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Blood, 15 November 2006, Vol. 108, No. 10, pp. 3428-3433. Prepublished online as a Blood First Edition Paper on August 3, 2006; DOI 10.1182/blood-2006-03-013821.
IMMUNOBIOLOGY Protein tyrosine phosphatase receptortype O truncated (PTPROt) regulates SYK phosphorylation, proximal B-cellreceptor signaling, and cellular proliferationFrom the Division of Hematologic Malignancies, Dana-Farber Cancer Institute, Boston, MA.
The strength and duration of B-cellreceptor (BCR) signaling depends upon the balance between protein tyrosine kinase (PTK) activation and protein tyrosine phosphatase (PTP) inhibition. BCR-dependent activation of the SYK PTK initiates downstream signaling events and amplifies the original BCR signal. Although BCR-associated SYK phosphorylation is clearly regulated by PTPs, SYK has not been identified as a direct PTP substrate. Herein, we demonstrate that SYK is a major substrate of a tissue-specific and developmentally regulated PTP, PTP receptortype O truncated (PTPROt). PTPROt is a member of the PTPRO family (also designated GLEPP, PTP-Ø, PTP-oc, and PTPu2), a group of highly conserved receptor-type PTPs that are thought to function as tumor suppressor genes. The overexpression of PTPROt inhibited BCR-triggered SYK tyrosyl phosphorylation, activation of the associated adaptor proteins SHC and BLNK, and downstream signaling events, including calcium mobilization and mitogen-activated protein kinase/extracellular signalregulated kinase (MAPK/ERK) activation. PTPROt overexpression also inhibited lymphoma cell proliferation and induced apoptosis in the absence of BCR cross-linking, suggesting that the phosphatase modulates tonic BCR signaling.
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