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Although 53BP1 has been established well as a mediator in DNA damage response, its function in mitosis is not clearly understood. We found that 53BP1 is a mitotic-binding partner of the kinases Plk1 and AuroraA, and that the binding with Plk1 increases the stability of 53BP1 by accelerating its interaction with the deubiquitinase USP7. Depletion of 53BP1 induces mitotic defects such as chromosomal missegregation, misorientation of spindle poles and the generation of extra centrosomes, which is similar phenotype to USP7-knockdown cells. In addition, 53BP1 depletion reduces the levels of p53 and centromere protein F (CENPF), interacting proteins of 53BP1. These phenotypes induced by 53BP1 depletion were rescued by expression of wild-type or phosphomimic mutant 53BP1 but not by expression of a dephosphomimic mutant. We propose that phosphorylation of 53BP1 at S380 accelerates complex formation with USP7 and CENPF to regulate their stability, thus having a crucial role in proper centrosome positioning, chromosomal alignment, and centrosome number.

Tumours are comprised of a highly heterogeneous population of cells, of which only a small subset of stem-like cells possess the ability to regenerate tumours in vivo. These cancer stem cells (CSCs) represent a significant clinical challenge as they are resistant to conventional cancer therapies and play essential roles in metastasis and tumour relapse. Despite this realization and great interest in CSCs, it has been difficult to develop CSC-targeted treatments due to our limited understanding of CSC biology. Here, we present evidence that specific histone deacetylases (HDACs) play essential roles in the CSC phenotype. Utilizing a novel CSC model, we discovered that the HDACs, HDAC1 and HDAC7, are specifically over-expressed in CSCs when compared to non-stem-tumour-cells (nsTCs). Furthermore, we determine that HDAC1 and HDAC7 are necessary to maintain CSCs, and that over-expression of HDAC7 is sufficient to augment the CSC phenotype. We also demonstrate that clinically available HDAC inhibitors (HDACi) targeting HDAC1 and HDAC7 can be used to preferentially target CSCs. These results provide actionable insights that can be rapidly translated into CSC-specific therapies.

Survivin is a dual regulator of cell proliferation and cell viability overexpressed in most human tumors. Although strategies to lower survivin levels have been pursued for rational cancer therapy, the molecular circuitries controlling survivin expression in tumors have not been completely elucidated. Here, we show that stimulation with insulin-like growth factor-1 (IGF-1) results in increased survivin expression in prostate cancer cells. This response is independent of de novo gene transcription, changes in mRNA expression or modifications of survivin protein stability. Instead, IGF-1 induced persistence and translation of a pool of survivin mRNA, in a reaction abolished by the mTOR (mammalian target of rapamycin) inhibitor, rapamycin. Forced expression of the mTOR target p70S6K1 reproduced the increase in survivin expression in prostate cancer cells, whereas acute ablation of endogenous p70S6K1 by small interfering RNA downregulated survivin levels. Rapamycin, alone or in combination with suboptimal concentrations of taxol reduced survivin protein levels, and decreased viability of prostate cancer cells. Therefore, IGF-1/mTOR signaling elevates survivin in prostate cancer cells via rapid changes in mRNA translation. Antagonists of this pathway may be beneficial to lower an antiapoptotic threshold maintained by survivin in prostate cancer.

The RET proto-oncogene encodes two major isoforms, RET9 and RET51, which differ at the carboxyl-terminal. Loss-of-function mutations in RET result in gut aganglionosis while gain of function mutations result in cancer syndromes. From studies on transgenic mice, RET9 is important for early development of the kidney and the enteric nervous system. Little is known about the function of RET isoforms in later life. Here we report the expression of RET isoforms and its signalling complex, GDNF and GFRalpha1, in foetal and adult human kidneys. We found their expression in both the developing and the adult renal collecting system. We further show that only RET51 but not RET9 could promote the survival and tubulogenesis of mIMCD3 (mouse inner medullary collecting duct) cells in collagen gel. Our results agree with the hypothesis that RET51 signalling is related to differentiation events in later kidney organogenesis. In addition, it may also have a function in the adult kidney. We further extend our study by showing increased RET and GDNF expression in collecting duct cysts of polycystic kidney patients. This suggests that GDNF/RET signalling may contribute to proliferation of the collecting duct epithelium in an autocrine/paracrine manner.

The c-ret proto-oncogene encodes a receptor tyrosine kinase which is important for the development of the kidney and the enteric nervous system. During nephrogenesis, c-ret is expressed in the ureteric bud epithelium and later in its derivative, the collecting duct. This takes place during 11-17.5 days post-coitum (d.p.c.) in the mouse and our immunohistochemical study showed that the RET protein co-localized with the transcript. At 18.5 d.p.c. the kidney is fully differentiated. At 18.5 d.p.c., 1 week and 10 weeks old, RET was found in the proximal convoluted tubules, which is formed from the condensed mesenchyme. This suggests that c-ret may also play a role in kidney function. For the 10 weeks old kidney, RET immunostaining in male was concentrated on the basolateral side while female had a stronger staining in the whole cell. Furthermore, cytoplasmic staining was observed in male whereas both cytoplasmic and nuclear staining was found in female. c-ret transcript was detected by RT-PCR, and in situ hybridization showed its expression throughout the kidney. The reason for the sex-specific staining and the role of RET in kidney function remain to be determined.