Conditional knockout mice reveal an essential role of protein phosphatase 4 in thymocyte development and pre-T-cell receptor signaling.
Okadaic acid-sensitive serine/threonine phosphatases have been shown to regulate interleukin-2 transcription and T-cell activation. Okadaic acid inhibits protein phosphatase 4 (PP4), a novel PP2A-related serine/threonine phosphatase, at a 50% inhibitory concentration (IC(50)) comparable to that for PP2A. This raises the possibility that some cellular functions of PP2A, determined in T cells by using okadaic acid, may in fact be those of PP4. To investigate the in vivo roles of PP4 in T cells, we generated conventional and T-cell-specific PP4 conditional knockout mice. We found that the ablation of PP4 led to the embryonic lethality of mice. PP4 gene deletion in the T-cell lineage resulted in aberrant thymocyte development, including T-cell arrest at the double-negative 3 stage (CD4(-) CD8(-) CD25(+) CD44(-)), abnormal thymocyte maturation, and lower efficacy of positive selection. PP4-deficient thymocytes showed decreased proliferation and enhanced apoptosis in vivo. Analysis of pre-T-cell receptor (pre-TCR) signaling further revealed impaired calcium flux and phospholipase C-gamma1-extracellular signal-regulated kinase activation in the absence of PP4. Anti-CD3 injection in PP4-deficient mice led to enhanced thymocyte apoptosis, accompanied by increased proapoptotic Bim but decreased antiapoptotic Bcl-xL protein levels. In the periphery, antigen-specific T-cell proliferation and T-cell-mediated immune responses in PP4-deficient mice were dramatically compromised. Thus, our results indicate that PP4 is essential for thymocyte development and pre-TCR signaling.
Shui
Jr-Wen
JW
Department of Immunology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
Hu
Mickey C-T
MC
Tan
Tse-Hua
TH
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000818:Animals; D017209:Apoptosis; D017252:CD3 Complex / Q000096:biosynthesis; D015704:CD4 Antigens / Q000096:biosynthesis; D016827:CD8 Antigens / Q000096:biosynthesis; D018960:Hyaluronan Receptors / Q000096:biosynthesis; D053645:Interleukin-2 Receptor alpha Subunit / Q000096:biosynthesis; D051379:Mice; D018345:Mice, Knockout; D009419:Nerve Tissue Proteins / Q000378:metabolism; D019319:Okadaic Acid / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000235:genetics* / Q000502:physiology*; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000378:metabolism*; D013950:Thymus Gland / Q000166:cytology* / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000378:metabolism; D010738:Type C Phospholipases / Q000378:metabolism; D051020:bcl-X Protein / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; C109221:Bin1 protein, mouse; D017252:CD3 Complex; D015704:CD4 Antigens; D016827:CD8 Antigens; D018960:Hyaluronan Receptors; D053645:Interleukin-2 Receptor alpha Subunit; D009419:Nerve Tissue Proteins; D025521:Tumor Suppressor Proteins; D051020:bcl-X Protein; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases; C080406:protein phosphatase 4; D010738:Type C Phospholipases