Induction of expression of osteopontin (OPN; secreted phosphoprotein) in metastatic, ras-transformed NIH 3T3 cells.
We have previously shown that transfection of NIH 3T3 cells with the T24 H-ras oncogene converts the cells to a tumorigenic and metastatic phenotype, in proportion to levels of ras expression. We hypothesize that ras-induced increases in malignancy occur via altered expression of various genes. We have identified OPN (osteopontin; also known as Secreted Phosphoprotein, 2ar, Eta-1, and transformation-associated phosphoprotein) as a ras-induced gene in these cells. We report here that expression of OPN RNA and secretion of OPN protein are increased in a series of ras-transformed NIH 3T3 cells, in proportion to levels of expression of ras. Detection of secreted OPN protein was facilitated by a barium citrate precipitation procedure. Although the function of this protein in tumor cells is not known, OPN contains a conserved GRGDS (glycine-arginine-glycine-aspartic acid-serine) amino acid sequence, which may function as a cell attachment site for this protein. We speculate that increased expression of OPN contributes to the increased malignancy of ras oncogene-transformed NIH 3T3 cells, perhaps by alterations in either adhesive properties or integrin-mediated signal transduction pathways.
Chambers
A F
AF
London Regional Cancer Centre, Ontario, Canada.
Behrend
E I
EI
Wilson
S M
SM
Denhardt
D T
DT
D016475:3T3 Cells; D000818:Animals; D002471:Cell Transformation, Neoplastic / Q000378:metabolism*; D011232:Chemical Precipitation; D002951:Citrates; D019343:Citric Acid; D011905:Genes, ras; D051379:Mice; D009362:Neoplasm Metastasis; D053495:Osteopontin; D010750:Phosphoproteins / Q000032:analysis*; D012333:RNA, Messenger / Q000032:analysis; D012795:Sialoglycoproteins / Q000032:analysis* / Q000235:genetics
D002951:Citrates; D010750:Phosphoproteins; D012333:RNA, Messenger; D012795:Sialoglycoproteins; C506896:Spp1 protein, mouse; D053495:Osteopontin; D019343:Citric Acid