Suramin enters and accumulates in low pH intracellular compartments of v-sis-transformed NIH 3T3 cells.

Using acridine orange as a reporter compound, we demonstrate that suramin enters and accumulates in low pH intracellular compartments (endosomes, lysosomes, and trans-Golgi complex) of normal and v-sis-transformed NIH 3T3 cells. The concentration of suramin in these acidic compartments is estimated to be > 150 microM, higher than the concentration known to completely inhibit interaction of the platelet-derived growth factor (PDGF) receptor and v-sis gene product. These results support the hypothesis that suramin reverses the transformed phenotype of v-sis-transformed cells by entering the cell via endocytosis and blocking interaction of the v-sis gene product and PDGF receptor in intracellular organelles.

Skin Necrosis Associated With Heparin-Induced Thrombocytopenia and Thrombosis.

Skin necrosis is a rare complication of heparin therapy. Strong evidence suggests an immune-mediated mechanism in which heparin-antibody complexes bind to platelets, resulting in platelet aggregation, thromboembolism, and ischemic necrosis. Heparin-induced thrombocytopenia (HIT) may also occur in response to immune-mediated platelet aggregation. The presence, of heparin-dependent antibodies can be confirmed by platelet aggregometry, (14)C-serotonin release assay (SRA), or enzyme-linked immunosorbent assay (ELISA). Clinical suspicion, early detection and immediate cessation of heparin therapy are important in preventing the potentially severe complications of heparin-induced platelet aggregation. Potential therapeutic approaches include plasmapheresis and alternative forms of anticoagulation such as warfarin, aspirin, dipyridamole, or other novel investigational agents.

Technetium-99m Sestamibi Scanning Reflects Marrow Activity in a ß-Thalassemia Patient Treated with an Allogeneic Bone Marrow Transplant.

ß-thalassemia major is a disorder of globin synthesis, resulting in anemia and compensatory bone marrow hyperproliferation. Conventional imaging studies do not measure bone marrow activity reliably. We report on the use of technetium-99m sestamibi (MIBI) in a ß-thalassemia major patient treated with an allogeneic bone marrow transplant. Pre-transplant and early post-transplant MIBI scannings demonstrated generalized marrow uptake, reflecting marrow hyperproliferation. After full engraftment, post-transplant MIBI showed disappearance of abnormal uptake in the skeleton, indicating normalization of the marrow activity. MIBI scan may be used as a noninvasive measure of bone marrow proliferation that may guide hypertransfusion therapy in thalassemia patients.

Differential processing and turnover of the oncogenically activated neu/erb B2 gene product and its normal cellular counterpart.

In nontransformed DHFR/G-8 cells (NIH 3T3 cells transfected with normal rat neu gene), the normal neu gene product was initially synthesized as a 170-kDa protein bearing endoglycosidase H-sensitive oligosaccharide chains and was then processed to a 175-kDa mature form with endoglycosidase H-resistant, endoglycosidase F-sensitive oligosaccharide chains. Most of this 175-kDa mature form appeared on the cell surface 2 h following synthesis and showed a half-life of approximately 3 h. In the presence of a growth factor(s) partially purified from bovine kidney, the half-life of this 175-kDa normal neu gene product was shortened to less than 30 min. In B104-1-1 cells (NIH 3T3 cells transfected with neu gene activated oncogenically by a point mutation that changes a valine residue to a glutamic acid residue in the putative transmembrane region), the oncogenically activated neu gene product was also synthesized as a 170-kDa precursor with endoglycosidase H-sensitive oligosaccharide chains. However, this 170-kDa precursor diminished very fast and was only partially processed to a 185-kDa mature form which exhibited a half-life of less than 30 min. The 185-kDa activated neu gene product possessed an unidentified post-translational modification in addition to N-linked oligosaccharide chains. Both the precursor and mature forms of the mutationally activated neu gene product showed increased tyrosine-specific phosphorylation as compared with those of their normal counterparts in DHFR/G-8 cells. The mutationally activated neu gene product in B104-1-1 cells shared several features which have been reported previously for the ligand-activated platelet-derived growth factor receptor in v-sis- or c-sis-transformed cells. These properties include: 1) accelerated turnover of the precursor and mature forms compared with the rates of turnover of its normal counterparts, 2) insensitivity of this rapid turnover to lysosomotropic amines, and 3) increased in vivo tyrosine-specific phosphorylation of both the precursor and mature forms. These findings suggest that the mutationally activated neu gene product may transform the cells by mimicking ligand-induced activation.