ABSTRACT
P27(Kip1) (p27) is a member of the Cip/Kip family of cyclin-dependent kinase inhibitors. Recently, a new function of p27 as transcriptional regulator has been reported. It has been shown that p27 regulates the expression of target genes mostly involved in splicing, cell cycle, respiration and translation. We report here that p27 directly binds to the transcriptional coactivator PCAF by a region including amino acids 91-120. PCAF associates with p27 through its catalytic domain and acetylates p27 at lysine 100. Our data showed that overexpression of PCAF induces the degradation of p27 whereas in contrast, the knockdown of PCAF stabilizes the protein. A p27 mutant in which K100 was substituted by arginine (p27-K100R) cannot be acetylated by PCAF and has a half-life much higher than that of p27WT. Moreover, p27-K100R remains stable along cell-cycle progression. Ubiquitylation assays and the use of proteasome inhibitors indicate that PCAF induces p27 degradation via proteasome. We also observed that knockdown of skp2 did not affect the PCAF induced degradation of p27. In conclusion, our data suggest that the p27 acetylation by PCAF regulates its stability.
Subject(s)
Cyclin-Dependent Kinase Inhibitor p27/metabolism , p300-CBP Transcription Factors/metabolism , Acetylation , Cell Cycle , Cyclin-Dependent Kinase Inhibitor p27/chemistry , HEK293 Cells , HeLa Cells , Humans , Lysine/metabolism , Protein Interaction Domains and Motifs , Protein StabilityABSTRACT
The objective of this study was to evaluate the effect of an artificially long photoperiod of 16 h of light and eight h of darkness on the length of the seasonally anovulatory period and the duration of the transitional period to ovarian activity in Criollo mares, located at 19° 9'N latitude. Twenty two adult Criollo mares, from three to 17 years old, were randomly divided in two groups. The animals on the experimental group (n = 14) were exposed to 16 h of light per day during four months from December to March. The control mares (n = 8) were exposed only to the natural photoperiod in open pens. The interval from the beginning of the artificial light treatment (December 1) to the first ovulation of the year in the experimental group was 88.4 ± 3.6 days and for the control group, 137.2 ± 15.0 days (P < 0.01); the interval between the development of the first follicle larger than 30 mm and the first ovulation (vernal transition) was 30.9 ± 2.2 days for the experimental group and 37.6 ± 6.6 days for the control group, this difference was not significant (P > 0.05). The mean diameter of the largest follicle increased gradually from week seven in the experimental group and from week 13, in the control group. Mares from both groups showed anovulatory estrus during the anovulatory season as well as during the transitional period. In the majority of the cases, estrous periods were irregular. The results indicate that exposure to an artificially photoperiod of 16 h of light and eight h of darkness, advances the onset of the vernal transition and the first ovulation in Criollo mares located at latitudes that are relatively close to the equator (19° 9'N); therefore, it can be used to anticipate the beginning of a reproductive program.
En el presente trabajo se evaluó el efecto de un fotoperiodo artificial de 16 horas de luz y ocho de oscuridad sobre la longitud del periodo anovulatorio y la duración del periodo de transición hacia la época ovulatoria en yeguas criollas, localizadas en la latitud 19° 9'N. Se utilizaron 22 yeguas criollas de tres a 17 años de edad, que fueron divididas al azar en dos grupos. Las yeguas del grupo experimental (n = 14) se mantuvieron bajo un programa de fotoperiodo artificial de 16 horas de luz por día durante cuatro meses, de diciembre a marzo. Las yeguas del grupo testigo (n = 8) se mantuvieron en condiciones de luz natural. El intervalo desde el inicio del tratamiento luminoso (1 de diciembre) a la primera ovulación del año en el grupo experimental fue de 88.4 ± 3.6 días, y para el grupo testigo fue de 137.2 ± 15.0 días (P < 0.01); la duración del periodo de transición invernal (intervalo entre el desarrollo del primer folículo mayor a 30 mm y la primera ovulación) fue de 30.9 ± 2.2 días para el grupo experimental y 37.6 ± 6.6 para el grupo testigo, esta diferencia no fue significativa (P > 0.05). El diámetro folicular promedio aumentó paulatinamente a partir de la semana siete en el grupo experimental y de la semana 13 en el grupo testigo. En ambos grupos se presentaron estros anovulatorios durante la época de anestro y durante la época de transición. Los intervalos entre estros fueron irregulares en su mayoría. Los resultados indicaron que en latitudes relativamente cercanas al ecuador (19° 9'N) la exposición de yeguas criollas a un fotoperiodo artificial de 16 horas de luz y ocho horas de oscuridad adelanta el inicio de la etapa de transición y de la etapa ovulatoria, por lo que puede ser utilizado para anticipar el inicio del programa reproductivo.
