No abstract

The nitrogen-related phosphotransferase system (Ntr-PTS) is a paralogous system working in parallel to the well-known carbohydrate:PTS. In a chain of phosphotransfer reactions, EINtr and NPr (PtsO) deliver phosphoryl groups to the EIIANtr (PtsN) protein. EIIANtr is implicated in important regulatory processes such as the sigmaE-dependent cell envelope stress response and regulation of K+ uptake. Phosphorylation is believed to trigger the output of EIIANtr in these regulations. EIIANtr is encoded within the gene cluster ptsN-yhbJ-ptsO, which is highly conserved in Proteobacteria. In this study, we investigated the phosphorylation of the Escherichia coli EIIANtr protein in vivo by 32P-labeling. We show that EIIANtr is readily phosphorylated in wild-type cells. This phosphorylation occurs at a single site, the histidine 73 in EIIANtr. YhbJ and NPr are dispensable for this phosphorylation. A detailed analysis revealed that both the energy coupling phosphotransferases of the Ntr-PTS as well as the 'sugar'-PTS contribute to the phosphorylation of EIIANtr, suggesting cross talk between both systems.

No abstract

Medullary thyroid carcinoma (MTC) is a neuroendocrine cancer of thyroid C-cells, for which few treatment options are available. We have recently reported a role for cyclin-dependent kinase 5 (CDK5) in MTC pathogenesis. We have generated a mouse model, in which MTC proliferation is induced upon conditional overexpression of the CDK5 activator, p25, in C-cells, and arrested by interrupting p25 overexpression. Here, we identify genes and proteins that are differentially expressed in proliferating versus arrested benign mouse MTC. We find that downstream target genes of the tumor suppressor, retinoblastoma protein, including genes encoding cell cycle regulators such as CDKs, cyclins and CDK inhibitors, are significantly upregulated in malignant mouse tumors in a CDK5-dependent manner. Reducing CDK5 activity in human MTC cells down-regulated these cell cycle regulators suggesting that CDK5 activity is critical for cell cycle progression and MTC proliferation. Finally, the same set of cell cycle proteins was consistently overexpressed in human sporadic MTC but not in hereditary MTC. Together these findings suggest that aberrant CDK5 activity precedes cell cycle initiation and thus may function as a tumor-promoting factor facilitating cell cycle protein expression in MTC. Targeting aberrant CDK5 or its downstream effectors may be a strategy to halt MTC tumorigenesis.

N-terminally truncated pyroglutamate amyloid-β (Aβ) starting at position 3 (AβpE3) represents a major fraction of Aβ peptides in Alzheimer's disease (AD). Recently, we have identified low molecular weight AβpE3 oligomers, which can be detected by 9D5, a novel mouse monoclonal antibody. In the present study, we analyzed the immunohistochemical staining profile in the brain of patients with AD and in the APP/PS1KI mouse model, as well as in aged rhesus monkeys. 9D5-positive microglia and blood vessels were found in many AD cases, in the transgenic mouse model, and in an aged macaque. The presence of 9D5-immunoreactivity in microglia indicates that low molecular weight AβpE3 oligomers may be phagocytosed, since in the APP/PS1KI model, Aβ is exclusively produced in neurons due to neuronal expression of transgenic AβPP.