What is the Origin of Term 12?

This term is a key concept in molecular endocrinology, established when the mechanism of steroid hormone action was elucidated, showing that these lipophilic hormones act via nuclear receptors. The discovery of the distinct PR-A and PR-B isoforms highlighted the complexity of progesterone signaling and the ability of a single hormone to elicit multiple, tissue-specific responses. Clinical therapeutics often rely on modulating these receptors.

What is the Mechanism of Term 12?

Progesterone, being lipid-soluble, passively diffuses across the cell membrane and binds to the inactive PR in the cytoplasm or nucleus, causing the receptor to undergo a conformational change. The activated hormone-receptor complex then dimerizes and translocates to the nucleus, where it binds to Progesterone Response Elements (PREs) on the DNA. This binding event either enhances or suppresses the transcription of specific target genes, leading to the biological effects of progesterone, such as endometrial differentiation.

Term 12 ∞ Area

Term 12

Meaning

Progesterone Receptors (PR) are intracellular proteins found in the nuclei of target cells, particularly in the uterus, breast tissue, brain, and bone, that bind to the hormone progesterone to mediate its diverse physiological effects. These receptors exist in two main isoforms, PR-A and PR-B, which are expressed in varying ratios across tissues and trigger distinct gene expression patterns. The functionality and density of these receptors are critical determinants of a tissue’s response to progesterone, influencing menstrual cycle regularity, gestation, and neuroprotection.