Biochemical cascade in the context of Basal cell carcinoma

Peyronie's disease (PD) is a benign, acquired penile connective tissue disease characterized by the occurrence of fibrotic plaques within the tunica albuginea — the dense elastic covering of the corpora cavernosa. The plaques cause abnormal curvature, pain, penile deformities (e.g., narrowing or indentation), and usually erectile dysfunction, particularly during erection. The condition typically leads to significant sexual and psychological effects, including difficulty with penetration and lowered self-esteem or evasiveness. Peyronie's disease is most often seen in middle-aged and older men with a median age of onset between 55 and 60 years, however it is also common in younger individuals and adolescents.

While the etiology of Peyronie's disease is still uncertain, the leading hypothesis is that it arises from dysregulated wound healing in response to chronic microtrauma of the erect penis. This triggers a cascade of profibrotic molecular pathways — most notably overexpression of transforming growth factor-beta 1 (TGF-β1) — that end in fibroblast proliferation, myofibroblast differentiation, and overproduction of type I collagen. Genetic predisposition is supported by family clustering and linkage with systemic fibrosing disorders such as Dupuytren's contracture. Risk factors include age, penile injury, diabetes mellitus, and cigarette smoking.

The cluster of differentiation (also known as cluster of designation or classification determinant and often abbreviated as CD) is a protocol used for the identification and investigation of cell surface molecules providing targets for immunophenotyping of cells. In terms of physiology, CD molecules can act in numerous ways, often acting as receptors or ligands important to the cell. A signal cascade is usually initiated, altering the behavior of the cell (see cell signaling). Some CD proteins do not play a role in cell signaling, but have other functions, such as cell adhesion. CD for humans is numbered up to 371 (as of 21 April 2016).

Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events. Proteins responsible for detecting stimuli are generally termed receptors, although in some cases the term sensor is used. The changes elicited by ligand binding (or signal sensing) in a receptor give rise to a biochemical cascade, which is a chain of biochemical events known as a signaling pathway.

When signaling pathways interact with one another they form networks, which allow cellular responses to be coordinated, often by combinatorial signaling events. At the molecular level, such responses include changes in the transcription or translation of genes, and post-translational and conformational changes in proteins, as well as changes in their location. These molecular events are the basic mechanisms controlling cell growth, proliferation, metabolism and many other processes. In multicellular organisms, signal transduction pathways regulate cell communication in a wide variety of ways.

Cell surface receptors (membrane receptors, transmembrane receptors) are receptors that are embedded in the plasma membrane of cells. They act in cell signaling by receiving (binding to) extracellular molecules. They are specialized integral membrane proteins that allow communication between the cell and the extracellular space. The extracellular molecules may be hormones, neurotransmitters, cytokines, growth factors, cell adhesion molecules, or nutrients; they react with the receptor to induce changes in the metabolism and activity of a cell. In the process of signal transduction, ligand binding affects a cascading chemical change through the cell membrane.

Guanylate cyclase (EC 4.6.1.2, also known as guanyl cyclase, guanylyl cyclase, or GC; systematic name GTP diphosphate-lyase (cyclizing; 3′,5′-cyclic-GMP-forming)) is a lyase enzyme that converts guanosine triphosphate (GTP) to cyclic guanosine monophosphate (cGMP) and pyrophosphate:

It is often part of the G protein signaling cascade that is activated by low intracellular calcium levels and inhibited by high intracellular calcium levels. In response to calcium levels, guanylate cyclase synthesizes cGMP from GTP. cGMP keeps cGMP-gated channels open, allowing for the entry of calcium into the cell.