MIZUNO Kazuya Tokyo Metropolitan Institute for Neuroscience, Tokyo Metropolitan Organization for Medical Research, Director of Department, 東京都神経科学総合研究所, 副参事研究員 (00219643)
OGIMOTO Mami Tokyo Metropolitan Institute for Neuroscience, Tokyo Metropolitan Organization for Medical Research, Staff Scientist, 東京都神経科学総合研究所, 研究員 (80158609)
KATAGIRI Tatsuo Tokyo Metropolitan Institute for Neuroscience, Tokyo Metropolitan Organization for Medical Research, Staff Scientist, 東京都神経科学総合研究所, 研究員 (00233742)
|Budget Amount *help
¥3,000,000 (Direct Cost: ¥3,000,000)
Fiscal Year 2000: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 1999: ¥1,600,000 (Direct Cost: ¥1,600,000)
Signaling events leading to B cell growth or apoptosis are beginning to be unraveled, but detailed information is still lacking. To identify signaling molecules involved in B cell antigen receptor (BCR)-initiated pathways, we used the immature B cell line, WEHI-231, to investigate protein tyrosine phosphatases (PTP) whose expression was modulated by BCR ligation. Among the PTPs cloned by reverse transcription-PCR, mRNA expression of the proline-, glutamic acid-, serine- and threonine-rich (PEST) domain phosphatase (PEP) was selectively elevated 3.1-fold within 3 h after anti-IgM antibody stimulation. In contrast, expression of another PEST domain phosphatase, PTP-PEST, was unaffected. Western blot analysis revealed that 71 % of PEP was located in the cytosolic fraction, while 29 % was in the membrane fraction. To examine the direct contribution made by PEP to BCR-initiated signal transduction, we transfected an antisense PEP cDNA into WEHI-231 cells. Two stable clones were established in which PEP expression was reduced by 34 % and 47 %, respectively. Stirikingly, BCR-mediated inhibition of DNA synthesis was significantly rescued in the clones, and G1 phase cell cycle arrest and apoptosis were almost completely ablated. Considered collectively, these results indicate that PEP is a positive, crucial regulator in determining B cell fate triggered by BCR engagement.
These results are not consistent with the findings in T cells showing that PEP is a negative regulator of TCR signaling. To resolve these differences, we are in the process of identifying PEP substrates in B cells and elucidating the regulatory mode of initial phases of BCR signalling ; activation of Src-family kinases, among others.