Antibodies Specific for the Human Retinoblastoma Protein Identify a Family of Related Polypeptides

The transcription factor E2F has been implicated in cell cycle control by virtue of its association with cyclins, cyclin-dependent kinases, and pRb-related tumor suppressor gene products. Eggs and embryos from the frog Xenopus laevis have been used to investigate the characteristics of E2F-like molecules in the Xenopus cell cycle and throughout early development. We find multiple E2F species in Xenopus eggs, at least one of which is modified by phosphorylation. The vast majority of E2F remains in the free form throughout the very early embryonic cell cycle, and it also remains predominantly free until some time after the mid-blastula transition, the onset of zygotic transcription. At this time, E2F complexes significantly to pRb but not to cdk2, although cdk2 binding is found in tissue culture cells from a very advanced stage in embryogenesis. This suggests that the complexing of E2F to cyclins, cyclin-dependent kinases, and tumor suppressor gene products may be controlled separately in early Xenopus development. Thus, the association of E2F with other molecules may not result solely from processes affecting cell cycle progression but may also reflect developmental and differentiation cues.

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

See 2 more Smart Citations

E2F and Its Developmental Regulation in Xenopus laevis

Philpott

Friend

1994

“…Polyclonal antisera to E2F-2 and E2F-3 were raised by injecting mice with GST fusion proteins containing amino acids 85 to 200 of E2F-2 or amino acids 132 to 230 of E2F-3 as described by Harlow and Lane (20a). The antibodies against pRB (C36 and XZ77), p107 (SD2, SD4, SD6, SD9, and SD15), simian virus 40 large T antigen (PAb419), and E2F-1 have been described previously (11,20,22,27).…”

Section: Methodsmentioning

confidence: 99%

The Retinoblastoma Protein Binds to a Family of E2F Transcription Factors

Lees

Saito

Vidal

et al. 1993

E2F is a transcription factor that helps regulate the expression of a number of genes that are important in cell proliferation. Recently, several laboratories have isolated a cDNA clone that encodes an E2F-like protein, known as E2F-1. Subsequent characterization of this protein showed that it had the properties of E2F, but it was difficult to account for all of the suggested E2F activities through the function of this one protein. Using low-stringency hybridization, we have isolated cDNA clones that encode two additional E2F-like proteins, called E2F-2 and E2F-3. The chromosomal locations of the genes for E2F-2 and E2F-3 were mapped to 1p36 and 6q22, respectfully, confirming their independence from E2F-1. However, the E2F-2 and E2F-3 proteins are closely related to E2F-1. Both E2F-2 and E2F-3 bound to wild-type but not mutant E2F recognition sites, and they bound specifically to the retinoblastoma protein in vivo. Finally, E2F-2 and E2F-3 were able to activate transcription of E2F-responsive genes in a manner that was dependent upon the presence of at least one functional E2F binding site. These observations suggest that the E2F activities described previously result from the combined action of a family of proteins.

E2F Mediates Dihydrofolate Reductase Promoter Activation and Multiprotein Complex Formation in Human Cytomegalovirus Infection

Wade

Kowalik

Mudryj

et al. 1992

The adenovirus immediate-early protein E1A activates the adenovirus E2 promoter and several cellular gene promoters through transcription factor E2F. The immediate-early proteins of human cytomegalovirus (HCMV) can complement an E1A-deficient adenovirus mutant and activate the adenovirus E2 promoter. HCMV also has been shown to activate the adenovirus E2 promoter. On the basis of these findings, we have investigated whether HCMV can activate the promoter of the cellular dihydrofolate reductase (DHFR) gene, which requires E2F binding for maximal promoter activity. We show that HCMV activates the DHFR promoter and that products of the HCMV major immediate-early gene region mediate the activation of the promoter specifically through the E2F site. We used gel mobility shift assays to search for potential molecular mechanisms for this activation and found an "infection-specific" multimeric complex that bound to the E2F sites in the DHFR and E2 promoters in extracts from HCMV-infected cells but not in extracts from uninfected cells. Several antibodies against HCMV immediate-early gene products had no effect on this infection-specific complex. Subsequently, the complex was found to contain E2F, cyclin A, p33cdk2, and p107 and to be similar to S-phase-specific complexes that recently have been identified in several cell types. A functional role for the binding of the cyclin A-p33cdk2 complex to cellular gene promoters has yet to be demonstrated; however, HCMV infection causes the induction of both cellular DNA replication and transcription of growth-related genes containing E2F sites in their promoters. The findings described above therefore may relate to both of these effects of HCMV infection. We also provide evidence that some of the molecular events associated with adenovirus infection are different from those associated with HCMV infection.