Graduation Date

Fall 12-16-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Programs

Cancer Research

First Advisor

Paul Sorgen

Abstract

Gap junctions are intercellular channels that permit the free passage of ions, small metabolites, and signaling molecules between neighboring cells. In the diseased human heart, altered ventricular gap junction organization and connexin expression (i.e., remodeling) are key contributors to rhythm disturbances and contractile dysfunction. Connexin43 (Cx43) is the dominant gap junction protein isoform in the ventricle which is under tight regulation by serine/tyrosine phosphorylation. Phosphorylation and dephosphorylation regulate many aspects of Cx43 function including trafficking, assembly and disassembly, electrical and metabolic coupling at the plaque, as well as to modulate the interaction with other proteins.

Serine phosphorylation has long been reported to regulate Cx43, however, the understanding of tyrosine kinases/phosphatases in the modulation of gap junction intercellular communication and subsequent down-stream effects on cellular processes is limited to Src. Using a combination of biophysical and cellular biology techniques, we identified and characterized a novel tyrosine phosphatase T-Cell Protein Tyrosine Phosphatase (TC-PTP) and a tyrosine kinase Tyrosine Kinase 2 (Tyk2) that directly interact with the Cx43 carboxyl terminal domain (CT). Cx43CT residues Y247 and Y265, which are phosphorylated by c-Src and v-Src, are also directly targeted by both TC-PTP and Tyk2. Additionally, activation of both TC-PTP and Tyk2 also indirectly affect serine phosphorylation of Cx43. Specifically, TC-PTP leads to dephosphorylation of Cx43 S368 by inactivating PKCα and PKCδ, while Tyk2 increases phosphorylation of S368 and S279/282 through activation of PKC and MAPK, respectively. These effects are independent of Src.

In the cardiovascular system, an increased level of angiotensin II (Ang II) is associated with increased risk of ventricular arrhythmia, hypertrophy, and sudden death. Ang II reduces TC-PTP expression while increasing Tyk2 activity. Our data show that TC-PTP dephosphorylation maintains Cx43 gap junctions at the plaque as well as partially reverses channel closure caused by v-Src phosphorylation. Conversely, Tyk2 inhibits gap junction communication and increases turnover rate by phosphorylating Cx43. These findings suggest that a decrease of TC-PTP and an increase of Tyk2 may mediate Cx43 gap junction remodeling by altering phosphorylation in Ang II induced cardiovascular pathology.

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