Abstract

Cadherins are membrane spanning proteins that play an important role in cellular adhesion. The extracellular region of E-cadherin adheres to other nearby cadherins through homotypic binding, holding cells together, while its cytoplasmic tail is anchored to the actin cytoskeleton with a complex of other proteins including beta-catenin. When Tyr-654 on beta-catenin is phosphorylated, it shows less affinity for E-cadherin binding and cell-cell adhesion is compromised. Previous work has shown that the protein tyrosine phosphatase, PTP1B, continuously dephosphorylates beta-catenin at the Tyr-654 residue, however more data has been gathered on PTP1B’s interactions with N-cadherin than E-cadherin. PTP1B and its interaction with beta-catenin is important to N-cadherin being properly trafficked from the ER to the cell membrane. The G12/13 subfamily of heterotrimeric guanine nucleotide binding proteins (G- proteins) have also been shown to interact with cadherins and cause decreased cell adhesion function. Gα12 and Gα13 both bind to a region on N-cadherin that overlaps with the PTP1B binding region. This region is highly preserved in E-cadherin, so it is predicted that PTP1B also binds with E-cadherin. Because the G12/13 class of G-proteins and PTP1B bind the cadherin cytoplasmic domain at overlapping positions, a hypothesis emerges that Gα12/13 displaces PTP1B from cadherins. It would be expected that without the binding of PTP1B, beta-catenin will remain in a phosphorylated state that hinders its binding to cadherins. To test this a myc-tagged PTP1B protein was engineered and transfected into cultured cells for protein interaction studies. Through pulldown analysis and immunoblotting it has been shown that PTP1B and E-cadherin do interact. Work is on going to determine if Gα12/13 signaling has an effect on PTP1B binding. Further experiments will examine beta-catenin to determine if Gα12/13 signaling effects on PTP1B also affect beta-catenin binding to E-cadherin.

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