RESUMO
Mounting evidence has shown that the insulin-like growth factor-1 receptor (IGF-1R) has critical roles in cancer cell growth. This has prompted pharmacological companies to develop agents targeting the receptor. Surprisingly, clinical trials using specific IGF-1R antibodies have, however, revealed disappointing results. Further understanding of the role of IGF-1R in cancer cells is therefore necessary for development of efficient therapeutic strategies. Recently, we showed that IGF-1R is sumoylated and translocated into the cell nucleus where it activates gene transcription. Several other studies have confirmed our findings and it has been reported that nuclear IGF-1R (nIGF-1R) has prognostic and predictive impact in cancer. To increase the understanding of IGF-1R in cancer cells, we here present the first study that proposes a pathway by which IGF-1R translocates into the cell nucleus. We could demonstrate that IGF-1R first associates with the dynactin subunit p150(Glued), which transports the receptor to the nuclear pore complex, where it co-localizes with importin-ß followed by association with RanBP2. Sumoylation of IGF-1R seems to be required for interaction with RanBP2, which in turn may serve as the SUMO E3 ligase. In the context of sumoylation, we provided evidence that it may favor nIGF-1R accumulation by increasing the stability of the receptor. Taken together, topographic and functional interactions between dynactin, importin-ß and RanBP2 are involved in nuclear translocation of IGF-1R. Our results provide new understanding of IGF-1R in cancer, which in turn may contribute to development of new therapeutic strategies.
Assuntos
Núcleo Celular/metabolismo , Proteínas Associadas aos Microtúbulos/metabolismo , Chaperonas Moleculares/metabolismo , Proteínas de Neoplasias/metabolismo , Neoplasias/metabolismo , Complexo de Proteínas Formadoras de Poros Nucleares/metabolismo , Receptor IGF Tipo 1/metabolismo , beta Carioferinas/metabolismo , Transporte Ativo do Núcleo Celular/genética , Linhagem Celular Tumoral , Núcleo Celular/genética , Núcleo Celular/patologia , Complexo Dinactina , Células HEK293 , Humanos , Masculino , Proteínas Associadas aos Microtúbulos/genética , Chaperonas Moleculares/genética , Proteínas de Neoplasias/genética , Neoplasias/genética , Neoplasias/patologia , Complexo de Proteínas Formadoras de Poros Nucleares/genética , Receptor IGF Tipo 1/genética , Sumoilação/genética , beta Carioferinas/genéticaRESUMO
The insulin-like growth factor 1 receptor (IGF-1R) is crucial for growth and survival of malignant cells. Experience in targeting IGF-1R in cancer models has shown that strategies promoting downregulation of the receptor are much more efficient in inducing apoptosis than those inhibiting the IGF-1R activity. Recently, we found that the cyclolignan picropodophyllin (PPP) inhibits phosphorylation of IGF-1R and activation of downstream signaling without interfering with the highly homologous insulin receptor (IR). Furthermore, PPP treatment caused strong regression of tumor grafts and prolonged survival of animals with systemic tumor disease. Here we demonstrate that PPP also downregulates the IGF-1R, whereas the IR and several other receptors were not affected. PPP-induced IGF-1R downregulation required expression of the MDM2 E3 ligase, which recently was found to ubiquitinate and cause degradation of the IGF-1R. In addition knockdown of beta-arrestin1, the adaptor molecule known to bridges MDM2 and IGF-1R, prevented downregulation of the receptor and significantly decreased PPP-induced cell death. All together these data suggest that PPP downregulates IGF-1R by interfering with the action of beta-arrestin1/MDM2 as well as the achieved receptor downregulation contributes to the apoptotic effect of PPP.