Image-based high-throughput mapping of TGF-β-induced phosphocomplexes at a single-cell level

Abstract

Protein interactions and posttranslational modifications orchestrate cellular responses to e.g. cytokines and drugs, but it has been difficult to monitor these dynamic events in high-throughput. Here, we describe a semi-automated system for large-scale in situ proximity ligation assays (isPLA), combining isPLA in microtiter wells with automated microscopy and computer-based image analysis. Phosphorylations and interactions are digitally recorded along with subcellular morphological features. We investigated TGF-β-responsive Smad2 linker phosphorylations and complex formations over time and across millions of individual cells, and we relate these events to cell cycle progression and local cell crowding via measurements of DNA content and nuclear size of individual cells, and of their relative positions. We illustrate the suitability of this protocol to screen for drug effects using phosphatase inhibitors. Our approach expands the scope for image-based single cell analyses by combining observations of protein interactions and modifications with morphological details of individual cells at high throughput.

Monitoring drug–target interactions through target engagement-mediated amplification on arrays and in situ

“…Circularizing oligonucleotides (padlock probes) were designed with 5′ and 3′ ends complementary to adjacent segments of the oligonucleotides conjugated to the drug molecules. Once converted to oligonucleotide circles by ligation, the probes were replicated through localized RCA, primed by the drug-conjugated oligonucleotides, and visualized using fluorescence-labeled hybridization probes to the repeated sequence of the RCA products ( 61 , 62 ). RCA offers a signal enhancement of several hundredfold over singly fluorophore labeled compounds, permitting visualization of even single bound drug probes (Figure 2A ).…”