Abstract 4128: A novel approach to the measurement of tyrosine phosphorylation dynamics in intact single cells using capillary electrophoresis.
Authors: Phillips Ryan M. , Lawrence David S. , Sims Christopher E. , Allbritton Nancy L. 
Published: August 2014

Receptor tyrosine kinases (RTKs) are key components of physiological and pathological cell signaling, and are normally subject to tight regulation by protein tyrosine phosphatases (PTPs). Irregularities on either side of this equilibrium can lead to inflammation, metabolic disease, and cancer. While many established and emerging techniques have been used to characterize these signaling pathways, few approaches are well adapted to the analysis of single primary cells, and fewer still measure enzyme activity directly. We report a new method for measuring the balance between RTK and PTP activity using fluorescent peptide substrates in conjunction with capillary electrophoresis. Briefly, live cells are visualized on an inverted microscope, microinjected with a fluorescent peptide substrate which is acted upon by RTKs and/or PTPs. After the desired time interval, a single cell is lysed using a microsecond laser pulse and cell contents are aspirated into a fused-silica capillary where electrophoresis is performed and reporter species are separated and quantified based on phosphorylation status. We have applied this technique to the characterization of PTP inhibition in single A431 cells by several components of diesel exhaust particles, an important component of air pollution linked to cancer. We have also adapted this system to measure the effects of small-molecule epidermal growth factor receptor (EGFR) inhibitors on RTK activity in tumor cell lines as well as tumor xenograft models, also at the single cell level.

This approach provides a unique set of advantages over alternative techniques and is a valuable tool for the study of cell signaling in cancer. The integrated microscopy permits selection of cells for analysis based on morphology, viability, or vital staining, an important consideration for analysis of heterogeneous samples such as tumor specimens, especially when total sample size is small. High-sensitivity detection allows chemical cytometry data from individual cells to be gathered and the presence of phenotypic subpopulations is not lost by observing only the average behavior of a large population. Additionally, peptide substrate reporters can be tuned for enzyme specificity, and the analytical separation allows multiple reporter pairs to be separated and detected in a single experiment, permitting simultaneous analysis of multiple enzymes. The introduction of reporter peptides by microinjection preserves cellular architecture, while being equally applicable to immortalized and primary cells since no genetic manipulation is necessary. This array of advantages makes our approach uniquely well suited to the study of RTK and PTP signaling in both cultured tumor cell lines and patient specimens and a valuable new tool for cancer research.

Citation Format: Ryan M. Phillips, David S. Lawrence, Christopher E. Sims, Nancy L. Allbritton. A novel approach to the measurement of tyrosine phosphorylation dynamics in intact single cells using capillary electrophoresis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4128. doi:10.1158/1538-7445.AM2013-4128