Polyoma small T upregulates the expression of cytoskeletal proteins in mammalian cells during mitosis

Polyomavirus Small T Antigen Induces Apoptosis in Mammalian Cells through the UNC5B Pathway in a PP2A-Dependent Manner

UNC5B is a dependence receptor that promotes survival in the presence of its ligand, netrin-1, while inducing cell death in its absence. The receptor has an important role in the development of the nervous and vascular systems. It is also involved in the normal turnover of intestinal epithelium. Netrin-1 and UNC5B are deregulated in multiple cancers, including colorectal, neuroblastoma, and breast tumors. However, the detailed mechanism of UNC5B function is not fully understood. We have utilized the murine polyomavirus small T antigen (PyST) as a tool to study UNC5B-mediated apoptosis. PyST is known to induce mitotic arrest followed by extensive cell death in mammalian cells. Our results show that the expression of PyST increases mRNA levels of UNC5B by approximately 3-fold in osteosarcoma cells (U2OS) and also stabilizes UNC5B at the posttranslational level. Furthermore, UNC5B is upregulated predominantly in those cells that undergo mitotic arrest upon PyST expression. Interestingly, although its expression was previously reported to be regulated by p53, our data show that the increase in UNC5B levels by PyST is p53 independent. The posttranslational stabilization of UNC5B by PyST is regulated by the interaction of PyST with PP2A. We also show that netrin-1 expression, which is known to inhibit UNC5B apoptotic activity, promotes survival of PyST-expressing cells. Our results thus suggest an important role of UNC5B in small-T antigen-induced mitotic catastrophe that also requires PP2A.IMPORTANCE UNC5B, PP2A, and netrin-1 are deregulated in a variety of cancers. UNC5B and PP2A are regarded as tumor suppressors, as they promote apoptosis and are deleted or mutated in many cancers. In contrast, netrin-1 promotes survival by inhibiting dependence receptors, including UNC5B, and is upregulated in many cancers. Here, we show that UNC5B-mediated apoptosis can occur independently of p53 but in a PP2A-dependent manner. A substantial percentage of cancers arise due to p53 mutations and are insensitive to chemotherapeutic treatments that activate p53. Unexpectedly, treatment of cancers having functional p53 with many conventional drugs leads to the upregulation of netrin-1 through activated p53, which is counterintuitive. Therefore, understanding the p53-independent mechanisms of the netrin-UNC5B axis, such as those involving PP2A, assumes greater clinical significance. Anticancer strategies utilizing anti-netrin-1 antibody treatment are already in clinical trials.

Quantitative proteomic analysis reveals high interference on protein expression of H9c2 cells activated with glucose and cardiotonic steroids

In recent decades, the incidence of death and morbidity due to diabetes has increased worldwide, causing a high social and economic impact. Diabetes is a major cause of blindness, kidney failure, heart attack, stroke and lower limb amputation. However, the molecular mechanisms that make the heart and kidneys the main targets of diabetes are not completely understood. To better understand the complex biochemical mechanism of diabetic cardiomyopathy, we investigated the effects of hyperglycemia with concomitant digoxin and ouabain stimulation in H9c2 cells. Total extracted proteins were analyzed by label-free LC-MS/MS, quantified by Scaffold software and validated by parallel reaction monitoring (PRM) methodology. Here, we show that the eukaryotic initiation factors (Eifs) and elongation factors (Eefs) Eif3f, Eef2 and Eif4a1 are overexpressed following cardiotonic steroid (CTS) stimulation. Similarly, the expression of four 14-3-3 proteins that play a key role in cardiac ventricular compaction was altered after CTS stimulation. In total, the expression of nine protein groups was altered in response to the stimulation of H9c2 cells. Here, the biological consequences of these changes are discussed in depth. SIGNIFICANCE: Hyperglycemia is the main physiological condition that provokes tissue and vascular injuries in heart of diabetic patients. However, the changings at large scale in the expression of proteins of cardiomyocytes generated by this condition was not yet studied. Here we report for the first time the altered biosynthesis of nine groups of proteins of H9c2 cells activated by high glucose concentrations and by cardiotonic steroids (CTS). Furthermore, the increased biosynthesis of Eifs, Eefs and 14-3-3 protein groups by CTS, which play a crucial role in cardiomyopathies are original data reported in this work. These findings not only enhance our knowledge concerning to the effects of hyperglycemia and CTS on H9c2 cells but also indicate potential molecular targets to interfere in diabetes cardiomyopathy progression.