Loss of endogenous bone morphogenetic protein-6 aggravates renal fibrosis.

Bone morphogenetic protein-6 (BMP-6) suppresses inflammatory genes in renal proximal tubular cells and regulates iron metabolism by inducing hepcidin. In diabetic patients, an increase of myofibroblast progenitor cells (MFPCs), also known as fibrocytes, was found to be associated with decreased BMP-6 expression. We hypothesized that loss of endogenous BMP-6 would aggravate renal injury and fibrosis. Wild type (WT) and BMP-6 null mice underwent unilateral ureteral obstruction. In WT mice, ureteral obstruction down-regulated BMP-6. Obstructed kidneys of BMP-6 null mice showed more casts (1.5-fold), epithelial necrosis (1.4-fold), and brush border loss (1.3-fold). This was associated with more inflammation (1.8-fold more CD45(+) cells) and more pronounced overexpression of profibrotic genes for αSMA (2.0-fold), collagen I (6.8-fold), fibronectin (4.3-fold), CTGF (1.8-fold), and PAI-1 (3.8-fold), despite similar BMP-7 expression. Also, 1.3-fold more MFPCs were obtained from BMP-6 null than from WT mononuclear cell cultures, but in vivo only very few MFPCs were observed in obstructed kidneys, irrespective of BMP-6 genotype. The obstructed kidneys of BMP-6 null mice showed 2.2-fold more iron deposition, in association with 3.3-fold higher expression of the oxidative stress marker HO-1. Thus, ureteral obstruction leads to down-regulation of BMP-6 expression, and BMP-6 deficiency aggravates tubulointerstitial damage and fibrosis independent of BMP-7. This process appears to involve loss of both direct anti-inflammatory and antifibrotic action and indirect suppressive effects on renal iron deposition, oxidative stress, and MFPCs.

The von Hippel-Lindau tumour suppressor interacts with microtubules through kinesin-2.

Synthesis and maintenance of primary cilia are regulated by the von Hippel-Lindau (VHL) tumour suppressor protein. Recent studies indicate that this regulation is linked to microtubule-dependent functions of pVHL such as orienting microtubule growth and increasing plus-end microtubule stability, however little is known how this occurs. We have identified the kinesin-2 motor complex, known to regulate cilia, as a novel and endogenous pVHL binding partner. The interaction with kinesin-2 facilitates pVHL binding to microtubules. These data suggest that microtubule-dependent functions of pVHL are influenced by kinesin-2.

Fibronectin is a hypoxia-independent target of the tumor suppressor VHL.

The von Hippel-Lindau (VHL) tumor suppressor gene regulates the extracellular matrix by controlling fibronectin deposition. To identify novel VHL target genes, we subjected mRNA from VHL-deficient RCC cells (786-0-pRC) and a transfectant re-expressing wildtype VHL (786-0-VHL) to differential expression profiling. Among the differentially expressed genes, we detected that fibronectin is upregulated in the presence of VHL, while it is not affected by hypoxia. Thus regulation of fibronectin deposition by VHL occurs at the transcriptional level, irrespective of oxygen levels.

NS-398, a selective cyclooxygenase-2 inhibitor, reduces experimental bladder carcinoma outgrowth by inhibiting tumor cell proliferation.

OBJECTIVES: To evaluate the efficacy of the selective cyclooxygenase-2 (COX-2) inhibitor NS-398 in treating experimental T24 bladder carcinoma, and to assess its effect on tumor cell proliferation and survival and tumor vascularization. COX-2 overexpression is frequently observed in bladder carcinoma and has been correlated with an increased disease stage and with reduced patient survival. METHODS: NS-398 was used to inhibit COX-2 selectively in human T24 bladder carcinoma cells. Lentiviral transduction of the firefly luciferase gene allowed us to assess the effect of NS-398 on orthotopic bladder carcinoma growth over time in a noninvasive manner. Immunohistochemistry on bladder tissue sections was performed to determine the effect of NS-398 treatment on tumor cell proliferation (Ki-67), apoptosis (cleaved caspase-3), and angiogenesis (von Willebrand factor; CD31). RESULTS: T24 cells expressed COX-2 and secreted prostaglandin E2 (PGE2). Selective COX-2 inhibition using NS-398 abrogated PGE2 secretion and inhibited cell proliferation in vitro in a dose-dependent manner, without affecting cell viability. In vivo administration of NS-398 reduced the outgrowth of experimental orthotopic T24 bladder carcinoma. This was accompanied by a significant reduction in Ki-67-positive tumor cells but not by a reduction in tumor cell viability or tumor vascularization. CONCLUSIONS: Selective COX-2 inhibition by NS-398 reduces the outgrowth of T24 human bladder carcinoma in an orthotopic mouse model. The therapeutic activity was most likely caused by inhibition of tumor cell proliferation, rather than by inhibition of angiogenesis or tumor cell survival.

Tumor suppression by the von Hippel-Lindau protein requires phosphorylation of the acidic domain.

The tumor suppressor function of the von Hippel-Lindau protein (pVHL) has previously been linked to its role in regulating hypoxia-inducible factor levels. However, VHL gene mutations suggest a hypoxia-inducible factor-independent function for the N-terminal acidic domain in tumor suppression. Here, we report that phosphorylation of the N-terminal acidic domain of pVHL by casein kinase-2 is essential for its tumor suppressor function. This post-translational modification did not affect the levels of hypoxia-inducible factor; however, it did change the binding of pVHL to another known binding partner, fibronectin. Cells expressing phospho-defective mutants caused improper fibronectin matrix deposition and demonstrated retarded tumor formation in mice. We propose that phosphorylation of the acidic domain plays a role in the regulation of proper fibronectin matrix deposition and that this may be relevant for the development of VHL-associated malignancies.