Galectin-1: biphasic growth regulation of Leydig tumor cells

Galectin-1 (Gal-1) is a widely expressed beta-galactoside-binding protein that exerts pleiotropic biological functions. To gain insight into the potential role of Gal-1 as a novel modulator of Leydig cells, we investigated its effect on the growth and death of MA-10 tumor Leydig cells. In this study, we identified cytoplasmic Gal-1 expression in these tumor cells by cytofluorometry. DNA fragmentation, caspase-3, -8, and -9 activation, loss of mitochondrial membrane potential (DeltaPsim), cytochrome c (Cyt c) release, and FasL expression suggested that relatively high concentrations of exogenously added recombinant Gal-1 (rGal-1) induced apoptosis by the mitochondrial and death receptor pathways. These pathways were independently activated, as the presence of the inhibitor of caspase-8 or -9 only partially prevented Gal-1-effect. On the contrary, low concentrations of Gal-1 significantly promoted cell proliferation, without inducing cell death. Importantly, the presence of the disaccharide lactose prevented Gal-1 effects, suggesting the involvement of the carbohydrate recognition domain (CRD). This study provides strong evidence that Gal-1 is a novel biphasic regulator of Leydig tumor cell number, suggesting a novel role for Gal-1 in the reproductive physiopathology.

An electrophoretic analysis of proteolipids from different rat brain subcellular fractions

Proteolipid proteins were extracted from adult rat brain subcellular fractions and purified by chromatography on Sephadex LH-60. Polyacrylamide gel electrophoresis of the delipidized proteins, in the presence or absence of 8 M urea, was carried out with all fractions. The distribution of the various types of proteolipid proteins was studied and their molecular weight calculated by the Ferguson relationship. Several bands of proteolipid proteins were found in the five membrane fractions analyzed. Some of them, such as the 17.5 K and 37 K components were very prominent in mitochondria and synaptosomes. The 30 K component was found in myelin-derived membranes and in microsomes, while the 20 K and 25 K proteolipid proteins were present in all subcellular fractions. The 30 K component (proteolipid protein (PLP)), typical of the purified myelin membranes, showed a similar distribution to that of 2',3'-cyclic-nucleotide 3'-phosphohydrolase (EC 3.1.4.37) activity, while the other major proteolipid protein present in all subcellular fractions (25 K) did not show such parallelism, indicating that it might not be an exclusive component of myelin. The electrophoretic pattern of microsomal proteolipid proteins did not show the high molecular weight components (aggregates of PLP) which are found in myelin. Furthermore, the 30 K component showed a smaller Y0 value than that of the 30 K found in myelin. Thus the presence of 30 K proteolipid protein in microsomes should not be considered as being due to myelin contamination.

Rapid purification of proteolipids from rat brain subcellular fractions by chromatography on a lipophilic dextran gel

Proteolipids from adult rat brain subcellular fractions were purified by a one-step procedure involving chromatography through Sephadex LH-60 eluted with an acidified chloroform-methanol mixture. The protein peak was eluted with the void volume and was free of adventitious lipids. The degree of purification was similar to that attained with the neutral-acidified chloroform-methanol dialysis method with the advantage that this new procedure can be carried out in only 3 h, with a recovery of proteins of 95-100%. Samples containing different lipid/protein ratios passed through the gel gave similar elution profiles. When labeled amino acids or palmitic acid were added to myelin total lipid extracts, no radioactivity was eluted with the protein, indicating that the proteolipid apoproteins purified by this method do not adsorb hydrophobic low-molecular-weight compounds.