Unmasking a Growth-promoting Effect of the Adrenocorticotropic Hormone in Y1 Mouse Adrenocortical Tumor Cells

Claudimara F.P Lotfi,Zana Todorovic,Hugo A Armelin,Bernard P Schimmer

doi:10.1074/jbc.272.47.29886

Claudimara F.P Lotfi, Zana Todorovic + Show 2 more

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https://doi.org/10.1074/jbc.272.47.29886

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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 G1 possibly 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.

Highlights

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
ACTH-induced inhibition of cell proliferation has been observed in the Y1 mouse adrenocortical tumor cell line [1] as well as in normal adrenocortical cells isolated from a variety of
We expected that ACTH would inhibit MAP kinase activity in Y1 cells, consistent with the growth-inhibitory effects of the hormone, we find that ACTH activates the MAP kinase cascade via a signaling mechanism that is cAMP-independent

Summary

Introduction

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. The results demonstrate a dual effect of ACTH on cell cycle progress, a cAMP-independent growth-promoting effect early in G1 possibly mediated by mitogen-activated protein kinase and c-FOS, and a cAMP-dependent inhibitory effect at mid-G1. Several lines of evidence indicate that the growth-inhibitory effect of ACTH is mediated by cAMP with the most compelling data arising from studies of Y1 adrenal tumor cells harboring dominant inhibitory mutations in cAMP-dependent protein kinase (PKA) that disrupt cAMP-dependent signaling pathways [6]. We examined the regulation of the MAP kinase pathway in Y1 mouse adrenocortical tumor cells to reconcile the growth-inhibiting effect of ACTH in vitro with the conflicting biochemical data that suggests an underlying mitogenic effect of the hormone. ACTH Stimulates Cell Cycle Progression in Y1 Adrenal Cells results suggest that we have unmasked a cAMP-independent, growth-promoting effect of ACTH that has new implications for the mitogenic effects of the hormone on the adrenal cortex

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