Cytochrome b5 expression in gonadectomy-induced adrenocortical neoplasms of the domestic ferret (Mustela putorius furo)

Abstract

Whereas the adrenal glands of healthy ferrets produce only limited amounts of androgenic steroids, adrenocortical neoplasms that arise in neutered ferrets typically secrete androgens or their derivative, estrogen. The 17,20-lyase activity of cytochrome P450 17alpha-hydroxylase/17,20-lyase (P450c17) must increase to permit androgen biosynthesis in neoplastic adrenal tissue. We screened ferret adrenocortical tumor specimens for expression of cytochrome b(5) (cyt b(5)), an allosteric regulator that selectively enhances the 17,20-lyase activity of P450c17. Cyt b(5) immunoreactivity was evident in 24 of 25 (96%) adrenocortical adenomas/carcinomas from ferrets with signs of ectopic sex steroid production. Normal adrenocortical cells lacked cyt b(5), which may account for the low production of adrenal androgens in healthy ferrets. Other markers characteristic of gonadal somatic cells, such as luteinizing hormone receptor, aromatase, and GATA4, were coexpressed with cyt b(5) in some of the tumors. We concluded that cyt b(5) is upregulated during gonadectomy-induced adrenocortical neoplasia and is a marker of androgen synthetic potential in these tumors.

Fig. 1

Steroid hormone biosynthesis in normal (solid lines) versus neoplastic (dashed lines) adrenocortical cells. All steroidogenic cells share the capacity to mobilize and cleave cholesterol. The repertoire of enzymes distal to P450scc determines the steroidogenic capacity of a given cell. Note that P450c17 has both 17α-hydroxylase and 17,20-lyase activities. Cyt b₅ selectively enhances the 17,20-lyase activity of P450c17 through allosteric effects. Abbreviations: 3β-HSD, 3β-hydroxysteroid dehydrogenase; 17β-HSD, 17β-hydroxysteroid dehydrogenase; cyt b₅, cytochrome b₅; DOC, deoxycorticosterone; DHEA, dehydroepiandrosterone; P450aldo, aldosterone synthase; P450c11, cytochrome P450 11β-hydroxylase; P450c17, cytochrome P450 17α-hydroxylase/17,20-lyase; P450c21, cytochrome P450 21-hydroxylase.

Fig. 2

Adrenal gland, adrenocortical carcinoma; ferret. The junction between the zona reticularis (zr) and medulla (m) is shown. Note that normal cells in the zr lack expression of cyt b₅ and GATA4, whereas adrenocortical carcinoma (acc) cells express both of these markers of gonadal cell differentiation. 2a) HE. 2b) cyt b₅, avidin-biotin-peroxidase complex method. 2c) GATA4, avidin-biotin-peroxidase complex method. Bar = 100 μm.

Fig. 3

Adrenal gland, adrenocortical carcinoma; ferret. Note that cyt b₅, LHR, aromatase, and P450c17 are co-expressed in the tumor cells. 3a) cyt b₅, avidin-biotin-peroxidase complex method. 3b) LHR, avidin-biotin-peroxidase complex method. 3c) aromatase, avidin-biotin-peroxidase complex method. 3d) P450c17, avidin-biotin-peroxidase complex method. Bar = 50 μm.