When collision is unavoidable, a different phenomenon occurs whereby growth of the cells of the culture itself eventually stops in a cell-density dependent manner.
[2] Both types of contact inhibition are well-known properties of normal cells and contribute to the regulation of proper tissue growth, differentiation, and development.
However, contact inhibition of locomotion and proliferation are both aberrantly absent in cancer cells, and the absence of this regulation contributes to tumorigenesis.
[6] Moreover, it is important to note that such an inhibition of mitotic activity is a local phenomenon; it occurs between a select few cells in a likely heterogeneous culture.
[7] This property is known as contact inhibition of proliferation and is essential to proper embryonic development, as well as tissue repair, differentiation, and morphogenesis.
This pathway consists primarily of a phosphorylation cascade involving serine kinases and is mediated by regulatory proteins, which regulate cell growth by binding to growth-controlling genes.
The phosphorylation of YAP serves to export it from the nucleus and prevent it from activating growth-promoting genes; this is how the Hippo-YAP pathway inhibits cell growth.
[10] More importantly, the Hippo-YAP pathway uses upstream elements to act in response to cell-cell contact and controls density-dependent inhibition of proliferation.
For example, cadherins are transmembrane proteins that form cellular junctions via homophilic binding[11] and thus act as detectors for cell-cell contact.
In fact, it has been shown that contact-inhibited cells resume normal proliferation and mitogen signaling upon being replated in a less confluent culture.
[17] In most cases, when two cells collide they attempt to move in a different direction to avoid future collisions; this behavior is known as contact inhibition of locomotion.
This produces significant elastic tension across the entire cell bodies, not only at the local site of contact, and likewise causes the adhesion complex's disassembly.