Morphological reprogramming of the endoplasmic reticulum by cellular mucins

About This Grant

Project Summary/Abstract The endoplasmic reticulum (ER) is an interconnected membrane compartment that is comprised of distinct functional morphologies, including tubules and sheets. How the cell reprograms the ER morphology to support different functionalities in normal and disease states is not fully resolved. Recently, we have uncovered that transmembrane mucin biopolymers can generate membrane curvature and that some prominent mucins, such as Muc1, have prolonged ER residency. In this project, we will test the central hypothesis that transmembrane mucins act as membrane curvature generators on the luminal face of the ER to regulate the ER morphology, function, and interactions with other organelles. Implicit in this hypothesis is the new notion that changes in cellular mucin expression could dynamically reprogram the functional morphology of the ER. Our aims are to (1) determine how transmembrane mucins generate forces in the ER to regulate the ER structure and function, (2) identify the molecular determinants that govern the accumulation of transmembrane mucins in the ER, and (3) investigate the downstream consequences of the mucin-reprogrammed ER on mitochondria and other cellular organelles that interact with the ER. To complete our aims, we will leverage our unique expertise in engineering the molecular structure of mucins and controlling their genetic expression. We will combine this expertise with state-of-the-art imaging approaches that include expansion microscopy (ExM) for resolution of the ER morphology, spectral imaging for dissection of organelle interactions, and optical reporters for quantitative analysis of protein trafficking through the secretory system. New optical biosensors will directly measure the entropic forces that are hypothesized to underlie membrane curvature generation by mucins. These tools will be used in parallel with traditional approaches within the field of cell biology for assessment of organelle structure/function. Theoretical models on mucin force generation will be used to support the analysis and interpretation of our results. The expression of Muc1 and other transmembrane mucins can change dramatically with changes in cell fate, oncogenic transformation, inflammation, and conditions of stress. For instance, professional secretory cells and most carcinoma cells express high levels of Muc1. Our project aims to mechanistically dissect a heretofore unrecognized role for mucins in physically shaping the ER structure and its interactions with other cellular organelles. Given the ubiquity of transmembrane mucin expression in normal secretory cells and cancer, the fundamental understanding that we seek is of broad significance to human health.