Enhancement of transforming growth factor-alpha synthesis in multicellular tumour spheroids of A431 squamous carcinoma cells.
Multicellular tumour spheroids are cellular aggregates that can be prepared from many types of tumour cells. These three-dimensional structures provide a model for analysing the effects of cell-cell contact and intercellular microenvironments on phenomena such as autocrine regulation of growth factor synthesis. Autoregulation of the synthesis of transforming growth factor-alpha (TGF-alpha) was investigated at the message and protein levels in spheroid and monolayer cultures prepared from the A431 human squamous carcinoma cell line. The epidermal growth factor receptor (EGF-R) of these monolayer A431 cells had an average surface density of 2.2 x 10(6)/cell. Constitutive expression of TGF-alpha mRNA was an average of 3-fold greater in A431 spheroids than in monolayers, even for densely packed, confluent monolayers. This effect did not depend on hypoxic stress within the spheroids. TGF-alpha protein synthesis was enhanced in comparison with that in monolayer culture, reaching a value of up to 2-fold greater on a per cell basis. These results are discussed in the context of a TGF-alpha/EGF-R autocrine loop operating within cells that produce high local concentrations of TGF-alpha in the three-dimensional architecture of a spheroid.
Laderoute
K R
KR
Laboratory of Cell and Molecular Biology, SRI International, Menlo Park, California 94025.
Murphy
B J
BJ
Short
S M
SM
Grant
T D
TD
Knapp
A M
AM
Sutherland
R M
RM
D015152:Blotting, Northern; D002294:Carcinoma, Squamous Cell / Q000378:metabolism* / Q000473:pathology; D002449:Cell Aggregation; D002450:Cell Communication; D002452:Cell Count; D004815:Epidermal Growth Factor / Q000494:pharmacology; D006801:Humans; D012333:RNA, Messenger / Q000032:analysis*; D011863:Radioimmunoassay; D013997:Time Factors; D016211:Transforming Growth Factor alpha / Q000096:biosynthesis*; D014407:Tumor Cells, Cultured
D012333:RNA, Messenger; D016211:Transforming Growth Factor alpha; D004815:Epidermal Growth Factor