Abstract
Genetic disruption of protein-tyrosine phosphatase 1B (PTP1B) in mice leads to increased insulin sensitivity and resistance to weight gain. Although PTP1B has been implicated as a regulator of multiple signals, its function in other physiological responses in vivo is poorly understood. Here we demonstrate that PTP1B-null mice are resistant to Fas-induced liver damage and lethality, as evident by reduced hepatic apoptosis in PTP1B-null versus wild type mice and reduced levels of circulating liver enzymes. Activation of pro-apoptotic caspases-8, -9, -3, and -6 was attenuated in livers from PTP1B-null mice following Fas receptor stimulation, although components of the death-inducing signaling complex were intact. Activation of anti-apoptotic regulators, such as the hepatocyte growth factor/Met receptor tyrosine kinase, as well as Raf, ERK1/2, FLIP(L), and the NF-kappaB pathway, was elevated in response to Fas activation in livers from PTP1B-null mice. Using PTP1B-deficient primary hepatocytes, we show that resistance to Fas-mediated apoptosis is cell autonomous and that signals involving the Met, ERK1/2, and NF-kappaB pathways are required for cytoprotection. This study identifies a previously unknown physiological role for PTP1B in Fas-mediated liver damage and points to PTP1B as a potential therapeutic target against hepatotoxic agents.
Highlights
Possessing a N-terminal catalytic domain followed by tandem prolinerich motifs [2, 3]
protein-tyrosine phosphatase 1B (PTP1B) has been implicated as a regulator of diabetes and obesity, its function in other physiological responses regulated in vivo by tyrosine kinase signaling is poorly understood
To determine whether PTP1B plays a role in regulating signals involved in liver damage and survival, we determined the sensitivity of PTP1B-null and wild type (WT) mouse hepatocytes to FasR activation, using two complementary experimental systems: whole liver in vivo and in vitro primary cultures
Summary
WT and PTP1B-null mice are hybrids of 129S/v and BALB/c backgrounds [12]. The antibodies were obtained as follows: monoclonal anti-Jo-2, anti-c-Raf, anti-phosphotyrosine (PY20), and polyclonal anti-EGFR (BD Biosciences, San Diego, CA); polyclonal anti-FLIP (Axxora LLC, San Diego, CA), polyclonal anti-PTP1B antibody (Upstate Biotechnology, Inc., Lake Placid, NY); mouse monoclonal anti-Met, polyclonal anti-Fas, anti-IB␣, anti-insulin receptor, and anti-IGF1 receptor (Santa Cruz Biotechnology, Santa Cruz, CA); polyclonal anti-caspase-9 and anticaspase-8 (Stressgen, Victoria, Canada); polyclonal anti-caspase-3, anticaspase-6, anti-ERK1/2 antibody, and anti-phospho-ERK1/2 pTpY202/204 antibody (Cell Signaling Technology, Beverly, MA); rabbit polyclonal antic-Raf pYpY340/341 antibody and polyclonal pIR/IGF1RpYpYpY1158/1162/1163 (Biosource, Camarillo, CA). Wild type and PTP1B-null mice were injected intraperitoneally with 0.3 g/g body weight of Jo-2 in 200 l of phosphate-buffered saline. The livers were fixed by immersion in 10% buffered formalin and embedded in paraffin. All of the mouse manipulations were carried out in accordance with McGill University animal care guidelines
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