Honors Theses
Date of Award
5-2025
Document Type
Undergraduate Thesis
Degree Name
BS
Department
Biomedical Sciences
Faculty Mentor
Phoibe Renema
Advisor(s)
Terrence Ravine, Sarah Sayner
Abstract
Pseudomonas aeruginosa (P. aeruginosa) is the most common cause of ventilator-associated pneumonia in intensive care unit patients. P. aeruginosa utilizes a type III secretion system that injects exoenzymes U, S, T, and/or Y into the host cell cytosol. A majority of clinically isolated P. aeruginosa strains express ExoY often in combination with ExoU and ExoT, or ExoS and ExoT. Host signaling mechanisms in response to intoxication with individual exoenzymes have been extensively studied, yet little is known about host cell response to co-intoxication. In this study, pulmonary microvascular endothelial cells (PMVECs) were infected with P. aeruginosa strains expressing different combinations of exoenzymes S, T, and Y. ExoS alone induced significant caspase activation and cell death in PMVECs. Importantly, ExoY significantly decreased ExoS-induced caspase activation, but not cell death. ExoY is a nucleotidyl cyclase; its activity is measured via cNMP production. ExoY-induced elevated intracellular cAMP is ablated by the presence of ExoS. Despite this, ExoY inhibits ExoS-induced caspase activation regardless of cAMP production. To determine whether ExoY enzymatic activity was necessary to inhibit ExoS-induced caspase activation, recombinant P. aeruginosa strains were generated to express ExoS in combination with either catalytically active or inactive ExoY. Enzymatically active ExoY inhibited ExoS-induced caspase activation whereas enzymatically inactive ExoY did not. Thus, we conclude that ExoY enzymatic activity inhibits ExoS-induced caspase activation but not cell death in PMVECs.
Recommended Citation
Holm, Connor, "Pseudomonas Aeruginosa Exoenzyme Y Enzymatic Activity Inhibits Exoenzyme S-Induced Caspase Activation but not Cytotoxicity in Pulmonary Microvascular Endothelial Cells" (2025). Honors Theses. 112.
https://jagworks.southalabama.edu/honors_college_theses/112
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