p27^Kip1 and p130 Cooperate To Regulate Hematopoietic Cell Proliferation In Vivo

Abstract

To investigate the potential functional cooperation between p27^Kip1 and p130 in vivo, we generated mice deficient for both p27^Kip1 and p130. In p27^Kip1−/−; p130^−/− mice, the cellularity of the spleens but not the thymi is significantly increased compared with that of their p27^Kip1−/− counterparts, affecting the lymphoid, erythroid, and myeloid compartments. In vivo cell proliferation is significantly augmented in the B and T cells, monocytes, macrophages, and erythroid progenitors in the spleens of p27^Kip1−/−; p130^−/− animals. Immunoprecipitation and immunodepletion studies indicate that p130 can compensate for the absence of p27^Kip1 in binding to and repressing CDK2 and is the predominant CDK-inhibitor associated with the inactive CDK2 in the p27^Kip1−/− splenocytes. The finding that the p27^Kip1−/−; p130^−/− splenic B cells are hypersensitive to mitogenic stimulations in vitro lends support to the concept that the hyperproliferation of splenocytes is not a result of the influence of their microenvironment. In summary, our findings provide genetic and molecular evidence to show that p130 is a bona fide cyclin-dependent kinase inhibitor and cooperates with p27^Kip1 to regulate hematopoietic cell proliferation in vivo.

Supplemental material for this article may be found at http://mcb.asm.org/.

We thank Nicola Hardwick for her help on [³H]thymidine and cell cycle analyses.

Inês Soeiro is a recipient of a fellowship from Fundação para a Ciência e a Tecnologia, Portugal. Azim Mohamedali, Nicholas Lea, and Stephen Orr were supported by the Charles Wolfson Charitable Trust. Shaun Thomas's work is supported by the Leukemia Research Fund and the Charles Wolfson Charitable Trust. David Mann and Emma Child were funded by the BBSRC. Eric Lam's work is supported by Leukemia Research Fund and Cancer Research UK.