Thesis (Ph. D.)--University of Rochester. School of Medicine & Dentistry. Dept. of Microbiology and Immunology, 2015.
Nontypeable Haemophilus influenzae (NTHi), a gram-negative bacterium, is the primary cause of otitis media in children and the exacerbation of chronic obstructive pulmonary disease in adults. A hallmark of both these infections is an overactive inflammatory response, including the up-regulation of chemokines, such as interleukin-8 (IL-8) and granulocyte-macrophage colony-stimulating factor (GM-CSF). While inflammation is critical for the clearance of pathogens, it can be detrimental to the host if left unchecked and, therefore, must be tightly regulated. Our data suggest that the deubiquitinase cylindromatosis (CYLD) plays a critical role
in negatively regulating NTHi-induced IL-8 expression via the ERK pathway. MAP kinase phosphatase (MKP)-1 is a known negative regulator of the ERK pathway by dephosphorylating ERK. Previously, our lab reported that phosphodiesterase (PDE) 4 regulates both CYLD and MKP-1. Here, we showed that CYLD positively regulates
MKP-1 mRNA expression. Furthermore, we determined that CYLD depletion leads to enhancement of ERK phosphorylation and IL-8 expression in an MKP-1-dependent manner. Additionally, we examined the regulation of another NTHi-induced proinflammatory mediator, GM-CSF, and determined that CYLD negatively regulates it
in a similar fashion. We next investigated the therapeutic potential in controlling inflammation by upregulating CYLD via the PDE4b inhibitor, Roflumilast. Interestingly, while Roflumilast inhibited IL-8 in a CYLD-dependent manner, PDE4b regulation of GM-CSF appears to be CYLD-independent. Further analysis determined that GM-CSF is regulated by the second messenger, cAMP, specifically via protein kinase A. Taken together, our data suggest that there are multiple mechanisms of regulating NTHi-induced inflammation via the ERK pathway. These studies may lead to the identification of novel therapeutic strategies for limiting the overactive inflammatory response, without the significant adverse effects resulting from directly targeting other
pathways, such as NF-κB. Additionally, the insights from this study can not only be applied to other bacterial infections, but also to other ERK-associated pathological processes, such as hyperplasia, tissue repair, and tumorigenesis.
