The presence of pyruvate carboxylase in the human brain and its role in the survival of cultured human astrocytes.

Pyruvate carboxylase (PC) is a mitochondrial, biotin-containing enzyme catalyzing the ATP-dependent synthesis of oxaloacetate from pyruvate and bicarbonate, with a critical anaplerotic role in sustaining the brain metabolism. Based on the studies performed on animal models, PC expression was assigned to be glia-specific. To study PC distribution among human neural cells, we probed the cultured human astrocytes and brain sections with antibodies against PC. Additionally, we tested the importance of PC for the viability of cultured human astrocytes by applying the PC inhibitor 3-chloropropane-1,2-diol (CPD). Our results establish the expression of PC in mitochondria of human astrocytes in culture and brain tissue and also into a subpopulation of the neurons in situ. CPD negatively affected the viability of astrocytes in culture, which could be partially reversed by supplementing media with malate, 2-oxoglutarate, citrate, or pyruvate. The provided data estimates PC expression in human astrocytes and neurons in human brain parenchyma. Furthermore, the enzymatic activity of PC is vital for sustaining the viability of cultured astrocytes.

Analysis of sera from SV40-immunized and tumor-bearing hosts for blocking activity and antibody-dependent cellular cytotoxicity.

The role of serum factors in tumor immunity to cells transformed by PARA-(defective SV40)-adenovirus 7 was investigated. It was found that sera from SV40-sensitized hosts did not block the specific cytotoxicity of SV40-sensitized spleen cells for PARA-7 cells. However, such sera could collaborate with nonsensitized spleen cells to produce specific killing. This activity could be absorbed out by PARA-7 cells but not by cells transformed by cytomegalovirus. The activity of sera from hamsters bearing tumor isografts depended upon when, after transplantation, the specimens were obtained. Sera collected greater than or equal to 10 days after grafting completely blocked immune spleen cell cytotoxicity and did not mediate target cell killing in the presence of normal spleen cells. Sera obtained at an earlier time, i.e., 3 to 6 days after transplantation, consistently were active in the antibody-dependent cellular cytotoxicity test and exhibited reduced or no blocking of antibody-independent cellular cytotoxicity. Thus, there appears to be an inverse correlation in the capacity of serum from tumor bearing hosts to block effector cell cytotoxicity and mediate antibody-dependent cellular cytotoxicity.