MODULATION OF APOPTOSIS IN HUMAN URETHRAL EPITHELIAL CELLS BY WILD-TYPE NEISSERIA GONORRHOEAE AND ITS ISOGENIC MinD MUTANT STRAIN
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The obligate human pathogen, Neisseria gonorrhoeae, has evolved mechanisms to manipulate the apoptotic machinery in human epithelial cells in favor of host niche adaptation. In the present research, I investigated the apoptotic effect of N. gonorrhoeae on transduced human urethral epithelial cells (THUEC) and the underlying mechanism of apoptosis modulation. Flow cytometric analysis showed that gonococcal infection conferred an anti-apoptotic effect in early infection, but induced apoptosis during prolonged infection periods in THUEC. Intracellular gonococci were required to provide the anti-apoptotic effect. Furthermore, immunoblotting analysis of the mitogen-activated protein kinase (MAPK) pathways mapped the apoptosis resistance to a signaling cascade involving epidermal growth factor receptor (EGFR), extracellular signal-regulated kinases (ERK), and Bim/Bad, in which the inhibition of ERK activation by N. gonorrhoeae contributed to the anti-apoptotic effect on THUEC. A N. gonorrhoeae minD mutant strain harboring an insertionally inactivated minD gene that encodes an essential component within the cell division system, exhibits aberrant cell morphology and reduced adherence to and invasion of THUEC when compared to the parent strain. I investigated the impact of minD mutation on apoptosis and MAPK signaling in THUEC. Compared to the parent strain, infection with the minD mutant displayed reduced and delayed apoptosis during prolonged infection, and enhanced the inhibition of ERK activation from 6 h onwards. No alterations were observed on p38 and Jun N-terminal kinases (JNK) activation. Interestingly, the unexpected regulation of Bim and Bad coupled with enhanced inhibition of ERK activation in the minD mutant infected THUEC, followed by the stronger actin rearrangement induced by the minD mutant relative to the parent strain as revealed by confocal microscopy, suggest a mechanism of bacterial cell shape-mediated modulation of host cell signaling through cytoskeleton rearrangement. Collectively, my data indicate the role for ERK pathway in N. gonorrhoeae mediated apoptosis resistance in THUEC, as well as a plausible impact of bacterial cell shape on host cell signaling.
DegreeMaster of Science (M.Sc.)
CommitteeDillon, Jo-Anne R.; Bonham-Smith, Peta C.; Griebel, Philip J.; Chedrese, Jorge P.; Misra, Vikram
Copyright DateNovember 2012