RBPs temporally coordinate Angiotensin II-induced gene expression and steroidogenesis
Human adrenal steroidogenesis is an ideal model to study how dynamic RBP-RNA regulatory interactions temporally coordinate stimulus-induced gene expression. We chose this system for the following key reasons:
This is a ligand-induced system in which the small peptide Angiotensin II (AngII) binds to its receptor on adrenocortical cells to stimulate the production of aldosterone, the master regulator of blood pressure. Aldosterone is a small nonpolar molecule that readily passes through the cell membrane upon production and there is no mechanism to store or control the release of aldosterone. Thus, tight control of regulatory timing is required since it must be rapidly produced de novo from cholesterol in response to AngII.
Aldosterone is easy to measure and thereby we can assess the quantitative contribution of individual or combinations of RBPs or their binding sites to a cellular phenotype.
There is a steroidogenic cell line (H295R) that produces aldosterone in response to AngII. We have genetically engineered loxP sites into this cell such that we can stably and inducibly express any construct.
Using this system, we recently demonstrated that RBPs and regulated RNA decay control AngII-stimulated expression kinetics to facilitate normal aldosterone production (see figure above).
We want to undersand how stimulus-induced changes that modulate RBP-mRNA regulation. Example mechanisms are:
Our research indicates that coordination between transcription and decay temporally coordinates the expression kinetics of the regulatory modules important for steroid biosynthesis. On the left is one example we think is important to prevent the overproduction of aldosterone. AngII activates the transcription of pro-steroidogenic transcripts, while simultaneously activating the transcription of mRNA decay factors that repress pro-steroidogenic mRNAs by increasing their turnover. These regulatory architectures have very interesting emergent properties that would be important for steroid hormone homeostasis.
Adrenal differentiation and cellular heterogeneity
Defects resulting in either under- or over-production of these steroid hormones are pathological. For example, over-production of aldosterone is responsible for ~%10 of hypertensive individuals. Very recently scientists discovered clusters of aldosterone producing cells (APCCs) that are thought to be precursors to the adrenal adenomas that cause primary aldosteronism and often hypertension. We are using human adrenal tissue to understand the gene expression signature of APCCs and the heteroigeneity between APCCs using spatial transcriptomics. This powerful approach also allows us to better understand the differentiation of adrenocortical stem cells in normal, aging, and pathological adrenal glands. This work is in collaboration with the labs of Lauren Fishbein and Katja Kisseljak-Vassiliades.