The extracellular matrix signals through protein kinase MEKK‐3 and transcription factor ATF‐7 to activate cytoprotective genes

Abstract

Animal cells secrete proteins and carbohydrates to create an extracellular matrix (ECM) that provides mechanical support for tissues. Rather than being an inert scaffold, the ECM is a dynamic, physiologically active component in living tissues. Barrier ECMs stand at the surface of animals and are the first of line defense against many environmental stressors such as osmotic pressure changes, toxins, and biological pathogens. Activation of cytoprotective genes is the second line of defense against environmental stress. Cytoprotective genes are conserved and influence adaptation to climate change, disease progression and pathogenesis, and aging. Therefore, a molecular understanding of fundamental signaling mechanisms that control cytoprotective genes has broad relevance. The molecular signaling pathways that sense and regulate cytoprotective responses within cells have been studied in detail, but far less is known about how barrier ECMs interact with environmental stress to influence cytoprotective gene regulation. The nematode model organism Caenorhabditis elegans is covered by a complex barrier ECM termed the cuticle. Given that the cuticle directly interacts with the environment, we hypothesize that it may include a sensor for stress. We recently used RNAi screening, collagen mutations, and RNAseq in C. elegans to demonstrate that disruption of specific bands of collagen, called annular furrows, significantly induce organic osmolyte, detoxification, and immunity cytoprotective genes (p<0.05) (Dodd et al., 2018 Genetics 208:1467). To identify regulators of cytoprotective gene transcription downstream of annular furrows, we conduced an RNAi screen of all C. elegans' protein kinases and transcription factors in annular furrow mutants expressing fluorescent cytoprotective gene reporters. This screen and subsequent RT‐qPCR analysis identified protein kinase MEKK‐3 and transcription factor ATF‐7 as significantly required for expression of cytoprotective genes* in annular furrow mutants (p>0.001; *atf‐7 knockdown did not significantly repress immunity gene induction). Previous C. elegans' literature indicates that MEKK‐3 regulates longevity with dietary restriction and that ATF‐7 regulates innate immunity. Importantly, both of these proteins are conserved in humans where they regulate diverse stress responses and are implicated in tumorigenesis. We are now leveraging the experimental tractability of C. elegans to determine how these two conserved signaling genes function to confer protection to environmental stress in this novel ECM‐initiated context.Support or Funding InformationNSF, UF Graduate School Fellowship, McKnight Doctoral Fellowship, William Townsend Porter Predoctoral Fellowship from the American Physiological SocietyThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.