Comparison of variability and sensitivity between nuclear translocation and luciferase reporter gene assays

Noncanonical CDK4 signaling rescues diabetes in a mouse model by promoting β cell differentiation

Expanding β cell mass is a critical goal in the fight against diabetes. CDK4, an extensively characterized cell cycle activator, is required to establish and maintain β cell number. β cell failure in the IRS2-deletion mouse type 2 diabetes model is, in part, due to loss of CDK4 regulator cyclin D2. We set out to determine whether replacement of endogenous CDK4 with the inhibitor-resistant mutant CDK4-R24C rescued the loss of β cell mass in IRS2-deficient mice. Surprisingly, not only β cell mass but also β cell dedifferentiation was effectively rescued, despite no improvement in whole body insulin sensitivity. Ex vivo studies in primary islet cells revealed a mechanism in which CDK4 intervened downstream in the insulin signaling pathway to prevent FOXO1-mediated transcriptional repression of critical β cell transcription factor Pdx1. FOXO1 inhibition was not related to E2F1 activity, to FOXO1 phosphorylation, or even to FOXO1 subcellular localization, but rather was related to deacetylation and reduced FOXO1 abundance. Taken together, these results demonstrate a differentiation-promoting activity of the classical cell cycle activator CDK4 and support the concept that β cell mass can be expanded without compromising function.

High-Content Reporter Assays

While luminescent reporter gene assays allow for a rapid and relatively interference free assessment of the activation state of a luminescent reporter, fluorescent reporters do not. They suffer from artifacts such as compound fluorescence and cellular debris which makes the assessment of whole well fluorescence signals difficult. However, the use of high-content screening allows for the isolation of individual cells, segmentation and thus enables the screener to utilize fluorescent reporters to assess the activation state of such a high-content reporter on a cell by cell level, thus minimizing artifacts. Here we discuss the use of such a high-content reporter that enables screening for compounds useful for HIV reactivation on Jurkat cells with high-content screening.

A high-content screen identifies inhibitors of nuclear export of forkhead transcription factors

Class O forkhead box (FOXO) transcription factors are downstream targets of the PI3K/AKT signaling pathway, which is upregulated in many tumors. AKT phosphorylates and inactivates FOXO1 by relocating it to the cytoplasm. Because FOXO1 functions as a tumor suppressor by negatively regulating cell cycle progression and cell survival, compounds that promote FOXO1 localization to the nucleus might have therapeutic value in oncology. Here the authors describe the identification of such compounds by using an image-based, high-content screen. Compounds that were active in retaining FOXO1 in the nucleus were tested to determine their pathway specificity and isoform specificity by using high-content assays for Rev and FOXO3, respectively.