Michelle A. Wood, Ph.D.
Endocrinology Postdoctoral Research Fellow
(Member of the Hammer Lab Since August 2009)
B.S. in Biotechnology from Elizabethtown College
Ph.D. in Molecular and Cellular Physiology from the University of Pittsburgh
The expression of Nuclear receptor subfamily 5, group A, member 1 (Nr5a1, also known as Sf1 or Ad4bp) is critical for growth and differentiation of adrenocortical cells. Adrenocortical cells are specialized for the production of glucocorticoids, mineralocorticoids, and androgens (Morohashi 1997; Kim et al. 2009). Proper development and maintenance of the adrenal cortex is necessary for an adequate stress response and the control of salt and carbohydrate homeostasis (Kim et al. 2009). Maintenance of the adrenal cortex occurs through centripetal displacement of cortical cells from the outer cortex inwards toward the medulla (Kim and Hammer 2007). The progenitor cells responsible for homeostatic maintenance remains to be identified but are proposed to reside within the adrenal capsule. We postulate that adrenocortical cell progenitors lack expression of Nr5a1 and that differentiated Nr5a1-positive (+) cells are continually derived from Nr5a1-negative (-) stem/progenitor cells (Fig. 1). This proposed mechanism by which Nr5a1(-) cells give rise to Nr5a1(+) cells is regulated by active repression and dynamic activation of Nr5a1.
Regulation of Sf1/Nr5a1 Expression
The expression of Nr5a1 is controlled by the binding of differentiation-regulating transcription factors, Upstream stimulatory factors 1 and 2 (Usf1 and Usf2), to an E-box element in the Nr5a1 proximal promoter (Figure 2). Usf proteins contain a helix-loop-helix (HLH) domain to facilitate protein-protein interactions and a basic DNA binding motif that facilitates DNA-protein interactions at a consensus site, CANNTG (Murre et al. 1994; Atchley and Fitch 1997; Jones 2004). Basic HLH (bHLH) proteins are involved in the differentiation of multiple tissues (Murre et al. 1994; Atchley and Fitch 1997; Jones 2004); however, the role of bHLH proteins in adrenocortical cell differentiation has not been evaluated.
Tcf21/Pod1 as a Negative Regulator of Sf1/Nr5a1
The bHLH protein family member transcription factor 21 (Tcf21, also known as Pod1, epicardin, capsulin) is able to inhibit Nr5a1 promoter activity (Hidai et al. 1998; Tamura et al. 2001; Cui et al. 2004). Tcf21 knockout adrenals have increased expression of Nr5a1 within the capsule which normally lacks Nr5a1 expression (Kim et al. 2009). The exact mechanism of Tcf21 inhibition of Nr5a1 remains unknown. Since Usf proteins are known to drive Nr5a1 expression and given that Usf proteins and Tcf21 are members of the same protein family with the potential to interact, we hypothesize that Tcf21 is a negative regulator of Usf-mediated Nr5a1 expression in the quiescent stem/progenitor cells of the adrenal cortex and that loss of Tcf21 inhibition drives adrenocortical cell differentiation (Fig. 1 and Figure 2). In our model, Nr5a1(-), Tcf21(+) progenitor cells give rise to Nr5a1(+), Tcf21(-) cells. The objective of the proposed studies is to determine how Tcf21 negatively regulates Nr5a1 at the molecular level and if Tcf21(+) cells are able to give rise to Nr5a1(+) cells of the adrenal cortex.
Understanding steroidogenic cell development and maintenance can provide key insights into diseases of steroid deficiencies/excesses, adrenal hyperplasias/hypoplasias and organ homeostasis. Clinically, an excess of NR5A1 can induce adrenocortical cell proliferation, and is correlated with adrenal cancer aggressiveness (Doghman et al. 2007; Giordano et al. 2009), and endometriosis (Xue et al. 2007; Utsunomiya et al. 2008). Emerging data suggest that NR5A1 dosage can be a prognostic factor in adrenocortical carcinomas and adenomas (Doghman et al. 2007; Giordano et al. 2009).. TCF21 has been found to be down-regulated in multiple cancers (Cutcliffe et al. 2005; Smith et al. 2006; Tessema et al. 2008) including adrenocortical adenomas and carcinomas (Giordano et al. 2009). Understanding the mechanism of Tcf21 inhibition of Nr5a1 may facilitate the development of therapies which regulate Nr5a1 expression, possibly through the up- or down-regulation of Tcf21 or which mimic the action of Tcf21.
- Atchley, W. R. and W. M. Fitch (1997). "A natural classification of the basic helix-loop-helix class of transcription factors." Proc Natl Acad Sci U S A 94(10): 5172-5176.
- Cui, S., A. Ross, et al. (2004). "Disrupted gonadogenesis and male-to-female sex reversal in Pod1 knockout mice." Development 131(16): 4095-4105.
- Cutcliffe, C., D. Kersey, et al. (2005). "Clear cell sarcoma of the kidney: up-regulation of neural markers with activation of the sonic hedgehog and Akt pathways." Clin Cancer Res 11(22): 7986-7994.
- Doghman, M., T. Karpova, et al. (2007). "Increased steroidogenic factor-1 dosage triggers adrenocortical cell proliferation and cancer." Mol Endocrinol 21(12): 2968-2987.
- Giordano, T. J., R. Kuick, et al. (2009). "Molecular classification and prognostication of adrenocortical tumors by transcriptome profiling." Clin Cancer Res 15(2): 668-676.
- Hidai, H., R. Bardales, et al. (1998). "Cloning of capsulin, a basic helix-loop-helix factor expressed in progenitor cells of the pericardium and the coronary arteries." Mech Dev 73(1): 33-43.
- Jones, S. (2004). "An overview of the basic helix-loop-helix proteins." Genome Biol 5(6): 226.
- Kim, A. C., F. M. Barlaskar, et al. (2009). "In search of adrenocortical stem and progenitor cells." Endocr Rev 30(3): 241-263.
- Kim, A. C. and G. D. Hammer (2007). "Adrenocortical cells with stem/progenitor cell properties: recent advances." Mol Cell Endocrinol 265-266: 10-16.
- Morohashi, K. (1997). "The ontogenesis of the steroidogenic tissues." Genes Cells 2(2): 95-106.
- Murre, C., G. Bain, et al. (1994). "Structure and function of helix-loop-helix proteins." Biochim Biophys Acta 1218(2): 129-135.
- Smith, L. T., M. Lin, et al. (2006). "Epigenetic regulation of the tumor suppressor gene TCF21 on 6q23-q24 in lung and head and neck cancer." Proc Natl Acad Sci U S A 103(4): 982-987.
- Tamura, M., Y. Kanno, et al. (2001). "Pod-1/Capsulin shows a sex- and stage-dependent expression pattern in the mouse gonad development and represses expression of Ad4BP/SF-1." Mech Dev 102(1-2): 135-144.
- Tessema, M., R. Willink, et al. (2008). "Promoter methylation of genes in and around the candidate lung cancer susceptibility locus 6q23-25." Cancer Res 68(6): 1707-1714.
- Utsunomiya, H., Y. H. Cheng, et al. (2008). "Upstream stimulatory factor-2 regulates steroidogenic factor-1 expression in endometriosis." Mol Endocrinol 22(4): 904-914.
- Xue, Q., Z. Lin, et al. (2007). "Transcriptional activation of steroidogenic factor-1 by hypomethylation of the 5' CpG island in endometriosis." J Clin Endocrinol Metab 92(8): 3261-3267.
Available UROP Projects
Michelle will be looking for an undergraduate at the University of Michigan who is participating in the Undergraduate Research Opportunity Program starting in the summer of 2011. Projects available related to Michelle's research are listed below:
- How does Tcf21 regulate SF1 at the molecular level in adrenocortical cells? Student would learn cell culture techniques and would also learn key molecular biology assays including PCR and Western blotting as the project progressed.
- Can Tcf21 cells give rise to differentiated adrenocortical cells? Student would learn how tissues are processed for analysis, including sectioning and immunocytochemistry, and would analyze tissues by microscopy.
- Does Tcf21 have a similar role in the regulation of SF1 in Leydig cells of the testes? Depending on interest, student could explore the molecular or physiological expression and role of Tcf21 in Leydig cells. Techniques learned would be similar to those in Projects 1 and 2.
For more information or to set up a meeting, please email Michelle directly at firstname.lastname@example.org. When inquiring, please include a resume and a brief description of your long term career goals.
Publications by M.A. Wood
- Wood, M.A. and G.D. Hammer. "Adrenocortical Stem and Progenitor Cells: Unifying Model of Two Proposed Origins." (2010) Molecular and Cellular Endocrinology, doi:10.1016/j.mce.2010.11.01.
- Gassei, K., J. Ehmcke, M.A. Wood, W.H. Walker, and S. Schlatt. "Immature rat seminiferous tubules reconstructed in vitro express markers of Sertoli cell maturation after xenografting into nude mouse hosts." (2010) Molecular Human Reproduction, 16(2): 97-110.
- Viswanathan, P.*, M.A. Wood*, and W.H. Walker. "FSH Transiently Blocks FSH Receptor Transcription by Increasing ID2 and Decreasing Upstream Stimulatory Factor (USF) Expression in Rat Sertoli Cells." (2009) Endocrinology, 150(8):3783-91.
* Both authors contributed equally to this work.
- Wood, M.A. and W.H. Walker. "USF1/2 transcription factor DNA-binding activity is induced during rat Sertoli cell differentiation." (2009) Biology of Reproduction, 80(1): 24-33.
- Yu, J., P. Wang, L. Ming, M.A. Wood, & L. Zhang. "SMAC/Diablo mediates the proapoptotic function of PUMA by regulating PUMA-induced mitochondrial events." (2007) Oncogene, 26(29):4189-98.
- Mburu, Y.K., J. Wang, M.A. Wood, W.H. Walker, & R.L. Ferris. "CCR7 Mediates Inflammation-Associated Tumor Progression." (2006) Immunologic Research, 36(1-3): 61-72.
- Wood, M.A. and J.F. Cavender. "Beta-galactosidase Staining as a Marker of Cells Enduring Stress." (2004) BIOS, 75(4): 139-146.
* This article reprinted in: "Lab Reports and Scientific Papers." Biology 120 General Biology I Laboratory Experiments and Exercises. Ed. Patrick A. Thorpe. Stiples Publishing L.L.C.: Academic Year 2005-2006 edition, pp 125-132.
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