Identification of the glucocorticoid suppressible mitogen from rat hepatoma cells as an angiogenic platelet-derived growth factor A-chain homodimer.
We have previously shown that BDS.1 rat hepatoma cells are hypersensitive to the antiproliferative effects of glucocorticoids, and secrete a glucocorticoid suppressible mitogenic activity (denoted GSM). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that GSM purified to near homogeneity migrated as a 28-kDa protein under nonreducing conditions and as a single 15-kDa polypeptide in the presence of sulfhydryl reducing agents suggesting a homodimeric structure. Anti-platelet-derived growth factor (PDGF) A-chain specific antibodies selectively immunodepleted the mitogenic activity which can be extracted from nonreducing gels in the 26-30-kDa fraction and, in Western blots, recognized the 15-kDa reduced form of GSM. Western blot analysis further showed that dexamethasone suppressed the level of secreted PDGF A-chain protein in BDS.1 cells but not in glucocorticoid receptor-deficient hepatoma cells. Northern blots revealed that dexamethasone reduced expression of the PDGF A-chain 2.3- and 1.7-kilobase transcripts in proportion to the level of detectable PDGF-AA protein. Similarly to PDGF-AA, the hepatoma cell-derived GSM has a potent angiogenic activity. Taken together, our results demonstrate that the predominant glucocorticoid suppressible mitogen secreted from rat hepatoma cells is a PDGF A-chain homodimer and suggest that in vivo glucocorticoids may potentially regulate hepatoma growth by modulating PDGF-stimulated tumor vascularization.
Department of Molecular and Cell Biology, University of California, Berkeley 94720.
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T
Haraguchi
D B
DB
Alexander
D S
DS
King
C P
CP
Edwards
G L
GL
Firestone
D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D004273:DNA, Neoplasm / Q000096:biosynthesis; D003907:Dexamethasone / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D006133:Growth Substances / Q000737:chemistry* / Q000494:pharmacology; D008114:Liver Neoplasms, Experimental / Q000378:metabolism*; D010982:Platelet-Derived Growth Factor / Q000235:genetics / Q000378:metabolism*; D012334:RNA, Neoplasm / Q000235:genetics; D051381:Rats; D013438:Sulfhydryl Compounds / Q000737:chemistry; D014158:Transcription, Genetic / Q000187:drug effects; D014407:Tumor Cells, Cultured
D004273:DNA, Neoplasm; D006133:Growth Substances; D010982:Platelet-Derived Growth Factor; D012334:RNA, Neoplasm; D013438:Sulfhydryl Compounds; D003907:Dexamethasone