RESUMEN
Porcupine O-acyltransferase (PORCN) is considered essential for Wnt secretion and signaling. However, we observed that PORCN inhibition does not phenocopy the effects of WNT4 knockdown in WNT4-dependent breast cancer cells. This suggests a unique relationship between PORCN and WNT4 signaling. To examine the role of PORCN in WNT4 signaling, here we overexpressed WNT4 or WNT3A in breast cancer, ovarian cancer, and fibrosarcoma cell lines. Conditioned media from these lines and co-culture systems were used to assess the dependence of Wnt secretion and activity on the critical Wnt secretion proteins PORCN and Wnt ligand secretion (WLS) mediator. We observed that WLS is universally required for Wnt secretion and paracrine signaling. In contrast, the dependence of WNT3A secretion and activity on PORCN varied across the cell lines, and WNT4 secretion was PORCN-independent in all models. Surprisingly, WNT4 did not exhibit paracrine activity in any tested context. Absent the expected paracrine activity of secreted WNT4, we identified cell-autonomous Wnt signaling activation by WNT4 and WNT3A, independent of PORCN or Wnt secretion. The PORCN-independent, cell-autonomous Wnt signaling demonstrated here may be critical in WNT4-driven cellular contexts or in those that are considered to have dysfunctional Wnt signaling.
Asunto(s)
Aciltransferasas/metabolismo , Proteínas de la Membrana/metabolismo , Vía de Señalización Wnt , Proteína Wnt3A/metabolismo , Proteína Wnt4/metabolismo , Aciltransferasas/antagonistas & inhibidores , Aciltransferasas/genética , Línea Celular Tumoral , Proliferación Celular , Técnicas de Cocultivo , Medios de Cultivo Condicionados/química , Fulvestrant/farmacología , Humanos , Péptidos y Proteínas de Señalización Intracelular/antagonistas & inhibidores , Péptidos y Proteínas de Señalización Intracelular/genética , Péptidos y Proteínas de Señalización Intracelular/metabolismo , Proteínas de la Membrana/antagonistas & inhibidores , Proteínas de la Membrana/genética , Comunicación Paracrina , Transporte de Proteínas , Interferencia de ARN , ARN Interferente Pequeño/metabolismo , Receptores Acoplados a Proteínas G/antagonistas & inhibidores , Receptores Acoplados a Proteínas G/genética , Receptores Acoplados a Proteínas G/metabolismo , Vía de Señalización Wnt/efectos de los fármacos , Proteína Wnt3A/antagonistas & inhibidores , Proteína Wnt3A/genética , Proteína Wnt4/antagonistas & inhibidores , Proteína Wnt4/genéticaRESUMEN
Centrosomes are the major microtubule-organizing centers in animal cells and regulate formation of a bipolar mitotic spindle. Aberrant centrosome number causes chromosome mis-segregation, and has been implicated in genomic instability and tumor development. Previous studies have demonstrated a role for the DNA replication factors MCM5 and Orc1 in preventing centrosome reduplication. Cyclin A-Cdk2 localizes on centrosomes by means of a modular centrosomal localization sequence (CLS) that is distinct from that of cyclin E. Here, we show that cyclin A interacts with both MCM5 and Orc1 in a CLS-dependent but Cdk-independent manner. Although the MRAIL hydrophobic patch is contained within the cyclin A CLS, binding of both MCM5 and Orc1 to cyclin A does not require a wild-type hydrophobic patch. The same domain in MCM5 that mediates interaction with cyclin E also binds cyclin A, resulting in centrosomal localization of MCM5. Finally, unlike its function in DNA synthesis, MCM5-mediated inhibition of centrosome reduplication in S-phase-arrested CHO cells does not require binding to other MCM family members. These results suggest that cyclins E and A sequentially prevent centrosome reduplication throughout interphase by recruitment of DNA replication factors such as MCM5 and Orc1.
Asunto(s)
Proteínas de Ciclo Celular/fisiología , Centrosoma/fisiología , Ciclina A/fisiología , Complejo de Reconocimiento del Origen/fisiología , Animales , Células CHO , Proteínas de Ciclo Celular/química , Proteínas de Ciclo Celular/genética , Proteínas de Ciclo Celular/metabolismo , Centrosoma/metabolismo , Cricetinae , Cricetulus , Ciclina A/genética , Ciclina A/metabolismo , Técnica del Anticuerpo Fluorescente , Células HeLa , Humanos , Inmunoprecipitación , Centro Organizador de los Microtúbulos/metabolismo , Complejo de Reconocimiento del Origen/genética , Complejo de Reconocimiento del Origen/metabolismo , TransfecciónRESUMEN
Cyclin E-Cdk2 is known to regulate both DNA replication and centrosome duplication during the G1-S transition in the cell cycle, and disruption of centrosomes results in a G1 arrest in some cell types. Localization of cyclin E on centrosomes is mediated by a 20 amino acid domain termed the centrosomal localization sequence (CLS), and expression of the GFP-tagged CLS displaces both cyclin E and cyclin A from the centrosome. In asynchronous cells, CLS expression inhibits the incorporation of bromodeoxyuridine (BrdU) into DNA, an effect proposed to reflect a G1 arrest. Here we show in synchronized cells that the reduction in BrdU incorporation reflects not a G1 arrest but rather direct inhibition of the initiation of DNA replication in S phase. The loading of essential DNA replication factors such as Cdc45 and proliferating cell nuclear antigen onto chromatin is blocked by CLS expression, but DNA synthesis can be rescued by retargeting active cyclin E-Cdk2 to the centrosome. These results suggest that initial steps of DNA replication require centrosomally localized Cdk activity and link the nuclear cycle with the centrosome cycle at the G1-S transition.
Asunto(s)
Centrosoma/metabolismo , Ciclina E/metabolismo , Quinasa 2 Dependiente de la Ciclina/metabolismo , ADN/biosíntesis , Animales , Bromodesoxiuridina/metabolismo , Células CHO/metabolismo , Cricetinae , Cricetulus , Replicación del ADN , Fase G1 , FosforilaciónRESUMEN
Centrosomes are the primary microtubule-organizing centers in animal cells and are required for bipolar spindle assembly during mitosis. Amplification of centrosome number is commonly observed in human cancer cells and might contribute to genomic instability. Cyclin E-Cdk2 has been implicated in regulating centrosome duplication both in Xenopus embryos and extracts and in mammalian cells. Localization of cyclin E on centrosomes is mediated by a 20-amino acid domain termed the centrosomal localization sequence (CLS). In this paper, cyclin E is shown to directly interact with and colocalize on centrosomes with the DNA replication factor MCM5 in a CLS-dependent but Cdk2-independent manner. The domain in MCM5 that is responsible for interaction with cyclin E is distinct from any previously described for MCM5 function and is highly conserved in MCM5 proteins from yeast to mammals. Expression of MCM5 or its cyclin E-interacting domain, but not MCM2, significantly inhibits over-duplication of centrosomes in CHO cells arrested in S-phase. These results indicate that proteins involved in DNA replication might also regulate centrosome duplication.
