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The progesterone receptor A (PR-A) is one of three known 
PR-A is 164 residues shorter than PR-B in humans and anywhere from 128-165 residues shorter in other organisms. Each isoform binds its natural ligand, progesterone, but also demonstrates the ability to bind a number of other agonists including norethindrone, a synthetic progestin.
isoform
A protein isoform, or "protein variant", is a member of a set of highly similar proteins that originate from a single gene and are the result of genetic differences. While many perform the same or similar biological roles, some isoforms have uniqu ...
s of the progesterone receptor
The progesterone receptor (PR), also known as NR3C3 or nuclear receptor subfamily 3, group C, member 3, is a protein found inside cells. It is activated by the steroid hormone progesterone.
In humans, PR is encoded by a single ''PGR'' gene resi ...
(PR), the main biological target
A biological target is anything within a living organism to which some other entity (like an endogenous ligand or a drug) is directed and/or binds, resulting in a change in its behavior or function. Examples of common classes of biological targets ...
of the endogenous
Endogeny, in biology, refers to the property of originating or developing from within an organism, tissue, or cell.
For example, ''endogenous substances'', and ''endogenous processes'' are those that originate within a living system (e.g. an ...
progestogen
Progestogens, also sometimes written progestins, progestagens or gestagens, are a class of natural or synthetic steroid hormones that bind to and activate the progesterone receptors (PR). Progesterone is the major and most important progestoge ...
sex hormone
Sex hormones, also known as sex steroids, gonadocorticoids and gonadal steroids, are steroid hormones that interact with vertebrate steroid hormone receptors. The sex hormones include the androgens, estrogens, and progestogens. Their effects a ...
progesterone
Progesterone (; P4) is an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. It belongs to a group of steroid hormones called the progestogens and is the ma ...
. The other isoforms of the PR include the PR-B and PR-C.
PR-A is 164 residues shorter than PR-B in humans and anywhere from 128-165 residues shorter in other organisms. Each isoform binds its natural ligand, progesterone, but also demonstrates the ability to bind a number of other agonists including norethindrone, a synthetic progestin.
Expression and overexpression
PR-A and PR-B are generally expressed in equal ratios, but PR-A is expressed in larger amounts in uterine stromal cells normally. A spike in PR-A expression in the myometrium has been observed to initiate parturition in placental mammals. PR-A is the isoform most commonly observed to be overexpressed in human breast cancer and patients with PR-A rich carcinomas, as opposed to patients with PR-B rich carcinomas, have faster recurrence rates.See also
*Membrane progesterone receptor
Membrane progesterone receptors (mPRs) are a group of cell surface receptors and membrane steroid receptors belonging to the progestin and adipoQ receptor (PAQR) family which bind the endogenous progestogen and neurosteroid progesterone, as well as ...
References
Intracellular receptors Progestogens Transcription factors {{receptor-stub