Corticosterone Supplementation Reduced Selective Protein Kinase C Isoform Expression in the Epidermis of Adrenalectomized Mice 1 Diane F. Birt, 2 Ellen Duysen, Weiqun Wang, and Ann Yaktine 3 Department of Food Science and Human Nutrition, Iowa State University, Ames, Iowa 50011-1061 [D. F. B., W. W.]; Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, Nebraska 68198-6805 [D. F. B., E. D., A. Y.]; and Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, Nebraska 68198-4525 [D. F. B., A. Y.] Abstract Previous research in this laboratory demonstrated elevated plasma corticosterone and reduced protein kinase C (PKC) activity and selective isoform expression in the epidermis of dietary energy-restricted mice. Because PKC is implicated in skin carcinogenesis and because both energy restriction and glucocorticoid hormone inhibit skin carcinogenesis, the purpose of the present research was to determine whether the elevated glucocorticoid hormone in the energy-restricted mouse contributed to the changes in PKC protein expression. Two strategies were used to control corticosterone in adrenalectomized mice: (a) corticosterone-containing pellets were implanted in mice, and a dose response increase in corticosterone was observed with 5-, 10-, and 35-mg corticosterone implants with average peak values of 68  22 ng/ml (P < 0.01); and (b) corticosterone was administered in the drinking water, and plasma corticosterone was elevated in a dose-dependent manner in mice killed at 6:00 – 6:30 p.m. (P < 0.01; peak values of 300 – 400 ng/ml). The expression of PKC, PKC, and PKC protein were not consistently altered by corticosterone with the two strategies. PKC protein expression was elevated in the adrenalectomized mice administered 3 or 60 g of corticosterone/ml in drinking water (P < 0.01). PKC protein expression was reduced by all doses of corticosterone in the implant or drinking water (P < 0.05), and a reduction of 41% was achieved with the mice administered 60 g of corticosterone/ml in drinking water. In mice fed control or energy-restricted diet, with or without adrenalectomy, PKC protein was reduced in sham-operated, energy-restricted mice in comparison with control diet, sham-operated mice (P < 0.02), whereas PKC protein was not significantly different between adrenalectomized control and adrenalectomized, energy-restricted mice. These data indicate that administration of corticosterone in drinking water most closely mimicked the circulating corticosterone and epidermal PKC changes observed in dietary energy restriction. Elevated plasma glucocorticoid levels in the dietary energy-restricted mouse may contribute to the alteration of PKC protein levels in the epidermis. Introduction Previous research in the Birt laboratory demonstrated a selec- tive reduction in the expression of PKC 4  and  isoforms in the epidermis of dietary energy-restricted mice fed 40% of the energy intake of the control mice (1). Results also demonstrated an 60% reduction in PKC activity in the epidermis of the energy-restricted mouse (2). Because PKC proteins have criti- cal roles in cellular proliferation and differentiation and serve as a cellular receptor for the phorbol ester tumor promoters, we hypothesize that these alterations in PKC protein expression may be important in the inhibition of mouse skin carcinogenesis in the energy restricted mouse. However, because dietary en- ergy restriction influences many events and probably not all of these events contribute to skin tumor prevention in the energy- restricted mouse, additional studies are needed to support this hypothesis. Research by Pashko and Schwartz (3) demonstrated the importance of the adrenal gland in the prevention of skin cancer promotion in the diet-restricted mouse. When the adre- nal glands were removed, diet restriction failed to inhibit mouse skin carcinogenesis by 7,12-dimethylbenz(a)anthracene and TPA. Although this experiment did not demonstrate that GCH was responsible for the inhibition of cancer in the intact, diet- restricted mouse, data demonstrating cancer prevention by glu- cocorticoids (4) suggest that the elimination of corticosterone may have been a critical factor in the elimination of cancer prevention by diet restriction in the adrenalectomized mouse. Results from several laboratories have demonstrated that diet-restricted mice (3) and rats (5) had elevated corticosterone secretion. Furthermore, results from our laboratory indicated a Received 10/4/00; revised 3/8/01; accepted 3/14/01. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 1 This work was supported by Grants 95B126-REV and 97B039-REN from the American Institute for Cancer Research, Grant SIG-16 from the American Cancer Society, Grants R01 CA77451-01 and P30 CA36727 from the National Cancer Institute, and a grant from the United States Department of Agriculture-supported Center for Designing Foods to Improve Nutrition at Iowa State University. This is journal paper J-18674 of the Iowa Agriculture and Home Economics Experi- ment Station, Ames, Iowa, Project No. Iowa 3360, and supported by the Hatch Act and State of Iowa funds. 2 To whom requests for reprints should be addressed, at Department of Food Science and Human Nutrition, Iowa State University, 2312 Food Sciences Build- ing, Ames, IA 50011-1061. Phone: (515) 294-3011; Fax: (515) 294-8181; E-mail: dbirt@iastate.edu. 3 Present address: MGH Cancer Center, Molecular Oncology, Building 149, 13th Street, Charlestown, MA 02129. 4 The abbreviations used are: PKC, protein kinase C; AIN, American Institute of Nutrition; ERK, extracellular response kinase; GCH, glucocorticoid hormone; GR, glucocorticoid receptor; MAPK, mitogen-activated protein kinase; TPA, 12-O-tetradecanoylphorbol 13-acetate; GR, glucocorticoid receptor; AP-1, acti- vator protein 1; adx, adrenalectomized. 679 Vol. 10, 679 – 685, June 2001 Cancer Epidemiology, Biomarkers & Prevention