Heterogeneous localization of adenylate and guanylate cyclases in R3230AC rat mammary adenocarcinoma cells

Adenylate and guanylate cyclase activities were demonstrated in R3230AC rat mammary adenocarcinomas by electron microscopic cytochemistry. Adenylate (AC) and guanylate (GC) cyclases were detected on plasma membrane of tumor epithelial cells, but not on fibroblasts and endothelial cells in the perivascular space. Both AC and GC activities were enriched in tumor epithelial cells at the periphery of the tumor lobular parenchyma rather than in cells in central core of the lobular parenchyma. Furthermore, the tumor cell plasma membranes facing the connective tissue stroma were in paucity or devoid of either enzyme activity. These heterogeneous distributions of both AC and GC among tumor epithelia suggest that R3230AC epithelial cells in different parts of the tumor mass may vary significantly in their regulation of cellular physiology.     

Insulin binding and glucose transport in the R3230AC mammary adenocarcinoma

Cells dissociated from the R3230AC mammary adenocarcinoma from intact and diabetic rats were examined for insulin binding and glucose transport. The K_d for insulin binding, ～ 10^?10 M, was similar in all tumors studied. However, the apparent number of receptor sites per cell increased in cells from diabetic rats. Kinetic analysis of 3-0-methyl glucose (3-OMG) entry showed both diffusional and passive carrier characteristics. Insulin (4 × 10^?9 M) in vitro did not affect diffusional entry, whereas the hormone altered the passive carrier system, as reflected by an increase in K_m and V_max. Insulin decreased initial velocity of glucose transport at 4–6 mM glucose levels but increased initial velocity of glucose transport at 20 mM glucose. An explanation of the role of insulin on tumor growth in vivo from effects on glucose transport in vitro is proposed.     

Glucose-6-phosphate dehydrogenase from lactating rat mammary gland and R3230AC adenocarcinoma.

A number of properties of glucose-6-phosphate dehydrogenase from lactating rat mammary gland and R3230AC rat mammary adenocarcinoma are compared. The main electrophoretic forms of the enzyme from these sources are indistinguishable with respect to charge and molecular weight whereas the minor forms show differences in these properties. The subunit molecular weight and steroid inhibition of the enzymes from the lactating gland and tumor are not significantly different. These results are contrasted with similar studies in mice.     

Acyl specificity in triacylglycerol synthesis by mammary adenocarcinoma R3230AC in Fischer rats

Activities and acyl specificities of both sn-glycero-3-phosphate and diacylglycerol acyltransferases in microsomal fractions isolated frorn homogenates of the mammary adenocardinoma R3230AC carried by Fischer rats were compared to those from normal mammary glands of lactating Fischer rats. Although the neoplasm exhibited lower activities for these two enzyme reactions, the specificities for acyl-CoAs as donors were quite similar to those found in the normal tissue counterpart. Long-chain acyl-CoAs were preferred substrates for the sn-glycero-3-phosphate acyltransferase reaction while acyltransferase with diacylglycerol as acceptor showed much less preference. With both normal and neoplastic tissues, the products of each reaction were the same i.e., phosphatides with sn-glycero-3-phosphate and triacylglycerol with diacylglycerol as acyl acceptors, respectively. All results support the concept of a non-random distribution of fatty acids in the triacylglycerol of this mammary adenocarcinoma in virgin rats which is the same as that from the normal tissue in lactating animals.     

Dual secretory and myoepithelial differentiation in the transplantable R3230AC rat mammary carcinoma

The hormone-responsive R3230AC mammary carcinoma, serially transplantable in Fisher rats, shows striking functional and morphological similarities to the normal mammary gland. We have studied its cellular composition by both light and electron microscopy, employing markers of myoepithelial and epithelial cells. We identified two cell types: the major cellular component corresponded to epithelial milk-protein secreting cells, while a second component showed immunocytochemical and ultrastructural characteristics of the myoepithelial cells. These cells were positive with a monoclonal antibody detecting alpha smooth muscle actin. The dual differentiation which normally occurs in breast ducts is therefore reproduced in a malignant experimental tumor. The coexistence of neoplastic cell populations, divergent in morphology and function, that persist in a tumor despite many transplant generations, leads to reconsideration of the relationship between cellular differentiation and malignant transformation.     

The hormonal regulation and interaction of concanavalin A and insulin binding in R3230AC mammary adenocarcinoma cells

To investigate the effects of concanavalin A on insulin binding to R323AC mammary carcinomas, initial experiments were performed to characterize binding of concanavalin A. Concanavalin A binding was found to be specific and saturable. Equilibrium binding experiments demonstrated that addition of low concentration of concanavalin A enhanced the binding of [³H]concanavalin A, suggestive of positively cooperative interactions. Binding of concanavalin A was responsive to hormonal alterations; tumor cells from diabetic rats showed enhanced binding of concanavalin A and insulin compared to cells from intact rats and administration of insulin to diabetic rats returned concanavalin A and insulin binding to levels seen in controls. Incubation of tumor cells with concanavalin A prior to addition of ¹²⁵I-labelled insulin resulted in a reduction of insulin-binding capacity; succinyl-concanavalin A did not affect binding of insulin. The percent inhibition of insulin binding by concanavalin A was highest at the lower insulin concentrations, providing a linearized Scatchard plot that yielded a calculated K_d value comparable to the low-affinity portion of the curvilinear Scatchard plot for insulin binding. The dissociation rate of bound insulin depended on receptor occupancy. Addition of concanavalin A after insulin binding reached equilibrium resulted in increased insulin binding hormone concentrations, decreased rates of dissociation of insulin and a loss of the correlation between receptor occupancy and dissociation rates. Concanavalin A alone demonstrated an insulin-like effect on glucose transport, which in these tumor cells represents a decrease in transport of 3-O-methylglucose. These suggest that binding of both concanavalin A and insulin to cells from this hormonally responsive neoplasm is under insulin regulation and demonstrates similar characteristics to those reported for a variety of normal cells. Furthermore, the interaction between concanavalin A and the cell membranes affects the affinity of the insulin receptor for insulin and appears to decrease the observed negative cooperativity.     

Cloning of differentially expressed genes in highly and low metastatic rat osteosarcomas by a modified cDNA-AFLP method.

To identify differentially expressed genes between highly and low metastatic rat transplantable osteosarcomas, we applied a modified AFLP (amplified fragment length polymorphisms) method for cDNA subtraction. The specific point of our modification is selective amplification using suppression PCR technique after restriction enzyme cutting. Our cDNA-AFLP gave high reproducibility (about 95%) in mRNA patterns and enabled us to clone four dominantly expressed genes in a highly metastatic tumor line. Three showed homology with known genes, encoding Ki-67, a proliferation-associated effective marker of malignancy, type IV collagen alpha-3, a major component of basement membrane, and KIAA77 for which the function is unknown. Although one fragment showed no database homology, we revealed a derivation from the rat homologue of the Drosophila melanogaster diaphanous gene (Dia) by cloning of longer cDNA. Dia genes, known to affect actin filament formation, are downstream effectors of Rho small GTPase. The results suggest that alterations in the expression of cytoskeletal protein, basement membrane elements, and proliferative markers may be important for metastasis of osteosarcomas.     

Characteristics of proline transport into R3230AC mammary tumor cells

Cells separated by enzyme treatment of the R3230AC mammary carcinoma were used to characterize the entry of proline. These cells showed minimal changes in cell viability and intracellular volume and were found to be suitable for transport studies, since the vi of proline was maintained for at least 4 h when cells were stored at 37 or 4 degrees C, or when transport was measured in the presence or absence of Na+. Proline was acitvely transported by these tumor cells, reaching a distribution ratio ([proline] intracellular/[proline] extracellular) of 20 after 2 h. Proline entry consisted of two processes, one saturable (carrier mediated) and the other, non-saturable. The carrier-mediated entry, Km - 0.83 mM and V = 151.10(-5) mumol/min per 5.10(6) cells, was Na+-dependent, sensitive to pH and metabolic inhibitors, and completely inhibited by alpha-(methylamino)-isobutyric acid (Ki = 0.34 mM). Proline entry in the absence of Na+ was 20% that in the presence of Na+ and was found to be due to a non-saturable process, since (a) vi of proline uptake in the absence of Na+ increases linearly with increasing proline concentration and (b) was not suppressed by either 20 mM alpha-(methyl-amino)-isobutyric acid, 50 mM glycine +20 mM phenylalanine, or 50 mM serine +20 mM phenylalanine when proline uptake was measured in the presence or absence of Na+. Therefore, under the conditions studied, we conclude that proline transport appears to be restricted to the A (alanine-preferring) system. Furthermore, these cells should provide a suitable model to study the effect of hormonal manipulations on the amino acid transport process.     

Identification of differentially expressed proteins in curcumin-treated prostate cancer cell lines

Due to high prevalence and slow progression of prostate cancer, primary prevention appears to be attractive strategy for its eradication. During the last decade, curcumin (diferuloylmethane), a natural compound from the root of turmeric (Curcuma longa), was described as a potent chemopreventive agent. Curcumin exhibits anti-inflammatory, anticarcinogenic, antiproliferative, antiangiogenic, and antioxidant properties in various cancer cell models. This study was designed to identify proteins involved in the anticancer activity of curcumin in androgen-dependent (22Rv1) and -independent (PC-3) human prostate cancer cell lines using two-dimensional difference in gel electrophoresis (2D-DIGE). Out of 425 differentially expressed spots, we describe here the MALDI-TOF-MS analysis of 192 spots of interest, selected by their expression profile. This approach allowed the identification of 60 differentially expressed proteins (32 in 22Rv1 cells and 47 in PC-3 cells). Nineteen proteins are regulated in both cell lines. Further bioinformatic analysis shows that proteins modulated by curcumin are implicated in protein folding (such as heat-shock protein PPP2R1A; RNA splicing proteins RBM17, DDX39; cell death proteins HMGB1 and NPM1; proteins involved in androgen receptor signaling, NPM1 and FKBP4/FKBP52), and that this compound could have an impact on miR-141, miR-152, and miR-183 expression. Taken together, these data support the hypothesis that curcumin is an interesting chemopreventive agent as it modulates the expression of proteins that potentially contribute to prostate carcinogenesis.     

Gene expression of PCNA/cyclin in adult tissues and the R3230AC mammary tumor of rat

We have investigated the gene expression of PCNA (Proliferating Cell Nuclear Antigen)/cyclin in rat tissues and the R3230AC mammary tumor. The steady-state mRNA level of PCNA/cyclin in a tissue is related to the proliferation of the tissue. The observation was confirmed with the results from the studies of the immunoblotting analyses and the DNA polymerase activity measurements. Furthermore, an overexpression of PCNA/cyclin was found in the R3230AC mammary tumor, which is accompanied by an altered PCNA/cyclin gene structure detected with the Southern blot analysis.     

Effects of diabetes and insulin on phosphoinositide metabolism in R3230AC mammary tumors.

The effects of diabetes and insulin administration on certain aspects of phosphoinositide metabolism in R3230AC mammary tumors were studied in vivo. Three weeks after diabetes was induced by streptozotocin, [3H]myoinositol incorporation into PI, PIP and PIP2 was increased in R3230AC tumors, whereas the formation of [3H]IP, [3H]IP2 and [3H]IP3 was decreased. Administration of protamine zinc insulin (3IU, twice daily, for 3 days) to diabetic rats decreased [3H]myoinositol incorporation into phosphoinositides and inositol phosphates in these mammary tumors. The R3230AC tumor from insulin-treated diabetic hosts had lower levels of unmetabolized [3H]-myoinositol compared to tumors from diabetic animals. Enzymatically-dissociated tumor cells from insulin-treated animals displayed decreased myoinositol transport in vitro. These findings suggest that the insulin-induced decrease in the turnover of inositol lipids in vivo in R3230AC mammary tumors could have resulted from the decreased level of [3H]myoinositol in these cells.     

Effect of insulin to decrease glucose transport in dissociated cells from the R3230AC mammary adenocarcinoma of diabetic rats.

Dissociated cells of the R3230AC mammary tumor were found to take up glucose by diffusion and by a passive carrier system. Using labeled 3-O-methylglucose as the probe, the following properties of the passive carrier were identified: (1) specificity for glucose, (2) competition by galactose and mannose but not by mannitol and fructose, (3) inhibition by phloretin but not by phloridzin, (4) temperature sensitivity, and (5) a Km for transport of 3-4 mM. The effects of insulin in vitro on carrier-mediated glucose transport were investigated in tumor cells from diabetic rats. At 10-9 M insulin, a time-related decrease in v for transport was observed resulting in an increased calculated Km (2- to 3-fold increase after 60-90 min incubation with insulin); only slight effects on V were obtained. This unusual response in v to insulin was observed when glucose was present in the medium at 2 mM and 5 mM, but not at 20 mM glucose. The effect of insulin to decrease the v was dose-related, with the major effects seen between 10-10M and 10-8M. The apparent decrease in glucose entry in vitro may in part explain the ability of insulin to inhibit growth of this tumor in vivo.     

Selection of highly metastatic rat MTLn2 mammary adenocarcinoma cell variants using in vitro growth response to transferrin

We previously found that the proliferative response to transferrin and the expression of transferrin receptors (TfR) on the cell surface of various rat 13762NF mammary adenocarcinoma cell sublines correlated with their spontaneous metastatic capability. To further assess the involvement of transferrin and TfR in metastasis, transferrin-responsive cells were selected from the poorly-metastatic, low-transfferin responsive 13762NF MTLn2 subline. When maintained in low serum (0.3%) conditions, MTLn2 cells failed to survive. However, if like medium was supplemented with 0.5 μmg/ml rat transferrin, some colonies emerged, presumably due to their ability to proliferate in response to the added transferrin. The surviving cells were expanded and exposed to ten or 20 similar cycles of transferrin growth selection to obtain the sublines MTLn2-Tf10 and MTLn2-Tf20, respectively. The MTLn2-Tf20 cells proliferated in response to transferrin at a rate similar to that of the high metastatic 13762NF sublines. Using immunofluorescent staining, Scatchard analysis, and affinity isolation of TfR, we discovered that the MTLn2-Tf20 cells had 5 to 6 times more TfR than did the parental MTLn2 line. When injected into the mammary fat pads of rats, the MTLn2-Tf20 line metastasized to the axillary lymph node in seven out of ten animals and to the lungs in six out of ten (median number = 13). No metastases were seen in the MTLn2 parental line. The MTLn2-Tf10 cells showed intermediate properties compared with the MTLn2 and MTLn2-Tf20 cells. The results indicate that variant cells with a high response to transferrin may be more metastatic than the bulk cells in a poorly metastatic population. The selection of cells with high levels of TfR and a higher proliferative response to transferrin results in sublines with greater potentials for spontaneous metastasis. J. Cell. Physiol. 174:48–57, 1998. © 1998 Wiley-Liss, Inc.     

Effects of trypsin on binding of insulin and concanavalin A and on glucose and proline transport in the R3230AC mammary adenocarcinoma

Effects of trypsin treatment on insulin and concanavalin A binding to, and glucose and proline transport in, dissociated R3230AC mammary adenocarcinoma cells were examined. Reduction of binding of ¹²⁵I-labelled insulin was dependent on the amount of trypsin used, the temperature and the time of the incubation period. Under conditions that reduced insulin binding by greater than 75%, transport of glucose and proline was reduced by less than 15%. Scatchard analysis of insulin binding after trypsin treatment yielded slopes similar to those from cells not exposed to trypsin, assuming either two classes of receptors or an average affinity, $\text{K}\text{?}{}_{\mathrm{<mtext>e</mtext>}}$. Dissociation of bound insulin from untreated or trypsin-treated cells was enhanced by addition of excess unlabelled ligand. Insulin added in vitro, which decreased glucose transport in untreated cells, produced a decrease in glucose transport in cells treated with trypsin for 5 min (insulin binding was decreased 35%), but not in cells treated for 45 min (insulin binding was decreased 90%). Binding of the plant lectin concanavalin A was also reduced by trypsin treatment, but to a lesser extent and with a different time-course than for insulin. Scatchard analysis of the binding of concanavalin A in untreated and trypsin-treated cells yielded comparable values for K_d. The insulinomimetic actions of concanavalin A on glucose transport were abolished after brief exposure to trypsin. Pre-treatment of cells with concanavalin A reduced insulin binding and partially protected insulin receptors from trypsin digestion, but the inability to remove all of the concanavalin A precluded its use as a method to protect insulin receptors. Thus, in this rat mammary tumor, the number, but not the affinity or functional activity, of insulin receptors can be reduced by trypsin treatment without significant effects on glucose or A system amino acid transport.