levels are significantly associated with disease severity and poor 90-day outcome in ICH patients, indicating that plasma PRPC may be used as a potential prognostic biomarker after ICH.

Anchorless risk or released benefit? An updated view on the ADAM10-mediated shedding of the prion protein

The prion protein (PrP) is a broadly expressed glycoprotein linked with a multitude of (suggested) biological and pathological implications. Some of these roles seem to be due to constitutively generated proteolytic fragments of the protein. Among them is a soluble PrP form, which is released from the surface of neurons and other cell types by action of the metalloprotease ADAM10 in a process termed 'shedding'. The latter aspect is the focus of this review, which aims to provide a comprehensive overview on (i) the relevance of proteolytic processing in regulating cellular PrP functions, (ii) currently described involvement of shed PrP in neurodegenerative diseases (including prion diseases and Alzheimer's disease), (iii) shed PrP's expected roles in intercellular communication in many more (patho)physiological conditions (such as stroke, cancer or immune responses), (iv) and the need for improved research tools in respective (future) studies. Deeper mechanistic insight into roles played by PrP shedding and its resulting fragment may pave the way for improved diagnostics and future therapeutic approaches in diseases of the brain and beyond.

Cellular Prion Protein Is Essential for Myocardial Regeneration but Not the Recovery of Left Ventricular Function from Apical Ballooning

This study tested the hypothesis that cellular prion protein (PrP^C) played an essential role in myocardial regeneration and recovery of left ventricular ejection fraction (LVEF) from apical takotsubo cardiomyopathy (TCM) induced by transaortic constriction (TAC). In vitro study was categorized into G1 (H9C2), G2 (H9C2-overexpression-PrP^C), G3 (H9C2-overexpression-PrP^C + Stelazine/1 uM), and G4 (H9C2 + siRNA-PrP^C), respectively. The results showed that the protein expressions of PrP^C, cell-stress signaling (p-PI3K/p-Akt/p-m-TOR) and signal transduction pathway for cell proliferation/division (RAS/c-RAF/p-MEK/p-ERK1/2) were lowest in G1, highest in G2, significantly higher in G3 than in G4 (all p < 0.001). Adult-male B6 mice (n = 30) were equally categorized in group 1 (sham-control), group 2 (TAC) for 14 days, then relieved the knot and administered BrdU (50 ug/kg/intravenously/q.6.h for two times from day-14 after TAC) and group 3 (TAC + Stelazine/20 mg/kg/day since day 7 after TAC up to day 21 + BrdU administered as group 2), and animals were euthanized at day 28. The results showed that by day 28, the LVEF was significantly higher in group 1 than in groups 2/3 and significantly higher in group 3 than in group 2, whereas the LV chamber size exhibited an opposite pattern of LVEF (all p < 0.0001). The protein expressions of PrP^C/p-PI3K/p-Akt/p-m-TOR/cyclin D/cyclin E and cellular-proliferation biomarkers (Ki67/PCNA/BrdU) exhibited an opposite pattern of LVEF (all p < 0.0001) among the three groups, whereas the protein expressions of RAS/c-RAF/p-MEK/p-ERK1/2 were significantly and progressively increased from groups 1 to 3 (all p < 0.0001). In conclusion, PrP^C participated in regulating the intrinsic response of cell-stress signaling and myocardial regeneration but did not offer significant benefit on recovery of the heart function in the setting of TCM.

Rapid tumor recurrence in a novel murine GBM surgical model is associated with Akt/PD-L1/vimentin signaling

Glioblastoma multiforme (GBM) is the most common primary malignant brain tumor without curable therapy. Surgical resection remains the first choice of patients with GBM but tumors relapse rapidly even combined with conventional chemoradiotherapy. The mechanism of GBM rapid recurrence is poorly understood, which is largely due to the lack of an appropriate animal model, thus heavily impedes the improvement of postoperative therapy. Here we established a highly reproducible mouse GBM surgical model by using the syngeneic G422^TN-GBM cells, which faithfully recapitulates the features of rapid recurrence of human GBM after surgery. Implanting 2 × 10³-5 × 10⁴ of G422^TN-GBM cells in mouse cerebral cortex caused death in all animal within 23 days, while surgery was an effective therapy but not curable. After complete removal of visible tumors on day 5-9 of tumor growth, the tumors recurred macroscopically within 5 days accompanied by increasing infiltrative cancer foci. Mechanistically, the rapid recurrence of resected tumors was positively correlated to early Akt activation, which subsequently upregulated PD-L1/Vimentin and promoted proliferation/migration of cancer cells. In addition, environmental astrocytic activation with strong PD-L1 signal was prominent. Taken together, we provided a novel GBM surgical recurrence model for preclinical studies and suggested complicated recurring mechanisms involving in strong oncogenic signaling as well as immune inhibitory signals from both GBM cells and their neighboring astrocytes.

Targeting stemness of cancer stem cells to fight colorectal cancers

Cancer initiating/ stem cells (CSCs) undergo self-renewal and differentiation that contributes to tumor initiation, recurrence and metastasis in colorectal cancer (CRC). Targeting of colorectal cancer stem cells (CCSCs) holds significant promise in eradicating cancer cells and ultimately curing patients with cancer. In this review, we will introduce the current progress of CCSC studies, including the specific surface markers of CCSCs, the intrinsic signaling pathways that regulate the stemness and differentiation characteristics of CCSCs, and the tumor organoid model for CCSC research. We will focus on how these studies will lead to the progress in targeting specific surface markers or signaling pathways on CCSCs by monoclonal antibodies, or by natural or synthetic compounds, or by immunotherapy. As CSCs are highly heterogeneous and plastic, we suggest that combinatory approaches that target the stemness network may represent an important strategy for eradicating cancers.

Cellular prion protein activates Caspase 3 for apoptotic defense mechanism in astrocytes

The cellular prion protein (PrP^C) is anchored in the plasma membrane of cells, and it is highly present in cells of brain tissue, exerting numerous cellular and cognitive functions. The present study proves the importance of PrP^C in the cellular defense mechanism and metal homeostasis in astrocytes cells. Through experimental studies using cell lines of immortalized mice astrocytes (wild type and knockout for PrP^C), we showed that PrPc is involved in the apoptosis cell death process by the activation of Caspase 3, downregulation of p53, and cell cycle maintenance. Metal homeostasis was determined by inductively coupled plasma mass spectrometry technique, indicating the crucial role of PrP^C to lower intracellular calcium. The lowered calcium concentration and the Caspase 3 downregulation in the PrP^C-null astrocytes resulted in a faster growth rate in cells, comparing with PrP^C wild-type one. The presence of PrP^C shows to be essential to cell death and healthy growth. In conclusion, our results show for the first time that astrocyte knockout cells for the cellular prion protein could modulate apoptosis-dependent cell death pathways.

Molecular and Cellular Mechanisms of Human Astrocytoma Progression: Advances in Knowledge to Reach Therapeutic Horizons

Human astrocytic tumors are primary central nervous system (CNS) tumors that arise either from astrocytes or from precursor cells. A growing number of epidemiological and incidence studies in different countries underlined that, in addition to increasing economic costs for health systems, these cancers are still representing one of the main hurdles in developing a successful therapeutic goal for patients. On the other hand, new-omics technologies are offering customized instruments and more and more advantageous results toward personalized medicine approaches, underlining the concept that each tumor mass undergoes a peculiar transformation process under the control of specific genes’ and proteins’ functional signatures. The main aim of this Special Issue was to collect novel contributions in the wide field of human tumor astrocytic basic and translational research, to suggest further potential therapeutic targets/strategies that might interfere, possibly at the earliest stage of transformation, with the tumor progression, and to increase the molecular-based arsenal to counteract the prognostic poverty of high-grade astrocytic tumors.