Dynamics and physiological meaning of complexes between ion channels and integrin receptors: the case of Kv11.1.

The cellular functions are regulated by a complex interplay of diffuse and local signals. Studying the latter is challenging, but experimental work in cell physiology has led to recognize that understanding a cell's dynamics requires a deep comprehension of local fluctuations of cytosolic regulators. Macromolecular complexes are major determinants of local signaling. Multienzyme assemblies limit the diffusion restriction to reaction kinetics by direct exchange of metabolites. Likewise, close coupling of ion channels and transporters modulates the ion concentration around a channel mouth or transporter binding site. Extreme signal locality is brought about by conformational coupling between membrane proteins, as is typical of mechanotransduction. A paradigmatic case is integrin-mediated cell adhesion. Sensing the extracellular microenvironment and providing an appropriate response are essential in growth and development and have innumerable pathological implications. The process involves bidirectional signal transduction by complex supramolecular structures that link integrin receptors to ion channels and transporters, growth factor receptors, cytoskeletal elements, and other regulatory elements. The dynamics of such complexes are only beginning to be understood. A thoroughly studied example is the association between integrin receptors and the voltage-gated K channels Kv11.1. These channels are widely expressed in early embryos, where their physiological roles are poorly understood and apparently different from the shaping of action potential firing in the adult. Hints about these roles come from studies in cancer cells, where Kv11.1 is often overexpressed and appears to reassume functions it presumably exerts during embryogenesis, such as controlling cell proliferation/differentiation, apoptosis, and migration. Kv11.1 is implicated in these processes through its linking to integrin subunits, which in turn regulates channel expression. Specific cellular functions, such as proliferation and migration, appear to be modulated by distinct conformational states of the channel (e.g., open and closed), whose balance is affected by the link with integrin subunits.