Insulin receptor substrate-1, p70S6K, and cell size in transformation and differentiation of hemopoietic cells.
After an initial burst of cell proliferation, the type 1 insulin-like growth factor receptor (IGF-IR) induces granulocytic differentiation of 32D IGF-IR cells, an interleukin-3-dependent murine hemopoietic cell line devoid of insulin receptor substrate-1 (IRS-1). The combined expression of the IGF-IR and IRS-1 (32D IGF-IR/IRS-1 cells) inhibits IGF-I-mediated differentiation, and causes malignant transformation of 32D cells. Because of the role of IRS-1 in changing the fate of 32D IGF-IR cells from differentiation (and subsequent cell death) to malignant transformation, we have looked for differences in IGF-IR signaling between 32D IGF-IR and 32D IGF-IR/IRS-1 cells. In this report, we have focused on p70(S6K), which is activated by the IRS-1 pathway. We find that the ectopic expression of IRS-1 and the inhibition of differentiation correlated with a sustained activation of p70(S6K) and an increase in cell size. Phosphorylation in vivo of threonine 389 and, to a lesser extent, of threonine 421/serine 424 of p70(S6K) seemed to be a requirement for inhibition of differentiation. A role of IRS-1 and p70(S6K) in the alternative between transformation or differentiation of 32D IGF-IR cells was confirmed by findings that inhibition of p70(S6K) activation or IRS-1 signaling, by rapamycin or okadaic acid, induced differentiation of 32D IGF-IR/IRS-1 cells. We have also found that the expression of myeloperoxidase mRNA (a marker of differentiation, which sharply increases in 32D IGF-IR cells), does not increase in 32D IGF-IR/IRS-1 cells, suggesting that the expression of IRS-1 in 32D IGF-IR cells causes the extinction of the differentiation program initiated by the IGF-IR, while leaving intact its proliferation program.
Valentinis
B
B
Kimmel Cancer Center and the Department of Pathology, Thomas Jefferson University, Philadelphia, PA 19107, USA.
Navarro
M
M
Zanocco-Marani
T
T
Edmonds
P
P
McCormick
J
J
Morrione
A
A
Sacchi
A
A
Romano
G
G
Reiss
K
K
Baserga
R
R
D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D002453:Cell Cycle; D002454:Cell Differentiation; D002455:Cell Division; D048429:Cell Size; D002471:Cell Transformation, Neoplastic; D016895:Culture Media, Serum-Free; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006412:Hematopoietic Stem Cells / Q000166:cytology*; D006801:Humans; D055504:Insulin Receptor Substrate Proteins; D007377:Interleukin-3 / Q000378:metabolism; D008099:Liver / Q000473:pathology; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D009374:Neoplasms, Experimental; D019319:Okadaic Acid / Q000494:pharmacology; D009195:Peroxidase / Q000378:metabolism; D010641:Phenotype; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D012333:RNA, Messenger / Q000378:metabolism; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism* / Q000502:physiology; D020123:Sirolimus / Q000494:pharmacology; D013154:Spleen / Q000473:pathology; D013912:Threonine / Q000737:chemistry; D013997:Time Factors; D014162:Transfection; D014407:Tumor Cells, Cultured
D000903:Antibiotics, Antineoplastic; D016895:Culture Media, Serum-Free; D004791:Enzyme Inhibitors; C526292:IRS1 protein, human; D055504:Insulin Receptor Substrate Proteins; D007377:Interleukin-3; C526295:Irs1 protein, mouse; D010750:Phosphoproteins; D012333:RNA, Messenger; D019319:Okadaic Acid; D013912:Threonine; D009195:Peroxidase; D019893:Ribosomal Protein S6 Kinases; D020123:Sirolimus