Activation of Tyk2 and Stat3 Is Required for the Apoptotic Actions of Interferon-β in Primary Pro-B Cells

Ana M Gamero,Ramesh Potla,Joanna Wegrzyn,Magdelena Szelag,Andrea E Edling,Kazuya Shimoda,Daniel C Link,Jozef Dulak,Darren P Baker,Yoshinari Tanabe,Jason M Grayson,Andrew C Larner

doi:10.1074/jbc.m509516200

Abstract

The growth-inhibitory effects of type 1 interferons (IFNs) (IFNalpha/beta) are complex, and the role of apoptosis in their antigrowth effects is variable and not well understood. We have examined primary murine interleukin-7-dependent bone marrow-derived pro-B cells, where IFNbeta, but not IFNalpha, induces programmed cell death (PCD). IFNbeta-stimulated apoptosis is the same in pro-B cells derived from wild type and Stat1(-/-) mice. However, in pro-B cells from Tyk2(-/-) mice, where there is normal activation of Stat1 and Stat2, IFNbeta-stimulated PCD is not observed. Loss of B cells in lymphocytic choriomeningitis virus-infected mice has been shown to be mediated through the expression of IFNalpha/beta (1). In wild type mice infected with lymphocytic choriomeningitis virus, there is a greater loss of B cells in the bone marrow and spleen than in Tyk2(-/-) mice infected with the virus, suggesting that the expression of this kinase plays an in vivo role in IFNalpha/beta-mediated PCD. In contrast to IFNbeta-stimulated tyrosine phosphorylation of Stat1 and Stat2, Stat3 tyrosine phosphorylation is defective in Tyk2(-/-) pro-B cells, suggesting that this Stat family member is required for apoptosis. In support of this hypothesis, inhibition of Stat3 activation in wild type B cells reverses the apoptotic effects of IFNbeta. Furthermore, expression of a constitutively active form of Stat3 in Tyk2(-/-) B cells partially restores IFNbeta-stimulated PCD. These results demonstrate an important role of Tyk2-mediated tyrosine phosphorylation of Stat3 in the ability of IFNbeta to stimulate apoptosis of primary pro-B cells.

Highlights

The growth-inhibitory effects of type 1 interferons (IFNs) (IFN␣/␤) are complex, and the role of apoptosis in their antigrowth effects is variable and not well understood
In wild type mice infected with lymphocytic choriomeningitis virus, there is a greater loss of B cells in the bone marrow and spleen than in Tyk2؊/؊ mice infected with the virus, suggesting that the expression of this kinase plays an in vivo role in IFN␣/␤-mediated programmed cell death (PCD)
Expression of Tyk2 Is Required for IFN␤-mediated Apoptosis of Murine Pro-B Cells—To examine the role of Tyk2 in IFN␤-stimulated apoptosis, we studied primary bone marrow-derived IL-7-dependent pro-B cells, since they have been shown previously to undergo PCD in the presence of a combination of IFN␣ and IFN␤ (16)

Summary

Introduction

The growth-inhibitory effects of type 1 interferons (IFNs) (IFN␣/␤) are complex, and the role of apoptosis in their antigrowth effects is variable and not well understood. Expression of a constitutively active form of Stat in Tyk2؊/؊ B cells partially restores IFN␤-stimulated PCD These results demonstrate an important role of Tyk2-mediated tyrosine phosphorylation of Stat in the ability of IFN␤ to stimulate apoptosis of primary pro-B cells. The Jak family of tyrosine kinases is an integral component in these signaling cascades (5) Expression of both Jak and Tyk is required for type 1 IFN activation of Stats in human cells, whereas in mouse cells, the actions of type 1 IFNs are only partially dependent upon Tyk (6, 7) in that Stat and Stat, but not Stat, are tyrosine-phosphorylated in Tyk2-null cells incubated with IFN␣. The best described system to examine type 1 IFN-stimulated apoptosis of primary cells is murine IL-7-dependent bone marrow-derived B cells These pro-B cells show both inhibited cell growth as well as apoptosis when incubated with a combination of virally produced IFN␣ and IFN␤ for 24 – 48 h. IFN␣ treatment of newborn mice inhibits the development of both T and B cell populations, and infection of mice with lymphocytic choriomeningitis virus (LCMV)

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Conclusion