6.2: Autocrine Signaling

Autocrine signaling is one of the many signaling mechanisms that function inside multicellular organisms to carry out intercellular communication. In this type of signaling mechanism, the same cell that secretes an extracellular signaling molecule also expresses the receptors to bind and respond to that signaling molecule.

Autocrine Signaling in Macrophages

Under normal physiological conditions, autocrine signaling is essential for maintaining homeostasis. This process is well characterized in the macrophages of the immune system. These cells secrete a variety of signals, such as the cytokine Interleukin-1 (IL-1), and also possess membrane receptors for IL-1. This means that, upon secretion, IL1 can bind to receptors on the macrophages and activate an intracellular signaling cascade. The resulting intracellular signals trigger the secretion of additional cytokines, including more IL-1, from the macrophages. Though IL-1 secreted by macrophages can also bind to receptors on other cell types, binding to the signaling cell is important to regulate signal production.

Autocrine Signaling & Cancer

Autocrine signaling is also a major signaling mechanism in cancer cells. Cancerous cells secrete a variety of self-sustaining growth signals that act as autocrine mediators and control cell division rates. For example, in the majority of breast cancer cases, cancer cells express progesterone receptors on their cell surface. These receptors bind to progesterone released from the cancer cells themselves, thus, acting in an autocrine manner to stimulate cell proliferation.

Multicellular organisms use four main means of chemical signaling pathways for communication— autocrine, paracrine, endocrine, and contact-dependent.

Autocrine signaling is a form of communication where a cell interacts with itself.

In this type of signaling, the cell secretes a chemical messenger called an autocrine agent. These molecules bind to the receptors present on the same cell surface. As a result, one cell acts as the signaling as well as the target cell.

For example, during infection, microbial products trigger white blood cells called T lymphocytes to release a class of small proteins known as cytokines.

The cytokines are autocrine agents which bind to the receptors present on the surface of T lymphocytes and activate intracellular cascades that can induce a response, such as cellular proliferation.