Protein-tyrosine phosphatase 1B (PTP1B) and T cell protein-tyrosine phosphatase (TCPTP) are closely related intracellular phosphatases implicated in the control of glucose homeostasis. PTP1B and TCPTP can function coordinately to regulate protein tyrosine kinase signaling and PTP1B has been implicated previously in the regulation of endoplasmic reticulum (ER) stress. In this study we assessed the roles of PTP1B and TCPTP in regulating ER stress in the endocrine pancreas. PTP1B and TCPTP expression was determined in pancreata from chow and high fat fed mice and the impact of PTP1B and TCPTP over- or under-expression on palmitate- or tunicamycin-induced ER stress signaling assessed in MIN6 insulinoma beta cells. PTP1B expression was increased and TCPTP expression decreased in pancreata of mice fed a high fat diet, as well as in MIN6 cells treated with palmitate. PTP1B over-expression or TCPTP knockdown in MIN6 cells mitigated palmitate- or tunicamycin-induced PERK/eIF2a ER stress signaling, while PTP1B deficiency enhanced ER stress. Moreover, PTP1B deficiency increased ER stress-induced cell death while TCPTP deficiency protected MIN6 cells from ER stress-induced death. ER stress coincided with the inhibition of Src family kinases (SFKs) which was exacerbated by PTP1B over-expression and largely prevented by TCPTP knockdown. Pharmacological inhibition of SFKs ameliorated the protective effect of TCPTP deficiency on ER stress-induced cell death. These results demonstrate that PTP1B and TCPTP play non-redundant roles in modulating ER stress in pancreatic beta cells and suggest that changes in PTP1B and TCPTP expression may serve as an adaptive response for the mitigation of chronic ER stress.
Bettaieb, A., Liu, S., Xi, Y., Nagata, N., Matsuo, K., Matsuo, I., Chahed, S., Bakke, J., Keilhack, H., Tiganis, T., & Haj, F. G. (2011). Differential regulation of endoplasmic reticulum stress by protein tyrosine phosphatase 1B and T cell protein tyrosine phosphatase. The Journal of Biological Chemistry, 286(11), 9225 - 9235. https://doi.org/10.1074/jbc.M110.186148