Unmasking a Growth-promoting Effect of the Adrenocorticotropic Hormone in Y1 Mouse Adrenocortical Tumor Cells*
- From the ‡Departmento de Bioquimica, Instituto de Quimica, Universidade de Sao Paulo, Sao Paulo, Brazil 05599-970 and¶Banting and Best Department of Medical Research and Department of Pharmacology, University of Toronto, Toronto, Ontario, Canada M5G 1L6
Abstract
The adrenocorticotropic hormone (ACTH) inhibits the growth of Y1 mouse adrenocortical tumor cells as well as normal adrenocortical cells in culture but stimulates adrenocortical cell growth in vivo. In this study, we investigated this paradoxical effect of ACTH on cell proliferation in Y1 adrenal cells and have unmasked a growth-promoting effect of the hormone. Y1 cells were arrested in the G1 phase of the cell cycle by serum starvation and monitored for progression through S phase by measuring [3H]thymidine incorporation into DNA and by measuring the number of nuclei labeled with bromodeoxyuridine. Y1 cells were stimulated to progress through S phase and to divide after a brief pulse of ACTH (up to 2 h). This effect of ACTH appeared to be cAMP independent, since ACTH also induced cell cycle progression in Kin-8, a Y1 mutant with defective cAMP-dependent protein kinase activity. The growth-promoting effect of ACTH in Y1 was preceded by the rapid activation of p44 and p42 mitogen-activated protein kinases and by the accumulation of c-FOS protein. In contrast, continuous treatment with ACTH (14 h) inhibited cell cycle progression in Y1 cells by a cAMP-dependent pathway. The inhibitory effect of ACTH mapped to the midpoint of G1. Together, the results demonstrate a dual effect of ACTH on cell cycle progress, a cAMP-independent growth-promoting effect early in G1possibly mediated by mitogen-activated protein kinase and c-FOS, and a cAMP-dependent inhibitory effect at mid-G1. It is suggested that the growth-inhibitory effect of ACTH at mid-G1 represents an ACTH-regulated check point that limits cell cycle progression.
Footnotes
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↵* This work was supported by the National Cancer Institute of Canada with funds provided by the Canadian Cancer Society (to B. P. S.) and by grants from Fundação de Amparo a Pesquisa do Estado de São Paulo and Conselho Nacional de Desenvolvimento Cientifico e Tecnológico (to H. A. A.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵§ Postdoctoral fellow from Fundação de Amparo a Pesquisa do Estado de São Paulo.
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↵1 The abbreviations used are: ACTH, adrenocorticotropic hormone; 8-Br-cAMP, 8-bromo-cAMP; DMEM, Dulbecco’s modified Eagle’s Medium; Erk1, p44 MAP kinase; Erk2, p42 MAP kinase; FGF, fibroblast growth factor; G protein, guanyl nucleotide-binding regulatory G protein; MAP kinase, mitogen-activated protein kinase; PKA, cAMPdependent protein kinase; PMA, phorbol 12-myristate 13-acetate; BrdUrd, bromodeoxyuridine.
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↵2 C. Frigeri and H. A. Armelin, unpublished observations.
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↵3 B. P. Schimmer and Z. Todorovic, unpublished observations.
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- Received June 18, 1997.
- Revision received August 18, 1997.
