p130 Is Dispensable in Peripheral T Lymphocytes: Evidence for Functional Compensation by p107 and pRB

ABSTRACT

The proteins encoded by the retinoblastoma gene family, pRB, p107, and p130, have been implicated in the regulation of cellular proliferation, differentiation, and transformation. Because interactions between p130 and E2F transcription factors have been proposed to play a role in the establishment and/or maintenance of quiescence in human peripheral T lymphocytes, we examined lymphoid differentiation and proliferation in p130-deficient mice. We show thatp130^−/− T cells proliferate normally in culture and exhibit normal cell-mediated immune function in vivo. However, p130^−/− T lymphocytes expressed elevated levels of p107, and the characteristic p130-E2F DNA binding complex was replaced by a p107-E2F complex. Adoptive transfer of fetal liver lymphoid progenitors allowed us to circumvent the neonatal lethality associated with loss of p130 and p107 and to analyze the phenotype of p130^−/−;p107^−/− peripheral T lymphocytes. These cells achieved a quiescent state, exhibited derepression of a subset of E2F target genes, and were hypersensitive to concanavalin A stimulation. Interestingly, a significant portion of the E2F-4 in p130^−/−;p107^−/− T cells was detected in a complex with pRB and an as-yet-unidentified protein. These findings provide a biochemical basis for functional compensation between pRB family proteins.

ACKNOWLEDGMENTS

We thank Bart Williams, Kay MacLeod, Elias Theodorou, and all members of the Jacks lab for helpful discussions and Bart Williams, Bob Weinberg, Mariana Nacht, Laura Attardi, Jenny-Sue Lanni, Sunil Hingorhani, and Karen Chikowski for critical reading of the manuscript. We also thank David Gerber, Glenn Paradis, and Arlene Sharpe for assistance in lymphocyte proliferative assays and cell sorting and advice on in vivo immune analysis, respectively. Thanks also go to M. Imperiale and J. Lees for gifts of pRB and E2F-4 antibodies and to Rob Hurford and Nick Dyson for communicating results prior to publication and providing cDNA probes for acidic ribosomal phosphoprotein PO, thymidine kinase, E2F-1, and E2F-4. Thanks also go to Phil Steiner and Lee Johnson for cyclin E and thymidine synthase probes, respectively.

T.J. is an Associate Investigator of the Howard Hughes Medical Institute.