Contact-Inhibited ERK Signaling is Determined by Cellular-Resolution Western Blotting.

Extracellular signal-regulated kinase (ERK) signaling is essential to regulated cell behaviors, including cell proliferation, differentiation, and apoptosis. The influence of cell-cell contacts on ERK signaling is central to epithelial cells, yet few studies have sought to understand the same in cancer cells, particularly with single-cell resolution. To acquire both phenotypic (cell-contact state) and proteomic profile (ERK phosphorylation) on the same HeLa cells, we prepend high-content, whole-cell imaging prior to endpoint cellular-resolution western blot analyses for hundreds of cancer cells cultured on chip. By indexing the phosphorylation level of ERK in each cell or cell-contact cluster to the imaged cell-contact state, we compare ERK signaling between isolated and in-contact cells. We observe attenuated (∼2×) ERK signaling in HeLa cells which are in contact versus isolated. Attenuation is sustained when the HeLa cells are challenged with hyperosmotic stress. The contact-dependent differential ERK-phosphorylation corresponds to the differential EGFR distribution on cell surfaces, suggesting the involvement of EGFRs in contact-inhibited ERK signaling. Our findings show the impact of cell-cell contacts on ERK activation with isolated and in-contact cells, hence providing a new tool into control and scrutiny of cell-cell interactions.