Clonal variation in the production of a platelet-derived growth factor-like protein and expression of corresponding receptors in a human malignant glioma.

Abstract

Two cell lines (U-343 MG and U-343 MGa) with different phenotypic characteristics were established from the same human glioblastoma multiforme biopsy. Previous studies have shown that a clonal derivative (Cl 2) of the U-343 MGa line produces a PDGF-like growth factor. In the present investigation glioma PDGF production and 125I-PDGF binding were found to be differently expressed in U-343 MG, U-343 MGa, and U-343 MGa Cl 2 cultures, providing evidence for a clonal variation in these properties. In order to investigate this point further, several clones were derived from low (23 clones) and high (30 clones) passage U-343 MGa cultures, as well as from U-343 MGa Cl 2 cells (30 clones). The clones could be divided into 4 groups according to morphology and growth pattern. A determination of the amount of PDGF receptor competing activity in serum-free conditioned media gave evidence for a clonal variation in the production of glioma PDGF, corresponding to 0-87 ng of authentic PDGF per ml. There was also a considerable range in 125I-PDGF binding (0-44 fmol of tracer bound per 10(6) cells). Scatchard plots performed on two clones confirmed the presence of saturable, high affinity PDGF receptors. High passage cultures were found to give rise to a higher number of high producing clones than did low passage cultures. There appeared to be a negative correlation between production of glioma PDGF and binding of 125I-PDGF, probably due to the receptor blocking activity of the endogenous growth factor. However, the presence of clones, apparently devoid of both glioma PDGF production and 125I-PDGF binding, suggests a true clonal variation in these two parameters. The growth rate in serum-free medium was found to correlate fairly well to the extent of glioma PDGF production. Production of glioma PDGF was found to have a morphological correlate and be most prominent among clones of "immature" looking, tightly growing cells. Clones that had large star-shaped cells with some resemblance to normal glia-like cells in culture were found to have a low production and a high 125I-PDGF binding capacity.