The activity and expression of the sulfotransferase 2B1 isoforms in human prostate, placenta, breast, and skin.

摘要

Sulfotransferases (SULTs) are the enzymes responsible for catalyzing conjugation reactions that transfer a sulfonate (SO₃− ) group of the donor compound, 3′-phospho-adenosine 5′-phosphosulfate (PAPS), to endogenous and xenobiotic compounds. In particular, the SULT2 family of enzymes, also known as the hydroxysteroid SULT family, sulfate hydroxysteroid compounds such as dehydroepiandrosterone (DHEA), pregnenolone, 3β-17β-androstenediol, androsterone, and epiandrosterone. Two members of the SULT2 family are the SULT2B1 isoforms, SULT2B1a and SULT2B1b, which are both encoded on one gene. The isoforms share a 94% identity and differ only at their 5′ termini. The SULT2B1 isoforms differ from other SULTs by having extended N- and C-terminal ends as compared to other amino acid sequences of known cytosolic SULTs. The SULT2B1 C-terminal ends are rich in proline residues, which are known to participate in protein binding.; The SULT2B1 isoforms have the greatest affinity for the sulfation of substrates containing a 3β-hydroxyl group (OH). Examples of such compounds are the 3β-hydroxysteroids such as DHEA, pregnenolone, and 3β-17β-androstenediol. During this investigation, the SULT2B1b mRNA and protein was identified in human prostate, placenta, skin, breast tumor, LNCaP prostate cancer cells, and MCF-7 breast cancer cells. The SULT2B1a mRNA was not detected by Northern blot analysis of human tissues; however, it may be detected by more sensitive techniques. The SULT2B1a protein was not detected in any human tissues by immunoblot analysis; however, SULT2B1a cDNA can be transcribed and translated during in vitro analysis. Immunohistochemical techniques localized the SULT2B1b protein to the cytoplasm of the prostate epithelial cells, the nuclei of placental trophoblast cells, the cytoplasm of normal breast and breast cancer cells, and the epidermis, hair follicle, sebaceous and sweat glands of human skin. SULT2B1b was found to catalyze the sulfation of DHEA in LNCaP, MCF-7, and BeWo placental cells stably expressing SULT2B1b.; The results presented in this dissertation represent the molecular, kinetic, and biochemical characterization of the human SULT2B1 isoforms. Future studies will allow this knowledge to be used to generate a better understanding of the role of these enzymes in the metabolism of hormones under normal and abnormal physiological conditions in the prostate, placenta, breast, and skin.