Pan1b (17βHSD11)-enzymatic activity and distribution in the lung

We describe a new member of the 17β-hydroxysteroid dehydrogenase group of enzymes. Human Pan1b displays greatest activity with 5α-androstan-3α,17β-diol (3α-Diol) as substrate, suggesting that it may be important in androgen metabolism. Enzymic activity was non-saturable with 3α-Diol but saturable with retinoids, although retinoids were not metabolized. Immunohistochemical studies on 10% formalin fixed and paraffin embedded sections of human tissues showed that Pan1b was present in acini and ciliated epithelia of the lung. In the fetus immuno reactivity was present in ciliated epithelia throughout gestation and staining appeared to be stronger in the second half of pregnancy. Pan1b was also expressed in the nonpigmented epithelium of the ciliary body, and in adrenocortical tumor cells. Although 3α-Diol is generally considered a degradation product of androgen metabolism it could have its own biological function. Pan1b may be an important modulator of the endocrine, or intracrine activity of this steroid.