Role of glial fibrillary acidic protein expression in the biology of human glioblastoma U-373MG cells

Object. The relationship between glial fibrillary acidic protein (GFAP) expression and glial tumor cell behavior has not been well defined. The goal of this study was to examine this relationship further. Methods. To investigate the relationship between GFAP expression and glial tumor cell behavior, the authors isolated clones from the human glioblastoma cell line, U-373MG, according to their level of GFAP expression. Immunochemical analysis demonstrated that one clone had consistently low GFAP expression (approximately 93% of cells were GFAP negative), whereas a second clone had consistently high GFAP expression (approximately 80% of the cells were GFAP positive). The structure, population doubling time, saturation density, anchorage-independent growth, migratory rate, and invasive potential of these two clones were determined in relation to their level of GFAP expression. Morphologically, both clones were composed of ameboid as well as stellate components. Although the population doubling times of the two clones were equally rapid, the clone with low GFAP expression demonstrated a slightly higher saturation density compared with the clone with high GFAP expression. In an anchorage-independent environment (soft agar), a greater difference in growth characteristics was noted between the two clones: the high-expression done formed more colonies and these colonies were compact, well defined, and spherical, whereas the low-expression clone formed predominantly smaller, two-dimensional colonies with vague boundaries and isolated cells or groups of cells at the periphery. In contrast to these minor differences between the clones, the low-expression clone showed a markedly increased migratory rate and invasive potential compared with the high-expression clone. Therefore, the clone with reduced GFAP expression appeared more aggressive, demonstrating decreased contact inhibition, increased migratory rate, and increased invasive potential. Conclusions. These results suggest a direct correlation between GFAP expression and some measures of aggressive tumor growth and transformation properties.