Regulation of membrane trafficking requires the concerted actions of rab proteins, their effectors and several phosphatidylinositol 3 0 -kinases. Rab7 is required for late endosomal transport and here we establish that the phosphatidylinositol 3 0 -kinase hVPS34 and its adaptor protein p150 are rab7 interacting partners. The hVPS34/ p150 complex colocalized with rab7 on late endosomes and hVPS34 activity was dependent on nucleotide cycling of rab7. In addition, total cellular phosphatidylinositol 3 0 -phosphate levels were modulated by rab7 expression, suggesting that rab7 activation impacted kinase cycling to early endosomes. The data identify rab7 as an important regulator of late endosomal hVPS34 function and link rab7 to the regulation of phosphatidylinositol 3 0 -kinase cycling between early and late endosomes.

Approximately 60,000 patients in the US are waiting for a kidney transplant due to genetic, immunologic and environmentally caused kidney failure. Adult human renal stem cells could offer opportunities for autologous transplant and repair of damaged organs. Current data suggest that there are multiple progenitor types in the kidney with distinct localizations. In the present study, we characterize cells derived from human kidney papilla and show their capacity for tubulogenesis. In situ, nestin+ and CD133/1+ cells were found extensively intercalated between tubular epithelia in the loops of Henle of renal papilla, but not of the cortex. Populations of primary cells from the renal cortex and renal papilla were isolated by enzymatic digestion from human kidneys unsuited for transplant and immuno-enriched for CD133/1+ cells. Isolated CD133/1+ papillary cells were positive for nestin, as well as several human embryonic stem cell markers (SSEA4, Nanog, SOX2, and OCT4/POU5F1) and could be triggered to adopt tubular epithelial and neuronal like phenotypes. Isolated papillary cells exhibited morphologic plasticity upon modulation of culture conditions and inhibition of asymmetric cell division. Labeled papillary cells readily associated with cortical tubular epithelia in co-culture and 3-dimensional collagen gel cultures. Heterologous organ culture demonstrated that CD133/1+ progenitors from the papilla and cortex, became integrated into developing kidney tubules. Tubular epithelia did not participate in tubulogenesis. Human renal papilla harbor cells with the hallmarks of adult kidney stem/progenitor cells that can be amplified and phenotypically modulated in culture while retaining the capacity to form new kidney tubules.

Rab7 is a key regulatory protein governing early to late endocytic membrane transport. In this study the proteasome ␣-subunit XAPC7 (also known as PSMA7, RC6 -1, and HSPC in mammals) was identified to interact specifically with Rab7 and was recruited to multivesicular late endosomes through this interaction. The protein interaction domains were localized to the C terminus of XAPC7 and the N terminus of Rab7. XAPC7 was not found on early or recycling endosomes, but could be recruited to recycling endosomes by expression of a Rab7-(1-174)Rab11-(160 -202) chimera, establishing a central role for Rab7 in the membrane recruitment of XAPC7. Although XAPC7 could be shown to associate with membranes bearing ubiquitinated cargo, overexpression had no impact on steady-state ubiquitinated protein levels. Most notably, overexpression of XAPC7 was found to impair late endocytic transport of two different membrane proteins, including EGFR known to be highly dependent on ubiquitination and proteasome activity for proper endocytic sorting and lysosomal transport. Decreased late endocytic transport caused by XAPC7 overexpression was partially rescued by coexpression of wild-type Rab7, suggesting a negative regulatory role for XAPC7. Nevertheless, Rab7 itself was not subject to XAPC7-dependent proteasomal degradation. Together the data establish the first direct molecular link between the endocytic trafficking and cytosolic degradative machineries.

Administration of recombinant human relaxin (rhRLX) to conscious, chronically instrumented rats increases GFR and effective renal plasma flow (ERPF) and decreases effective renal vascular resistance (ERVR) with no significant change in mean arterial pressure. The Munich Wistar albino rat shows progressive chronic nephrosis with age and therefore was used to determine the functional and histologic consequences of rhRLX on matrix remodeling in the kidney of older rats. RLX-infused rats showed increased GFR and ERPF with decreased ERVR. Furthermore, in a double-blinded examination, the renal histology showed a significant decrease in glomerular and tubular collagen deposition in the rhRLX-infused aged rats. During short-term rhRLX administration (24 h), gelatinase activity was found to be essential for renal vasodilation and hyperfiltration. Surprisingly, after 20 d, improved renal function was insensitive to the inhibition of gelatinase activity, suggesting that collagen degradation in these rats had permanently altered the matrix of the renal vasculature. In conclusion, long-term administration of rhRLX improves renal function and ameliorates renal pathology in an aging rat model. The biphasic action of rhRLX on the kidney indicates that, acutely, the vessels dilate, causing increased filtration and renal blood flow with decreased vascular resistance as a result of upregulation of gelatinase activity. Subsequently, the renal vessels undergo alteration in supporting matrix, showing increased blood supply even in the face of acute matrix metalloproteinase inhibition, most likely as a result of the inhibitory properties of RLX on collagen production or increased collagen breakdown. R elaxin (RLX) has numerous biologic effects. Its role in the reproductive tract has been well documented (1). More recently, we have shown it to be a potent vasodilator in the kidney (2-5). In long-term instrumented conscious rats, we demonstrated that RLX stimulates nitric oxide (NO)-dependent renal vasodilation and hyperfiltration in vivo, and reduces myogenic reactivity of small renal arteries in vitro via endothelin (ET) and the endothelial ET B receptor subtype (5). We also have documented a role for the matrix metalloproteinases (MMP) in this phenomenon. Vascular gelatinase activity converts big ET to ET 1-32 , which potently activates the endothelial ET B receptor. Using a novel inhibitor of the gelatinases, cyclic CTTHWGFTLC (CTT), we demonstrated that vascular gelatinase activity mediates renal vasodilatory action of RLX in rats (5). MMP-2 was specifically implicated in this phenomenon because an MMP-2-neutralizing antibody blocked the reduction in myogenic reactivity in isolated renal vessels that is typically caused by long-term RLX administration in vivo (5).RLX is widely known for its "matrix-degrading" properties that are associated with the stimulation of MMP and inhibition of collagen expression (6 -8). Specifically, RLX decreases synthesis and secretion of interstitial collagens, increases expression of the procollagenas...

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