PTPIP51 in Protein Interactions: Regulation and In Situ Interacting Partners

Abstract

This study investigated the regulation of 14-3-3β binding to PTPIP51 by the tyrosine phosphorylation status of PTPIP51. The tyrosine 176 residue is phosphorylated by c-Src. Up to now, nothing is known about the impact of such well-established phosphorylation events on the interaction profile of PTPIP51 with its partners of the mitogen-activated protein kinase (MAPK) pathway. In human keratinocytes the PTPIP51 phosphorylation was varied by inhibiting the phosphatase activity, thus enhancing the phosphorylation of PTPIP51. Differential blocking of Src kinase family members (despite c-Src) by PP2 increased the activity of c-Src and the tyrosine phosphorylation of PTPIP51 at position 176, which is the substrate of c-Src kinase. The amount of PTPIP51 interactions with 14-3-3β, Raf-1, PTP1B and c-Src was evaluated and the resulting data were compared to an untreated control group. The increased phosphorylation level resulted in a sharp drop of the 14-3-3β/PTPIP51 and 14-3-3β/Raf-1 interaction. Besides the 14-3-3 interaction of PTPIP51, the interaction with the two MAPK modulators, protein kinase A (PKA) and diacylglycerol kinase alpha (DAGKα), are also regulated by the tyrosine phosphorylation status of PTPIP51. Additional immunostaining experiments were done investigating the functional implication on these interactions of the phosphorylation in apoptotic processes. In the pervanadate- and PP2-treated HaCaT cells, higher amounts of apoptotic cells were not detected as compared to the control group. The presented data confirms a tyrosine phosphorylation-dependent interaction of PTPIP51 with 14-3-3β and Raf-1 in vivo and a tyrosine-dependent interaction profile with DAGKα and PKA. The non-interaction of PTPIP51 with 14-3-3 is not sufficient for triggering apoptosis.

PTPIP51—A New RelA-tionship with the NFκB Signaling Pathway

“…In recent studies PTPIP51 was identified to be strongly involved in the mitogen activated kinase (MAPK) signaling [ 1 , 2 ]. Here, PTPIP51 is under control of distinct kinases and phosphatases modulating its binding capability to Raf-1 and thereby titrating the MAPK signal [ 1 , 2 , 3 ]. Moreover, the protein interactions of PTPIP51 are associated with cell cycle progression and PTPIP51 plays a pivotal role during chromosome segregation [ 4 ].…”

PTPIP51 crosslinks the NFκB signaling and the MAPK pathway in SKBR3 cells and provides a bypass mechanism for NFκB inhibition

“…Since IKK activity is not inhibited, but even enhanced in the HER2 overactivated setting, IKK2 is still capable of phosphorylating the serine 212 of PTPIP51. The phosphorylation of PTPIP51 at serine 212 forces PTPIP51 into the Raf1/14-3-3/PTPIP51 complex and subsequently leads to a stimulation of MAPK signaling (15,17,18). Thereby, SKBR3 cells potentially evade the NFκB inhibition via the crosstalk with the MAPK signaling mediated by PTPIP51.…”

“…Thereby, SKBR3 cells potentially evade the NFκB inhibition via the crosstalk with the MAPK signaling mediated by PTPIP51. The interaction of PTPIP51 with Raf1 and 14-3-3 is not only subjected to the serine 212 phosphorylation of PTPIP51 but also to the tyrosine 176 phosphorylation of PTPIP51 (15,17,18). A crucial regulator of this phosphorylation site is the PTP1B (15,17,18,23).…”

“…Phosphorylation of the tyrosine 176 leads to a dissolution of the complex and an omission of the MAPK pathway stimulating effect. In contrast, the phosphorylation of serine 212 enhances the formation of the ternary complex (15,17,18). Both phosphorylation sites are under the control of several kinases, including receptor tyrosine kinases (e.g., the EGFR) and nonreceptor kinases (e.g., c-Src), and phosphatases (15,17,18).…”

“…The evaluation of the NFκB related interactome of PTPIP51 is not sufficient to explain the divergent effects on cell viability of the applied agents in the two cell lines.The MAPK pathway is one of the essential growth and proliferation promoting pathway in HER2 amplified breast cancer cells(9). PTPIP51 plays a pivotal role in the titration of the MAPK pathway activation(15)(16)(17)(18). The regulation of the MAPK related PTPIP51 interactome upon NFκB inhibition significantly differs between the two cell lines.…”