Integrin cytoplasmic domains mediate inside-out signal transduction

Prior research has shown that integrins regulate cell adhesion and signaling. It was already known that integrin affinity states influence ligand binding. However, the mechanism by which cytoplasmic domains modulate these states remains unclear. This gap motivated the investigation into how cytoplasmic domains affect integrin function. No prior work had resolved whether cytoplasmic domains alone could alter integrin affinity. This uncertainty drove the current study to explore cytoplasmic domain roles in affinity modulation. The study aimed to determine if cytoplasmic domains could confer energy-dependent high-affinity states. The research also sought to identify conserved motifs involved in integrin regulation.

The study aimed to determine how integrin cytoplasmic domains influence ligand binding affinity. Researchers focused on whether these domains could confer high-affinity states in a cell-specific manner. They also sought to identify conserved motifs that regulate integrin function. The motivation came from gaps in understanding cytoplasmic domain roles in signaling. The study tested if cytoplasmic domains could mediate inside-out signaling. It also aimed to explore whether mutations in conserved motifs affect integrin affinity. The research tested whether cytoplasmic domains alone could alter integrin function. The goal was to clarify how cytoplasmic domains modulate integrin affinity states.

Researchers constructed chimeric integrins using extracellular and transmembrane domains of alpha IIb beta 3. These chimeras were joined to cytoplasmic domains from various alpha subunits. The affinity of these chimeras was assessed using fibrinogen or PAC1 binding. Experiments were conducted in CHO and K562 cells to compare cell type effects. Cotransfection with truncated or mutated beta subunits was used to test functional dependencies. The GFFKR motif was disrupted to assess its role in affinity regulation. Binding assays measured ligand interactions under different conditions. The study used a combination of molecular biology and functional assays to analyze integrin behavior.

Chimeric integrins with alpha 5 beta 1 cytoplasmic domains conferred high-affinity binding in CHO cells. This effect was energy-dependent and absent in K562 cells. Three additional alpha cytoplasmic domains (alpha 2, alpha 6A, alpha 6B) also conferred PAC1 binding. In contrast, alpha M, alpha L, and alpha v cytoplasmic domains did not confer PAC1 binding. Cotransfection with mutated or truncated beta subunits abolished high-affinity binding. Disruption of the GFFKR motif resulted in high-affinity ligand binding. This high-affinity state was independent of cell type and energy. The GFFKR motif appears to maintain the default low-affinity state of integrins.

The cytoplasmic domains of integrins mediate inside-out signaling by modulating ligand affinity. These domains confer high-affinity states in a cell-specific and energy-dependent manner. The GFFKR motif is crucial for maintaining the default low-affinity state. Mutations in this motif result in high-affinity binding independent of cell type. The study shows that both alpha and beta cytoplasmic domains are required for affinity modulation. The findings suggest that cytoplasmic domains regulate integrin function through conserved motifs. The results support the idea that integrins use cytoplasmic domains for signaling. These conclusions align with the authors' stated implications in the abstract.