Exploration of simulated urine sample biochemistry for the diagnosis of diseases: A laboratory practical exercise.

The practical work described here is designed for third-year bachelor students in Life Sciences attending a kidney physiology course. It illustrates how urinary biochemistry can be used for a medical diagnosis. Students have to measure glucose, proteins, and creatinine concentrations in three simulated urine samples. First, they independently elaborate detailed protocols from the biochemical kit's technical sheets. Second, after correction of the protocols by the teacher, they perform the biochemical assays. Finally, students write a report in which they interpret the biochemical data and use them in the context of histological images assigned to each urine sample. With their results, their theoretical background and scientific articles supplied by the teacher, they establish the diagnosis indicating which patients are diseased and from which disease they are suffering (diabetes without nephropathy, diabetic nephropathy or hypertensive nephropathy). The originality of this practical work is to give student autonomy from the start of the project by requiring them to write the protocols, and determine the diagnosis by themselves. Simple and inexpensive, this practical forces students to mobilize their knowledge in renal physiology and pathophysiology as well as those acquired in other disciplines such as biochemistry or cellular biology. A survey conducted on two classes of students confirmed that this type of training helps students to better understand renal physiology, to realize the importance of interdisciplinarity (biochemistry, histology, and physiology) and to develop confidence in their ability to work independently.

Phosphorylation of the MNK1 substrate eIF4E is not required for response to acute pancreatitis.

BACKGROUND: The MNK1 protein kinase is directly activated by the MAPK pathway and is specifically expressed in pancreatic acinar cells. Both the MNK1 kinase and the MAPK pathway are required for response to pancreatitis, suggesting that their pharmacological targeting would be of therapeutic interest. Because the mRNA cap-binding protein and translation initiation factor eIF4E is the major known MNK1 substrate, one could anticipate that the protective function of MNK1 in pancreatitis is mediated by eIF4E phosphorylation. METHODS: Acute pancreatitis was induced by the intraperitoneal administration of cerulein in wild-type mice and in transgenic mice carrying two non-phosphorylatable Eif4e alleles. The expression and phosphorylation of proteins of the MNK1-eIF4E pathway was visualized by western-blotting. The severity of pancreatitis was monitored by the measure of serum amylase levels and by histopathology and immunohistochemistry using apoptosis and immune infiltrate markers. RESULTS: Despite a strong induction in MNK1 kinase activity in both wild-type and transgenic mice, precluding eIF4E phosphorylation has no impact on the severity of acute pancreatitis. Serum amylase is equally induced in both mouse genotypes and neither acinar cell apoptosis nor immune infiltrate is exacerbated. CONCLUSION: eIF4E phosphorylation is not required for response to pancreatitis indicating that the acinar-cell-specific MNK1 kinase acts in acute pancreatitis via another substrate.

Contribution of HIF-1α in 4E-BP1 gene expression.

The eukaryotic translation initiation factor 4E (eIF4E) is necessary for the translation of capped mRNAs into proteins. Cap-dependent mRNA translation can be however inhibited by the eIF4E-binding protein 1 (4E-BP1). The hypophosphorylated forms of 4E-BP1 indeed sequester eIF4E and thus block translation initiation and consequent protein synthesis. Different reports indicate that, in addition to hypophosphorylation, 4E-BP1 function can be also regulated at the level of protein expression. This is the case in contact-inhibited cells or in cells exposed to hypoxia. The molecular mechanisms responsible for 4E-BP1 protein accumulation in these conditions remain however unknown. In the present study, we found that 4E-BP1 gene promoter contains a hypoxia-responsive element (HRE) that mediates 4E-BP1 gene upregulation via the hypoxia-inducible factor-1 alpha (HIF-1α) transcription factor. Gene reporter assays then revealed that the presence of such HRE in the promoter of 4E-BP1 gene is involved in 4E-BP1 accumulation in contact-inhibited cells and in cells exposed to hypoxia. We also reveal that the TGF-ß-dependent transcription factor SMAD4 cooperates with HIF-1α to fully activate 4E-BP1 gene transcription under hypoxia. These data therefore suggest that HIF-1α contributes to 4E-BP1 gene expression under different conditions.

4E-BP restrains eIF4E phosphorylation.

In eukaryotes, mRNA translation is dependent on the cap-binding protein eIF4E. Through its simultaneous interaction with the mRNA cap structure and with the ribosome-associated eIF4G adaptor protein, eIF4E physically posits the ribosome at the 5' extremity of capped mRNA. eIF4E activity is regulated by phosphorylation on a unique site by the eIF4G-associated kinase MNK. eIF4E assembly with the eIF4G-MNK sub-complex can be however antagonized by the hypophosphorylated forms of eIF4E-binding protein (4E-BP). We show here that eIF4E phosphorylation is dramatically affected by disruption of eIF4E-eIF4G interaction, independently of changes in MNK expression. eIF4E phosphorylation is actually strongly downregulated upon eIF4G shutdown or upon sequestration by hypophosphorylated 4E-BP, consequent to mTOR inhibition. Downregulation of 4E-BP renders eIF4E phosphorylation insensitive to mTOR inhibition. These data highlight the important role of 4E-BP in regulating eIF4E phosphorylation independently of changes in MNK expression.

Changes in translational control after pro-apoptotic stress.

In stressed cells, a general decrease in the rate of protein synthesis occurs due to modifications in the activity of translation initiation factors. Compelling data now indicate that these changes also permit a selective post-transcriptional expression of proteins necessary for either cell survival or completion of apoptosis when cells are exposed to severe or prolonged stress. In this review, we summarize the modifications that inhibit the activity of the main canonical translation initiation factors, and the data explaining how certain mRNAs encoding proteins involved in either cell survival or apoptosis can be selectively translated.

Clinical review: Current scientific rationale for the use of somatostatin analogs and mTOR inhibitors in neuroendocrine tumor therapy.

CONTEXT: Among the innovative molecules used to manage neuroendocrine tumors, there is growing interest in combining the somatostatin analogs octreotide or pasireotide (SOM230) and everolimus (RAD001), an inhibitor that targets the protein kinase mammalian target of rapamycin (mTOR). EVIDENCE ACQUISITION: The aims of this review were to describe the signaling pathways targeted independently by somatostatin analogs and everolimus and to summarize the scientific rationale for the potential additive or synergistic antitumor effects of combined therapy. EVIDENCE SYNTHESIS: The somatostatin analogs (octreotide and lanreotide) have potent inhibitory effects on hypersecretion, thereby alleviating the symptoms associated with neuroendocrine tumors. Furthermore, the antitumor potential of octreotide is now well documented. Pasireotide, a somatostatin analog, has the advantage of targeting a wider range of somatostatin receptors (subtypes 1, 2, 3, and 5) than the analogs previously used in clinical practice (which preferentially target subtype 2) and thus has a broader spectrum of activity. Everolimus is a rapamycin analog that inhibits mTOR, but it is more soluble than rapamycin and can be administered orally. mTOR is a protein kinase involved in many signaling pathways, primarily those initiated by tyrosine kinase receptors. Sustained mTOR activity leads to the induction of cell growth, proliferation, and cell survival. Everolimus therefore has obvious potential in cancer therapy. CONCLUSIONS: The combination of somatostatin analogs and everolimus in therapeutic trials offers a promising treatment option for neuroendocrine tumors.