Functional analysis of pRb2/p130 interaction with cyclins.

Department of Microbiology-Immunology, Jefferson Cancer Institute, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
Cancer Research (Impact Factor: 9.28). 06/1996; 56(9):2003-8.
Source: PubMed

ABSTRACT The retinoblastoma (Rb) family consists of the tumor suppressor pRb and related proteins p107 and pRb2/p130. Ectopic expression of pRb and p107 results in a growth arrest of sensitive cells in the G1 phase of the cell cycle. We demonstrated here that the growth-suppressive properties of pRb2/p130 were also specific for the G1 phase. The A-, E-, and D-type cyclins as well as transcription factor E2F1 and the E1A viral oncoprotein were able to rescue the pRb2/p130-mediated G1 growth arrest in SAOS-2 cells. The rescue with cyclins A and E correlated with their physical interaction with pRb2/p130, which surprisingly has been found to occur over all phases of the cell cycle. The phosphorylation status as well as the kinase activity associated with pRb2/p130 dramatically increased near the G1-S-phase transition. This suggests that, like the other Rb family members, pRb and p107, the phosphorylation of pRb2/p130 is controlled by the cell cycle machinery and that pRb2/p130 may indeed be another key G1-S-phase regulator.

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    ABSTRACT: The pocket proteins retinoblastoma protein (pRb), p107 and p130 are the key targets of oncoproteins expressed by DNA tumor viruses. Some of these viral proteins contain an LXCXE motif that mediates the interaction with the three pocket proteins and the inhibition of the pRb SUMOylation. Kaposi's sarcoma herpesvirus (KSHV) contains at least two proteins that can regulate pRb function but, so far, a KSHV-encoded protein targeting p107 and p130 has not been identified. Here, we show that the KSHV latent protein LANA2 binds to pRb, p107 and p130. LANA2 contains an LXCXE motif that is required for bypassing pRb-mediated cell-cycle arrest and for inhibiting pRb SUMOylation. Finally, we demonstrate that, in addition to pRb, both p107 and p130 can be SUMOylated, and this modification is also inhibited by LANA2 in an LXCXE-dependent manner. These results demonstrate, for the first time, the SUMOylation of p107 or p130 and, so far, they represent the first example of a KSHV protein able to interact with the three pocket proteins and to inhibit their conjugation to SUMO.Oncogene advance online publication, 14 January 2013; doi:10.1038/onc.2012.603.
    Oncogene 01/2014; 33:495-503. DOI:10.1038/onc.2012.603 · 8.56 Impact Factor
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    ABSTRACT: Loss of RB1 gene is considered either a causal or an accelerating event in retinoblastoma. A variety of mechanisms inactivates RB1 gene, including intragenic mutations, loss of expression by methylation and chromosomal deletions, with effects which are species- and cell type- specific. RB1 deletion can even lead to aneuploidy thus greatly increasing cancer risk. The RB1gene is part of a larger gene family that includes RBL1 and RBL2, each of the three encoding structurally related proteins indicated as pRb, p107 and p130, respectively. The great interest in these genes and proteins springs from their ability to slow down neoplastic growth. pRb can associate with various proteins by which it can regulate a great number of cellular activities. In particular, its association with the E2F transcription factor family allows the control of the main pRb functions, while the loss of these interactions greatly enhances cancer development. As RB1 gene, also pRb can be functionally inactivated through disparate mechanisms which are often tissue specific and dependent on the scenario of the involved tumor suppressors and oncogenes. The critical role of the context is complicated by the different functions played by the RB proteins and the E2F family members. In this review, we want to emphasize the importance of the mechanisms of RB1/pRb inactivation in inducing cancer cell development. The review is divided in three chapters describing in succession the mechanisms of RB1 inactivation in cancer cells, the alterations of pRb pathway in tumorigenesis and the RB protein and E2F family in cancer. J. Cell. Physiol. © 2013 Wiley Periodicals, Inc.
    Journal of Cellular Physiology 08/2013; 228(8). DOI:10.1002/jcp.24329 · 3.87 Impact Factor

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