A Unique Domain of pRb2/p130 Acts as an Inhibitor of Cdk2 Kinase Activity

Abstract

The Cdk2 kinase has long been known to be involved in the progression of mammalian cells past the G 1 phase restriction point and through DNA replication in the cell cycle. The Rb family of proteins, consisting of pRb, p107, and pRb2/p130, has also been shown to monitor progression of G 1 phase, mostly through their interaction with E2F family members. p107 is able to inhibit Cdk2 kinase activity through this interaction via a p21-related domain present in the C terminus of the protein. We show here that pRb2/p130 also possesses this activity, but through a separate domain. Moreover, we correlate the increased expression of pRb2/p130 during various cellular processes with the decreased kinase activity of Cdk2. We hypothesize that pRb2/p130 may act not only to bind and modify E2F activity, but also to inhibit Cdk2 kinase activity in concert with p21 in a manner different from p107.

Cell cycle control and beyond: emerging roles for the retinoblastoma gene family

“…It has been revealed that Rb2/p130 could also contribute to G1 arrest through its unique spacer region, which grants the ability to suppress cdk2 kinase activity, thereby decreasing the activity of kinases that allow the cell to enter S-phase (De Luca et al, 1997). Furthermore, according to several studies using fibroblasts from knockout mouse embryos, the deficiency of Rb or of more than one family member exhibits a shortened G1 phase of the cell cycle and subsequent lengthening of S phase (Ruiz et al, 2004).…”

“…Also, Rb2/p130 and p107 contain a motif similar to the one found in the p21/cdk-inhibitor, which grants the ability to bind and inhibit cdks, suggesting that p107 and pRb2/p130 may also be responsible for an interaction that affects cdk activity (Woo et al, 1997). Rb2/p130 uniquely also possesses another distinct kinase inhibitory domain, found within its spacer region, which selectively inhibits cdk2 kinase activity (De Luca et al, 1997;Howard et al, 1998).…”

“…This timed regulation is demonstrated through the complexes formed with the E2F family. In vivo studies demonstrate that Rb2/p130 binds to E2F-4 and -5 in G0 and p107 is associated with E2F-4, especially in G1, whereas Rb/p105 binds to E2F-4 in S phase (Ginsberg et al, 1994;Sardet et al, 1995;Moberg et al, 1996;De Luca et al, 1997;Howard et al, 2000). This sequence is most likely guided by a sequential activation and deactivation of the Rb gene family.…”

“…Through this inhibition, pRb2/p130 also induces p27 Kip1 levels by impeding cyclin E-Cdk2 phosphorylation of p27 Kip1 , which in turn generates the proteolytic degradation of p27 Kip1 (Howard et al, 2000). Moreover, Rb2/ p130 possesses a kinase inhibitory domain in its spacer region that preferentially inhibits cdk2 kinase activity (De Luca et al, 1997). Interestingly, both cyclins A and E have been found to rescue Rb2/p130-induced cell cycle arrest, indicating the importance of this interaction in cell cycle progression (Claudio et al, 1996).…”

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“…p21 has been shown to suppress cell growth by enhancing formation of E2F-p130 complexes through disruption of the interaction between the cyclin-dependent kinase Cdk2 and the E2F-p130 complex (Shiyanov et al, 1996). p107 and p130 appear to both bind to Cdk2 and inhibit its activity (Coats et al, 1999;Castano et al, 1998;De Luca et al, 1997). The activity of Cdk2 is also regulatable by Bcl-2 (Gil-Gomez et al, 1998) and over-expression of Bcl-2 in tissue culture cells has been shown to reduce the amounts of Cdk2 in the nucleus (Meikrantz et al, 1994).…”