Interaction of plasminogen with dipeptidyl peptidase IV initiates a signal transduction mechanism which regulates expression of matrix metalloproteinase-9 by prostate cancer cells.

Both plasminogen (Pg) activation and matrix metalloproteinases (MMPs) are involved in the proteolytic degradation of extracellular matrix components, a requisite event for malignant cell metastasis. The highly invasive 1-LN human prostate tumour cell line synthesizes and secretes large amounts of Pg activators and MMPs. We demonstrate here that the Pg type 2 (Pg 2) receptor in these cells is composed primarily of the membrane glycoprotein dipeptidyl peptidase IV (DPP IV). Pg 2 has six glycoforms that differ in their sialic acid content. Only the highly sialylated Pg 2gamma, Pg 2delta and Pg 2epsilon glycoforms bind to DPP IV via their carbohydrate chains and induce a Ca(2+) signalling cascade; however, Pg 2epsilon alone is also able to significantly stimulate expression of MMP-9. We further demonstrate that the Pg-mediated invasive activity of 1-LN cells is dependent on the availability of Pg 2epsilon. This is the first demonstration of a direct association between the expression of MMP-9 and the Pg activation system.

Electrophysiological studies of primary cultures of rabbit distal tubule cells.

Primary monolayers grown from F1 band of a Percoll gradient centrifugation ("distal" monolayers) were studied, after confluency, 6-14 days after seeding. Transmission and scanning electron microscopy revealed that two cell types, resembling principal cells of the rabbit cortical collecting tubule (CCT) and intercalated cells of either CCT or connecting tubule, constitute approximately 96% of the monolayer. About two-thirds of the intercalated cells fluoresced when treated with fluorescent peanut lectin. Indirect specific immunocytofluorescent staining revealed fluorescence in 96% of the cells, confirming that the monolayers were derived from CCT or connecting tubule cells. Exposure of monolayers to vasopressin or isoproterenol increases adenosine 3',5'-cyclic monophosphate (cAMP) content in the cells and bathing medium, whereas parathyroid hormone was ineffective. Electrophysiological studies revealed a transepithelial voltage (VT) of -11 +/- 2 mV, and basolateral membrane voltage (Vb) of -77 +/- 5 mV (n = 20). The transepithelial electrical resistance (RT) was 1,870 +/- 250 omega X cm2 (n = 13). In three out of six monolayers, amiloride (10(-5) M) applied to the apical side produced an increase in apical membrane voltage (Va) from -71 +/- 1 to -89 +/- 9 mV) and a decrease in VT (from -10 +/- 1 to -2 +/- 1 mV). The RT did not change during amiloride exposure. Exposure of the apical membrane to 140 mM K+-depolarized Va from -67 +/- 7 to -39 +/- 11 mV (P less than 0.002) and hyperpolarized VT from -7 +/- 2 to -15 +/- 3 mV (P less than 0.005). Exposure to high K+ from the basolateral side depolarized Vb from -76 +/- 11 to -43 +/- 10 mV (P less than 0.001) and depolarized VT from -9 +/- to 8 +/- 5 mV (P less than 0.001). This preparation is suitable to study basic aspects of epithelial transport by electrophysiological methods and other techniques. The findings are consistent with several of the known properties of cortical collecting tubules from rabbits studied by the isolated perfused tubule technique.

Electrophysiological studies on primary cultures of proximal tubule cells.

Primary confluent monolayers were grown from proximal tubule fragments of rabbit kidneys. The fragments were obtained by gradient centrifugation and seeded on an ad hoc dish whose bottom was a permeable and transparent collagen membrane. The culture medium was a mixture of 50% Ham's F-12 and 50% Dulbecco's modified Eagle's medium supplemented with insulin, transferrin, ethanolamine, sodium selenite, and amino acids. The monolayers were studied at 6-14 days after seeding. Transmission electron microscopy revealed cuboidal cells 8.5-10.5 microns high, with a 1.5 to 2.5-microns apical brush border, abundant mitochondria, vacuoles, lysosomes, and irregular basal interdigitating processes. Cyclic AMP synthesis was stimulated by parathyroid hormone and was insensitive to vasopressin and isoproterenol. Electrophysiological studies performed with the same physiological salt solution on both sides revealed a transepithelial voltage of -2.6 +/- 0.6 mV (n = 10) and a basolateral membrane voltage of -51.0 +/- 4.5 mV (n = 13), both referred to the basal solution. The transepithelial electrical resistance was 7 +/- 2 omega X cm2. The apical membrane depolarized on addition of glucose to the apical side and hyperpolarized on removal of glucose. Changes in apical membrane voltage on addition of varying glucose concentrations (at [Na] = 135 mM, 37 degrees C) demonstrate the presence of a glucose transport system with an apparent Km of 3.54 +/- 0.54 and a Vmax of 7.2 +/- 0.4 mV. Thus this preparation exhibits morphological and electrophysiological characteristics of proximal tubule cells; these studies demonstrate the feasibility of the use of intracellular microelectrode techniques to study the transport properties of cultured epithelia.