Characterization of thread proteins expressed in neuroectodermal tumors.

Neuronal thread protein is a novel 21-kDa protein that accumulates in brains with Alzheimer's disease and exhibits developmentally associated changes in the level of expression. Recently, we discovered that primary human primitive neuroectodermal tumor (PNETs), malignant astrocytomas, and several human PNET and glioblastoma cell lines also express thread protein immunoreactivity. However, in addition to the 21-kDa species, there are approximately 17- and approximately 14-kDa thread protein-immunoreactive molecules expressed in both PNET and glioblastoma cell lines and a fourth approximately 8-kDa thread protein detected in glioblastoma cell lines. Metabolic labeling studies demonstrated that the 21-kDa thread proteins are phosphorylated, whereas the approximately 17-, approximately 14-, and approximately 8-kDa thread proteins are not. Glycosylated residues were not detected in either the PNET- or glioblastoma-derived thread proteins. Using a panel of monoclonal antibodies, we observed differences between PNET and glioblastoma cells suggesting that the thread proteins expressed in neuronal and glial cells are distinct. The levels of thread protein immunoreactivity in both PNET and glial cells were highest during the log phase of cell growth and lowest in serum-starved, nonproliferating cultures. The findings suggest that there are several distinct neuronal and glial derived thread proteins expressed in the central nervous system and that their levels of expression may be modulated with cell growth.