Differences in cholesterol transport by normal and malignant human kidney cells

High-Density Lipoprotein Components and Functionality in Cancer: State-of-the-Art

Cancer is the second leading cause of death in western countries, and thus represents a major global public health issue. Whilst it is well-recognized that diet, obesity, and smoking are risk factors for cancer, the role of low levels of high-density lipoprotein cholesterol (HDL-C) in cancer is less well appreciated. Conflicting evidence suggests that serum HDL-C levels may be either positively or negatively associated with cancer incidence and mortality. Such disparate associations are supported in part by the multitude of high-density lipoprotein (HDL) functions that can all have an impact on cancer cell biology. The aim of this review is to provide a comprehensive overview of the crosstalk between HDLs and cancer, focusing on the molecular mechanisms underlying this association.

Membrane properties of metastatic and non-metastatic cells cultured from C3H mice injected with LM fibroblasts

Little is known regarding the membrane properties of metastatic cells as compared to non-metastatic tumor cells. In order to remove variables such as site of growth and nutrition, C3H mice and LM fibroblasts were used as a model system to derive cell lines from local tumors and lung metastases. LM cells were injected subcutaneously into C3H mice and local skin tumors and secondary lung tumors were isolated, cultured in vitro and analyzed. The activities of lipid-sensitive membrane enzymes, membrane lipid composition, and membrane structure were correlated with metastatic ability. Plasma membranes and microsomes of the cultured metastatic cells had 3.8 +/- 0.5- and 5.4 +/- 0.6-fold elevated 5'-nucleotidase activity, respectively, as compared to plasma membranes and microsomes of cultured non-metastatic cells. The mitochondria of cultured metastatic cells had 3.5 +/- 0.5-fold decreased succinate-dependent cytochrome-c reductase activity as compared to mitochondria of the cultured non-metastatic cells. The lipids of plasma membranes from the metastatic cells had 30 +/- 2% and 46 +/- 7% lower phosphatidylinositol and sterol/phospholipid ratio, respectively, and 30 +/- 3% increased unsaturated/saturated fatty acid as compared to cultured non-metastatic cells. The lower sterol/phospholipid ratio correlated with a 30 +/- 1% lower level of cytosolic sterol carrier protein in the cultured metastatic cells as compared to cultured non-metastatic cells. Multifrequency phase and modulation fluorometry in conjunction with the fluorescence probe, 1,6-diphenyl-1,3,5-hexatriene, was used to determine the static and dynamic aspects of membrane fluidity. The plasma membranes and microsomes of cultured metastatic cells were more fluid than those of cultured non-metastatic cells as indicated by 24 +/- 3% and 7 +/- 1%, respectively, lower limiting anisotropy of 1,6-diphenyl-1,3,5-hexatriene in the membranes of the metastatic as compared to non-metastatic cells.

Biological markers in urologic cancer

Tumor markers (TMs) play an important part in the management of urologic cancer. Alpha-fetoprotein, human chorionic gonadotropin, and occasionally lactic dehydrogenase serological determinations have become indispensable in the management of nonseminomatous germ cell testicular tumor patients, particularly after initial therapy, whereas human chorionic gonadotropin and probably placental alkaline phosphatase are important in seminoma. Prostatic acid phosphatase has long been important for the monitoring of patients with carcinoma of the prostate. The availability of the immunologic assays instead of the enzymatic assays has improved sensitivity somewhat but clinical interpretation has also become more complicated. Prostatic specific antigen is already an important tissue marker for carcinoma of the prostate and promises to be an important serological one, possibly surpassing prostatic acid phosphatase in importance. Analysis of DNA by automated flow cytometry is becoming important in the early detection and follow-up of bladder cancer patients. Studies concerning the tissue analysis of blood group antigens in bladder cancer continue to demonstrate that this approach can provide unique clinical information and interesting biological insights, but its role in routine clinical management remains to be determined. Currently, TMs have little clinical significance in renal cell carcinoma, but the availability of monoclonal antibodies to renal cell carcinoma preferential antigens may change this deficiency soon. In fact, in the near future, monoclonal antibodies will probably reveal many new substances for many urological cancers which can be used for markers serologically, histochemically, and, with their corresponding antibody, for radioimmune imaging and possibly immunotherapy. Now, as then, familiarity with the nuances of the marker and good clinical judgement will be essential.

Transport of circulating serum cholesterol by human renal cell carcinoma

Clear cell renal cancer contains a large quantity of cholesterol ester (300-mg./gm. protein). To determine whether abnormalities in cholesterol transport could account for this sterol accumulation, the uptake, release, and imaging capabilities of intravenously injected 131I-6-iodomethyl-29-norcholesterol, a cholesterol analogue, were studied preoperatively in five patients with clear cell renal cancer. At surgery, samples of the liver, tumor, adrenal, and non-tumor kidney were obtained for analysis. 131I-sterol uptake by the tumor, when normalized for cholesterol content, was less than for adrenal, liver or kidney. In contrast, release of preloaded 131I-sterol from the human tumors was consistently slower than for normal kidney. The reduced release of free cholesterol from renal cancer cells may, in part, be responsible for the accumulation of cholesterol in human renal cancer.

Correlation of tumor metastasis with sterol carrier protein and plasma membrane sterol levels

Squalene and sterol carrier protein (SCP) levels and sterol/phospholipid molar ratios of whole cells and plasma membranes were measured in cultured primary tumor and metastatic cell lines. SCP is abundant in all cell lines. However, metastatic lines have significantly lower SCP levels and plasma membrane sterol/phospholipid ratios than do primary lines. The results indicate that extremely malignant, metastatic cells are unable to produce or maintain adequate levels of both SCP and plasma membrane sterols when grown in lipoprotein deficient media. This defect, in vivo, probably causes excess uptake of SCP and lipid.

Study of the normal human kidney and kidney cancer with monoclonal antibodies

The ability to establish immortal tissue culture lines of human renal cancer as well as short-term lines of autologous normal kidney epithelium offers a unique system to probe the differences between a neoplastic cell and its normal counterpart. Monoclonal antibodies have been prepared against cell surface differentiation antigens of normal and neoplastic human kidney. The detected antigens have been biochemically characterized, and the molecular phenotypes of these cells is being unraveled. Differences in gene expression are becoming apparent between the normal and neoplastic kidney cell. Preliminary results indicate that these differences appear to have clinical significance.

Regulation of Lipid Metabolism by a Lipid-Carrying Protein

The overall conclusion to be made from the information presented here is that for many reasons SCP is a highly unusual protein. Some of these reasons are, first, SCP serves as cofactor for a number of different membrane-bound enzymes catalyzing specific steps in lipid metabolism. Second, SCP is involved in intracellular transport or movement of both cholesterol and fatty acids. Third, SCP is remarkably abundant and ubiquitous; its structure is conserved throughout nature. Fourth, SCP is exported to the blood stream from its site of synthesis by some, perhaps unique, mechanism and then rapidly taken up by specific tissues, e.g., the adrenal. Fifth, SCP is free in the cytosol and can also move to the inner mitochondrial membrane, where it is tightly bound. Sixth, SCP undergoes a dramatic diurnal variation in amount, reflecting changes in synthetic rate. Its half-life is less than an hour. Seventh, the diurnal variation in amount is triggered by feeding and influenced by several hormones. The diurnal variation is lost but a high level of SCP is maintained in the face of debilitating conditions, i.e., starvation, diabetes. Eighth, malignant cells exhibit defects in the uptake, synthesis, or turnover of SCP. Ninth, the synthesis of SCP is regulated by the efficiency of translation of its ever abundant mRNA. Tenth, there is much more to be learned about the functions and regulation of SCP.

Changes in lipid profiles of estrogen-induced and transplanted renal carcinomas in Syrian hamsters

The lipid profiles of estrogen-induced primary renal carcinomas and hormone-dependent and -independent transplanted tumors were compared with those of both normal hamster kidneys and renal tissues of tumor-bearing animals. Autonomous tumors had only one-third the amount of triglycerides present in normal kidneys and hormone-dependent tumors contained intermediate levels. Host kidneys of animals bearing either primary or transplanted tumors contained no more than 50-60% of the triglyceride level found in normal kidneys. In contrast to triglycerides, cholesteryl esters in primary tumors were 200 times higher than in normal kidneys, exhibited a successive decline in hormone-dependent and -independent tumors, but remained 15 times higher in autonomous carcinomas than in normal kidneys. Cholesterol levels were similar in primary tumors, normal kidneys, and host kidneys of animals bearing renal tumors; however, both hormone-dependent and -independent neoplasms had only one-half to two-thirds as much cholesterol as normal kidneys. Total phospholipid levels in primary and transplanted carcinomas were about one-half those in normal kidneys. Host kidneys of animals bearing primary and transplanted, hormone-dependent neoplasms also contained lower phospholipid levels than normal kidneys, but renal tissues from animals with autonomous tumors contained similar levels to those found in kidneys from normal hamsters. The phospholipid composition of primary and transplanted renal tumors was similar, but different from that of normal kidneys, mainly in increased percentages of phosphatidylcholine and decreased percentages of sphingomyelin.

Cholesterol accumulation in heterotransplanted renal cell cancer

To date there have been no in vivo studies of the known propensity of human renal cell cancer (RCC) to accumulate large amounts of cholesterol. Caki-1, a human RCC line, was grown in the cheek pouches of immunosuppressed golden Syrian hamsters. Analysis of cholesterol levels revealed 2 to 4 times as much cholesterol in the heterotransplants as in any of the host tissues. After intraperitoneal injection of tumor-bearing hamsters with 4-14C-cholesterol, the tumors accumulated less radioactivity than did hamster liver and no more radioactivity than did hamster kidney or cheek pouch. It appears that accumulation of cholesterol by human RCC is not dependent on extensive uptake of extracellular cholesterol. Instead, an intrinsic defect in the cellular regulation of cholesterol synthesis and efflux is more likely to be responsible.

Association of HLA and renal cell carcinoma

HLA-A,B,C, and DR antigen frequencies were studied in a patient population with a history of renal cell carcinoma. HLA-DR5 was found in 54% of patients, which is significantly elevated over control values (20%; p less than .01). On the other hand, HLA-A,B, and C locus antigen frequencies were not abnormal compared to controls.