Haploinsufficiency of steroidogenic factor-1 in mice disrupts adrenal development leading to an impaired stress response

Adrenal steroids are essential for homeostasis and survival during severe physiological stress. Analysis of a patient heterozygous for the steroidogenic factor-1 (SF-1) gene suggested that reduced expression of this nuclear receptor leads to adrenal failure. We therefore examined SF-1 heterozygous (+/-) mice as a potential model for delineating mechanisms underlying this disease. Here we show that SF-1 +/- mice exhibit adrenal insufficiency resulting from profound defects in adrenal development and organization. However, compensatory mechanisms, such as cellular hypertrophy and increased expression of the rate-limiting steroidogenic protein StAR, help to maintain adrenal function at near normal capacity under basal conditions. In contrast, adrenal deficits in SF-1 heterozygotes are revealed under stressful conditions, demonstrating that normal gene dosage of SF-1 is required for mounting an adequate stress response. Our findings predict that natural variations leading to reduced SF-1 function may underlie some forms of subclinical adrenal insufficiency, which become life threatening during traumatic stress.

Crosstalk pathway for inhibition of glucocorticoid-induced apoptosis by T cell receptor signaling

Activation of the glucocorticoid receptor (GR) triggers apoptosis in T cells. However, activation of the T cell antigen receptor (TCR) blocks glucocorticoid-induced apoptosis, implying functional crosstalk between these two distinct signaling systems. By reconstructing or selectively blocking TCR-stimulated signaling pathways, we show here that TCR activation of the mitogen-activated protein kinase kinase/extracellular signal regulated kinase (MEK/ERK) cascade via Ras is necessary and sufficient to inhibit GR-mediated death in immortalized T and thymocyte cell lines and in primary T cells. Moreover, we found that activation of various pathway components (TCR, Ras, MEK1) altered the transcriptional regulatory activity of GR. In contrast, phosphatidylinositol 3-kinase and Akt, which down-regulate other lymphocyte apoptosis pathways, did not inhibit glucocorticoid-induced apoptosis. Our findings, which link signaling from the TCR cell surface receptor to that from the GR intracellular receptor, demonstrate the importance of the integration of signal transduction pathways in defining regulatory circuits. Because the TCR/Ras/MEK pathway has been shown previously to be essential for positive selection of thymocytes, the TCR/Ras/MEK signaling to GR crosstalk described herein may affect T cell development and homeostasis.

Activation of IL-2 receptor alpha-chain gene by individual members of the rel oncogene family in association with serum response factor

Expression of the IL-2R alpha gene is regulated by members of the c-Rel/NF-kappa B family of transcription factors binding to the kappa B site in the promoter. Previous work has not defined the role of individual members of the c-Rel family in the activation of the IL-2R alpha gene. Using the COS cell system, we were able to reconstitute the regulation of the IL-2R alpha promoter by expressing cloned Rel family members with serum response factor (SRF). We found that c-rel alone activated the IL-2R alpha promoter only weakly but worked with the p50 subunit of NF-kappa B (NFKB1) to give a higher level of expression. We showed that c-rel heterodimerizes with p50 and the amount of this heterodimer correlated with the level of IL-2R alpha gene expression. Our results provide evidence that c-rel/p50 heterodimers activate gene expression in the context of a cellular promoter. We show that c-rel or p65 can cooperate with SRF in the activation of this promoter and the transactivation by c-rel with SRF was enhanced by p50. Synergistic activation required both kappa B and CArG sites, and binding studies show that these adjacent sites can be occupied simultaneously. The transactivation observed with cloned transcription factors mimics the physiologic induction of the IL-2R alpha gene since multiple sequence elements cooperate to give gene activation. The data support the model that c-rel/p50 or p65 can cooperate with SRF to specifically target the expression of the IL-2R alpha gene in activated T cells.

Activation of IL-2 receptor alpha-chain gene by individual members of the rel oncogene family in association with serum response factor

Expression of the IL-2R alpha gene is regulated by members of the c-Rel/NF-kappa B family of transcription factors binding to the kappa B site in the promoter. Previous work has not defined the role of individual members of the c-Rel family in the activation of the IL-2R alpha gene. Using the COS cell system, we were able to reconstitute the regulation of the IL-2R alpha promoter by expressing cloned Rel family members with serum response factor (SRF). We found that c-rel alone activated the IL-2R alpha promoter only weakly but worked with the p50 subunit of NF-kappa B (NFKB1) to give a higher level of expression. We showed that c-rel heterodimerizes with p50 and the amount of this heterodimer correlated with the level of IL-2R alpha gene expression. Our results provide evidence that c-rel/p50 heterodimers activate gene expression in the context of a cellular promoter. We show that c-rel or p65 can cooperate with SRF in the activation of this promoter and the transactivation by c-rel with SRF was enhanced by p50. Synergistic activation required both kappa B and CArG sites, and binding studies show that these adjacent sites can be occupied simultaneously. The transactivation observed with cloned transcription factors mimics the physiologic induction of the IL-2R alpha gene since multiple sequence elements cooperate to give gene activation. The data support the model that c-rel/p50 or p65 can cooperate with SRF to specifically target the expression of the IL-2R alpha gene in activated T cells.