BackgroundGrb2 (Growth factor receptor-bound protein 2) is a key adaptor protein in maintaining the ERK activity via linking Sos1 (Son of sevenless homolog 1) or other proteins to activated RTKs, such as EGFR. Currently, little knowledge is available concerning the post-translational modification (PTM) of Grb2 except for its phosphorylation. Since emerging evidences have highlighted the importance of SUMOylation (Small ubiquitin-related modifier), a reversible PTM, in modulating protein functions, we wondered if Grb2 could be SUMOylated and thereby influences its functions especially involved in the Ras/MEK/ERK pathway.MethodsSUMOylation of Grb2 was analyzed with the in vivo SUMOylation assay using the Ni2+-NTA affinity pulldown and the in vitro E.coli-based SUMOylation assay. To test the ERK activity and cell transformation, the murine fibroblast cell line NIH/3T3 and the murine colon cancer cell line CMT-93 were used for the experiments including Grb2 knockdown, ectopic re-expression, cell transformation and migration. Immunoprecipitation (IP) was employed for seeking proteins that interact with SUMO modified Grb2. Xenograft tumor model in mice was conducted to verify that Grb2 SUMOylation regulated tumorigenesis in vivo.ResultsGrb2 can be SUMOylated by SUMO1 at lysine 56 (K56), which is located in the linker region between the N-terminal SH3 domain and the SH2 domain. Knockdown of Grb2 reduced the ERK activity and suppressed cell motility and tumorigenesis in vitro and in vivo, which were all rescued by stable ectopic re-expression of wild-type Grb2 but not the mutant Grb2K56R. Furthermore, Grb2 SUMOylation at K56 increased the formation of Grb2-Sos1 complex, which sequentially leads to the activation of Ras/MEK/MAPK pathway.ConclusionsOur results provide evidences that Grb2 is SUMOylated in vivo and this modification enhances ERK activities via increasing the formation of Grb2-Sos1 complex, and may consequently promote cell motility, transformation and tumorigenesis.

Prostate cancer (PCa) is the most prevalent malignant carcinoma among males in western countries. Currently no treatments can cure advanced prostate cancers, so new diagnostic and therapeutic strategies are in urgent need. At present limited knowledge is available concerning the roles of dysregulated microRNAs in prostate cancer metastasis. In this study, we found that the expression of miR-130b was significantly down-regulated in prostate cancer cell lines and clinical prostate cancer tissues. Enforced over-expression of miR-130b in prostate cancer cells suppressed whereas knock-down of miR-130b increased cell migration and invasion. Using mouse model, we revealed that miR-130b-expressed prostate cancer cells displayed significant reduction in tumor metastasis. Furthermore, we identified and validated matrix metalloproteinase-2 (MMP2) as a direct target of miR-130b. Ectopic expression of MMP2 rescued miR-130b-suppressed cell migration and invasion, and knock-down of MMP2 antagonized the effect of silencing miR-130b.Taken together, our data reveal for the first time that miR-130b exerts a suppressive effect in prostate cancer metastasis through down-regulation of MMP2.

BackgroundCDCA5 plays an important role in the development of various human cancers, but the associated mechanisms have not been investigated in hepatocellular carcinoma (HCC).Materials and methodsWe evaluated expression levels and functions of CDCA5 in HCC and showed that CDCA5 is upregulated in HCC tissues compared with paired or unpaired normal liver tissues.ResultsIncreased CDCA5 expression in HCCs was significantly associated with shorter survival of patients. Knockdown of CDCA5 using lentivirus-mediated shRNA significantly inhibited cell proliferation and suppressed cell survival, as well as induced cell cycle arrest at the G2/M phase and cell apoptosis of HCC cells. The tumor suppression effects of CDCA5 knockdown were mediated by decreased expression of cyclin-dependent kinase 1 (CDK1) and CyclinB1, which were increased in HCC tissues comparing with adjacent normal liver tissues. Moreover, upregulation of CDCA5 was positively associated with increased CDK1 and CyclinB1 expression in HCC tissues.ConclusionThe present data warrant consideration of CDCA5 as a prognostic biomarker and therapeutic target for HCC.

Receptor protein tyrosine phosphatase alpha (RPTPa), an activator of Src family kinases, is found significantly overexpressed in human cancer tissues. However, little is known about the regulation of RPTPa expression. miRNAs target multiple genes and play important roles in many cancer processes. Here, we identified a miRNA, miR-218 that binds directly to the 3 0 -UTR of RPTPa. Ectopic overexpression of miR-218 decreased RPTPa protein leading to decreased dephosphorylation of c-Src and decreased tumour growth in vitro and in vivo. A feedback loop between c-Src and miR-218 was revealed where c-Src inhibits transcription of SLIT2, which intronically hosts miR-218. These results show a novel regulatory pathway for RPTPa-c-Src signalling.