Research Summary

Current research in our lab is focused on crosstalk between two fundamental second messenger systems: Ca2+ and cyclic AMP (cAMP). We have been using a panel of molecular, biochemical, biophysical and fluorescence imaging tools to study how these signaling cascades intersect with one another in colonic epithelial cells. Our studies will help us to understand the normal functions of colonic epithelia, and potentially to understand whether aberrations in signaling precede or accompany certain disease states.

Our most recent studies have provided evidence for a new form of “store-operated” cAMP signaling that directly couples the Ca2+ content of the endoplasmic reticulum (ER) to cAMP production by adenylyl cyclases (ACs), independent of changes in cytosolic [Ca2+]. This mechanism co-exists with the more conventional regulation of ACs by cytosolic Ca2+ signaling events, but the physiological circumstances leading to the initiation of this process may be different. We further show that the activation of this pathway following ER Ca2+ depletion requires expression of an ER resident Ca2+ sensor protein, STIM1 and the re-localization and clustering of this protein in punctae near the plasma membrane. STIM1, a newly established mediator of store-operated or “capacitative” Ca2+ entry, may therefore fulfill broader functions than previously appreciated, serving as an organizer for a plasma membrane signaling complex that incorporates not only Ca2+ entry channels, but also adenylyl cyclases.

Our work is supported principally through a Merit Review Award from the Medical Research Service of the Veteran’s Administration, awarded to A.M. Hofer (Principal Investigator).

calcium signaling inside and outside of cells

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Equipment & Techniques

Metafluor Ratio Imaging System, (FRET, TIRF). Zeiss Multiphoton Microscope. Nikon C1si spectral confocal system. Z Novascan ESPM 3D AFM (Atomic Force Microscope).

General molecular biology techniques.

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Funding

1. Merit Review Award - Medical Research Service of the Veteran's Administration (PI: A.M. Hofer, 2007 - 2011) -- "Imaging cAMP in colon: inflammatory mediators and CA2+ - sensing receptors"

2. Harvard Digestive Diseases Center Pilot/Feasibility Award (PI: A.M. Hofer, 2007 - 2008) -- "cAMP microdomains in G.I. epithelia"

3. William F. Milton Fund - Harvard University (PI: A.M. Hofer, 2009) -- "The calcium / cyclic AMP connection in polycystic kidney disease”

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