Role for Wee1 in inhibition of G2-to-M transition through the cooperation of distinct human papillomavirus type 1 E4 proteins.
The infectious cycle of human papillomavirus type 1 (HPV1) is accompanied by abundant expression of the full-length E1;E4 protein (17-kDa) and smaller E4 polypeptides (16-, 11-, and 10-kDa) that arise by sequential loss of N-terminal E1;E4 sequences. HPV1 E4 inhibits G(2)-to-M transition of the cell cycle. Here, we show that HPV1 E4 proteins mediate inhibition of cell division by more than one mechanism. Cells arrested by coexpression of E1;E4 (E4-17K) and a truncated protein equivalent to the 16-kDa species (E4-16K) contain inactive cyclin B1-cdk1 complexes. Inactivation of cdk1 is through inhibitory Tyr(15) phosphorylation, with cells containing elevated levels of Wee1, the kinase responsible for inhibitory cdk1 phosphorylation. Consistent with these findings, overexpression of Wee1 enhanced the extent to which E4-17K/16K-expressing cells arrest in G(2), indicating that maintenance of Wee1 activity is necessary for inhibition of cell division induced by coexpression of the two E4 proteins. Moreover, we have determined that depletion of Wee1 by small interfering RNA (siRNA) alleviates the G(2) block imposed by E4-17K/16K. In contrast however, maintenance of Wee1 activity is not necessary for G(2)-to-M inhibition mediated by E4-16K alone, as overexpression or depletion of Wee1 does not influence the G(2) arrest function of E4-16K. Cells arrested by E4-16K expression contain low levels of active cyclin B1-cdk1 complexes. We hypothesize that differential expression of HPV1 E4 proteins during the viral life cycle determines the host cell cycle status. Different mechanisms of inhibition of G(2)-to-M transition reinforce the supposition that distinct E4 functions are important for HPV replication.
Knight
Gillian L
GL
Cancer Research UK Institute for Cancer Studies, University of Birmingham, Vincent Drive, Edgbaston, Birmingham B15 2TT, United Kingdom.
Turnell
Andrew S
AS
Roberts
Sally
S
D016203:CDC2 Protein Kinase / Q000378:metabolism; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D002455:Cell Division; D019926:Cyclin B / Q000378:metabolism; D056744:Cyclin B1; D016195:G2 Phase; D006367:HeLa Cells / Q000378:metabolism / Q000821:virology; D006801:Humans; D015603:Keratinocytes / Q000166:cytology / Q000378:metabolism / Q000821:virology; D009687:Nuclear Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D009856:Oncogene Proteins, Viral / Q000378:metabolism*; D027383:Papillomaviridae / Q000472:pathogenicity*; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D034741:RNA, Small Interfering / Q000494:pharmacology; D014443:Tyrosine / Q000378:metabolism
C534699:CCNB1 protein, human; D018797:Cell Cycle Proteins; D019926:Cyclin B; D056744:Cyclin B1; D009687:Nuclear Proteins; D009856:Oncogene Proteins, Viral; D034741:RNA, Small Interfering; C056651:oncogene protein E4, human papilloma virus type 1; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; C499349:WEE1 protein, human; D016203:CDC2 Protein Kinase