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We presently report the effects of human recombinant basic fibroblast growth factor (bFGF) on a newly established medulloblastoma cell line, UM-MB1. This predominantly adherent cell line has a mean doubling time of 39.3 hours and was found, by karyotypic analysis, to be near triploid. UM-MB1 consists of undifferentiated cells expressing markers of neuronal lineage such as the three neurofilament subunits as well as neuron-specific enolase, synaptophysin, and microtubule-associated proteins 1 and 5. In contrast, no immunoreactivity for glial fibrillary acidic protein was evident. When exposed to nanomolar amounts of bFGF, UM-MB1 cells began to extend neurite-like processes with arborizations and growth-cone-like structures. In addition, UM-MB1 cells treated with bFGF exhibited ultrastructural alterations that reflect their enhanced differentiation as well as the increased expression of at least one of the neurofilament subunits as evidenced both immunocytochemically and on Western blots. Furthermore, bFGF significantly decreased UM-MB1 cell growth as well as induced their death. UM-MB1 cells treated with bFGF for several days displayed DNA cleavage, nuclear shrinkage, and chromatin condensation while retaining their cytoplasmic and mitochondrial membrane integrity, all early indices of apoptosis. After this, cell death was evident with the concomitant appearance of the classical apoptotic bodies. By flow cytometry, bFGF was found to increase the proportion of cells in G1 before inducing their death by apoptosis. In conclusion, UM-MB1 cells can, when appropriately stimulated, be induced to differentiate along their neuronal lineage pathway. Their differentiation induced by bFGF, although incomplete, appears to promote or inhibit the expression of apoptotic effectors or suppressors in these cells, respectively, so to induce their death by an apoptotic-like mechanism.

A newly isolated virus from a patient with progressive multifocal leukoencephalopathy (PML) (Tokyo-1 strain) was found serologically identical to JC virus (Mad-1 strain) and showed high neurooncogenicity in hamsters. Twenty-one animals inoculated intracerebrally with the virus developed brain tumors during a period that averaged 5 months. The tumors were cerebellar medulloblastoma (n = 20); plexus tumor (n = 2) occurred in 1 animal as a single tumor and in another in combination with a medulloblastoma. Thalamic gliomatosis was also present in 6 animals with medulloblastoma. Five mock-infected animals did not develop tumors. Medulloblastoma cells were shown to contain papovavirus T-antigen. In 20 animals examined the medulloblastoma showed a close resemblance to the human medulloblastoma in its histologic, immunocytochemical, and ultrastructural features. Examination of the incipient tumors indicated that the hamster medulloblastoma originated in cells in the neonatal external granular layer. Following infection the cells apparently migrated into the internal granular layer, carrying integrated virus genes and expressing phenotypical transformation. These findings confirm previous reports on the oncogenicity of virus isolates from PML (ZuRhein and Varakis, 1979), but are novel in that with this new isolate tumors could be induced with comparatively low levels of virus inocula.

The majority of cells in a rapidly dividing human medulloblastoma cell line (D283 MED) are shown to express the two high-molecular-weight human neurofilament (NF) subunits, whereas a minority express the low-molecular-weight NF subunit. These three polypeptides are integral subunits of the intermediate filaments (IFs) found in normal neurons. Other cell type-specific IF proteins (keratin, desmin, and glial filament polypeptides) are not present in D283 MED cells. Further, the immunocytochemical, immunochemical and ultrastructural data suggest that the neurofilaments in these cells are abnormal, possibly because of a paucity of the low-molecular-weight NF subunit. This is the first human cell line derived from a central nervous system tumor that is capable of expressing all three NF triplet proteins. It is a unique model system for studies of normal and abnormal human NF metabolism as well as for probing the cell biology of medulloblastomas.