Review Question - QID 212600

A 28-year-old woman presents for evaluation by a gynecologist because she has been experiencing unusual bloody vaginal discharge over the last 4 months. Specifically, she has noticed sporadic and prolonged vaginal bleeding that does not appear to correspond to her normal menstrual cycle. She has no past medical history, does not smoke, and drinks alcohol socially. Pelvic exam reveals a mass within the vagina and a biopsy of the lesion is obtained. A histological section of this mass is shown in Figure A. Her physician informs her that this lesion was the result of excessive activation of a certain receptor. The most likely normal ligand for this receptor has which of the following properties?